Sunday, May 07, 2006
A Solar Home and NC GreenPower
Wouldn't it be great if everybody made their own electricity, so the power companies would stop building nuclear plants and trucking plutonium down the interstates? Duke Power is planning their fourth nuke plant, in Cherokee County SC, just 50 miles from Charlotte. AACK! We're surrounded!
Knowing that makes me appreciate people like Trip Overholt and Jeff and Bronwen Martin all the more. Their two families have gone solar - they've built homes that are mostly powered by photovoltaic panels. You can read about the Martin home in Solar Today magazine. Ken and I got a tour of the Martin home last weekend and it was impressive. I liked the front yard right off. No lawn, just native shrubs and flowers and ground cover. That's very cool. Wildlife benefit much more from native plants that they're adapted to. As soon as you step in the Martin's front door, you can tell the house has a passive solar design - which is totally separate from the photovoltaics. A passive solar home doesn't require any technology, but is heated and cooled passively, by virtue of its orientation, shape, and windows. An ideal passive solar house is a rectangle, with the long axis running north to south. The south wall has lots of big windows to admit warming rays of sunlight during winter. The south wall also has a big overhang to stop the sun from shining directly into the windows in summer. The overhang works because the sun is higher in the sky in summer. A passive solar house also has a thermal mass, something like a concrete floor, to absorb heat during the day and radiate the heat slowly into the air at night. The Martin's home has all these features.
As Jeff explained to me, a homeowner should have a passive solar design before adding photovoltaic panels to generate electricity. PV technology is expensive, and if you want most of your power to come from PV, then you need to do what you can to minimize your power use beforehand. The biggest energy drain in an American home is typically the heating and cooling system. Passive solar cuts way down on the amount of electricity a home might use for heating and cooling. Even just a blower for a heat pump uses a lot of power, and an air conditioner uses a ton. Trip, another PV homeowner, told me, "If you want PV power, that means no AC."
The second biggest user of power in a typical American home is the hot water heater. So a lot of PV homes have solar thermal systems to heat hot water. The Martins had that too. The roof on the southern side of their house had solar thermal panels across the top, and photovoltaic panels across the lower part of the roof. Water travels through channels in the solar thermal panels, which have a special black surface to absorb heat. The hot water travels to a water tank where it's stored until needed. The Martins also have radiant floor heat. Tubes from the hot water tank are imbedded in their concrete or gypcreet floor. When a thermostat triggers the system, hot water moves through the tubes, heating the floors and the rooms. Although, Jeff Martin told me, their passive solar works so well, they never use the thermal floor heat in most parts of the house.
We looked at all the electrical hardware in the Martin's basement for converting the power from the PV panels into AC (alternating current) electricity that the home can use, and the batteries for storing the power for nighttime use. The Martins often produce more power than they need, on very sunny days. They sell their excess power to NC GreenPower, a nonprofit that exists to support sustainable energy sources. We as consumers can get our own power from NC GreenPower by checking the box on our Duke Power bill and paying $4 extra per month. Jeff said NC was the 39th state to give consumers a green power option, so most states already have that. Apparently.
Anyway, it was all very cool. I read this weekend that a single home using conventional power is responsible for 34 tons of greenhouse gas emissions over its lifetime. You can avoid a big part of that by using photovoltaics for electricity, a solar thermal system to heat water, and a passive solar home design. If you can't afford the PV part, the other two are less expensive and go a long way toward cutting power needs.
Mike Beaver, the guy who installed the Martin's solar thermal panels, the radiant floor tubing and all their hot water apparatus was very helpful to me on the phone, answering my questions. Mike's company is Beaver Brothers, Inc. A helpful resource for finding solar professionals across the country is Find Solar. In North Carolina, NC Solar Center at NC State University and NC Sustainable Energy Asso. are useful sources of information and professional contacts. Even though photovoltaics are expensive now, everyone seems to agree that increasing demand will increase production and eventually decrease costs. That's what happened with the computer chip, which not too long ago was considered too expensive for widespread use. With demand, prices dropped. That's how it works. So thanks to folks like Trip and the Martins for being the frontrunners.