BACKUP GENERATION
Without an array of batteries or other back-up generator (usually fueled by diesel, propane, natural gas, or gasoline), a grid-connected solar electric (Photovoltaic or PV) system cannot provide any electricity during a utility power outage. For safety reasons, most grid-connected PV systems have inverters (the devices that convert DC electricity to AC) that are designed to shutdown completely if there is a power outage. A special type of inverter is needed if you want a backup generation system.
Homeowners with PV systems that regularly experience utility power outages or who highly value uninterrupted power, often choose to install a battery backup system. The benefits of battery backup systems with PV include the almost instantaneous delivery of backup power, emission-free back up energy, and the ability to provide power for an extended outage when delivery of fuel could be problematic. The disadvantages of incorporating batteries into a PV system includes more components and costs (generally starting around $3,000 and up), some maintenance, and the lowering of the PV system’s overall efficiency.
A minimal battery system that only powers one or two very critical devices (e.g. a refrigerator and furnace fan) could be an affordable option (possibly under $1000) to discuss with your solar contractor.
Which and how many appliances can be operated during a utility outage is dependent on the size of the PV and/or battery system. Use the list below as a very general guideline for the watts required to run certain appliances and functions.
| Device | Running Watts Required |
| Central air conditioner | 5,000 |
| Coffee maker | 1,000 |
| Computer | 250 |
| Clothes dryer (electric) | 4,800 |
| Freezer | 500 |
| Furnace fan | 500 |
| Garage-door opener | 600 |
| Hair dryer | 1,200 |
| Lights (5) | 400 |
| Microwave | 1,500 |
| Portable heater | 1,300 |
| Radio | 100 |
| Range (electric, 3 elements) | 4,500 |
| Refrigerator | 600 |
| Sump pump | 600 |
| Television | 350 |
| Washing machine | 400 |
| Water heater | 3,000 |
| Well pump | 400 |
| Window air conditioner | 1,000 |
If you are considering purchasing diesel, gasoline, propane, or natural gas back-up generator, you will need to add-up your power needs. Even a small generator can power several plug-in appliances, but you'll need a larger one and a transfer switch (about $600 installed) to power furnace fans and other devices hardwired to your home. Generators fall into four categories:
☼ Small portable generators (3,000 to 4,000 watts) can power the basics like a refrigerator, some lights, a TV, and a microwave. Price: $500 to $800 for most basic gasoline-powered models; more for inverter models that use a microprocessor-controlled circuit to improve power quality.
☼ Mid-sized portable generators (4,500 to 7,000 watts) can also power a portable heater or window air conditioner, computer, and, with a transfer switch, a furnace fan and water pump. Price: $600 to $1,000 for most.
☼ Large portable generators (10,000 watts) will run a water heater or central-air-conditioning unit in addition to the other devices listed. Price: $2,000 to $3,000.
☼ Stationary generators (10,000 to 15,000 watts) provide enough power to run a washer and dryer, too. Price: $5,000 to $10,000 or more, plus installation.
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