Click here for an excellent Home Power article written to help you understand the difference between grid-tied and off-grid PV systems and how to decide which is best for you.

A utility-intertied (“grid-tied”) PV power system works in combination with utility power. If you have utility power now and install a PV system, it will be a grid-tied power system. If you live beyond the reach of utility power and install a PV system, it will be an off-grid system.

When Positive Energy began in 1997, off-grid applications made up about 98% of our work. Although the amount of off-grid work remains robust, today it is less than 10% of our total business. This is simply because most of the tremendous recent growth in the solar power field has been with grid-tied systems – the mainstream application of solar power.

From time to time we will be asked to take an existing home off-grid. A homeowner may be concerned about grid unreliability or failure, or just may see the utility as an adversary. But in all of our years in business we have never taken an existing home with utility power off-grid, although we have explained to many why it is impractical, expensive, or both. This is because a PV power system that can provide abundant electric power for an off-grid home - that is, a home designed and built to use an independent electric power system, without connection to utility power--will not run a conventional home.

Off-grid homes are designed and built with solar electricity in mind. Lighting, appliances, electronics, and wiring are all selected and installed to make each watt-hour of electricity do as much work as possible. (A watt-hour is a basic unit of measure of electric power; a thousand of these make up a kilowatt-hour; eight cents on your electric bill). Tasks such as cooking, clothes drying, water heating, space (home) heating are shifted to natural gas, propane, wood, or solar heat. Done well, the result is a home that is bright, warm, and comfortable while using a tiny fraction of the electricity of a typical grid-tied home.

Conventional homes are seldom designed and built to this level of efficiency. Here's one way to look at the difference: A typical PV power system that can supply about three kilowatt-hours' worth of electricity on a winter's day might cost $20,000. With a small amount of backup generator power during cloudy periods, this is ample to meet the needs of a family. Supplied by the utility company, the bill would be less than ten dollars a month, plus base charge and taxes! Few utility customers have bills this small, because few have done the load shifting and high-efficiency improvements necessary to live comfortably on the amount of electricity supplied by an independent PV power system.