SOLAR PHOTOVOLTAIC ELECTRICITY
Evaluation
How does one decide to install photoelectric electricity generation? What is the optimal size or peak generating rate? The most common decision making tool is an economic evaluation. The factors which lead to a recommendation for solar photovoltaic collector array size are based upon initial cost plus the prevailing laws regarding net metering, sale of solar renewable energy credits (SRECs), tax deductions or credits and rebates. The evaluation can become sophisticated due to uncertainty of future energy use, future energy costs and fluctuating interest rates. The operating cost of the solar photovoltaic system is usually a minor contributor to the overall lifetime cost for the facility.
Solar Photovoltaic System Sizing
The solar energy flux on the facility is modeled for the specific site. Solar radiation calculations can be based on Bird and Hulstrom's model from publication "A Simplified Clear Sky model for Direct and Diffuse Insolation on Horizontal Surfaces" by R.E. Bird and R.L Hulstrom, (SERI Technical Report SERI/TR-642-761, Feb 1991. Solar Energy Research Institute, Golden, CO). This model (Solrad, an ExcelTM spreadsheet) can be downloaded from a Washington State Department of Ecology, Olympia, WA web site and used without modification. http://www.ecy.wa.gov/programs/eap/models.html
Another commonly used tool is the PVWATTS computer program developed and distributed by the U.S. Dept of Energy (DOE), National Renewable Energy Laboratory (NREL). http://www.nrel.gov/rredc/pvwatts/
Inputs to the calculation include the specific coordinates of the proposed facility. The model is run for all twelve months of the year.
When the results of the solar radiation calculations are plotted, the changes in the maximum energy flux from month to month as well as the daily variations are seen. Integration of the daily isolation produces the total daily energy incident upon a surface normal to the beam of sunlight. This integrated energy represents the theoretical, perfect amount of energy that can be collected by a 100% efficient solar collector, without atmospheric aberrations such as clouds or haze. This can be directly related to a perfectly tracking solar collector array. The theoretical maximum energy collection rates must be reduced to simulate real life conditions. If the collectors are fixed instead of tracking, the energy collection is further reduced to account for oblique incidence of the sunlight energy.
How Good are Solar Collectors?
The issue of how efficiently a solar collector converts sunlight to electricity seems intuitively to be important for the study. This intuition is not correct. Efficiency is the dominant concern when the area for installation of collectors is limited, as on artificial satellites, or even a small roof. If there is sufficient collecting area available, the primary economic concerns are the initial cost, reliability, maintenance and environmental impact.
When space is available, a larger array of low efficiency solar collectors that cost 1/2 the price of a smaller array of more efficient collectors to produce the same electricity is the economic choice.
As a practical matter, the maximum theoretical conversion of sunlight into electrical using silicon based photovoltaic cells is about 33% and the best currently available technology is around 24% efficient. Cost effective solar panels using commercially available solar cells are typically 17% efficient.
Payback?
The payback for a solar photovoltaic system for electricity in Hawaii is an economically justified alternative today. Depending upon which island the power is used, the rates vary from $0.22 to over $041 per kW-hour. Ouch!
Payback calculations generally produce less attractive results in the lower 48 states. This is not to say that any given facility cannot show economic justification on the continental United States. It depends upon financing options, local electricity cost, solar energy credit, net metering and tax benefits. Solar PV projects in the northeastern U.S. are the fastest growing energy producing technology. This shows that solar PV is cost effective in areas with much less sunlight than southern locations.
Evaluation
How does one decide to install photoelectric electricity generation? What is the optimal size or peak generating rate? The most common decision making tool is an economic evaluation. The factors which lead to a recommendation for solar photovoltaic collector array size are based upon initial cost plus the prevailing laws regarding net metering, sale of solar renewable energy credits (SRECs), tax deductions or credits and rebates. The evaluation can become sophisticated due to uncertainty of future energy use, future energy costs and fluctuating interest rates. The operating cost of the solar photovoltaic system is usually a minor contributor to the overall lifetime cost for the facility.
Solar Photovoltaic System Sizing
The solar energy flux on the facility is modeled for the specific site. Solar radiation calculations can be based on Bird and Hulstrom's model from publication "A Simplified Clear Sky model for Direct and Diffuse Insolation on Horizontal Surfaces" by R.E. Bird and R.L Hulstrom, (SERI Technical Report SERI/TR-642-761, Feb 1991. Solar Energy Research Institute, Golden, CO). This model (Solrad, an ExcelTM spreadsheet) can be downloaded from a Washington State Department of Ecology, Olympia, WA web site and used without modification. http://www.ecy.wa.gov/programs/eap/models.html
Another commonly used tool is the PVWATTS computer program developed and distributed by the U.S. Dept of Energy (DOE), National Renewable Energy Laboratory (NREL). http://www.nrel.gov/rredc/pvwatts/
Inputs to the calculation include the specific coordinates of the proposed facility. The model is run for all twelve months of the year.
When the results of the solar radiation calculations are plotted, the changes in the maximum energy flux from month to month as well as the daily variations are seen. Integration of the daily isolation produces the total daily energy incident upon a surface normal to the beam of sunlight. This integrated energy represents the theoretical, perfect amount of energy that can be collected by a 100% efficient solar collector, without atmospheric aberrations such as clouds or haze. This can be directly related to a perfectly tracking solar collector array. The theoretical maximum energy collection rates must be reduced to simulate real life conditions. If the collectors are fixed instead of tracking, the energy collection is further reduced to account for oblique incidence of the sunlight energy.
How Good are Solar Collectors?
The issue of how efficiently a solar collector converts sunlight to electricity seems intuitively to be important for the study. This intuition is not correct. Efficiency is the dominant concern when the area for installation of collectors is limited, as on artificial satellites, or even a small roof. If there is sufficient collecting area available, the primary economic concerns are the initial cost, reliability, maintenance and environmental impact.
When space is available, a larger array of low efficiency solar collectors that cost 1/2 the price of a smaller array of more efficient collectors to produce the same electricity is the economic choice.
As a practical matter, the maximum theoretical conversion of sunlight into electrical using silicon based photovoltaic cells is about 33% and the best currently available technology is around 24% efficient. Cost effective solar panels using commercially available solar cells are typically 17% efficient.
Payback?
The payback for a solar photovoltaic system for electricity in Hawaii is an economically justified alternative today. Depending upon which island the power is used, the rates vary from $0.22 to over $041 per kW-hour. Ouch!
Payback calculations generally produce less attractive results in the lower 48 states. This is not to say that any given facility cannot show economic justification on the continental United States. It depends upon financing options, local electricity cost, solar energy credit, net metering and tax benefits. Solar PV projects in the northeastern U.S. are the fastest growing energy producing technology. This shows that solar PV is cost effective in areas with much less sunlight than southern locations.
