Energy Return on Investment

Performance of solar cells as far as the environmentally is based on the amount of energy needed to build and maintain them verses the amount of energy they produce in their lifetime. This ratio is called the energy return on investment (EROI). This is very different from economic returns on an investment, which varies according to local energy prices, subsidies available and metering techniques. An idea related to this is the energy pay-back time. This means the time required to produce an amount of energy is as great as what was consumed during production.

Energy pay-back times of crystalline silicon PV systems presently are at 1.5-2 years for South-European locations and 2.7-3.5 years for Middle-European locations. There are clear prospects for a reduction of energy input in silicon technology, and an energy pay-back of 1 year may be possible within a few years. Thin film technologies now have energy pay-back times in the range of 1-1.5 years (S.Europe).With lifetimes of such systems of at least 30 years, the EROI is in the range of 10 to 30.

There are alternative theories of energy accounting which have a more pessimistic calculation for EROI of photovoltaics. Howard Odum's "Energy" concept and Price-Estimated EROI calculations arrive at EROI closer to 1:1 for photovoltaics. Another theory estimates $7/watt to install a PV system, then the total energy needed to manufacture and install that watt is assumed to be the amount of energy you could buy for $7. This approach produces an EROI of 1:1 for any source of energy. What's the EROI of oil? Using this approach, the total energy invested including distribution costs, refining costs, and feeding the crew that monitors the supertanker, must be about $3/gallon.

Grid parity
Grid parity means photovoltaic power is equal to or cheaper than grid power. Grid parity is already reached in some regions. Grid parity has been reached in Hawaii and many other islands that use diesel fuel to produce electricity.
In Italy PV power has been cheaper than grid electricity since 2006. One kWh costs 21.08 -€cent/kWh. Italy has an average of 1,600 kWh/m2 (Sicily even 1,800 kWh/m2) sun power/year. At 4 % costs of capital, 25 years of depreciation and costs (including installation) of 4,600 €/kWp PV current costs are 20.91 €-cent/kWh. At large scale plants with 3,900 €/kWp the costs reduces to 17.75 €-cent/kWh and is 15 % cheaper. To reach a 19% PV power coverage in Italy, 34,000 MWp power must be installed. This means 0.09 % of the size of Italy. 9 % of the size of Sicily could produce 25 % of the power of the complete European Union (ca. 2,100 TWh/year).



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