A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Impacts of Array Configuration 

on Land-Use Requirements for 

Large-Scale Photovoltaic 

Deployment in the United States 

Preprint 

Paul Denholm and Robert M. Margolis 

National Renewable Energy Laboratory

Presented at SOLAR 2008 - American Solar Energy Society (ASES) 

San Diego, California 

May 3–8, 2008 

Conference Paper 

NREL/CP-670-42971 

May 2008 

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IMPACTS OF ARRAY CONFIGURATION ON LAND-USE REQUIREMENTS FOR LARGESCALE PHOTOVOLTAIC DEPLOYMENT IN THE UNITED STATES

Paul Denholm 

National Renewable Energy Laboratory 

1617 Cole Blvd 

Golden, CO 80401 

 paul_denholm@nrel.gov 

Robert M. Margolis 

National Renewable Energy Laboratory 

901 D. Street SW, Suite 930 

Washington, D.C. 20024 

robert_margolis@nrel.gov 

ABSTRACT 

Land use is often cited as an important issue for 

renewable energy technologies. In this paper we examine 

the relationship between land-use requirements for largescale photovoltaic (PV) deployment in the U.S. and PVarray configuration. We estimate the per capita land 

requirements for solar PV and find that array 

configuration is a stronger driver of energy density than 

regional variations in solar insolation. When deployed 

horizontally, the PV land area needed to meet 100% of an 

average U.S. citizen’s electricity demand is about 100 m2

.

This requirement roughly doubles to about 200 m2

 when 

using 1-axis tracking arrays. By comparing these total 

land-use requirements with other current per capita land 

uses, we find that land-use requirements of solar 

photovoltaics are modest, especially when considering the 

availability of zero impact “land” on rooftops. Additional 

work is need to examine the tradeoffs between array 

spacing, self-shading losses, and land use, along with 

possible techniques to mitigate land-use impacts of largescale PV deployment. 

1. INTRODUCTION

The installed price of PV systems has dropped 

considerably over the past couple of decades and is 

expected to continue to decline over the next two decades. 

As the price approaches grid-parity, PV systems are likely 

to become a significant component of future electric 

power systems. The fact that solar energy is a diffuse 

resource, in particular compared to fossil and nuclear 

fuels, is both a strength and a potential liability. It is a 

strength in that solar energy can be captured and utilized 

to provide energy services where these services are 

needed, and it is a potential liability in that it may need to 

compete with other uses for limited land areas. In this 

paper we examine the land area required for PV to 

contribute a significant fraction of a region’s electricity 

demand in the U.S. 

The actual land requirements are driven by both the solar 

resource and the configuration of the PV system. Several 

aspects of the land-use requirements of solar PV are 

considered in this analysis. First, we quantify the 

relationship between PV energy yield and land use, 

considering various array configurations and spacing. 

Second, we quantify the actual land area required to meet 

the electricity demand in several regions of the United 

States using PV in different configurations. Finally, we 

discuss the implications of this land use, and consider 

further steps needed to understand and potentially 

minimize land-use and environmental impacts from largescale PV deployment. 

2. PV POWER AND ENERGY DENSITY

A major consideration for land-use requirements is the PV 

energy density, or the energy yield per unit of land (or 

surface area) occupied by a PV system. The energy 

density is a function of the array power density (power 

per unit land area occupied) and the PV generation 

(energy generated per unit of power). For any given site 

and PV module, the energy density is ultimately a 

function of how the system is configured. If PV systems 

are tilted (or mounted on tracking arrays) the energy yield 

per unit of module power increases, but the spacing 

between modules needs to increase in order to avoid selfshading and to allow for maintenance. Ground-based 

arrays have the additional complication of requiring 

minimum spacing between rows to allow for service 

vehicles. 

