This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

NIST Technical Note 1844 

Potential Research Areas in 

Residential Energy Storage for NIST’s 

Engineering Laboratory 

M. A. Kedzierski 

W. V. Payne 

H. M. Skye 

http://dx.doi.org/10.6028/NIST.TN.1844 
             

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

NIST Technical Note 1844 

Potential Research Areas in Residential 

Energy Storage for NIST’s Engineering 

Laboratory 

M. A. Kedzierski 

W. V. Payne 

H. M. Skye 

Energy and Environment Division 

Engineering Laboratory 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1844 

September 2014 

U.S. Department of Commerce 

Penny Pritzker, Secretary 

National Institute of Standards and Technology 

Willie May, Under Secretary of Commerce for Standards and Technology and Acting Director 
             

   

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Certain commercial entities, equipment, or materials may be identified in this 

 document in order to describe an experimental procedure or concept adequately. 

Such identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1844 

Natl. Inst. Stand. Technol. Tech. Note 1844, 31 pages (September 2014) 

CODEN: NTNOEF

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1844 
             

 

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Potential Research Areas in Residential Energy Storage for NIST’s 

Engineering Laboratory 

M. A. Kedzierski1
 

W. V. Payne 

H. M. Skye
 

National Institute of Standards and Technology 

Gaithersburg, MD 20899 

ABSTRACT 

This paper recommends research that is required to develop and, thus, enable cost effective, 

residential electricity storage systems for renewable energy. As residential electricity generation 

from renewable sources becomes more prevalent, residential energy storage will become an 

important factor in ensuring the stability of the electrical grid; grid operators will be able to timeshift demand to smooth peaks and match supply capacity. However, local storage of excess 

energy from renewable sources is currently not economically attractive due to the long payback 

period required to recover capital costs. NIST Engineering Laboratory is well positioned to 

make significant contributions to the relatively neglected field of residential energy storage. 

Possession of the NIST’s Net-Zero Energy Residential Test Facility makes it possible to work 

collaboratively with other laboratories within NIST to demonstrate field performance of new 

ideas in energy storage technologies such as batteries, super capacitors, superconducting 

magnets, and hydrogen storage. In addition, EL staff and facilities are well matched to projects 

in Phase Change Material (PCM) facades and PCM evaporators, pumped hydro, solar water 

heaters and cost/benefit analyses. Potential project ideas are provided for these areas of research. 

Keywords: electricity, energy storage, residential 

1

 Corresponding author. Tel./fax: (301) 975-5282/(301) 975-8973. E-mail address: Mark.Kedzierski@NIST.gov 

iii 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

TABLE OF CONTENTS
 

ABSTRACT............................................................................................................................ iii
 

TABLE OF CONTENTS ...................................................................................................... iv
 

LIST OF FIGURES ............................................................................................................... iv
 

INTRODUCTION................................................................................................................... 1
 

GENERAL RESEARCH NEEDS FOR VARIOUS ENERGY STORAGE METHODS 2
 

POTENTIAL ENERGY STORAGE RESEARCH ............................................................. 9
 

SIZE OF RESIDENTIAL ENERGY STORAGE SYSTEM ............................................ 20
 

CONCLUSIONS ................................................................................................................... 22
 

ACKNOWLEDGEMENTS ................................................................................................. 22
 

NOMENCLATURE.............................................................................................................. 23
 

LIST OF FIGURES 

Figure 1 Fraunhofer ISE classification of electrical energy storage systems ................... 3
 

according to energy form (IEC, 2011)................................................................................... 3
 

Figure 2 Fraunhofer ISE comparison of rated power, energy .......................................... 6
 

content and discharge time of different EES technologies (IEC, 2011) ............................. 6
 

Figure 3 Comparison of PHCA to equivalent PHES system (Wang et al., 2013) ............ 9
 

Figure 4 Passive cooling with external PCM wall (IRENA, 2013) .................................. 10
 

Figure 5 Classical and advanced façade designs with and without PCMs in................. 11
 

“AdvFacSy” Toolbox [(a) Multi-layer wall; (b) Ventilated opaque multi- ..................... 11
 

layer wall; (c) Ventilated transparent multi-layers walls] (Zhai et l., 2013) ................... 11
 

Figure 6 Cross-section of NBS hot box test apparatus 1937 – 1964 ................................ 12
 

(Whittemore et al., 1943)...................................................................................................... 12
 

Figure 7 NBS hot box test apparatus 1967 - 1980 ............................................................. 12
 

Figure 8 Proposed PCM evaporator for investigation ..................................................... 13
 

Figure 9 Delphi Automotive PCM evaporator................................................................... 15
 

Figure 10 External PCM evaporator where PCM re-condenses refrigerant before the 

refrigerant enters the second evaporator coil ........................................................ 16
 

Figure 11 External PCM evaporator where the PCM is pumped through the first 

evaporator coil........................................................................................................... 17
 

Figure 12 Model of NIST plumbing tower ......................................................................... 18
 

Figure 13 Net zero house electricity net generation and usage (Fanney et al., 2014) ..... 20
 

Figure 14 Fraction of excess electricity stored as a function of the size of the ................ 21
 

storage system........................................................................................................................ 21
 

iv 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

INTRODUCTION 

Compared to residential electricity generation from photovoltaic (PV) systems and wind 

turbines, residential electricity energy storage is essentially non-existent. As long as utilities buy 

excess renewable electricity generation from residences at supply prices, a practice called net 

metering, there is little incentive for home owners to consider energy storage to handle their 

excess electricity production. However, as renewables energy generation becomes more 

prevalent, it is not expected that power companies will continue net metering without 

transferring some of the grid maintenance costs to the PV homeowner to ensure that they pay 

their fair share (CPUCED, 2005). Furthermore, in the event of high market penetration of 

residential renewable energy, on-site generation would no longer be welcomed nor fully used by 

the existing utility grid (Pless and Torcellini, 2010). The reason for this is that excess electricity 

from renewables may cause grid instabilities (Scaini, 2012) and blackouts due to low demand 

and insufficient electricity storage capacity (Bruch et al., 2011). Excess electricity from 

renewable resources makes it difficult for grid operators to balance electricity supply and 

demand. The effects of variable renewable electricity generation have already been seen in 

European markets, most notably in Germany, which forced negative pricing of conventionallyproduced electricity during certain times of the day due to high renewable output and low 

demand (DGE, 2012). Local electricity storage could reduce the strains on a utility’s reserve 

capacity by providing electrical power at or near the source of use thus eliminating the 

inefficiencies of ramping fossil fuel based generation capacity, and of transmitting the power 

during periods of high demand. Both the phase-down of net metering and the need for greater 

grid stability will drive demand for residential energy storage. However, local storage of excess 

electrical energy from renewable electricity sources is currently not economically attractive due 

to the long payback period required to recover capital costs. Electricity Storage (ES) capital 

costs are well above the $100/kWh (IREA, 2012) that the United States Department of Energy 

has determined would make a system economically attractive. Reaching the target of $100/kWh 

could be accelerated by focusing future research on the most viable technologies and concepts. 

Electrical grid supply/demand mismatch, as well as peak demand shaving, can also be addressed 

by thermal energy storage. Thermal energy storage is attractive because it can be used to reduce 

energy use by taking advantage of cooler ambient temperatures at night and warmer ambient 

temperatures during the day. Heating and/or cooling energy can be stored during times of excess 

renewable resource or favorable outdoor conditions, and then used during peak grid demand or 

when renewable resources are not available. Thermal storage can effectively be used to store 

both thermal (e.g. solar thermal) and electrical (e.g. PV or wind turbine driven heat pump hot 

water heater) energy. Unlike electricity, a utility does not exist that will purchase a 

homeowner’s low grade thermal energy at generated value. Consequently, thermal energy 

storage is likely to appear more appealing than electrical storage as a residential capital 

investment at the present time. In fact, Hudon et al. (2012) report that solar water heaters are on 

their way to becoming cost-competitive with conventional natural gas water heaters in most 

regions of the United States. 

Considering the National Institute of Standards and Technology’s (NIST’s) mission of 

“enhanc[ing] economic security and improve[ing the] quality of life” by “advancing 

measurement science, standards, and technology” there is a clear fit/justification for NIST 

bringing its expertise to bear on the problem of cost-effective residential energy storage. The 

1 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

question is what research should NIST be focused on that will result in the greatest impact for 

the U.S. consumer while remaining within the realm of NIST’s charter. NIST research is 

confined to measurement science that falls within one of the following categories: 

(1) The development of performance metrics, measurement and testing methods, predictive 

modeling and simulation tools, knowledge modeling, protocols, technical data, and 

reference materials and artifacts. 

