Life Cycle Analysis of a Field, Grid-Connected, Multi-Crystalline PV
Plant:

A Case Study of Tucson Electric Power's Springerville PV Plant

Final Report Prepared for Tom Hansen, Tucson Electric Power

November 5, 2004

Prepared by

James Mason, Ph.D.

Solar Hydrogen Education Project

Direct Correspondence to:

James Mason, Director, Solar Hydrogen Education Project, 52 Columbia
Street,

Farmingdale, NY 11735. Phone: (516) 694-0759; E-mail:
cjjmason5@earthlink.net.

Life Cycle Analysis of a Field, Grid-Connected, Multi-Crystalline PV
Plant:

A Case Study of Tucson Electric Power's Springerville PV Plant

This report investigates the energy and greenhouse gas emissions
embodied in the life cycle of Tucson Electric Power's Springerville
multi-crystalline photovoltaic (pv) plant. The Springerville pv plant
located in eastern Arizona is one of the world's largest pv plants. The
electricity produced by the pv plant powers the water pumps at the
Springerville coal-fired, electricity generating plant. When the water
pumps are not operational, the pv electricity is distributed over the
electricity transmission grid for general consumption. While pv produces
energy-free and non-polluting electricity directly from sunlight, the
manufacture, transport and disposal of pv modules and balance of system
components consume fossil fuels, which release greenhouse gases (GHG).
With the mounting need for fossil fuel conservation and GHG mitigation,
it is important to assess the energy savings and GHG mitigation
potential of field pv plants. This is important because field pv plants
can be used for distributed electricity generation for large commercial
and industrial electricity consumers and for the production of hydrogen
gas by electrolysis of water for the emerging fuel cell vehicle market.

PV research indicates that the energy embodied in the balance of system
components of field pv installations is significantly greater than the
energy embodied in the balance of system components of roof-mounted pv
installations (Frankl *et al*., 1998; Blakers and Weber, 2000; Alsema,
2000). Estimates of the energy embodied in balance of system components
of field pv plants range from 4,362 kWh to 5,785 kWh per kW~p~ DC of
installed pv. In contrast, the estimated energy embodied in the balance
of system components of rooftop pv installations is 1,653 kWh per kW~p~
DC of installed pv. The reason stated for the higher energy requirement
of field compared to rooftop pv installations is that field pv plants
require concrete foundations and greater quantities of metal for pv
support structures. The analysis of the Springerville pv plant is
interesting because the plant design utilizes pv support structures
without concrete foundations, which should translate into a significant
energy reduction.

Data and Methods

Life cycle analysis (LCA) is the appropriate method to evaluate the
energy and GHG emissions embodied in the life cycle of products and
services. The scope of this analysis is "cradle to grave" for all pv
plant components. The life cycle stages are: Stage 1 -- materials
production, which includes ore extraction, processing and
transportation; Stage 2 -- parts casting and stamping; Stage 3 --
product manufacture and assembly; Stage 4 -- product transport for
distribution; Stage 5 -- product utilization; and Stage 6 -- product
disposal. In addition, the analysis includes plant construction,
administration, maintenance, security and employee vehicle use for
travel to and from work.

The energy and GHG emissions estimates used to generate the results for
the life cycle stages are from Weiss *et al*. (2000), Singh (1998), the
energy software GREET1.6 (Wang, 2001), the LCA software LISA and
Environdec's Environmental Product Declarations. I take a conservative
approach and do not allocate energy or GHG emissions credits for product
end-of-life material recycling or energy recovery. This is because of
ambiguity regarding the actual integration of recycled materials into
new material production and the environmental consequences of using
recycled materials as fuel sources, particularly PVC. When calculating
energy and GHG emissions estimates with GREET1.6, I assume an U.S.
average fuel mix for electricity generation with 5% combined cycle
natural gas power plants and 5% advanced coal power plants, and an
average power plant efficiency of 39% in terms of converting primary
energy into consumable electricity. All other power plant and fuel
parameters are the default values of GREET1.6. All energy emissions
estimates are reported at the low heating value in terms of kWh~prim~
(primary energy) per kW~p~ DC of installed pv. Primary energy is the
total fuel cycle energy per unit of energy consumed and accounts for the
energy expended to extract, refine and deliver fuels. The GHG emissions
are carbon dioxide, nitrous oxide and methane and are reported in terms
of CO~2~ equivalencies per kW~p~ DC of installed pv.