To determine the PV array energy density for different 

regions of the U.S., we used data from the National Solar 

Radiation Database (NSRDB) for the years 2003-2005 

1
(1). We used the NSRDB data in conjunction with the 

PVWATTS/PVFORM model (2), assuming a 1-kW 

(Standard Test Conditions) module, and an average 

system DC-AC conversion efficiency of 77%. We then 

calculated an average PV array energy density over the 3 

year period 2003-2005, aggregated at the state level by 

weighing each weather station site by the amount of 

electricity demand in the assigned region. Figure 1 

illustrates the allocation of weather stations in the 

southwestern United States by census tract. A more 

detailed discussion of the modeling methodology is 

provided in reference 3. 

Figure 1. Allocation of the NSRDB Weather Station Data 

in the Southwestern United States by Census Tract 

Figure 2 illustrates the resulting PV array energy density 

for four states (Arizona, California, Missouri, and New 

Jersey), and the national average, as a function of array 

configuration. The most notable feature of this figure is 

the strong dependence of energy density on system 

configuration, which is significantly greater than the 

dependence of energy density on the difference in solar 

resource. 

0

20

40

60

80

100

120

140

160

180

200

Arizona California Missouri New

Jersey

U.S. Avg 

Energy Density (kWh/land m2/year)

Flat S10o S 25o 1-Axis Flat 2-Axis

Figure 2. PV Energy Density in Four States by Array MT Configurations. OR

ID

The highest deployable energy density is a flat array 

configuration, an approach often used on large 

commercial building rooftops. However, there are 

numerous tradeoffs between energy yield, mounting 

requirements, roof loading limits, etc., which often lead to 

deployment of PV systems at a low tilt angle in order to 

increase the collector yield. Rooftop-type systems with a 

10o tilt angle increased collector yield by about 10% with 

a modest decrease in overall system energy density. 

NV

CA UT

CO

Increasing the tilt angle, or deploying tracking arrays can 

considerably increase the yield per unit of collector area – 

by over 50% moving from flat to 2-axis tracking. 

However, in terms of energy density, the increased yield 

from using tilted and tracking arrays does not make up for 

the significant additional land area required to avoid self 

shading. The energy density for tilted- and single-axis 

tracking arrays are around half of the energy density of a 

flat, rooftop system, while 2-axis tracking system may 

produce about 1/3rd of the energy per unit of land area. 

Ultimately, this represents a tradeoff between land costs 

and PV-collector costs. PV costs are such that a premium 

is placed on maximizing yield from each installed unit. 

This tends to encourage array designs that minimize selfshading. It also promotes the use of tracking arrays, 

especially when the value of additional yield exceeds the 

incremental cost of the added mechanical and structural 

components. 

AZ NM

TX

3. TOTAL LAND AREA REQUIREMENTS

The impact of array configuration on total land 

requirements of PV can be examined by comparing 

system energy density to total regional electricity use. The 

annual electricity production in each state was compared 

to the annual simulated yield from PV for the years 2003-

2005 (4). We estimated the boundary condition land-use 

requirement, i.e., where PV provides 100% of each state’s 

electricity demand. Meeting this condition requires the 

2
use of energy storage. In estimating the energy storage 

requirements, we assumed a 75% round trip storage 

efficiency, and that 70% of all consumed electricity 

would pass through storage, resulting in a required 

electricity production equal 1.23 times the actual demand. 

Two land-use metrics are useful for understanding the 

potential land-use requirements. The first is the percapita land-use requirement, which could be considered 

part of the ecological footprint associated with each 

individual’s electricity use if derived from PV. 

Figure 3 illustrates the per-capita land-use requirement for 

several states in the U.S. 

0

50

100

150

200

250

300

350

400

450

500

Arizona California Missouri New

Jersey

U.S. Avg 

Per-Capita Solar Footprint (land 

m2/person)

Flat S10o S 25o 1-Axis Flat 2-Axis

Figure 3. Solar PV Per Capital Land-use Requirement for 

Four States. 