(2) The conduct of inter-comparison studies and calibrations 

(3) The evaluation and/or assessment of technologies, systems, and practices including 

uncertainty analysis. 

(4) The development of the technical basis for standards, codes, and practices—in many 

instances via testbeds, consortia, standards development organizations, and/or other 

partnerships with industry and academia 

Accordingly, this paper identifies research that can facilitate the commercialization of residential 

energy storage while conforming to one of the above four measurement science categories. 

GENERAL RESEARCH NEEDS FOR VARIOUS ENERGY STORAGE METHODS 

Figure 1 taken from the Fraunhofer Institute for Solar Energy Systems shows the five different 

classifications of electrical energy storage systems: (1) mechanical, (2) electrochemical, 

(3) chemical, (4) electrical, and (5) thermal. Mechanical energy storage includes pumped hydro 

storage (PHS), compressed air energy storage (CAES), and flywheel energy storage (FES). 

Electrochemical energy storage includes secondary batteries and flow batteries. Chemical 

energy storage is primarily focused on using electricity to produce hydrogen. Electrical energy 

storage includes double-layer capacitors and superconducting magnetic coils. Thermal energy 

storage includes sensible heat storage and latent heat storage (not shown in Fig. 1). 

Mechanical Energy Storage 

Pumped hydro: Pumped hydro is used to store over four-fifths of the world’s renewable 

electricity (IRENA, 2012). However, commercial PHS for residential storage does not presently 

exist. Typical PHS consists of two bodies of water at different elevations. Electricity is stored 

by pumping water from the lower reservoir to the upper reservoir. The electricity is retrieved 

when the water is allowed to flow back down from the upper reservoir through a turbine and into 

the lower reservoir. The turbine operates a generator that produces electricity. The efficiency of 

a PHS ranges between 70 % and 85 % (IEC, 2011). 

No commercial residential PHS exist because the cost effectiveness of PHS increases with the 

size of the system and the traditional system requires two large bodies of water separated by 

100 m or more in elevation. Therefore, working towards a smaller PHS that is suitable for the 

home is counterintuitive. In addition, most homes do not have the hilly topography that is 

required of traditional PHS. However, rather than having a lake on top of a small mountain 

above a damned river, the elevation difference for residential PHS could be achieved with 

alternate reservoirs. For example, Martin and Baines (2007) suggest that PHS which would 

consist of drilling a well and galleries as an underground lower reservoir, with an integrated 

pump/turbine at the surface or just below the upper reservoir at ground level. The required depth 

of the well could be reduced by using compressed air and/or a piston weight. Advocates for 

2 
             

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

smaller PHS, like Islam (2012), argue that PHS will have a greater overall efficiency than most 

technologies and can be maintained using local technical expertise. An additional advantage of 

PHS is that it can be sized to meet a few days’ energy requirements of a particular home by 

selecting the correct diameter and depth of the well. Otherwise, a community PHS may also be 

an option if smaller systems cannot be made cost effective. 

Figure 1 Fraunhofer ISE classification of electrical energy storage systems 

according to energy form (IEC, 2011) 

Compressed air: CAES stores energy in tanks or caverns in the form of compressed air. Energy 

is retrieved by expanding the compressed air through a turbine to produce electricity. According 

to Zhai et al. (2013), CAES are reliable, have negligible self-discharge, are non-toxic, and have 

very long lifetimes. One disadvantage of CAES is that it has a low thermodynamic efficiency 

because there is a rise in temperature of the air during compression, which causes heat to be lost 

to the surroundings. In addition, the air has to be heated during expansion (Zhai et al., 2013). 

Recuperators can be used to improve the efficiency by exchanging heat between the compressed 

and expanded air (IEC, 2011). Havel (2103) suggests that further improvements in efficiency 

and cost reductions can be achieved by using non-underground nano-porous material for 

compressed air storage. Similar to PHS, CAES can be sized for residential use (Kim and Favrat, 

2008). 

Flywheel: FES is currently used as relatively short discharge time by power plants for load 

leveling and as uninterruptible power supply (UPS) devices. Flywheels store electricity from a 

motor as kinetic energy in the form of a spinning disk of significant mass. The energy is 

retrieved from the flywheel when it is used to drive the motor as a generator. The amount of 

energy stored depends upon the speed and the mass of the disk (Reading, 2004). Short discharge 

time flywheels are used for stabilizing voltage and frequency, while longer duration flywheels 

are suitable for damping load fluctuations (Deal et al., 2010). According to Reading (2004), 

3 
             

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

flywheels are most suitable to discharge times in the order of seconds to a few minutes. 

Consequently, FES appears not to be suitable for residential energy storage. However, potential 

research areas could focus on extending the discharge duration and evaluation tests. 

Electrochemical Energy Storage 

Battery: Batteries are one of the most popular areas of research for energy storage because they 

are very efficient and have a large power output. However, battery capacity diminishes over 

time, they experience self-discharge, and they typically use toxic and/or flammable materials 

(Zhai et al., 2013). Most of the current research is focused on ways to make batteries safer and 

cheaper via lower-cost materials and chemistries. 

NIST’s Center for Nanoscale Science and Technology is currently using nanowires to investigate 

how to improve the performance of lithium-ion batteries.2 The nanowire is being used as a tag 

so that changes in the micro-structure of the battery during charging and recharging can be 

visualized. Similarly, NIST’s Material Measurement Laboratory researchers have 

collaboratively developed a promising lithium-sulfur (Li-S) battery that weighs roughly half as 

much but contains twice as many ions as a lithium-ion battery (Simmonds et al., 2014). The 

battery is expected to be less expensive than the lithium-ion battery and survive the same number 

of recharging cycles. The Engineering Laboratory could work with both or either of these 

projects to demonstrate the improved batteries as used in residential energy storage applications. 

Chemical Energy Storage (CES) 

Hydrogen: Electricity can be used to produce hydrogen from water with conventional 

electrolysis. Electrolysis is done by passing a direct current through a dilute water solution of an 

electrically conductive acid or base (Pilar, 1979). The process separates water into gaseous 

hydrogen and oxygen that collect at the cathode and anode, respectively. The hydrogen can be 

stored and used to operate engines, fuel cells, or other devices that use hydrogen as fuel. 

Electricity may be retrieved from the hydrogen by using a fuel cell, which is essentially 

electrolysis in reverse. A fuel cell converts hydrogen and oxygen into electricity by ionizing the 

elements in the presence of an electrolyte. Like a battery, a fuel cell is an electrochemical energy 

conversion device, but rather than storing energy it converts it. 

In one type of fuel cell, the hydrogen ions flow to the cathode inducing a flow of electrons, i.e., 

current flow, from the anode to the cathode. Most fuel cell research is done to improve the 

efficiency of the use of hydrogen because the efficiency of the conversion of electricity to 

hydrogen and back to electricity via a fuel cell is only around 20 %3 . For example, NIST’s 

Center for Nanoscale Science and Technology is currently working on improving the efficiency 

of the catalysts used in the water-splitting process with additives in iron oxide (Bohn et al., 

2012). However, despite low efficiency, hydrogen could achieve low and attractive costs3 . 

There are several projects being conducted in NIST’s Material Measurement Laboratory (MML) 

dealing with improving materials for containing hydrogen and the efficiency of fuel cells that use 

hydrogen. Research on materials for use with hydrogen is important because hydrogen can 

penetrate and embrittle some metals and alloys. One project in MML has developed a facility 

2

 http://www.nist.gov/cnst/erg/nanowire_li_ion_battery.cfm 3

 http://ec.europa.eu/energy/infrastructure/doc/energy-storage/2013/energy_storage.pdf 

4 
             

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

for testing the suitability of pipes, valves, fittings and pumps for transporting and delivering 

hydrogen.4

 In addition, the Materials Measurement Science Division of MML is working on 

solar-powered hydrogen generation as a cost-effective way to generate hydrogen directly from 

water and sunlight with a silicon-based device (Esposito et al., 2013). The Engineering 

Laboratory (EL) could work with both or either of these projects to demonstrate the use of 

hydrogen in residential energy storage applications. The concepts for improving the efficiency 

of fuel cells could be examined with the fuel cell rating procedure that was developed in EL by 

Davis et al. (2006). In addition, basic characteristics and concept testing of CES components and 

systems including technical evaluation (capacity, power, discharge time, lifetime, etc.) could lead 

to guides for implementation of CES. 

