South-facing
Roof: While one half of the roof is
dedicated to generating hot water, the other half is our electric
power plant.
A roof has traditionally been designed to protect the interior of a house by keeping the weather, birds, leaves, etc. out. It is usually the largest surface area as well. Why not put it to work?
In our case, the roof has been "solarized." When you start from scratch, the architect can meld the various functions into the overall design. There are no shingles--actually, it's shingled in glass which covers the solar thermal panels and is part of the photovoltaic panels.
This is a view of work on the south-facing roof taken in the late fall. It took about three weeks to ever-so-carefully get it in place. Only the leaves fell.
Photovoltaics: Sixteen
4'x6' panels provide 4200 watts of dc power at 48 volts to an
inverter in the basement. They are essentially designed for
commercial use and were built by ASE of Billerica, MA (formerly Mobil
Solar). The inverter's output is 240 volts ac. We anticipate
generating in excess of 4.5 megawatt hours on an annual basis. During
our first day hooked up to the sun, the inverter's output reached 3.9
kw (we came online at 12:30 p.m., March 3, 1995). Several days later,
the digital meter on the Pacific Inverter displayed 4.01 kw--only a
5% reduction from the rated power of the panels. Central Maine Power
installed two meters, one to measure consumption of grid power and
the other to register our excess production. The consumption meter
reduces its spin-rate noticeably when our inverter's output is added
to the mix. Since Maine is a "net metering" state, it is quite likely
that we'll receive a check from CMP at some point later in the
year.
This diagram is a modification of a graphic from Michael Potts.
A new Trace inverter
was installed near the end of September, 1996. The previous inverter
(by another manufacturer) had failed four times in a year and a
half--in my book, it's "four strikes and you're out." It's a pure
sine wave inverter, capable of handling the 4200 watt/hr input from
the panels.
On our building plans we located a site for a wind generator--in case we want to expand our generating capacity. During the winter, there is quite a brisk nor'westerly that would more than compensate for that season's reduced solar gain. However, I'm more inclined to add additional PV panels than add a mechanically complex turbine.