12 75-watt Siemens SP75 modules |
With interior space of this 800 sq.ft. passive solar home
at a premium, the owners wanted all the space to be livable. This meant
there would be no space for a mechanical room, and therefore mandated that
mechanicals be located in an outbuilding, called a powershed.
Inside the shed resides the power system, including a backup propane
generator, and an 82 gallon water pressure tank. Both AC power and domestic
water are supplied to the house from the shed. The building is kept
from freezing in winter by a small direct-vent propane heater.
A hot water tank is situated in a small heated space off a side porch.
The tank provides household hot water as well as heat to a radiant floor
system. When space heat is called for, domestic hot water circulates through
a exchanger, giving heat to the radiant floor loop also circulating through
it. There are no complex heating controls to act as a phantom load on the
inverter.
The array consists of 12 75-watt peak Siemens modules, wired at 12vdc
for a total of 900W output. The 12vdc system configuration was selected
primarily because of the close proximity of the array to the controls.
There would be no cost advantage to a 24vdc configuration in this instance. |
The homeowner chose a Xantrex SW2512 inverter to provide clean AC power
to standard household loads. Other controls include a Photron SolarUPS
power center. The SolarUPS includes a 100-amp pulse width modulated charge
control, a battery state-of-charge monitor, and 250-amp DC rated circuit
breaker protecting the inverter and dc load disconnects. A Bogart
Tri-metric voltage, current, and amp-hour meter (to monitor the batteries
state of charge) is mounted in the house for remote system monitoring.
A manual transfer switch allows the generator to bypass the inverter and
power the house directly when system maintenance is required.
The battery bank consists of 10 Trojan J185 12-volt, 195 ahr batteries
(the 12-volt equivalent of the 6v, 350 ahr L16), for a total of 24.57 kilowatt-hrs
of storage. The batteries are resting in covered plastic enclosures
which are vented outside.
An Onan 6.3k NHE propane generator provides backup battery charging
(the Xantrex inverter automatically starts & stops the generator as
necessary) when the sun can't keep up with demand. The generator
can also be run manually via a remote start/switch in the house.
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Batteries |
Xantrex SW2512 inverter & Photron SolarUPS |
Onan 6.3k propane generator |
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