As Figure 2 from the Fraunhofer Institute for Solar Energy Systems shows, hydrogen has the 

potential for the highest energy content and power of most of the energy storage technologies. In 

addition, the Fraunhofer report shows that the most research is needed in this area to get it to 

product and to increase efficiencies from the present values of 35 % to 45 %. Possible areas of 

research include methods to enhance performance and lower costs of electrolysis, and to develop 

underground and solid storage. Otherwise, hydrogen stored as vapor requires large tanks, while 

hydrogen stored as liquid requires cryogenic temperatures and energy to achieve the low 

temperatures. 

Electrical Energy Storage 

Double-Layer Capacitor: The double-layer capacitor is also known as the super capacitor or the 

ultracapacitor. Like traditional capacitors, the double-layer capacitor is an electrical device that 

consists of two oppositely charged metal plates separated by an insulator. What makes a doublelayer capacitor different is that the insulator is an ionic fluid that enables the capacitor to behave 

as two capacitors in series (Deal et al., 2010). Energy is stored in the capacitor by charge 

accumulation on the metal plates. Energy is discharged when the electric charges are released by 

the metal plates. Given that capacitors are suitable for short-duration applications as in 

providing backup power during brief interruptions, they are not really applicable to residential 

storage. However, EL could test super capacitor prototypes for use in residential applications. 

Currently, NIST’s Electromagnetics Division in Boulder is researching ways in which to use 

graphene in the construction of super capacitors to extend the duration of energy release. 

4

 http://www.nist.gov/mml/acmd/hydrogen_021610.cfm 

5 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Figure 2 Fraunhofer ISE comparison of rated power, energy 

content and discharge time of different EES technologies (IEC, 2011) 

Superconducting magnetic coil (Superconducting magnets): Superconducting magnetic energy 

storage (“SMES”) stores energy in the magnetic field produced by a superconducting winding. 

One disadvantage of SMES is that the superconducting wire of the windings requires cryogenic 

refrigeration for the wire to function as a superconductor. Current research is focused on 

increasing the temperatures at which wire superconductivity can be achieved and increasing the 

duration of energy release (Deal et al., 2010). 

NIST has been conducting superconductivity research since 1916 (Lundy et al., 1989). Several 

divisions at NIST have active material research for superconducting material that function at 

temperatures greater than 100 K. In general, because SMES only offer a few hours of storage, 

they have limited application to residential storage. However, there are opportunities for EL to 

work together with other NIST laboratories in their efforts to demonstrate extended duration and 

higher operating temperatures. 

Thermal Energy Storage 

Thermal energy storage can be integrated with both direct-thermal systems (e.g. solar thermal) 

and indirect-thermal (e.g. PV driven heat pump hot water heater). Similar to electrical storage, 

thermal energy storage time-shifts loads on electrically-driven thermal machinery (spaceconditioning and water heating equipment) to minimize electricity import/export and peak 

demand; energy is stored during times of excess renewable resource, favorable outdoor 

temperatures, or low grid demand, and then utilized at the residence during peak load times. An 

6 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

additional benefit of thermal energy storage is that the peak capacity rating (and subsequently 

size, cost, and cycling inefficiencies) of thermal machinery can be reduced. A small thermal 

system can operate as a hybrid with the storage to provide peak loads, where during periods of 

low loads the thermal system can be charging the energy storage system. 

Sensible heat storage: Electricity is used to either heat or cool a single phase fluid for later use 

for space heating or cooling, respectively. When electricity is used to heat a fluid it is called 

active heating. When heat is collected from the sun it is called passive solar heating. Generally, 

sensible heat storage (SHS) is done without re-electrification (Deal et al., 2010). Hot water tanks 

are used to store hot water produced by either electricity or solar energy (IRENA, 2013). The 

hot water can be used for either residential hot water usage or heating during the night. 

Aquifer thermal energy storage can be used for both space heating and cooling by pumping 

ground water through a heat exchanger. In the summer, ground water is drawn from one side of 

the well to air condition. The warmed water from the air-conditioning heat exchanger is returned 

to a part of the well that is a sufficient distance from the pumped side of the well. The warmer 

water is stored until it is needed for heating in the winter. In winter, the direction of flow is 

reversed so that the cooled water is returned to the cooler side of the well. Significant research is 

done on ways to isolate the warm and cool sides of the aquifer in order to maintain temperature 

stratification (Zhai et al., 2013). Chung et al. (2008) have found that the degree of temperature 

stratification has a significant effect on the efficiency of the system. Stratification can be 

improved with properly designed shape and position of the suction and discharge to the aquifer, 

and other devices to reduce mixing. 

Research needs for sensible heat storage would include ways to enhance the single-phase heat 

transfer of water and secondary fluids. Enhancement techniques would include passive internal 

tube flow enhancements like those shown in Webb and Kim (2005) and the use of nanofluids as 

recommended by Kedzierski (2013). Similarly, Fox et al. (2011) showed the benefit of 

nanofluids as nanoparticle-enhanced ionic liquids (NEILs) for increasing the energy stored per 

volume in concentrated solar power units. 

Latent heat storage: Latent heat storage (LHS) uses phase change materials (PCMs) to store 

thermal energy. According to Sharma et al. (2009), most PCMs are designed to release heat 

when they change from liquid to solid and to store heat when they change from a solid to liquid 

having 5 to 14 times more heat per unit volume than liquid water. PCMs are advantageous 

compared to sensible heat storage because of high energy density, and, the nearly constant 

discharging temperature (Dincer and Rosen, 2002). PCMs more typically phase change between 

solid and liquid, but liquid-gas PCMs exist. PCMs are used to reduce peak-hour cooling loads. 

According to Kośny et al. (2008), PCMs have been used in buildings for at least 40 years. PCMs 

can be classified as organic (fatty acids, eutectic mixtures, fatty alcohols, neopentyl glycol, and 

paraffinic hydrocarbons, alkanes) or inorganic (salt hydrates) (Pinel et al., 2011 and Kośny et al., 

2008). Water is also considered to be a PCM when it is used in ice storage. 

Passive solar heating collects heat from the sun and stores it in a PCM. For active heating, the 

PCM is heated by electrically driven machinery. The heat is released at night when it is cooler. 

PCMs can also be used to store energy at cooler night temperatures for cooling during the day. 

7 
             

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Significant material research is done to find organic and inorganic PCMs at specific design 

working temperatures, to have large heat of fusion, high thermal conductivity, low toxicity, low 

corrosiveness, and distinctive phase separation characteristics. PCMs other than water are 

necessary to store energy for heating so that the phase change occurs near the heating application 

temperature. Baetensa et al. (2010) state that only a few materials are known to transition around 

the comfort temperature, and these have a relatively low heat of fusion. NIST is not currently 

conducting research on PCMs for energy storage. However, the National Renewable Energy 

Laboratory (NREL) has an extensive research program on the subject (NREL, 2011). NREL’s 

research on new PCMs is focused on characterizing the melting point temperature, the 

chemically stable working temperature range, the chemical compatibility with materials, the heat 

capacity, the latent heat, the thermal conductivity, the viscosity, the liquid and solid densities, 

and the cost. 

PCMs can be integrated into residential thermal conditioning systems in several different 

configurations. For example, PCMs can be used in heat exchangers where the PCM is pumped 

to another (sink) heat exchanger for use; alternatively, a secondary fluid can be pumped between 

the PCM source and sink heat exchangers. Another option includes using PCMs as part of the 

construction material of the walls of the home. For example, small pellets of PCM material can 

be embedded in the gypsum of drywall that forms the interior wall of a home, and/or the PCM 

material can be a full layer in the wall construction as done in advanced façade construction 

(Zhai et al., 2013). 

PCMs can be used strictly to store and reuse thermal energy (Heller, 2013), or they can be used 

to generate electricity with concentrated solar power (CSP), a steam generator and a turbine 

(Kotzé1 et al., 2011). Whether the PCM is used to store thermal energy or to make electricity, 

heat transfer research is required to adequately size and rate the heat exchanger and improve the 

efficiency of the heat transfer. 

