Primer

Before telling you about our system, here's a little primer for those not familiar with home power systems.

Since the most important thing with such systems is to reduce the amount of electricity they need to produce, many designs start off with propane-powered refrigeration, cooking, and space heating.

The heart of an off-grid system is a battery bank. These come in various shapes and types, but they are often little more than several golf-cart batteries wired together. The object is to be able to store enough energy so that the system will run overnight and when there's no sun, so several days' storage capacity is best.

Batteries provide direct current (DC), but most appliances use alternating current (AC). A device called an inverter therefore is incorporated to convert the battery power to household power. Inverters come in many flavors, ranging from an inexpensive thing you can buy at Wal-Mart to sophisticated units costing thousands of dollars.

The batteries are usually charged by solar panels, wind generators, or water-driven generators. Solar panels (properly called photovoltaic modules, or PV) are the most expensive, but so long as there is sunshine they're predictable and reliable. Wind-power generators cost a lot less, but the machines require tall towers, some maintenance, and the wind can be capricious. Water-power generators can be cheap and powerful but few locations have the necessary running stream or other supply.

The batteries will be damaged if they are overcharged, so several types of charge controllers are available to prevent that.

Load centers are electrical junction boxes with various accessories designed to provide fuse protection, emergency shut-off capability and a convenient central point to connect all the components together.

System monitors are electronic gauges used to evaluate system status, such as how fully charged the batteries are, and how much electricity is flowing to the batteries or loads.

Engine-driven generators are usually connected to the system to provide a back-up source of power.

While our system is off-grid, similar systems are increasingly being used in homes that are connected to the grid. Sometimes the purpose is simply to offset the home's energy use thereby reducing the monthly bill. Other times the system is designed to do that, plus provide emergency power if the grid fails. Systems connected to the grid often dispense with batteries, instead using the grid for storage, for a big savings in equipment cost and maintenance.

Brochures describing home power equipment  will often say things like "better power than from the utility company". Statements like this are only partly true. The fact is that living in an off-grid home will require compromises that many people are not prepared to make. The biggest adjustment is that the owner of such a system is now his own power company. The concept of being in charge of sometimes complicated electrical equipment will require some acclimatization for those who are used to calling an electrician to change a blown fuse.

Our Setup

The batteries are a heavy-duty type designed for tough service. They aren’t all that big, about 3 by 2 by 2 ft, but they weigh about 2000 pounds. They're installed in a ventilated enclosure in the garage.

The batteries are connected to the load center with large cables. The load center contains a fused disconnect, the circuitry for the solar charge controller, and the system monitor.

Power comes out of the load center into the two wall-mounted inverters, which weigh about 130 pounds each. These are pretty sophisticated units, with dozens of settings which are adjustable via an electronic control panel. Each inverter produces 110 volts AC (regular house current). They're connected via a communication cable so that they work in tandem to produce 220 volts, which is what a clothes dryer or well pump uses. Power quality is comparable to the grid but slightly different.

There is a third, smaller inverter, which delivers better quality power, and this is used to supply the computer, television, etc. It’s not that these items need better power, just that supplying them independently assures that they aren’t subject to the variations in output of the main inverters at certain times.

There are 24 solar panels, divided into three arrays. Each array is mounted on a motorized tracker, which follows the sun's arc during the day, and then returns to the east to be ready for sunrise.

There are two wind generators mounted on a 65 foot tower. The larger one is at the top, with a smaller one some distance down. Together the wind generators deliver about as much power as the solar panels, so long as the wind is howling. The wind generators are covered in more detail on a separate page. 

There is a small system monitor, a sophisticated gauge which displays voltage, current in and out, total energy consumed, battery state of charge, and several other items.

There is also a small, quiet, gasoline-fueled DC generator outside for backup on cloudy or calm days. A large welder/generator is also occasionally used for AC back-up power.

This system is larger than most. The cost of all the components is about $25,000. If we had paid someone to do the installation work, that might have added another $5000. All of the components are widely available. About the only thing we did slightly different than most was to mount the indoor components in such a way that the bulk of the conduit is hidden behind removable panels. This makes modification more convenient, and avoids the "Frankenstein's lab" look which afflicts some systems.

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