The House on Hummingbird Hill is off the grid. That means that there is no connection to the local power company. Which means they had to become their own. By making the house really efficient, they didn’t need to become a big power company, just a small one.
A rule of thumb is that it costs three to five times more to generate power than to be efficient with it. So what that meant was they only needed 630 watts of photovoltaic cells like the one at right. Normal systems, at a minimum, are three times that size.
They tried to keep the system as simple and efficient as possible, so the inverter is used for larger AC loads, but smaller loads, like lighting, are all done by 24 volts DC.
Thus, there are two sets of power sockets in the house. They tried to limit the number of AC outlets to keep from invoking the main inverter too often.
There are two inverters, one of which is shown at left. The main one “sleeps” most of the time, while the smaller one is “awake” most of the time. The small one powers always-on loads, such as an answering machine, while the main one waits for a load big enough to wake it up.
By adopting this system, the Weingartens were able to keep the size of the system about two-thirds of what it would otherwise be, and saved about a thousand dollars worth of solar panels.
It has become a problem in the United States that losses from phantom loads have become an ever-increasing waste of energy.
As an example of a phantom load, most televisions draw 40 percent of their power while they’re off.
The Weingartens wanted to keep such loads under 15 watts to keep from waking up the main inverter.