Using stored ice as a PCM is a popular way to provide air conditioning for large buildings. The 

benefit is that ice is made during the night when commercial electricity rates are significantly 

lower than during the day when the demand for electricity is high. In addition, chillers for 

making ice can be smaller than those large enough to meet the building’s immediate cooling 

demand because the smaller chillers can operate continuously throughout the night to make 

enough ice for the peak day’s use (ASHRAE, 2012). Residential electricity rates typically do not 

vary with the time of day, so making ice with imported energy during the night has limited 

application to the home. However, ice storage can provide an alternative to exporting excess 

renewable electricity to the grid. As an example a wind turbine that produces more electricity 

during the night than during the day could be used to drive an ice-making machine for storage. 

Ice made at night would be done at greater or comparable system efficiency due to lower outdoor 

air/condensing temperatures as compared to daytime temperatures (ASHRAE, 2012). The home 

might require two separate systems for cooling: a relatively small chiller for making ice and a 

heat pump to meet the cooling demands when there is no stored ice. Ice slurry and melt-ice-oncoil heat transfer studies like those done by Kumano et al. (2014) and Lo ́pez-Navarro et al. 

(2013), respectively, would have to be either adapted or re-done for residential applications. 

8 
             

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Combined Energy Storage Methods 

Combined Technologies: Energy storage technologies are combined in an attempt to mitigate 

the shortcomings of a particular technology. Most of the combined technologies currently in the 

literature involve compressed air systems. For example, Bi et al. (2013) and Wang et al. (2013) 

have investigated combining pumped hydro with compressed air, i.e., PHCA. The advantage of 

the PHCA system is that it avoids the inefficiencies of adding heat during the expansion process 

of the compressed air system. As shown on the left of Fig. 3, rather than using the compressed 

air to run a turbine, the air is use to pressurize water that is used to drive a pump. Wang et al. 

(2013) have calculated that a tank pressure (P) of 5 MPa is equivalent to a dam with a height (h) 

of 500 m as shown on the right side of Fig. 3. 

Figure 3 Comparison of PHCA to equivalent PHES system (Wang et al., 

2013) 

Lemofouet and Rufer (2005) show that combining compressed air with supercapacitors improves 

the flexibility and the dynamic performances of the storage system without the need for fuel to 

reheat air. The supercapacitors serve to increase the stability and “smoothness” of the variable 

output of the system and result in efficiency improvements. 

Havel (2013) reduces the required pressures of CAES by adsorbing the air in nano-porous 

materials. Adsorption of the air provides an equivalent air density of 100 bar at less than 20 bar. 

The modified energy storage system is temperature rather than pressure controlled and as a result 

is less costly and more efficient than traditional CAES. 

POTENTIAL ENERGY STORAGE RESEARCH 

This section highlights projects that might be particularly successful in the EL laboratory 

because they capitalize on existing strengths of the organization. 

9 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

PCM Facades 

Figure 4 shows a passive cooling of a room with external walls containing phase change 

material, i.e., PCM facades (IRENA, 2013). PCMs make it possible to turn the inconvenience of 

outdoor temperatures transitioning from too hot to too cold into a means for energy conservation. 

During the day when the incident sun causes the temperature of the outside wall of a home to 

increase, the insulation and the wall materials act to delay the increase in temperature of the wall 

inside the house. The specific heat and the thermal conductivity of the insulation and the wall 

materials determine how quickly the inside wall temperature increases for given outside 

conditions. A wall with a large specific heat and a small thermal conductivity exhibits inside 

temperatures that respond more slowly to the outside temperature and incident sun than 

otherwise. The use of PCMs significantly increases the response time of the inside wall 

temperature by adding an additional energy storage term (heat of fusion) to the wall’s effective 

heat capacitance. If the melting point of the PCM is chosen correctly, it will be near the desired 

room temperature and solid when the outside temperature begins to increase. Because the PCM 

typically melts at a constant temperature, the increase in the outdoor temperature acts to melt the 

PCM at TPC. As long as some solid PCM remains, the hotter outside temperature is prohibited 

from increasing the inside wall temperature greater than TPC. Rather, the energy incident from 

the outside is stored in the PCM as a higher energy state, i.e., liquid. During the night the PCM 

in liquid form works to keep the house warm by remaining at a constant, comfortable 

temperature as the night air freezes the PCM. Likewise, as long as some liquid remains in the 

PCM, the colder outside temperature is not seen by the inside of the house. Baetensa et al. 

(2010) state the above more succinctly: “the principle behind phase change materials is excess 

energy at elevated temperatures is stored and given back at a certain temperature, resulting in an 

increased thermal mass in a narrow temperature range.” 

Figure 4 Passive cooling with external PCM wall (IRENA, 2013) 

Figure 5 shows some of the many forms that PCM facades can take. Some facades have air 

cavities that can be selectively ventilated. The ventilation can be achieved with a blower (active 

ventilation) or by natural convection (passive ventilation). As shown in Fig. 5, Zhai et al. (2013) 

investigated several different multilayer walls, some with multilayer PCMs. They developed the 

Advanced Façade Systems “AdvFacSy” tool that models the heat transfer through various PCMs 

walls like those shown in Fig. 5. The AdvFacSy uses an enthalpy method with an iterative 

correction scheme to account for weather conditions and solar radiation. 

10
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Figure 5 Classical and advanced façade designs with and without PCMs in 

“AdvFacSy” Toolbox [(a) Multi-layer wall; (b) Ventilated opaque multilayer wall; (c) Ventilated transparent multi-layers walls] (Zhai et l., 2013) 

Considering the above, the first area of potential research for EL in PCM facades is to build on 

the work of Zhai et al. (2013) toward determining the favorable design and material selection for 

PCMs in residential facades. Entire house simulations, like those done by EL’s Office of 

Applied Economics (Kneifel, 2010), could then be done to determine which PCMs, and in what 

configuration are the best for a particular climate. Building cost databases for the various PCMs 

façades would have to be developed. These would serve as input for the whole building energy 

consumption simulations that are used to determine the life-cycle cost-effectiveness and carbon 

emissions of each design. NIST’s Building for Environmental and Economic Sustainability 

(BEES) software (Lippiatt, 2007) could be used to compute the life-cycle costs analysis as was 

done by Kneifel (2010). 

The second area of potential research in PCM facades would be to measure the performance of 

various PCM walls in a calibrated hot box. NIST has an extensive history using several versions 

of a calibrated hot box for measuring the heat transferred through compound walls (Zarr, 2001). 

Figure 6 shows a schematic of the cross section of the hot box envisioned by R. S. Dell and 

completed in 1937 (Whittemore et al., 1943). The wall specimen is shown sandwiched between 

a cold and a hot box. The hot box was heated by electric heaters and the power was measured 

with a watthour meter. A fan was used to gently mix the air so that the air temperature was 

nearly uniform. The cold side of the box was cooled by mechanical refrigeration. The outer 

walls of the cold box and the hot box were maintained at their respective air temperatures so as 

to minimize heat loss/gain from the surroundings. 

11
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Figure 6 Cross-section of NBS hot box test apparatus 1937 – 1964 

(Whittemore et al., 1943) 

Figure 7 shows a photograph of the calibrated hot box that was in EL from 1967 to 1980. 

Currently, EL does not have a calibrated hot box. The advantage of this is being able to design a 

new hot box so that it is tailored for use with PCM facades. The calibrated hot box could be 

designed for measuring the heat, air, and moisture transfer of room-sized exterior wall specimens 

Figure 7 NBS hot box test apparatus 1967 - 1980 

12
 
             

 

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

under a range of simulated climatic conditions. 

PCM Evaporator for Residential Air Conditioner 

Integrated PCM 

A new concept that EL could investigate is the direct expansion PCM evaporator for highefficiency air conditioner shown in Fig. 8. The PCM evaporator resembles a conventional 

residential evaporator in that it is a tube-and-plate-fin geometry with air flowing between the 

aluminum plate fins and evaporating refrigerant flowing inside nominally 9 mm OD copper 

tubes. However, the refrigerant tubes are inside of a larger copper tube thus forming an annulus 

that is filled with PCM material. The melting temperature of the PCM material is proposed to be 

approximately 2 K less than the dew point of the humid air so that dehumidification occurs on 

the evaporator fins. The tubes are orientated nearly vertically to prevent voids in the PCM 

material from forming in the annulus so as to keep the outer wall of the annulus wetted with 

phase change material during the melting process. The PCM does not flow in the annulus, 

rather, each tube is closed on both ends. The tilt of the fins allows for condensate drainage from 

the fins to occur by gravity. 