A complete inventory of all components in the Springerville
multi-crystalline (mc-Si) pv installations is provided by Tucson
Electric Power. The material composition of the pv plant components is
estimated from information provided by product manufacturers and Tucson
Electric Power. The results for this report are based on a thirty-year
pv plant life cycle, which is the life expectancy of the pv modules. All
pv plant components are scaled for a thirty-year life cycle. It is
assumed that inverters and transformers require replacement parts every
ten years amounting to 10% of their total material composition.

The assignment of life cycle energy parameters for mc-Si pv modules is
somewhat problematic because of a wide range in published estimates,
which is attributable to uncertainty about the energy requirement for
silicon feedstock and purification. Life cycle energy estimates for
framed, mc-Si pv modules range from 2,900 to 7,700 MJ/m^2^ (Alsema,
2000). The life cycle energy estimate for framed, mc-Si pv modules used
in this report is 4,700 MJ/m^2^, which is equivalent to 10,880 kWh~prim~
per kW~p~ DC of installed pv assuming 12.0% efficient modules.

To evaluate energy and GHG emissions reductions accruing from pv
electricity production, it is necessary to estimate the pv electricity
production rate and the corresponding amount of primary energy for the
power plant electricity that is replaced by the pv electricity. The
annual electricity output of the Springerville mc-Si pv installations is
1,730 kWh of AC electricity per kW~p~ DC of installed pv. The quantity
of primary energy from power plant electricity production replaced by
the pv electricity is 4,436 kWh with an average power plant efficiency
of 39%. The estimated GHG emissions rate from power plant electricity
generation is 0.604 pounds of CO~2~ equivalent emissions per kWh of
primary energy. To assess the effect of variances in life cycle
parameter estimates on results, sensitivity analyses are performed, and
the results for the effects of a plus and minus 25% variance in life
cycle parameters is reported.

Results

The life cycle energy and GHG emissions findings are presented in
Table 1. The total energy embodied in the life cycle of the
Springerville mc-Si pv installations is 12,352 kWh per kW~p~ DC of
installed pv. The estimated energy payback time is 2.8 years. The total
life cycle GHG emissions are 7,394 pounds of CO~2~ equivalent emissions
per kW~p~ DC of installed pv, and the payback time is 2.8 years. The
electricity produced by a pv plant over its thirty-year life reduces GHG
emissions by 36.5 tons of CO~2~ equivalent emissions per kW~p~ DC of
installed pv. This is a 91% reduction in GHG emissions compared to the
electricity produced by U.S. average power plants. If an average
insolation level of 1,700 kWh/m^2^/year is applied rather than the
relatively high Springerville insolation level of \< 2,100
kWh/m^2^/year, the energy payback time increases to 3.5 years -- 0.4
years for balance of system components and 3.1 years for mc-Si pv. The
primary energy embodied in the life cycle of balance of system
components is 1,480 kWh per kW~p~ DC of installed pv. The life cycle
balance of system GHG emissions are 825 pounds of CO~2~ equivalent
emissions per kW~p~ DC of installed pv. The balance of system energy and
GHG emissions payback times are 0.33 and 0.31 years respectively. The
results of the sensitivity analyses indicate that a plus/minus 25%
change in total balance of system values will change the energy payback
time by less than 0.1 years. Therefore, it is reasonable to assume that
the true balance of system energy and GHG emissions payback times are
within a range of three to five months for the Springerville mc-Si pv
installations. Because recycling credits are not allocated, the true
payback times are likely skewed toward the low end of the estimated
range.

The estimated primary energy embodied in the mc-Si pv modules is 10,872
kWh per kW~p~ DC of installed pv, and the GHG emissions estimate is
6,569 pounds of CO~2~ equivalent emissions per kW~p~ DC of installed pv.
The energy and GHG emissions payback times are each 2.4 years. The mc-Si
pv modules account for 87% of the total energy payback time for the
mc-Si pv plant. The sensitivity results reflect the large impact of the
mc-Si pv modules. A 25% change in the mc-Si manufacturing parameters
results in a seven month change in the energy payback time. The
sensitivity analyses suggest that the true energy payback time ranges
from 1.8 to 3.1 years. Confidence that the true value lies within this
range is relatively low because of the wide range in energy estimates
for silicon production and purification for mc-Si pv modules.

