So you want to install solar panels on your home. You're tired of forking over big bucks to the electric, gas and oil companies. You're starting to think that global warming from greenhouse gases (emitted by power plants and vehicles) may be more reality than sci-fi movie plot. You're progressive, darn it, and proud of it. Whatever you're reasoning, you want to go solar. So where do you begin?

Well, before you call a photovoltaic installer, you'll need to do some research (sorry). First, consult your electric and other utility bills to see how much power you've consumed in the last year and how much it cost. This will determine the size of the photovoltaic (PV) system you'll need. Next, measure the amount of roof space you have and determine if there's any shading from trees. The roof area should be south facing to capture the most sun, but east and west can also work.

A 1 kW PV system needs 100-150 square feet of roof space. This size system produces 135-145 kWh per month. The average U.S. family uses 888 kWh in a month, according to the U.S. Department of Energy. So the typical household needs a 6.5 kW system and 800 square feet of installation space.

(Here's a quick refresher: 1 watt (W) equals enough energy to light a match. One-thousand watts equals 1 kilowatt (kW). And consuming 1,000W for an hour is a kilowatt-hour (kWh). So running a 3,500W air conditioner for an hour is 3.5 kWh of electricity.)

Now you have enough information to call a PV installer. A good resource for finding installers in your area is FindSolar.com. This Web site also has a cost estimator for the likely price tag of your system and how much you'll save with solar panels (based on your current electric bills). You should expect to spend at least $15,000 on your system. But there are numerous financing and federal and state rebate programs for solar. The federal tax deduction for PV systems is about $2,000. [Check out TheSolarGuide.com]

It's a good idea to get all rebates and permit fees included in the installer's written estimate (so you don't have surprises later). Also, make sure that the contractor's license is up to date and there's at least a five year warranty on all parts and labor.

You'll have a number of choices to make about the components of your PV system.

Solar panels come in single crystalline, multi-crystalline and thin film varieties.

Single- (or mono-) crystalline panels are very efficient (up to 25 percent of the sun's rays captured by the panels are turned into electricity). They also have long warranties.

Multi- (or poly-) crystalline panels are a little bit less efficient because they use a lower grade of silicon in the cells.

Thin film can absorb about half as much energy as crystalline panels. Therefore, you'll need to put more of it on your roof to provide the same amount of power. The benefits of thin film are it works better in the shade and the installation is easier. It's about as thick as film negatives and can be rolled onto a roof.

Crystalline panels are much heavier and thus need to be mounted more securely to the roof. It's actually easier to install the panels when you replace your roof.

And there are some "building integrated" PV products on the market now. Manufacturers sell panels that act as roof shingles. Also, you can buy window glass with solar receptors inside, which is perfect for sun rooms.

[For a PV buyer's guide on the various solar panels, check out Home Power 121 (download for $5)]

So how does the PV system convert the sun's rays to electricity? Well, solar cells are semiconductors made out of silicon or a similar element and emit electrons when hit by sunlight. The home's inverter converts this direct current to alternating current, which is the same electricity in your wall outlet. [See the California Energy Commission's Consumer Energy Center Web site]

Up to now, we've focused on electricity, but the sun can also heat water. Solar thermal systems are often used to heat pools and spas.

Cold water from the home is pumped to the roof's "thermal energy collector," where it's warmed by the sun. The water is then pumped to the home's electric or natural gas water heater. This system can save the typical family about $500 per year. [Click here for more on thermal systems]

Another example is the solar thermal system in the Project7ten house in Venice, Calif., one of the greenest houses on the West Coast. Three solar panels on the roof heat antifreeze surrounding a water tank. The hot water provides radiant heating underneath the concrete floors, as well as drinking and bathing water. (Thermal heating systems are cleaner and healthier than dry air duct systems.) [See "Extreme Green Building"]

There are a few other advantages to PV systems in many states.

Homeowners with PV systems often only use electricity from the utility grid at night (when the sun isn't shining). A number of electric companies now offer "time of use metering." Solar customers get free energy from the sun when grid electricity is the most expensive and use cheap electricity at night when demand is lowest.

Electric companies also allow PV users to sell excess electricity back to the grid. Usually this is a credit against the power used at night.

In California, homeowner's associations and cities can't prevent someone from installing panels on their house. Additionally, the state does not include the value of the PV system when calculating property taxes. (Check if the same applies in your own state.)

Photovoltaic and thermal solar systems should be looked at as investments that will pay dividends in 20 to 30 years, as you've locked in electricity and other energy costs for the life of the panels.