As shown in figure 3, when deployed horizontally, the PV 

land area needed to meet 100% of an average U.S. 

citizen’s electricity demand is about 100 m2 with 

California having the lowest requirement at about 50 m2 

per person due not only to good solar resource, but also 

the lowest per capita electricity consumption in the 

nation. When using 1-axis tracking arrays, the U.S. per 

capita PV area roughly doubles to over 200 m2 on 

average, and about 100 m2 per person in California. 

In states with a low population density, this per-capita 

area represents a relatively small fraction of the total state 

area. However, in states with a high population density, 

this per-capita area can be a significant fraction of total 

state area. Figure 4 illustrates the fraction of land 

required by solar arrays in various configurations to meet 

the 100% boundary condition. In the mid-western and 

western states, this is a relatively small fraction of total 

land area. However in some eastern states, the 

combination of lower insolation and higher population 

density would require a substantial fraction of the state’s 

area to meet the entire electricity demand with solar PV. 

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

Arizona California Missouri New

Jersey

U.S.

Total 

Land Occupation Fraction

Flat S10o S 25o 1-Axis Flat 2-Axis

Figure 4. Fraction of Land Required to Meet 100% of 

Electricity Demand in Four States. 

4. IMPLICATION OF PV LAND USE

The potential use of large amounts of area for PV raises a 

number of questions regarding the availability of land for 

and the potential land-use impacts of wide-scale PV 

deployment. Perhaps the most obvious issue is the 

availability of zero-impact “land” on rooftops. There is, 

however, considerable uncertainty in the estimates of 

available rooftop space that is suitable for PV in the U.S. 

While no comprehensive study has been performed, 

several estimates of the rooftop space appropriate for PV 

are available. One estimate assumes that 18% of all 

residential roofspace and 65% of all commercial 

roofspace are available and suitable for PV deployment 

(5). This results in a national average of about 65 m2

 of 

rooftop area available per person in the U.S. Assuming 

flat deployment, this number would imply that rooftop PV 

deployment alone could provide around two-thirds of the 

nation’s electricity supply. However, this estimate does 

not take into account the sub-optimal orientation of many 

buildings and assumes that the PV system on each 

building is sized to completely fill the available 

roofspace, as opposed to applying a typical size to meet 

the economic needs of the individual building. This 

number is also unsatisfactory in that it assumes a uniform 

shading factor throughout the United States, which is 

extremely unlikely given the variation in vegetation 

between the eastern and western U.S. A more recent 

estimate splits the country into two zones, increasing the 

overall estimate of roofspace available in the southern and 

southwestern United States (6). 

Despite tremendous uncertainty in overall availability, it 

is clear that roofspace could provide a significant fraction 

of the total area needed for PV to become a major 

contributor to the nation’s electricity supply. It should be 

noted that rooftop space is not entirely without 

opportunity costs, since rooftop PV will compete with 

3
other applications, such as solar water heating, green 

roofs, daylighting etc. 

Beyond rooftops, if it assumed that large-scale ground 

based PV systems will be deployed, then some 

consideration of actual land use and land-use impacts 

should be considered. Several land-use applications 

provide a useful comparison. Golf courses and airports 

each currently occupy about 35 m2 per person in the 

United States, while land used to grow corn for ethanol 

production exceeds 200 m2 per person, although this land 

is concentrated in a fairly small number of states. 

Comparisons between PV and other land uses must be 

placed in context of the actual degree to which they 

impact the land and potentially alter local ecosystems. 

Deploying tightly packed PV arrays would create the 

most disruption but would require the least amount of 

land area. In contrast, the use of pole-mounted 2-axis 

arrays would require significantly more land but could be 

substantially less disruptive. This difference is important, 

especially when considering the extremely low energy 

density of 2-axis arrays. The substantial amount of land 

surrounding each 2-axis array could potentially support 

multiple land uses such as grazing and the cultivation of 

shade tolerant crops. 

