Contributed by Robert Lyman ©2016

Many people believe that renewable energy sources will be able to substitute for fossil fuels or nuclear energy to meet the needs of modern economies in future. There exist, however, very few scientifically sound studies that substantiate this impression. In a paper published in the journal Energy Policy in October 2016, Ferruccio Ferroni and Robert Hopkirk examine the case of photovoltaic (PV) power sources in Germany and Switzerland, areas of moderate insolation (the amount of solar radiation that reaches the earth’s surface) by using the concept of Energy Return on Energy Invested (EROI). Their findings are relevant to the use of PV systems in countries like Canada.


The paper draws upon an analysis published in 2013 by Dale and Benson of 28 published reports on different PV installations using one of the currently available technologies. Dale and Benson found widely divergent energy demands required by these technologies.  The cumulative energy demands range from a minimum of 300 kWh per square meter of module area to a maximum of 2000 kWh per square meter. This is an indication that the reports were not using the same criteria in determining the boundaries of the PV system (i.e. the sources of energy demand associated with the construction and operation of the system).


According to official Swiss energy statistics (Swiss Federal Office of Energy, 2015), the average electricity production per square meter of PV module in Switzerland for the last 10 years was 106 kWh per square meter per year. While vendors of PV modules quote a lifetime of 30 years, the average lifetime of the modules has been about 17 years. On average, efficiency and hence performance degradations have occurred at the rate of about 1% per year. Assuming, however, that the modules operate for a life of 25 years, Ferroni and Hopkirk estimate the total energy returned over plant lifetime to be 88.1 times 25, or 2203 kWh per square meter.


The energy produced varies considerably by time of day and season. In Germany, the PV module produces during winter at its peak power for the equivalent of only 1.7 hours per day on average; in the summer period, it produces for only 3.3 hours per day. Due to the intermittent nature of the electricity production, a parallel electricity supply infrastructure has to be provided.


Ferroni and Hopkirk examine the energy costs of the PV modules in terms of the material, labour, capital and energy required to supply them. The average weight of a PV module is 16 kg per square meter and the weight of the support system, inverter and balance of the system is at least 25 kg per square meter (not including the weight of the concrete). The components are mainly steel, aluminum and copper. In addition, production requires the use of 3.5 kg of concentrated hydrochloric acid. PV systems are also quite labour and capital intensive.


In calculating the EROI, Ferroni and Hopkirk depart from the methodology used by the International Energy Agency (IEA). The IEA’s methodology is based on information provided by companies in the photovoltaic industry and, in their view, is more suitable for comparing different PV technologies than for determining the efficiency and sustainability of the PV system as an energy source. Ferroni and Hopkirk list a number of other deficiencies of the IEA approach. Other experts, who use the IEA guidelines, found the EROI of PV system to range from 4.95 to 5.9.


Ferroni and Hopkirk use an “extended” definition of EROI based on the work of the ecologist Howard Odum. In Odum’s book, “Environmental Accounting: Energy and Environmental Decision Accounting” (1995), he showed that, considering the energy integrated in the construction, operation and decommissioning of a PV system, no “net energy” is obtained. The total energy required to produce a PV system and integrate it into the grid, plus that invested for the labour, capital and energy to build and operate the module totaled 2662 kWh per square meter.


The energy returned per square meter of module is 2203 kWh and the energy invested is 2662 Kwh, for a ratio of 0.82. Ferroni and Hopkirk estimate these numbers to have a possible error of plus or minus 15%. In other words, an electricity supply system based on today’s PV technologies cannot be termed an energy source, but rather “a non-sustainable energy sink or a non-sustainable energy net loss”.


To read the main references to this summary, see here: