Rooftop solar: an underutilized resource

By Drs. Robert & Sonia Vogl 

A study by the National Renewable Energy Lab released in 2016 indicated that roughly 40 percent of the roofs in the country are suitable for solar panels. The greatest technical potential for installing solar electric system is on roofs of buildings with less than 5000 square feet, which includes homes. It is the sheer number of roofs in this size category that provides the greatest technical potential. The 40 percent percent technical potential also applies to Illinois.

A new rooftop solar tool available at Google claims that as many as 80 percent of the roofs in the country are technically viable for rooftop solar. While the 80 percent figure appears high to some, it does suggest opportunities are far greater than last year’s estimates from NREL.

While the cost of solar systems continues to fall, extension of the Federal Investment Tax Credit until 2021, the ability to sell the carbon free energy credits and net metering in Illinois help reduce the overall cost of the systems in the state.

Currently the average price of electricity in Illinois is 12 cents per kilowatt hour (kWh).

Estimates regarding the value of solar energy to society indicate benefits could be as high as 14-18 cents per kWh. Owners of PV systems can sell the electricity they do not use back to the utility at the retail rate and have its value deducted from their electric bill. While some utilities have claimed that net metering forces other consumers without solar systems to subsidize system owners, numerous studies indicate customers without PV also benefit from the lower cost of solar energy and the reduced need to invest in expanding the electric grid. All customers benefit from reductions in air pollution and carbon emissions and lower electrical bills from low cost renewable energy sources.

As the costs of solar systems have fallen and people have become more familiar with them, the size of the systems has increased dramatically. For several years, the Illinois Clean Energy Foundation increased public awareness of the potential of solar electricity by subsidizing the installation of one kilowatt PV systems on public schools at a cost of about $10,000 per system.

Since those initial efforts the Foundation contributed to a $3 million project which installed 1800 panels on each of two Libertyville elementary schools. The installation, which was completed in 2014, is estimated to save a third of each building’s annual electrical costs.

Seven schools in Waukegan, benefit from the electricity produced on their roofs thanks to funding by NRG energy which operates a coal plant in the community. The roughly 2200 PV panels installed on school roofs represent 681 kWh of maximum power. It is estimated they could save as much as $50,000 on a school’s annual energy costs. Installations include monitoring systems in the lobby of each school along with fact sheets and presentations for use by teachers in their classes. The district is assessing the costs and benefits of installing solar panels on other buildings it owns.

As prices of solar installations continue to fall, there is a growing awareness on the part of individuals, businesses and communities of the economic opportunities rooftop solar provide to lower their energy bills while curtailing air pollution.

Drs. Robert and Sonia Vogl are the President and Vice President of the Illinois Renewable Energy Association.

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