5. CONCLUSIONS AND FUTURE WORK

The land-use requirements for wide-scale deployment of 

PV are modest when considering both the large area of 

rooftop availability and when compared to other uses of 

land in the United States. Additional studies are needed 

to better understand the potential opportunities and 

impacts of PV on land use. First, a more comprehensive 

estimate of rooftop availability is needed on a national 

basis. This includes detailed statistical sampling of 

homes and commercial buildings, considering the 

distribution of rooftop orientation, pitch, shading, and 

other availability factors. Second, better understanding of 

actual shading impacts of ground based PV arrays is 

required. Installers may be conservative when performing 

shading analysis, spacing arrays to produce every last 

possible kWh out of the system. It may be that actual 

shading impacts, considering real weather patterns during 

periods of low sun angle may not warrant the large array 

spacing calculated by traditional shading analysis. This 

could allow for increased packing density and a 

corresponding reduction in land-use impacts, limited of 

course by maintenance requirements. Evaluation of 

increased array density and increased shading losses at 

low sun angles could also consider the potentially lower 

value of electricity during these typically off-peak time 

periods. Finally, actual ecosystem impacts of large-scale 

PV deployment need to be evaluated. This includes 

studies and evaluation of shade tolerant native and 

beneficial species that could be grown under large-scale 

PV arrays. This also includes evaluation of best practices 

to minimize the use of herbicides and other chemicals, 

and the use of installation and maintenance techniques to 

provide minimum impact such as soil compaction and 

erosion. 

6. REFERENCES

(1) National Renewable Energy Laboratory, 2007. 

National Solar Radiation Database 1991–2005 Update: 

User’s Manual, NREL/TP-581-41364 

(2) Marion, B.; Anderberg, M.; Gray-Hann, P., 2005. 

Recent Revisions to PVWATTS. NREL/CP-520-38975. 

(3) Denholm, P., Margolis, R. M., 2007. The Regional 

Per-Capita Solar Electric Footprint for the United States. 

NREL/TP-670-42463. 

(4) Energy Information Administration, 2007. Form EIA861 Database. 

http://www.eia.doe.gov/cneaf/electricity/page/eia861.html 

(5) Chaudhari, M., Frantzis, L., and T. E. Hoff. “PV Grid 

Connected market Potential in 2010 under a Cost 

Breakthrough Scenario,” 2004. Via 

www.ef.org/documents/EF-Final-Final2.pdf 

(6) J. Paidipati, L. Frantzis, H. Sawyer, and A. Kurrasch 

2008 Rooftop Photovoltaics Market Penetration 

Scenarios. NREL/SR-581-42306 

4
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Impacts of Array Configuration on Land-Use Requirements for 

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14. ABSTRACT (Maximum 200 Words)

Land use is often cited as an important issue for renewable energy technologies. In this paper we examine the 

relationship between land-use requirements for large-scale photovoltaic (PV) deployment in the U.S. and PV-array 

configuration. We estimate the per capita land requirements for solar PV and find that array configuration is a stronger 

driver of energy density than regional variations in solar insolation. When deployed horizontally, the PV land area 

needed to meet 100% of an average U.S. citizen’s electricity demand is about 100 m2. This requirement roughly doubles 

to about 200 m2 when using 1-axis tracking arrays. By comparing these total land-use requirements with other current 

per capita land uses, we find that land-use requirements of solar photovoltaics are modest, especially when considering 

the availability of zero impact “land” on rooftops. Additional work is need to examine the tradeoffs between array spacing, 

self-shading losses, and land use, along with possible techniques to mitigate land-use impacts of large-scale PV 

deployment. 

15. SUBJECT TERMS

NREL; Paul Denholm; Robert Margolis; solar photovoltaics; PV; land use; large-scale PV deployment; solar 

insolation; rooftop solar; solar arrays; electricity demand 

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