This Solar House
Many
people think to have a zero-energy* solar home, you need to start with new
construction, spend a small fortune, and/or lose comfort or convenience. But we
found that was not the case. In just over a year, we transformed our 1960s tract
house in southern California into a solar-powered, energy-efficient home. While
the initial investment was substantial, we funded it through an affordable
home-equity loan. The makeover will pay for itself in seven years, after which
the energy for our home (and our electric car) will be entirely free. And with
these changes, we annually offset at least 21,000 pounds of carbon
dioxide—a key pollutant in global warming—that our pre-upgrade home
and car would otherwise have added to the atmosphere. In this feature, let us
show you in detail how we went about our zero-energy retrofit, which saves
money, energy, and the global climate.—Norma and Alan Williamson
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Solar,
Part 1 (Dec 2003) We moved
into our 2,300-square-foot house around Thanksgiving 2003. Within a month, in
order to make use of state rebates that would decrease after the first of the
year, we purchased a 6-kilowatt photovoltaic (PV) system. Installation occurred
in two phases. First, in December, we installed the 4-kW array of 35
sapphire-blue PV panels that you can see on the south-facing side of our main
roof; eight months later we added the 2-kW set over the garage (see "Solar, Part 2" below). This 6-kW PV system supplies all our energy needs, from our
home's heating and air conditioning to the "fuel" for our
electric car. (To learn how PV panels work, see Inside a Solar Cell.) Cost:
$36,000 (6-kW system; after rebates and tax incentives totaling $17,500, our out-of-pocket expenditures came to $18,500)
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Insulation (Jan–Feb 2004) As part
of our goal to make our home net-zero-energy—that is, generating more
energy than is consumed—we set about improving our home's
insulation. In January, we contracted a company to inject cellulose (recycled
paper) insulation into the walls, bringing them up to an R15 level. (The
R-value indicates the resistance of a material to the passage of heat and
cold.) The following month, we replaced our leaky, single-glaze aluminum
windows with dual-pane thermal windows. These are so-called
"low-emissivity" windows, which keep winter heat in and summer heat
out. We left our front picture window (behind car in main image and at left) intentionally
non-low-emissivity, so the winter sun could warm our living room—a
passive solar technique. Cost: $1,300
(insulation), $10,000 (dual-pane windows)
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Roof (Mar–Jul 2004) To
further increase thermal resistance, we decided to replace the roof and upgrade
our attic insulation. In March, we removed the 4-kW solar array as well as the
existing, substandard roof tiles. The following month, we brought the attic
insulation up to an R30 level. Then, in June, we installed aluminized solar
sheathing on the roof. This is a thermal reflective plywood that keeps external
heat out and reflects interior heat back in. We also installed roof jacks (to
hold up the solar array) and then a new composite shingle roof. Finally, in
July, we put in a whole-house cooling fan and whole-house heat-recirculating
system (as well as two skylights, one seen in the center of the roof). The fan
cools the attic and ceilings when outside temperatures are high, while the heat
fan shuttles warm air from the attic to the ground floor when outside
temperatures are low. Cost: $300 (attic
insulation), $23 per 4' x 8' board (solar sheathing), $4,000 (new
roof), $600 (whole-house fan), $570 (whole-house heater), $1,450 (two
skylights)
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Solar,
Part 2 (Aug 2004) This
month we reinstalled the 4-kW solar array over our main roof and put in place
the 2-kW, triangle-shaped array of 14 panels over our garage. Our now 6-kW
solar system includes a 4-kW inverter to convert the DC electricity coming from
the solar panels into AC to power our appliances. Most homes wouldn't
require a 6-kW system; we added the extra 2-kW solely to power up the 24 nickel
metal hydride batteries in our Toyota RAV4 all-electric vehicle (seen in main
image). In fact, because we now generate more solar energy than we can use, we
welcome friends who own electric vehicles over to charge their car batteries
for free. Cost: included in costs
noted in "Solar, Part 1"
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Battery
Backup (Sep 2004) To be
prepared in case of blackouts, we installed an 8-kW battery reserve system.
This includes an inverter and charge controller that regulate energy flow to
and from the batteries. If the utility grid goes down and we have a string of
very overcast days, our batteries will give us about three days worth of
conservative electric use. If the sun is shining, we have unlimited
energy, of course. Cost: included in costs
noted in "Solar, Part 1"
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Solar,
Part 3 (Oct 2004) This
month we replaced our natural gas-fired water heater with an
active, closed-loop solar hot water system (see the two gray solar panels visible
on the left side of the roof) and a new 220-volt electric hot-water heater. Cost: $2,500
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New
Heating/Cooling (Jan 2005) The final
step in making our house comfortable involved replacing the old, five-ton
heating, ventilation, and air conditioning (HVAC) system with a split-ductless
heat pump/HVAC system. This is a three-zone system, with small units in the
den, dining room, and upstairs master bedroom. The system has an outside
central operating unit and a compressor-heat exchanger that is about half the
size of a typical air conditioner. Cost:
$4,200
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Costs
& Benefits After
$18,500 in rebates and tax incentives, the total cost for all our
energy-efficient improvements and our solar system, including labor, came to
$43,000. We calculated that, if we had not made the retrofit, our energy bills
for 2004, including fuel and oil for a gas-powered car, would have come to
$6,000. With the upgrades, we have no energy costs (except for $5 a month for
the one therm of natural gas we use, mostly for cooking). Thus, our entire
energy makeover will pay for itself in just over seven years ($43,000/$6,000 =
7.2). And because our loan for these improvements is based on home equity, the
interest payments are tax-deductible.
Since we
remain connected to the utility grid, Southern California Edison's
time-of-use billing program measures our overall electricity consumption and
production. Rates vary depending on season and peak versus off-peak hours. With
normal sunshine, we can actually see our meter "feeding the grid."
Our electricity production earns us "use-it-or-lose-it" credit from
the utility. In summer peak hours (10 a.m. to 6 p.m.), we can earn over 40
cents per kilowatt-hour; even during off-peak summer hours and in winter, we
can earn credit. Each year, our credit amounts to between $200 and $300.
It's
true that we live in warm, sunny California, which has some of the best rebates
and tax incentives for going solar in the nation. But wherever you live, you
can benefit from energy-efficiency and renewable-energy upgrades to your
existing home and become part of the solution to global warming. See
Resources for more general information.
For more specifics on the Williamsons' retrofit, see this article published in Solar Today Magazine, from which our feature was drawn.
*Note: "Zero-energy" here refers to energy purchased, not energy used.
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