Use of a PCM evaporator will allow the air conditioning unit to be much smaller and operate 

Figure 8 Proposed PCM evaporator for investigation 

more efficiently than the traditional unit. The required capacity is reduced because the peak load 

is met by the combined capacity of the mechanical air-conditioning and the melting of the PCM 

material. The efficiency is improved because the unit runs nearly continuously instead of 

cycling on and off to meet the load. Dampers would be required to close off the ducted air flow 

while the PCM was in recharge mode. 

The first phase of the project should be to design the evaporator for the correct size and the 

correct total mass of PCM for a given cooling duty. The evaporator should have four rows and 

the space between the annulus should be large enough so that there is sufficient PCM to remain 

solid through the peak demand time. Preliminary measurements from the NIST net-zero house 

13
 
             

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

show that an additional 4 kWh to 6 kWh of cooling would be required to “shave” the peak load. 

Using the latent heat of fusion of a commercially available PCM (PureTemp 8)5,6of 180 kJ/kg 

with a density of 860 kg/m3, it would require approximately 120 kg of PCM to meet 6 kWh. A 

typical residential air conditioner has approximately 40 m of evaporator tubing. Assuming that 

the diameter of the inner refrigerant tube of the PCM evaporator shown in Fig. 8 is 9 mm, the 

outer diameter would need to be approximately 67 mm to hold 120 kg of PCM within the 

annulus. This outer tube diameter is physically possible but can be reduced by using a PCM of a 

larger heat of fusion or more tubing length. In addition, geometries other than that shown in 

Fig. 8 can be investigated that result in smaller evaporators. Other investigated geometries could 

include remote PCM storage tanks where the evaporator refrigerant is circulated through peak 

loads. 

The second phase of the project should be to characterize the heat transfer of the PCM in a 

simplified version of the evaporator in the laboratory. Heat transfer coefficients as a function of 

the percent solid mass of PCM should be developed in order to calculate the transient heat 

transfer of the evaporator. The third phase of the project should be to manufacture a PCM 

evaporator and install it in a residential unit and evaluate the performance in the environmental 

chambers. The fourth phase of the project should be to install the PCM evaporator in the NIST’s 

Net-Zero Energy Residential Test Facility (net-zero house) (Fanney et al., 2014) for field testing. 

The final phase of the project should be to explore ways that the same PCM heat exchange could 

be used in heating as well as cooling as is done in a residential heat pump. A possible technique 

to make a PCM-integrated heat exchanger both an evaporator and a condenser would be to 

charge the PCM annuli with equal parts heating and cooling PCM. Alternatively, a PCM 

mixture that is capable of shifting composition and thus melting temperatures could be used for 

both heating and cooling modes. The composition shift could be achieved by distillation, 

filtering as in a reverse osmosis system, or by shifting the water content of a salt hydrate PCM. 

All in all, the PCM evaporator is expected to be a worthwhile project to pursue. Support of this 

premise was found when the authors were able to find a prototype PCM evaporator for 

automotive air conditioning. Figure 9 shows an automotive PCM evaporator currently under 

development; in 2012 it was expected to be in production by the year 20157 . The automotive 

PCM evaporator is expected to be lower cost and more efficient than a traditional system. In 

addition, EL has experienced staff and facilities for testing heat pumps and novel heat transfer 

devices and surfaces. 

Discrete PCM 

A second concept for the PCM evaporator locates the PCM external to the air handler within its 

own heat exchanger. Storing the PCM external to the evaporator eliminates the concern of 

having sufficient PCM mass within a limited evaporator volume and footprint, but adds some 

complexity as additional valves are needed for control. 

5

 http://www.puretemp.com/technology.html 

6 Certain trade names and company products are mentioned in the text or identified in an illustration in order to adequately specify the 

experimental procedure and equipment used. In no case does such an identification imply recommendation or endorsement by the National 

Institute of Standards and Technology (NIST), nor does it imply that the products are necessarily the best available for the purpose. 

7 http://johndayautomotivelectronics.com/delphi-air-conditioning-technology-with-pcm-evaporator-keeps-start-stopvehicles-cooler-longer/ 

14
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Figure 9 Delphi Automotive PCM evaporator 

One possible configuration for this system is shown in Fig. 10. The system is comprised of two 

evaporator coils with an intermediate PCM heat exchanger, two electronic expansion valve 

(EXVs), and a bypass valve. Using EXVs, rather than thermostatic expansion valves (TXVs), 

allows the system to use control logic to completely close the EXV when a particular refrigerant 

circuit is not needed. Depending on the current and anticipated loads, the system would operate 

in three modes: charge, release, and normal. The only difference between the modes is which 

heat exchanger acts as the evaporator load for the rest of the air-conditioning system. For 

example, for the charge mode, only the PCM heat exchanger provides a cooling load for the 

system. Similarly, evaporator coils 1 and 2 act as the evaporator for the normal mode with the 

PCM heat exchanger bypassed. In the release mode, all three heat exchangers are used. 

In the charge mode, the PCM is cooled and solidified by the refrigerant flowing from the 

condenser with its mass flow controlled by a dedicated expansion valve (EXV2 in Fig. 10). No 

air flows in the air handler during the charge mode. In the release mode, the refrigerant flows 

from the condenser and through the EXV1, both evaporator coils, and the PCM tank. The 

refrigerant evaporates in the first evaporator coil, re-condenses in the PCM heat exchanger, and 

then evaporates again in the second evaporator coil. The release mode combines the capacity of 

the air conditioner with that of the PCM to temporarily increase the system cooling potential. 

The system would run in the normal mode when the PCM is fully charged or when predicted 

future loading conditions do not require the extra energy stored in the PCM material. The PCM 

tank is bypassed in the normal mode to reduce losses related to the pressure drop and the heat 

leak through the PCM tank. Normal mode uses both coils, which is a large heat exchange 

surface relative to the capacity of the heat pump alone (i.e. without the PCM). This results in a 

higher air-side pressure drop than would occur if just the first coil was used. Additional fan 

15
 
             

 

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Figure 10 External PCM evaporator where PCM re-condenses refrigerant before the 

refrigerant enters the second evaporator coil 

power would be required to overcome the pressure drop; however, these losses would at least 

partially be offset by the compressor efficiency gains related to higher saturation temperature 

(achieved via the larger evaporator surface area). 

The system shown in Fig. 10 would require a phase transition temperature below the evaporation 

temperature of the refrigerant (about 7 °C (45 °F)) in order to re-condense the refrigerant exiting 

the first evaporator coil. When the PCM material is being charged, the refrigerant saturation 

temperature must be even lower than the PCM transition temperature; therefore the charging 

process will occur at a reduced COP relative to normal operation. Furthermore, the insulation 

losses in the PCM tank will be higher because of the low storage temperature. 

Figure 11 shows another possible configuration for a discrete/external PCM evaporator, where 

the PCM is pumped through an evaporator coil as a slurry to cool the air. The system features 

two evaporator coils, two independent EXVs to control the PCM and the second evaporator coil 

circuits; and the pump to circulate the PCM slurry, respectively. This system can be operated in 

four modes including normal, charge, release, and combination. In the normal mode, the 

refrigerant flows only through EXV2 and the second evaporator coil. During charging, 

refrigerant cools the PCM after expanding in EXV1. The maximum system capacity is achieved 

in release mode, where the PCM slurry is circulated through the first evaporator coil, and the 

refrigerant is circulated through EXV2 and the second evaporator coil. Finally, the system can 

operate in a combined mode where both EXVs are open. Here, the refrigerant simultaneously 

cools the second evaporator coil and the PCM material. 

The PCM material can operate with a higher phase transition temperature than the normal 

refrigerant saturation temperature (about 7 °C (45 °F)) in this configuration because it is used to 

directly cool the air, rather than to re-condense the refrigerant as it does in the Fig. 10 

configuration. The PCM evaporator effectively pre-cools the air for the refrigerant evaporator

16
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

coil. The PCM evaporator provides mostly sensible cooling, whereas the colder refrigerant 

evaporator coil provides both sensible and latent cooling. 

The Fig. 11 configuration offers two distinct advantages compared to the Fig. 10 configuration, 

including the higher PCM transition temperature (which allows the charge mode to operate with 

a higher COP), as well as the ability to operate in combination mode. However, the PCM 

evaporator restricts the airflow even when not in use, and provides no offsetting benefit. 

