WASHINGTON, DC, USA,
September 5, 2007.
A solar industry group in the United States wants to develop a statistical methodology for calculating the capacity of PV.
The Solar Electric Power Association has released a working paper, ‘Developing Consensus on a Capacity Methodology for PV Generation,’ that will be discussed later this month following a solar power conference. The paper is designed to bring utilities and the solar industry together to discuss the methodologies for calculating PV capacity, “an important technical valuation that is currently under-utilised in utility generation planning.”
“Photovoltaic installations have an intuitively strong correlation with electricity demand, as hot days are often sunny ones,” explains SEPA. “However, photovoltaics are a variable generation source and are not considered firm, controllable power from an electric utility perspective.”
“Several methodologies have been developed by researchers to show statistical capacity values but, from a practical standpoint, they have not been readily adopted by the utility industry,” it adds. “Valuing photovoltaic capacity could provide economic and technical benefits for both utilities in planning generation supplies, as well as photovoltaic generators.”
The workshop will discuss different methodologies to calculate PV capacity and “attempt to narrow down the options through common understanding and consensus.” The paper was developed with funding from the U.S. Department of Energy’s ‘Solar America Initiative’ which wants the solar industry, electric utility and research communities to work in a consensus-oriented process.
“Maintaining adequate generating capacity to meet electricity demand is a fundamental principle for the electric utility industry,” it notes. “For dispatchable power generating sources, a summer and winter nameplate generating capacity is calculated based on the technology design parameters. Their dispatch can be managed around the demand for electricity and their marginal operating costs. In contrast, photovoltaic technology has an electrical output that varies with the installation characteristics, site conditions, and daily and seasonal solar resource variations, and has essentially zero marginal operational costs.”
The solar resource variations are “clearly not random and have some statistical capacity value” and developing a framework for calculating PV capacity and determining the risk of variation, “will provide a means for utilities and generators to calculate and innovate around the new economic propositions that an industry recognised PV capacity calculation method would present.” The statistical calculation of photovoltaic capacity can be altered by the distributed nature of solar PV and “the risk mitigation benefits that geographic diversity and the aggregation of performance across geographies could provide.”
That issue is important for short-term output variability, as five PV plants across a 50 mile area would have a lower risk of minute-by-minute capacity variation than a single plant, and would be a reasonable assumption for determining a contribution to overall system capacity planning. The analysis assumes that PV resource is dispersed in nature and that aggregated capacity credit within the considered context is utilised.
The Solar Electric Power Association is a non-profit organization with 200 utility, electric service provider, manufacturer, installer, government, and research members. Its mission is to facilitate solutions for the use and integration of solar electric power by utilities, electric service providers, and their customers.
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