If you've been to Portland, Oregon, you've probably also been to Powell's Books.

In December, the famed bookstore will use its visibility for a good cause— solar energy.

The store, which spans a city block and encompasses multiple buildings, plans on installing one of the largest solar electric systems in the state.

The 100 kilowatt photovoltaic system on the store's warehouse roof will generate 110,900 kWh each year, or about a quarter of the building's annual energy use. Powell's warehouse building houses the company's online division, as well as administrative and marketing offices.

And Powell's has even bigger plans in the future—if budget constraints allow, the bookstore will get a renovation that may include a green roof with a rainwater catchment system. 

Whether or not the renovation ends up happening, Powell's solar panels serve as a model for all buildings in the city.