Discussion

The balance of system life cycle results are impressive. The balance of
system energy payback time of three to five months is 60% to 75% lower
than the lowest published estimates for field pv plants. The
Springerville pv plant has achieved significant reductions in the
balance of system life cycle energy and GHG emissions by simplifying the
design of pv support structures, which utilize the weight of the pv
modules to eliminate the need for concrete foundations. With forward
planning and design Tucson Electric Power is optimizing resource
allocation for construction, wiring and electrical components. Also,
Tucson Electric Power is realizing cost benefits by incorporating
standardized products and volume purchasing. The Springerville pv plant
establishes a template for the design of large field pv plants and
reduces learning curve penalties. Tucson Electric Power has made an
important contribution to the advancement of pv technology by revealing
the potential of large field pv plants for distributed electricity
generation, green electricity marketing and electrolytic hydrogen gas
production.

Another significant development is a reduction in the installed cost of
balance of system (BOS) components at the Springerville pv plant. Tucson
Electric Power reports that the total installed cost of BOS components
for the most recent pv installations is \$0.92 per W~p~ DC of installed
pv, which includes site preparation, labor, pv support structures,
wiring, inverters, transformers and all electrical and grid connections
(Hansen, 2003). The results indicate that the embodied energy and cost
of field pv plants are less than those of rooftop pv installations. It
is worth noting that inverters and their support software account for
43% of total BOS cost, which implies that the BOS cost for hydrogen
electrolysis plants using pv electricity is below \$0.60 per W~p~ DC of
installed pv since electrolysers use DC electricity and do not require
AC inverters.

Future reductions in field pv plant cost, embodied energy and GHG
emissions will occur with the large-scale mass manufacture of both thin
film pv and standardized BOS components (Keshner and Arya, 2004). The
projected total cost of future field pv plants is \$1.00/W~p~. Thin film
pv requires 50%--75% less energy to manufacture than mc-Si pv modules.
The elimination of aluminum frames creates further reductions. Tucson
Electric Power is currently testing both framed and frameless, low
wattage, thin film modules at the Springerville pv plant. An analysis of
these installations is not performed because low-wattage thin film pv
modules are used, which increase the land area to produce the same
amount of electricity as the mc-Si pv installations and hence introduces
comparative distortions in the BOS material resource requirements.

Table 1. Life Cycle Embodied Energy and GHG Emissions Results for a
Grid-Connected,

Field PV Plant (Framed, 300 W~p~, mc-Si PV Modules)

+----------------------------------+----------+------+-------+-------+
| # Balance of System Components   | Primary  | \%   | GHG   | E     |
|                                  | Energy   | of   | Emis  | nergy |
|                                  | (        | T    | sions | S     |
|                                  | kWh~prim | otal | (lbs  | ensit |
|                                  | ~/kW~p~) | En   | CO2   | ivity |
|                                  |          | ergy | Eq/k  | ± 25% |
|                                  |          |      | W~p~) | (Pa   |
|                                  |          |      |       | yback |
|                                  |          |      |       | Ch    |
|                                  |          |      |       | ange) |
+----------------------------------+----------+------+-------+-------+
| Construction (Site Preparation   | 37.4     | 0.3% | 26.5  | 0.00  |
| and Installation)                |          |      |       |       |
+----------------------------------+----------+------+-------+-------+
| PV Support Structures            | 251.6    | 2.0% | 138.1 | 0.01  |
+----------------------------------+----------+------+-------+-------+
| PV Wiring, Conduit and Junction  | 293.1    | 2.4% | 209.3 | 0.02  |
| Boxes                            |          |      |       |       |
+----------------------------------+----------+------+-------+-------+
| Inverters and Transformers       | 502.2    | 4.1% | 214.9 | 0.03  |
+----------------------------------+----------+------+-------+-------+
| Grounding Components             | 113.5    | 0.9% | 61.1  | 0.01  |
+----------------------------------+----------+------+-------+-------+
| Miscellaneous                    | 88.2     | 0.7% | 51.1  | 0.01  |
+----------------------------------+----------+------+-------+-------+
| Administration, Maintenance and  | 193.8    | 1.6% | 124.3 | 0.01  |
| Security                         |          |      |       |       |
+----------------------------------+----------+------+-------+-------+
| Sub-Total (Balance of System)    | 1,479.7  | 1    | 825.4 | 0.08  |
|                                  |          | 2.0% |       |       |
+----------------------------------+----------+------+-------+-------+
| Payback Time (Years)             | 0.33     |      | 0.31  |       |
+----------------------------------+----------+------+-------+-------+
|                                  |          |      |       |       |
+----------------------------------+----------+------+-------+-------+
| **PV Modules**                   |          |      |       |       |
+----------------------------------+----------+------+-------+-------+
| mc-Si PV Module Manufacturing    | 10,789.7 | 8    | 6,    | 0.61  |
|                                  |          | 7.4% | 519.3 |       |
+----------------------------------+----------+------+-------+-------+
| Module Transport from Factory to | 69.0     | 0.6% | 41.7  | 0.00  |
| PV Plant                         |          |      |       |       |
+----------------------------------+----------+------+-------+-------+
| Module Disposal                  | 13.4     | 0.1% | 8.1   | 0.00  |
+----------------------------------+----------+------+-------+-------+
| Sub-Total (PV Modules)           | 10,872.1 | 8    | 6,    | 0.61  |
|                                  |          | 8.0% | 569.1 |       |
+----------------------------------+----------+------+-------+-------+
| Payback Time (Years)             | 2.45     |      | 2.45  |       |
+----------------------------------+----------+------+-------+-------+
|                                  |          |      |       |       |
+----------------------------------+----------+------+-------+-------+
| Totals (Balance of System + PV   | 12,351.8 | 10   | 7,    | 0.70  |
| Modules)                         |          | 0.0% | 394.5 |       |
+----------------------------------+----------+------+-------+-------+
| Payback Time (Years)             | 2.78     |      | 2.76  |       |
+----------------------------------+----------+------+-------+-------+

