An Assessment of Solar Power on Rooftops

Date: 2 May 2005 | posted in: Energy, Energy Self Reliant States | 0 Facebooktwitterredditmail

In March 2005, the Energy Foundation released a study prepared for them by Navigant Consulting and Clean Energy Research. The study was completed in September 2004 and claims to be the first of its kind to do an assessement and estimate of the rooftop solar photovoltaic market potential on a state-by-state basis.

We here at Democratic Energy applaud the nicely done section of the report that calculates the square footage of residential and commercial rooftops that could be available for solar installations for each state. The author’s produced detailed tables that will make it much easier to calculate the possibilities that photovoltaics can provide in different areas of the country.

The authors make some well considered yet aggressive assumptions for their analysis. The efficiency gains and cost reductions projected by the study are ambitious and depend on many factors coming together to bring about the rosy conclusions of gigawatts of annual PV market penetration after 2010.

1. The study assumes that the power density of generating electricity from solar cells increases from 8.7 watts per sq. ft. in 2003 to 10.2 W/sq. ft. in 2010 and 12.3 W/sq. ft. in 2025.

2. The study assumes that 65 percent of commercial roof space could be used for solar installations and that 22 percent of roof space for residential applications (including flat-roofed apartments) could be used for solar installations.

3. The study’s breakthough PV costs of $2.00-$2.50/Watt (installed) by 2010, represents a 53 percent reduction from the business as usual scenario (Note: We here at Democratic Energy feel that the 3 percent annual cost reduction of the business as usual scenario is also an agressive assumption). The author’s say, "We [Navigant] emphasize that these cost reductions can only be achieved with strong, continued government support in the near term that creates a positive investment climate for private investors."

4. The study calculates that 6 percent of the overall market potential would be developed by 2025.

Calculations from the study show that in 2010:

– At $2.00-2.50 per installed watt, the annual market potential for grid-connected residential and commercial building PV applications is estimated at 2,900 MW, representing an annual market of about $6.6 billion (equipment and installations).

– Rooftop space is not a constraining factor for solar development. Residential and commercial rooftop space in the U.S. could accommodate up to 710,000 MW of solar electric power (if all rooftops were fully utilized, taking into account proper orientation of buildings, shading from trees, HVAC equipment, and other solar access factors). For comparison, total electricity-generating capacity in the U.S. today is about 950,000 MW.

– The Pacific and Mid-Atlantic regions together would account for 52% of the potential residential and commercial sector demand.

– California alone has the potential for about 40% of the total building rooftop market potential through a combination of favorable sunlight levels and high retail energy prices


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John Farrell

John Farrell directs the Energy Democracy initiative at the Institute for Local Self-Reliance and he develops tools that allow communities to take charge of their energy future, and pursue the maximum economic benefits of the transition to 100% renewable power.