Figure 11 External PCM evaporator where the PCM is pumped through the first 

evaporator coil 

The storage needs and development cycle for the external PCM evaporator are very similar to the 

annulus-filled PCM evaporator described in the preceding “PCM Evaporator for Residential Air 

Conditioner - evaporator-integrated PCM” section. The storage needs to meet the peak would be 

approximately 4 kWh to 6 kWh of energy stored in 120 kg of PCM. 

The development of this system would begin with a modeling study of the system to determine 

feasibility and optimization of the system. A system prototype can be constructed and tested in 

the environmental chambers, as well as the NIST net-zero house. 

Pumped Hydro 

Figure 12 shows a model of the existing structure of the plumbing tower in EL. The overall 

height of the tallest portion of the tower is approximately 18 m. The EL plumbing tower could 

be used to test scaled versions of advanced pumped hydro with/out compressed air for residential 

applications. Chanson (1999) provides guidance on how to properly scale a physical hydraulic 

model with consideration given to the boundary and flow conditions. According to Chanson 

(1999) physical hydraulic models are used to optimize hydraulic systems and to guide design 

decisions. 

17
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

A prototype of the full-scale PHS would allow the exploration of the value of adding compressed 

air to the system and other hybrid techniques. In the meantime, the tests would be considerably 

less expensive than a full scale test and could be done under controlled laboratory conditions and 

allow for the development of concise predictive models. 

Figure 12 Model of NIST plumbing tower 

Water Heaters 

EL has studied water heater performance for more than a decade (Fanney et al., 2000, Healy et 

al., 2003, and Healy et al., 2011). The NIST studies deal with general thermal performance, 

efficiency, and rating methodologies for water heaters. These skills could be used to investigate 

solar water heaters (SWHs) and heat pump water heaters (HPWH). 

Solar water heaters use energy from the sun to directly or indirectly heat water. Indirect water 

heating requires a secondary heat transfer fluid to travel between the solar heat exchanger and 

the water heater tank. A PCM may be used as a stationary “secondary fluid.” Sharma et al. 

(2009) state that research is needed to improve the heat exchange between the PCM and the 

water. EL has the personnel and the laboratory experience to carry out the necessary studies that 

would be required to characterize the fundamental heat transfer characteristics of PCM as 

secondary fluids. According to Hudon et al. (2012), another crucial area of research for SWHs is 

to enable operation in cold climates. In addition, Hudon et al. (2012) claim that SWH systems 

can already meet the hot water demand for a typical household, but that the major barrier to 

achieving significant market acceptance is the capital cost (Sharma et al., 2009). 

Heat pump water heaters use a heat pump to assist electric resistance heating elements to heat 

water in a tank. Hudon et al. (2012) note that commercially available HPWHs operate more 

efficiently in warmer climates. Zimmerman (1986) states that HPWHs have been manufactured 

18
 
             

 

 

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

since the late 1950’s. Consequently, there may be fewer research opportunities for advancing 

HPWH technology as compared to that for the SWH. 

Radiant Floor Heating 

Radiant floor heating and cooling is done by pumping a heat transfer fluid through tubing. Some 

systems circulate water in heat exchanger panels while others directly condition either the floor 

or the ceiling slabs. PCM plates with polystyrene insulation can be used below the floor instead 

of tubing (Sharma et al., 2009). Feng et al. (2013) measured the performance of radiant cooling 

panels in an environmental chamber. EL has the capabilities for conducting similar studies using 

its environmental chambers. In addition, the basement slab of the NIST’s net-zero house has a 9­

circuit radiant floor heating system (Fanney et al., 2014) that is available for field testing. 

Field Testing 

Evaluation of the performance of residential energy storage systems in a real home is intended to 

result in valuable practical information to facilitate the commercialization of residential EES. 

NIST’s net-zero home is well suited for the evaluation of the EES projects recommended in this 

manuscript. In addition, the load simulator developed by NIST (Guo et al. 2014) could be an 

integral part of the field testing by making it easy to simulate loads that EES should expect to 

meet. NIST’s new load simulator can simulate appliances by consuming electricity as scheduled 

according to typical load profiles with programmable power, power factor and operating time. In 

addition, the load simulator can be used to properly size and select the EES that has the desired 

compromise between performance and capital costs. 

Smart Grid 

Energy storage will naturally become an integral part of the Smart Grid. Bi-directional power 

flow, which is an essential consideration for the Smart Grid, can be significantly influenced by 

energy storage. Nationally, Smart Grid research funding significantly exceeds that for energy 

storage (SBC, 2013). Below are three of many NIST Smart Grid research projects that would 

benefit from energy storage research: 

1) Power Conditioning Systems for Renewables, Storage, and Microgrids project under the 

Smart Grid Project8

: advanced smart grid-interactive Power Conditioning System (PCS)­

based generator and microgrid functions developed as a result of this project enable 

solutions to these and many other issues and will enable distributed generators to provide 

grid interactive functions that increase their value proposition. 

2) Smart Grid Communication Networks Project9

: develop communication standards for 

smart grid interaction between houses, power plants, and renewable energy sources. 

3) Smart Grid System Testbed Facility Project10: the testbed will implement network 

communication by way of a home microgrid protocol and the Building Automation and 

Controls Network (BACnet) data protocol. 

8

 https://eli.nist.gov/program/PROGRAM_PROJECTS/Project_48.aspx 

9

 https://eli.nist.gov/program/PROGRAM_PROJECTS/Project_62.aspx 

10 https://eli.nist.gov/program/PROGRAM_PROJECTS/Project_64.aspx 

19
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

EES Cost and Benefits 

An EL project could be developed to compare the costs and benefits of various types of EES. 

This would require a cost-benefit methodology for EES to be developed by possibly modifying 

or applying the cost analysis given in Zheng et al. (2014). It would have to define, quantify and 

monetize the full range of EES costs and benefits. According to Pedram et al. (2010), in order to 

achieve high energy cost savings, an ideal EES system should possess many features such as 

high charge/discharge efficiency, high energy density, low cost per unit capacity and long cycle 

life. 

SIZE OF RESIDENTIAL ENERGY STORAGE SYSTEM 

The storage capacity, in kWh, of a residential energy storage system (Qs) is directly proportional 

to the capital cost of the energy storage system. The size of the system determines how much of 

the unused residential electricity generation is captured and saved. A system designed large 

enough to store all of the excess electricity produced may be too expensive and physically too 

large to build on a residential site. Consequently, the energy storage system must be sized with 

the trade-off between storing as much energy as possible and the system cost in mind. This 

engineering calculation requires the net electricity generation/usage characteristics of the house 

in question such as that shown in Fig. 13. 

Figure 13 Net zero house electricity net generation and usage (Fanney et al., 2014) 

Figure 13 shows the daily and cumulative net electricity excess-generation/deficit-usage of 

NIST’s net-zero home (Fanney et al., 2014). The facility is a 223 m2

, two-story residential home 

20
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

that is fully instrumented to measure its energy consumption. Figure 13 shows the house’s net 

generation/usage for each day over a year where a positive value indicates that the PV of the 

house produced more electricity than that required by the house for that day. Negative values 

indicate that the PV did not produce enough electricity to meet that day’s electricity needs. 

Figure 13 shows measurements from July 2013 through June 2014 where the house produced 

378 kWh more electrical energy than it consumed. 

The net electricity measurements of Fig. 13 were used to illustrate, in Fig. 14, the required size 

of an energy storage system (Qs) for NIST’s house. Figure 12 shows the fraction of the total 

excess electricity generated in a year (Qg) that was stored in an energy storage system over that 

same year (Qy). The fraction of excess electricity stored is shown as a function of the size of the 

storage system. In general, larger energy storage systems can be used to store a larger fraction of 

the excess generation. Solid lines, in Fig. 14, represent energy storage starting in July (consistent 

with Fig. 13) while dashed lines represent energy storage starting in October. Comparison of the 

solid and dashed lines show that more energy can be stored in a year for a given system size if 

storage begins in the summer as compared to the fall. The lower two curves of Fig. 14 show that 

a 25 kWh and a 250 kWh storage system are able to store approximately 15 % and 30 % of 

excess generation in a year, respectively. For this case, storing twice as much energy in a year 

requires an order-of-magnitude larger energy storage system. As Fig. 13 shows, the PV for the 

test house was oversized considering that it produced more electricity than it used in a year. In 

Figure 14 Fraction of excess electricity stored as a function of the size of the 

storage system 

21
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

order to understand the energy storage size requirements for a house with less PV, the two upper 

curves of Fig. 14 show these characteristics for 80 % of the PV shown in Fig. 13 but with the 

electricity usage requirements unchanged. For this case, a 25 kWh and a 250 kWh storage 

system are able to store approximately 30 % and 60 % of excess generation in a year, 

respectively. Consequently, the size of the PV should be designed with consideration of the size 

of the energy storage system and vice versa. Otherwise, a significant amount of PV electricity 

generation may go unused if it cannot be put on the grid. 

