Whether you decide to buy or lease a system, there are many decisions to make, and the most important is selecting an installer.

Click here to read customer reviews of solar energy system installers we've collected; but because so few homeowners have purchased them, we unfortunately don’t yet have a lot of ratings in our database. (If you’ve bought or leased a system, please help your fellow consumers by submitting ratings about your experience.) Another source of referrals, of course, is to ask neighbors and friends who have gone solar.

In addition to a trove of info about solar energy, two websites can help you find installers. SolarReviews.com offers customer reviews of installers, and unlike many companies that host online ratings, many of the reviews posted with it are negative.

The website of the North American Board of Certified Energy Practitioners (NABCEP) lists companies that have completed its certification process (see below for accreditation info).

Contact at least three companies to discuss options and obtain recommendations and price quotes. Ask about the following points, and if you live in the District or Maryland and plan to lease, click here for even more to consider.

Are you certified?

The NABCEP is the largest certifying organization for installers. For its certification, NABCEP requires staff have advanced training by an accredited institution, demonstrated decision-making experience with several completed and inspected installations, successful completion of a comprehensive examination, and agreement to comply with the group’s code of ethics. There are other programs, including certificates from community colleges and vocational centers. While no certification program guarantees that installers will perform good work and provide accurate advice, because these programs seem to be well-conceived, well-managed efforts, we think it’s worth seeking out only certified companies.

How long have you been installing solar energy systems?

You don’t want your home to be a guinea pig for an inexperienced installer.

Can you supply references from recent customers in my area who received installations similar to mine?

You probably won’t hear many discouraging words from this group—it’s not as if companies will refer you to customers suing them for botched jobs—but references can give you some idea of an installer’s abilities. Ask former customers if they’re happy with the work and if it was performed on schedule for the quoted price. Also check with the Better Business Bureau to make sure each company has a clean complaint history.

Is my home a good candidate for solar? If so, what size and type of system do you recommend?

Compare companies’ size and cost-benefit estimates with what you obtained when you ran your info through the PVWatts Calculator, Google’s Project Sunroof, and Solar-Estimate.org.

Ask for thorough explanations of recommendations that seem wrong. As we’ve already mentioned, it’s important to avoid buying more generating capacity than your home actually uses in a year. But when our undercover shoppers asked a sampling of installers to propose systems that would generate 100 percent of the electricity their homes used during the previous year, some suggested they buy systems that were 20 to 77 percent bigger than what we estimated was needed.

Where on my roof will panels be installed? How much space will they cover?

Does the company offer a choice of panels?

If so, how do upfront costs and energy savings of more efficient panels compare to those of less efficient models?

Will the company secure all necessary permits? How much experience does the company have connecting solar energy systems to my utility company’s grid?

Again, you don’t want to be a test case for an inexperienced company. In addition to obtaining local building permits for installing your system, connecting it to the grid requires obtaining utility permits and approvals. The process often takes more time than for other home-improvement projects. You want an installer that knows how to take care of paperwork and red tape efficiently—and does not leave you with an illegally or improperly connected system.

Are you adequately licensed and insured?

Solar installations involve electricity, which poses serious risks to workers, your family, and your property. Make sure any installer you consider has an electrical contractor’s license; then verify it with the licensing authority. Also, ask installers for proof that they carry liability and workers’ compensation insurance.

Will it use subcontractors?

If so, ask it to provide a list of all subs and proof that each is properly licensed, insured, and certified.

How much will it cost?

If you plan to lease, click here for advice on comparing prices. If you plan to buy, know that although prices for solar energy systems continue to decline, it’s still an expensive purchase. Our undercover shoppers collected prices from several installers for two homes, seeking systems that would generate 100 percent of the electricity used by the families during the previous 12 months. We then used the PVWatts calculator to determine what size system was needed and multiplied that total kilowattage by the per-watt prices quoted by the companies.

We found big company-to-company price differences for each project. For one home, prices ranged from $12,240 to $22,464 for a 4.8 kW system; for the other, prices ranged from $14,280 to $23,408 for a 5.6 kW system.

The lesson? Collecting several prices to identify reasonably priced installers can mean saving $10,000 or more.

If I want to finance my purchase, does your company offer that? If so, what are the terms?