References

Alsema, E. A. 2000. Energy pay-back time and CO~2~ emissions of pv
systems. Progress in

Photovoltaics: Research and Applications 8(1), pp. 17-25.

Blakers, Andrew and Klaus Weber. 2000. The energy intensity of
photovoltaic systems.

Centre for Sustainable Energy Systems, Engineering Department,
Australian National

University, Camberra, Australia.

Environdec. 2004. Environmental Product Declarations. EPD project
sponsored by the

Swedish Environmental Management Council, http://www.environdec.com.

Frankl, P., A. Masini, M. Gamberale, and D. Toccaceli. 1998. Simplified
life-cycle analysis of

pv systems in buildings -- present situation and future trends. Progress
in Photovoltaics:

Research and Applications 6(2), pp. 137-146.

Hansen, Thomas N. 2003. The promise of utility scale solar photovoltaic
(pv) distributed

generation. Paper presented at POWER-GEN International, 10 December
2003, Las

Vegas, NV.

Keshner, M. S. and R. Arya. Study of potential cost reductions resulting
from super-large-scale

manufacturing of pv modules. Final Subcontract Report,
NREL/SR--520--36846, October

2004, National Renewable Energy Laboratory, U. S. Department of Energy,
Golden, CO.

Singh, Margaret. 1998. Total Energy Cycle Assessment of Electric and
Conventional Vehicles:

An Energy and Environmental Analysis, Volume I: Technical Report and
Volume II:

Appendices A-D to Technical Report. Prepared by Argonne National
Laboratory,

National Renewable Energy Laboratory and Pacific Northwest National
Laboratory for

U.S. Department of Energy, Office of Energy Efficiency and Renewable
Energy.

Washington, D.C.

Wang, Michael. 2001. GREET Version 1.6. Center for Transportation
Research, Argonne National Laboratory, University of Chicago, Chicago,
IL.,

http://www.transportation.anl.gov/software/GREET/index.html

Weiss, Malcolm A., John B. Heywood, Elisabeth M. Drake, Andreas Schafer,
and Felix F.

AuYeung. 2000. On the Road in 2020: A life cycle analysis of new
automobile

technologies. Energy Laboratory Report \# MIT EL 00-003. Energy
Laboratory,

Massachusetts Institute of Technology, Cambridge, MA,
http://[www.mit.edu/energylab](http://www.mit.edu/energylab).

Wibberley, Louis. 2002. LISA, LCA in Sustainable Architecture, LCA
software developed by

Sustainable Technology, BHP Billiton Technology,
[http://www.lisa.au.com](http://www.lisa.au.com/).

Zweibel, Ken. 2004. PV as a major source of global electricity. Paper
presented at the

University of Toledo, 24 February 2004. The National Renewable Energy
Laboratory,

U.S. Department of Energy, Golden, CO.