You've seen pre-paid cell phones. Now get ready for pre-paid power bills. A few utilities in the U.S. are looking at implementing pre-paid, or pay-as-you-go, power bills, according to Adrian Tuck, CEO of Tendril, a start-up specializing in household energy management. The concept is simple. You pay money to the utility at the beginning of the month, and they keep the lights on as long as your cash holds out. The concept was started in Europe, he noted. Utilities in England, in fact, used to put coin slots in buildings so residents could chalk up another 50p of power when they needed it. Now, people mostly pay through their cell phones. It's mostly for people with bad credit (i.e. temp workers, band members and former Bear Stearns partners.) Nonetheless, it's now a huge part of the market now. The system is also popular with owners of apartment buildings who don't want to get stuck with the power bills of departing tenants. Tendril, by the way, makes Zigbee-enabled devices such as thermostats that allow the resident or the utility to control heating, lighting and other energy hogs from a distance. The company designs and sells hardware as well as management services. While there are a bunch of companies in this market, they seem to be emerging pretty well from the pack.

Xerocoat wants to pull off the triple in the solar world: sell the same product to solar thermal, crystalline PV and thin film manufacturers. The Redwood City-based company has come up with an anti-reflective, porous glass coating that can boost the efficiency of solar components by essentially preventing incoming solar energy from bouncing. The material can increase the relative efficiency of crystalline solar panels by approximately 3 percent, according to CEO Tom Hood. Over a 25-year period, that results in 4 percent more kilowatt hours generated by the same panel, he claimed. By integrating the coating, manufacturers can effectively upsell their panels. “We increase the nameplate capacity,� he said. Right now, only around 5 percent of PV makers apply supplementary anti-reflective coatings to their panels, he added. In solar thermal systems, the coating is applied to the external glass tube of the concentrator. (Concentrators in traditional solar thermal systems contain two vacuum-sealed tubes: an external one that lets heat in and shields the internal tube from the elements, and an internal tube that holds oil that gets heated by the sun’s energy. ) The company is currently conducting a trial with a U.S. solar thermal company building a 1 megawatt demonstration plant in California. The coating is applied as a liquid. When cured, pores measuring five to 20 nanometers across permeate it. Xerocoat expects key patents for its process to issue later this year. Nth Power and Southern Cross Venture Partners have invested in the company.