There are several ways to pay for solar projects. We describe here financing options for home-improvement jobs. In addition, almost all solar installation companies offer financing, usually through a third-party lender. When our undercover shoppers collected proposals for two local homes, the APRs the financing installers offered ranged from two to six percent; loan length varied from 15 to 25 years.

Keep in mind that borrowing will increase your overall costs, in some cases adding thousands of dollars to the price of your system. And carefully read truth-in-lending statements before you sign; especially watch out for super-high default interest rates that kick in if you fall behind with payments.

What tax credits, rebates, and incentives are available?

Click here for a list of incentives. Also check with your utility to learn what’s available or visit the Database of State Incentives for Renewables & Efficiency, a site operated by the North Carolina Clean Energy Technology Center, which tracks programs nationwide. Ask installers to put in writing any available credits, rebates, and incentives that you’ll get.

What’s the payback period?

Take the upfront cost of your system, subtract any tax credits or rebates, and compare that net price tag (including interest, if you’re borrowing) against other incentives and annual electricity savings to find out how long it will take for your monthly energy savings and incentives to recoup the cost. Companies can do this for you—just remain vigilant of overly optimistic projections.

To do the math, compare the system’s estimated production (as measured in kilowatt-hours) to what you typically use each year to determine how much of your usual electricity costs will be offset by the new solar energy system. That will give you a rough idea of how much you’ll save each year on electricity costs.

Keep in mind that the cost of electricity rose an average of about 2.8 percent per year in this region, according to the U.S. Energy Information Administration; use that benchmark to estimate the increasing price of electricity from the grid that you’ll avoid paying over the next 20 years if you go solar. To do that, multiply what you spent last year for electricity by 1.028 to estimate how much you’ll save in Year 1 with solar. Then multiply that result by 1.028 to get the Year 2 total. Repeat this step 18 more times for Years 3 through 20, then add up all the annual results. Also take into consideration the federal and any state tax credit, green energy performance payments, and solar rebates. This will roughly estimate your electricity savings.

Remain realistic.

In addition to overly optimistic assumptions about energy production and payback periods, the proposals you receive might include important-sounding terms drawn from the world of finance, like “return on investment” or that use the language of environmentalism to pat you on the back for reducing “X metric tons of carbon dioxide.” Solar panels aren’t retirement accounts or mutual funds, and while solar energy for sure can play a very important role in reducing your fossil fuel usage, these are expensive purchases that you should approach very carefully.

What’s the warranty?

You’ll want to minimize repair costs. Panel and microinverter warranties from manufacturers should run at least 20 to 25 years; inverters should be covered for at least 10 years.

Workmanship warranties from your installer, for the design and construction of your system, can vary from one to 10 years; look for the longest term possible.

“It’s becoming increasingly common for manufacturers to offer their own workmanship warranty, typically only if you work with specific installers in a manufacturer’s certified network,” said Nick Liberati with EnergySage.com.

For example, LG Solar endorses installers to sell and install their solar panels through their LG PRO network. If you hire one of them, the manufacturer provides a 25-year workmanship warranty covering up to $450 in labor costs if your panels need to be removed and brought to the diagnostic team, said Liberati. Similarly, customers get a 15-year workmanship warranty if they use a CertainTeed “Credentialed” installer and a 25-year warranty if they use a CertainTeed “Master” installer.

How long will it take to get things done?

Try to nail down start and finish dates, including the time needed to secure necessary building permits and permissions from your utility company.

What’s the payment schedule?

If you can, avoid making a big deposit before work starts. Usually, $1,000 or more is due when you sign the contract, and then another payment is due when installation begins, with the balance upon completion. By withholding as much money as possible until work is complete, you retain maximum leverage to make sure the work is done correctly and promptly. If possible, arrange to withhold at least a small portion of the final payment until the system is up and running long enough for you to get a new electricity bill.

Will the system require me to regularly do anything? How can I monitor its performance to make sure it’s working properly?

Don’t bother with a maintenance agreement.

Some installers will propose a fee to monitor your system and make repairs for free. For most products, these types of agreements are bad deals, and that’s no different for solar energy systems. Properly installed solar systems rarely need routine maintenance.

Once you decide which company to hire, nail down all the details in a contract.

Read everything, and ask the company to clarify anything you don’t understand before you sign.