One of the major obstacles preventing many homeowners from installing solar panels on their roofs is, well, it's expensive. At least in the short term. True, the panels may pay for themselves over the course of several years, especially if they reduce the amount of electricity you need to buy from the utility (or, much rarer, if you can sell excess power back to the grid). But the upfront costs can be formidable for many people.

Two years ago, however, the city of Berkeley figured out an easy financing trick to get around this problem—the city itself just issues a bond to pay for the upfront costs of installing the panels, and the homeowner then repays the government over the course of 20 years via a small line item on the property-tax bill. (This way, if the home is sold, the costs of the panels get passed on to the new owner getting the benefits.)

It's a small policy tweak, but quite sensible. No mandates, no regulations, just offering homeowners an extra option if they choose. So it's not surprising to hear that, as Kate Galbraith reports today, the idea's been proliferating like crazy: This year alone, eight states have followed California's lead by giving their municipalities permission for this sort of financing, including Colorado, New Mexico, Ohio, Oklahoma, Texas, Vermont, Virginia, Wisconsin. (Apparently, a lot of cities need permission from the states before they can mess with property-tax bills.)

--Bradford Plumer