CONCLUSIONS 

NIST Engineering Laboratory is well positioned to make significant contributions to the 

relatively neglected field of residential energy storage. Possession of the NIST’s Net-Zero 

Energy Residential Test Facility makes it possible to work collaboratively with other laboratories 

within NIST to demonstrate new ideas in energy storage including batteries, super capacitors, 

superconducting magnets and hydrogen storage. 

In addition, EL staff and facilities are well matched to projects in Phase Change Material (PCM) 

facades and PCM evaporators, pumped hydro, solar water heaters, and cost/benefit analysis. 

Accordingly, new heat exchanger and system designs with PCMs were proposed for 

investigation. The PCM investigation would require both heat transfer and system performance 

measurements. In addition, it was proposed to use the existing EL plumbing tower for hydro 

storage studies and to rebuild a calibrated hot box for PCM façade investigations. Other 

potential project ideas were also provided for these areas of research. 

ACKNOWLEDGEMENTS 

This work was funded by NIST. Thanks go to Prof. J. S. Brown of The Catholic University of 

America and to the following NIST personnel for their constructive criticism of the draft 

manuscript: W. Guo, and P. Domanski. 

22
 
             

 

 

 

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

NOMENCLATURE 

English symbols 

h height (m) 

P pressure (Pa) 

T temperature (K) 

Q energy (W) 

Greek symbols 

P pressure drop (kPa) 

Subscripts 

g excess generation 

PC phase change 

s storage system 

y excess electricity over a year 

Abbreviations 

AC Air Conditioning 

AdvFacSy Advanced Façade Systems 

BACnet Building Automation and Control network 

BEES Building for Environmental and Economic Sustainability 

CAES Compressed Air Energy Storage 

CES Chemical Energy Storage 

CSP Concentrated Solar Power 

DLC Double Layer Capacitor 

EES Electrical Energy Storage 

EL Engineering Laboratory (laboratory within NIST) 

ES Electricity Storage 

EXV Electronic eXpansion Valve 

FES Flywheel Energy Storage 

HPWH Heat Pump Water Heater 

ID Inner Diameter 

LHS Latent Heat Storage 

Li-S Lithium-Sulfur (battery) 

MES Mechanical Energy Storage 

MML Material Measurement Laboratory (laboratory within NIST) 

NBS National Bureau of Standards (now called NIST) 

NEIL Nanoparticle-Enhanced Ionic Liquids 

NIST National Institute of Standards and Technology (in US Department of Commerce) 

NREL National Renewable Energy Laboratory 

OD Outer Diameter 

PC Phase Change 

PCHA Pumped Hydro with Compressed Air 

PCM Phase Change Material 

PCS Power Conditioning System 

PHS Pumped Hydro Storage 

PV Photovoltaic 

23
 
             

 

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

SHS Sensible Heat Storage 

SMES Superconducting Magnetic Energy Storage 

SWH Solar Water Heaters 

TES Thermal Energy Storage 

TXV Thermostatic eXpansion Valve 

UPS Uninterruptible Power Supply 

U.S. United States 

24
 
             

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

REFERENCES 

ASHRAE, 2012, 2012 ASHRAE Handbook -HVAC Systems and Equipment, Chapter 51, 

Atlanta, GA, p. 51-1. 

Baetensa, R., Jelle, B. P., and Gustavsend, A., 2010, “Phase change materials for building 

applications: A state-of-the-art review,” Energy and Buildings, Vol. 42, pp. 1361–1368. 

Bi, J., Jiang, T., Chen, W., and Ma, X., 2013, “Research on Storage Capacity of Compressed Air 

Pumped Hydro Energy Storage Equipment*, Energy and Power Engineering, Vol 5, 26-30. 

Bohn, C. D., Agrawal, A. K., Walter, V. M., Vaudin, V. A., Herzing, A., Haney, P. M., Talin, A. 

A., and Szalai, V. A., 2012, “Effect of tin doping on α-Fe2O3 photoanodes for water splitting,” 

The Journal of Physical Chemistry, Vol. 116, pp. 15290–15296. 

Bruch, M., Münch, V., Aichinger, M., Kuhn, M., Weymann, M., Schmid, G., 2011, “Power 

Blackout Risks Risk Management Options Emerging Risk Initiative – Position Paper,” CRO 

briefing on Power Blackout Risks, p. 6. 

Chanson, H , 1999, “Physical Modelling of Hydraulics. In Chanson, H., Hydraulics of Open 

Channel Flow: an Introduction, Edward Arnold, 1st ed., London, UK, pp. 261-283. 

Chung, J. D., Cho, S. H., Tae, C. S., and Yoo, H., 2008, “The effect of diffuser configuration on 

thermal stratification in a rectangular storage tank,” Renewable Energy, vol. 33, no. 10, pp. 

2236–2245. 

CPUCED (California Public Utilities Commission Energy Division), 2005, “Update On 

Determining The Costs And Benefits Of California’s Net Metering Program As Required By 

Assembly Bill 58” 

Davis, M. W, Ellis, M. W., Dougherty, B. P., 2006, “Proposed Test Methodology and 

Performance Rating Standard for Residential Fuel Cell Systems,” NISTIR 7301, U.S. 

Department of Commerce, Washington, D.C. 

Deal, M., Churchill, S., Chaset, L., and Villarreal C., 2010, “Electric Energy Storage: An 

Assessment of Potential Barriers and Opportunities,” CPCU Policy and Planning Division Staff 

White Paper. 

DGE, 2012, “Quarterly Report on European Electricity Markets,” DG Energy, Market 

Observatory for Energy, Vol. 5, Issue: 1, January 2012 to March 2012, European Commission, 

Directorate-General for Energy. 

Dincer, I., and Rosen, M. A., 2002, Thermal Energy Storage-Systems and Applications, Wiley, 

West Sussex, p. 1. 

25
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Esposito, D.V., Levin, I. T., I. Moffat I., and Talin A.A., 2013, “H2 evolution at Si-based 

metal–insulator–semiconductor photoelectrodes enhanced by inversion channel charge collection 

and H spillover,” Nature Materials, doi:10.1038/nmat3626. 

Feng, J., Bauman, F., Schiavon, S., 2013, ”Experimental comparison of zone cooling load 

between radiant and air systems,” Energy and Buildings: HVAC Systems, October, 

http://escholarship.org/uc/item/9dq6p2j7 

Fanney , A. H., Payne, V., Ullah, T., Ng, L., Boyd, M., Omar, F., Davis, M., Skye, H., 

Dougherty, B., Polidoro, B., Healy, W., Pettit, E., 2014,” The National Institute of Standards and 

Technology’s Net-Zero Energy Residential Test Facility,” Submitted to Energy and Buildings 

Fanney, A.H., Zarr, R.R., and Ketay-Paprocki, J.D, 2000,"Thermal Performance of Residential 

Electric Water Heaters Using Alternative Blowing Agents" ASHRAE Transactions 2000, Vol. 

106, No. 2, 1-13. 

Fox, E. B., Visser, A. E., Bridges, N., Gray, J. R., Garcia- Diaz, B., Maginn, E. J., and Khan, J. 

A., Report to DOE:Thermally-stable ionic liquid carriers for nanoparticle-based advanced heat 

transfer in concentrating solar energy applications,3rd quarter FY11 progress report, SRNL-STI2011-00543, Savannah River National Laboratory, Aiken, SC,2011. 

Havel, T. F., 2013, “Adsorption-Enhanced Compressed Air Energy Storage,” Proceedings of 

Electrical Energy Storage Applications and Technologies (EESAT) conference, San Diego, CA. 

Healy, W. M., Ullah, T, and Roller, J., 2011, “Input-Output Approach to Predicting the Energy 

Efficiency of Residential Water Heaters Testing of Gas Tankless and Electric Storage Water 

Heaters,” ASHRAE Trans, Vol. 117. 

