Easy, Accurate, Clear – Calculating Solar Potential in your city

The economics of a solar power project can be tricky – especially when you don’t have access to the information you need. While it is pretty easy to generalize – “Arizona is sunny – Seattle, not so much” – trying to calculate how much electricity you’ll be able to generate from the panels on your rooftop can be frustrating. And this problem isn’t just felt at home – as cities and counties take a harder look at their parking lots and garages as potential generation stations, knowing how much sun they have to work with becomes critical.

Last week, the American Institute of Physics published a paper on a new way to calculate, compile and graphically show the amount of solar energy potential in a specific region (for example, county or city).  The new methodology presented in this paper provides an easy way for you, or members of your city council, to determine the amount of energy that the sun beams down (called solar irradiance) in your area. You can even sort this information by time of day or year, to see how those panels are going to perform at 4pm in January versus 11am in July.

Developed by former graduate student David M. Wogan (of The Daily Wogan) and his advisors, Dr. Michael E. Webber and Dr. Alexandre K. da Silva at The University of Texas at Austin, the aim of this project was to make solar data more meaningful to people who wish to use this renewable resource. In their paper, they discuss how the methodology works (lots of data + computer program + pretty graphs) and apply it to Texas as a case study. Pretty cool.

If you would like to read the paper, you can access it for free here at The Journal of Renewable and Sustainable Energy.

[Image was found using Creative Commons, using the search term “sunshine.”]

Solar panels back at the White House

It looks like solar power will be returning to the White House grounds after more than 30 years of absence. According to an announcement made today by Secretary Chu (Department of Energy) and Chair Sutley (Council on Environmental Quality), solar panels and solar hot water heaters will be installed as a part of the “greening” of the White House projects. These projects have stemmed largely from last year’s Executive Order, where the President outlined his desire for the federal government to look  inward to find energy savings and in doing so lower its environmental impact.

Many have commented on the similarity of this initiative to President Carter‘s solar power installation. During President Cater’s term in office, solar panels were installed on the White House roof, only to be taken down by President Reagan.

Solar powered home in Boulder, CO

Solar panels being installed on the roof of Johnson's house

One year ago, Engineer Steve Johnson decided to take the plunge and install solar panels on the rooftop of his Boulder,Colorado home. His south-facing asphalt shingle roof (extending over a 4-car garage) had few surrounding trees (minimizing shade on the rooftop) and the house itself was newly built. Perhaps most importantly, the Boulder area is exposed to 157 sunny days and 184 partly sunny days per year.

Johnson was able to use local rebates from his electric utility (Xcel) to cover the cost of the panels, leaving him to foot the installation bill that he was able to write off (up to $2000 of the bill) on his federal tax bill at the end of the year. He chose the system size using NREL’s PVWatts Solar Calculator – eventually settling on a 5.88 kW system, enough to cover 100% of his annual electricity needs (in a gross sense, without considerations like when he needed the electricity versus when it was generated).

His final costs:

Cost of system (pre-rebates and incentives): $43,000

Johnson’s Final Cost (after rebates and incentives): $15,014

In Boulder, Johnson is able to capitalize on friendly net-metering policies that allow him to sell his excess power back to the grid, receiving a credit for each kWh returned to the wires.

In the year since he installed the panels, he has dropped his utility bill by more than $1100 – roughly giving his panels a 15 year payback period (versus 40+ without incentives).

Check out the article that Johnson wrote about his experience here, including a discussion of the downsides of his new solar installation.