Solar power's detractors frequently describe solar as ‘secretly’ non-environmentally-friendly. They point to the PV module manufacturing process, utility-scale arrays' potential impacts to land and wildlife, and concentrating solar power (CSP) plants' on-site water usage as examples of attributes that negate the environmental benefits of deploying this renewable energy source.
But when all of the impacts are considered and all the costs are tallied, how does solar compare to other common energy sources? A new report called ‘The Hidden Costs of Electricity: Comparing the Hidden Costs of Power Generation Fuels’ suggests that the indirect or externalized costs of fossil fuels, nuclear power and biomass still outweigh those of solar power.
Researchers analyzed solar power and five other energy sources (biomass, coal, nuclear, natural gas and wind) in several categories: water impacts, climate change impacts, air pollution impacts, planning and cost risk, subsidies and tax incentives, land impacts and other impacts.
The report, prepared by Synapse Energy Economics Inc. for the nonprofit and nonpartisan Civil Society Institute and the Environmental Working Group, concluded that ‘huge demands on increasingly scarce water are a major hidden cost of a business-as-usual approach to American electricity generation that needs to be more fully understood by policymakers and the public.’
Solar power, however, did not rank as a prime offender in this critical water-usage category. Rather, nuclear power, coal-fired power, biomass and natural gas (obtained via fracking) were called out as particularly water-intensive energy sources. Open-looped coal-fired power plants, for instance, use between 20,000 and 50,000 gallons/MWh. Although most of the water is reclaimed, it is returned at a higher temperature and lower quality.
‘By contrast, wind and solar photovoltaic power requires little water in the electricity generation process,’ the report states. ‘Concentrating solar power requires water for cooling purposes, but new technologies are placing greater emphasis on dry cooling.
‘Solar power plants with dry cooling use only around 80 gallons per megawatt-hour – about a tenth of the low-end estimate for nuclear power and one-sixth of the low-end estimate for coal-fired power generation,’ the report adds.
Breaking down costs
The report summarizes each energy source's hidden costs by assigning a color-coded level: red (high costs), yellow (moderate costs) or green (low costs). Solar appears to boast one of the most favorable color-code profiles of the six energy sources examined.
Both PV and CSP are deemed to pose low costs (green level) for planning and cost risk, climate-change impacts, air-pollution impacts and ‘other impacts.’ Naturally, larger projects can present more planning risk than smaller-scale projects, but because most projects are developed by non-utility companies, ratepayer risk is reduced.
For certain types of thin-film PV, the usage of toxic cadmium has provoked criticism. According to the report, one recent study of lifecycle cadmium emissions for systems using cadmium-telluride modules measured such emissions to be approximately 0.3 g/GWh.
‘The use of heavy metals in PV cells raises questions about the disposal of panels at the end of their useful lives,’ the report warns. ‘Regulations governing the handling and recycling of retired PV panels are needed to ensure that metals do not leach into soil or groundwater.’
In response to these concerns and other considerations, the solar sector has stepped up recycling efforts in recent years. Earlier this week, for instance, Tempe, Ariz.-based pv recycling llc and CERES, a Paris-based nonprofit, entered a new partnership agreement to provide module manufacturers in the U.S. and Europe with coordinated recycling services.
Solar's subsidies and tax incentives, as well as land impacts, are rated as moderate. Although distributed-generation rooftop PV occupies no land, some utility-scale plants have caused concern regarding their impact on threatened species' habitat, the report notes.
Not surprisingly, PV ranks ahead of CSP in the water-usage category. Lifetime water withdrawals for PV are estimated to be between 225 and 520 gallons/MWh, with thin film generally beating out crystalline silicon. Wet-cooled parabolic-trough CSP plants may use approximately 1,240 gallons/MWh, whereas dry-cooled plants may use approximately 290 gallons/MWh.
The preliminary findings on CSP water usage ‘provide useful starting points for assessing lifecycle CSP water impacts,’ the report notes, adding that additional research is needed.
Overall, although the report does not explicitly call for greater usage of solar power or other renewable energy sources over others, it strongly encourages utilities, policymakers and the public to consider more than the more commonly examined direct costs when evaluating various energy options.
‘Too often left out of the equation are a number of important hidden costs â�¦ associated with each generation technology,’ says Geoff Keith, senior associate at Synapse Energy Economics, in the report. ‘While direct costs (the monetary cost to build and operate a generating plant) are important to consumers, so too are these indirect costs, whether or not they can be easily expressed in monetary terms.’