Almost all the rest of power in the U.S. is generated from renewable sources, such as hydroelectric (6%), wind turbines (4.4%), biomass (1.7%) and geothermal (0.4%).
Remarkably, providing for all of the power needs in the U.S. would require a relatively small amount of real estate. According to a 2008 analysis by the National Renewable Energy Laboratory, supplying those needs with photovoltaic solar energy would require that roughly 0.6% of the country's land area be covered by solar panels -- about 1,948 square feet per person.
New installations of solar power capacity are already growing at consistently high double-digit rates. So far this year, solar installations surpassed those of wind and coal for the second year in a row, accounting for 32% of all new electrical capacity, according to a report released earlier this year by GTM and the SEIA.
"Hillary Clinton's 33% installation target is double [considering] what the government is currently forecasting," said Raj Prabhu, CEO of Mercom Capital Group, a clean energy research firm.
Clinton's target of 140GW of total capacity can be reached if the U.S. solar market grows at an annual rate of 32% from 2017-2020. That's roughly on par with the 36% annual growth rate GTM projected from 2013-2016.
"In other words, the market just needs to keep growing at the same rate for another four years," Kann stated. "But that won't happen under business-as-usual conditions, hence the big difference between our 2020 forecast and Clinton's goal."
With no changes to the nation's policies, solar capacity would only grow to about 70GW by 2020, according to GTM Research. That's because under current policies, tax incentives and other growth programs are set to expire next year.
For example, the federal government's solar investment tax credit (ITC), which offers a 30% tax credit for residential and business installations, will run out next year and drop to a more permanent 10%.
The main catalyst of growth in solar installations in the U.S. has been the 30% ITC, Prabhu said. Forecasts indicate a decline in the solar growth rate in 2017 "assuming there are no miracles to save the ITC from expiration."
"Looking at the current scenario, a 700% forecasted growth by 2020 looks overly aggressive," Prabhu said of Clinton's plan.
Considering the current expiration of the ITC, Kann also characterized Clinton's goal as a "highly aggressive goal" and one that would require a new set of policy drivers and incentives, especially considering she wouldn't take office until 2017.
Another challenge Clinton would have as president would be her limited influence over local utility markets and how utilities companies treat their solar customers.
Currently, residential solar is economically viable due to net metering policies, which force utilities to buy back any excess power generated by rooftop solar installations.
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