Healy, W. M., Lutz, J. D., and Lekov, A. B., 2003, “Variability in Energy Factor Test Results for 

Residential Electric Water Heaters,” HVAC&R Research Journal 9:4, pp. 435-449. 

Heller, L., 2013,“Literature Review on Heat Transfer Fluids and Thermal Energy Storage 

Systems in CSP Plants,” STERG Report 

Hudon, K., Merrigan, T., Burch, J., Maguire, J., 2012, “Low-Cost Solar Water Heating Research 

and Development Roadmap,” NREL Report No. TP-5500-54793. 

Guo, W., Ullah, T., and Healy, W. M., 2014, “Deployment of a Load Simulator in Simulating 

Residential Household Appliances,” IN WERB REVIEW 

IEC, 2011, “Electrical Energy Storage,” White Paper. http://www.iec.ch/whitepaper/pdf/iecWPenergystorage-LR-en.pdf 

IRENA, 2013, “Thermal Energy Storage,” Technology Brief , E17, EA-ETSAP and IRENA, p. 

6. 

26
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

IRENA, 2012, “Renewable Energy Technologies: Cost Analysis Series,” Hydropower Volume 

1: Power Sector Issue 3/5. 

IREA, 2012, “Electricity Storage and Renewables for Island Power: A Guide for Decision 

Makers,” International Renewable Energy Agency, Issue 3/7. 

Islam, S. M., 2012, “Increasing wind energy penetration level using pumped hydro storage in 

island micro-grid system,” Int. J. Energy and Environmental Engineering, Vol. 3, 9. 

Kedzierski, M. A., 2013, “Nanofluids, Heat-Transfer Equipment and Plain-Vanilla,” Journal of 

Enhanced Heat Transfer, Vol. 20, No. 1, pp. 93-94. 

Kim, Y. and Favrat, D., 2008, “Energy and Exergy Anaysis of a Micro Compressed Air Energy 

Storage and Air Cycle Heating and Cooling System,” International Refrigeration and Air 

Conditioning Conference at Purdue, paper 2149. 

Kneifel, J. D., 2010, “Cost-effectiveness of Energy Efficiency Measures Exceeding Current 

Standards in New Commercial Buildings,” Proceedings of the International Council for 

Research and Innovation in Building and Construction World Building Congress 2010 - Building 

a Better World, 

Kośny, J., Yarbrough, D., Miller, W., Petrie, T., Childs, P., Syed, A. M., and Leuthold, D., 2008, 

“PCM-Enhanced Building Envelopes in Current ORNL Research Projects,” Oak 

Ridge National Laboratory Report ORNL/TM-2007/186. 

Kotzé1, J. P., von Backström, T. W., and Erens, P. J., 2011, “A Combined Latent Thermal 

Energy Storage and Steam Generator Concept Using Metallic Phase Change Materials and 

Metallic Heat Transfer Fluids for Concentrated Solar Power,” Proceedings of SolarPACES, 

Granada, Spain.
 

Kumano, H., Asaoka, T., and Sawada, S., 2014, “Effect of Initial Aqueous Solution 

Concentration and Heating Conditions on Heat Transfer Characteristics of Ice Slurry,” Int. J. 

Refrigeration, Vol. 41, pp. 72-81. 

Lemofouet, S., and Rufer, A., 2005, “Hybrid Energy Storage System based on Compressed Air 

and Super Capacitors with MEPT,” Proceedings of the International Power Electronics 

Conference, pp. 461-468. 

Lippiatt, B., 2007, Building for Environmental and Economic Sustainability (BEES) 4.0 

software, National Institute of Standards and Technology, 

http://www.bfrl.nist.gov/oae/software/bees/. 

Lo ́pez-Navarro, A., Biosca-Taronger, J., Torregrosa-Jaime, B., Martı ́nez-Galva ́, I.,Corbera ́ J. 

M., Esteban-Matı ́ J.C., and Paya ́, J., 2013, “Experimental Investigation of the Temperatures 

and Performance of a Commercial Ice-Storage Tank,” Int. J. Refrigeration, Vol. 36, pp. 1313­

1318. 

27
 
             

 

This publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Lundy, D. R., Swartzendruber, L. J., and Bennett, L. H., 1989, ”A Brief Review of Recent 

Superconductivity Research at NIST,” J. of Research of the National Institute of Standards and 

Technology, Vol 94, No 3, pp. 147-178. 

Martin, G. D., and Barnes, F. S., 2007, “Aquifer Underground Pumped Hydroelectric Energy 

Storage,” In Proceedings of the Electrical Energy Storage Applications & Technologies 

Conference, San Francisco. 

Nguyen, T., and Savinell, R. F., 2010 “Flow Batteries,” The Electrochemical Society Interface, 

fall issue, pp. 54-56. 

Pedram, M., Chang, N., Kim, Y., Wang, Y., 2010, “Hybrid Electrical Energy Storage Systems”, 

ISLPED, Proceedings of the 16th ACM/IEEE international symposium on Low power 

electronics and design, Pages 363-368, August 18-20, 2010, Austin, Texas USA. 

Pilar, F. L., 1979, “Chemistry, the Universal Science,” Addison Wesley, Reading, MA, p. 376. 

Pinel, P., Cruickshank, C. A., Beausoleil-Morrison, I., and Wills, A., 2011, “A Review Of 

Available Methods For Seasonal Storage Of Solar Thermal Energy In Residential Applications,” 

Renewable and Sustainable Energy Reviews, Vol. 15, No. 7, pp. 3341–3359. 

Pless, S., and Torcellini, P., 2010, “Net-Zero Energy Buildings: A Classification System Based 

on Renewable Energy Supply Options,” Technical Report NREL/TP-550-44586, p. 2. 

Reading, M. M., 2004, “Flywheel Energy Storage System,’ California Energy Commission, 

Sacramento, CA. 

Scaini, V., 2012, “Grid Support Stability For Reliable, Renewable Power,” White Paper 

WP083002EN. 

Sharma, A, Tyagi, V.V., Chen, C.R., Buddhi, D., 2009, “Review on thermal energy storage with 

phase change materials and applications,” Renewable and Sustainable Energy Reviews, Vol. 13, 

No. 22, pp. 318–345. 

Simmonds, A. G., Griebel, J. J., Park, J., Kim, K. R., Chung, W. J., Oleshko, V. P., Kim, J., 

Kim, E. T., Glass, R. S., Soles, C. L., Sung, Y-E., Char, K., and Pyun P., 2014, “Inverse 

Vulcanization of Elemental Sulfur to Prepare Polymeric Electrode Materials for Li−S Batteries,” 

ACS Macro Lett, 3, pp. 229−232. 

Wang, H., Wang, L., Wang, X., and Yao, E., 2013, “A Novel Pumped Hydro Combined with 

Compressed Air Energy Storage System,” Energies, Vol. 6, pp. 1554-1567. 

Webb, R. L., and Kim, N-H., 2005, Principles of Enhanced Heat Transfer, 2nd ed., Taylor & 

Francis, New York. 

28
 
This              publication is free of charge from: http://dx.doi.org/10.6028/NIST.TN.1844

Whittemore, H. L., Phelan, V., B., and Dill, R. S., 1943, “Structural and Heat-Transfer Properties 

of “Multiple Box-Girder Plywood Panels” for Walls, Floors, and Roofs Sponsored by Loren H. 

Wittner,” Washington, D.C.: U.S. Dept. of Commerce, National Bureau of Standards. 

Zarr, R. R., 2001, “A History of Testing Heat Insulators at the National Institute of Standards 

and Technology,” ASHRAE Transactions, Vol. 107, Pt. 2. 

Zhai, Z., Abarr,M. L., AL-Saadi, S., N., and Yate, P., 2013, “Energy Storage For Residential 

Buildings: Review And Advances,” APEC Conference on Low-carbon Towns and Physical 

Energy Storage, Changsha, China Paper ID: ACLE2013-E08-10 

Zheng, M., Meinrenken, C. J., and Lackner, K. S., 2014, “Electricity storage in buildings for 

residential sector demand response: Control algorithms and economic viability evaluation,” 

NIST GCR in review, Washington D.C. 

Zimmerman, K. H., 1986, “Heat Pump Water Heater Laboratory Test and Design Model 

Validation,” Oak Ridge National Laboratory, ORNL/CON-173. 

29