I understand the basics of PV systems: Solar electric modules, placed either on the roof  or on an unshaded part of the yard, transform sunlight into electricity. An inverter converts the DC current generated by the system into the AC current that powers our homes. In states such as California where there’s a net metering law, the PV system is typically tied into the utility grid and homeowners receive credit on their utility bills for the electricity  that their system feeds into the grid. It sounds straightforward, but how do I figure out whether it makes sense in my situation?

Typically, we wouldn’t even need to come to your house to do an initial assessment. When a potential customer calls us and says, “We want solar,” we prequalify them over the phone. The first thing we do is [call up a satellite image of their house using] Google Earth. Sometimes we can’t even see their house because of all the trees, but if they have unshaded roof area, they’re probably a candidate for PV. In that case, we’ll ask them to take out their electricity bills—the past 12 months if possible—and tell us what their electricity usage is in kilowatt-hours. With that, we can give them a rough estimate of the size of system they need, its cost, and their savings. Given your electricity bills—last year you used 3,300 kilowatt-hours and so far this year it’s a bit lower—and given the amount of available sun hours in the Bay Area, a 2-kilowatt system is in the right ballpark. That’s about half the size of the average residential PV system in California, but it’s not unexpected because this is a small house with no air-conditioning, and there are only two people in the family. The ballpark cost of a system this size is $20,000. That’s before California rebates and a $2,000 federal tax credit; combined, they would bring your cost down to $13,000 or $14,000.

That’s more palatable than $20,000, but still makes me wince.

We do our financial analysis based on a 30-year life cycle, and we’ve found that a typical system pays for itself after about 15 years. We expect these systems to last 30 or 40 years, so one question is whether $13,000 or $14,000 is a reasonable price to pay to zero out your electric bill for the rest of your life.

Do people usually pay cash or do they finance the purchase?

Most people get a home equity loan. For you, the cost of doing nothing is $33 a month this year—that’s what you’re paying for electricity now. But next year it might be $36 a month, $40 a month the year after that, $44 a month the year after that. Add up the numbers over the years as electricity rates keep increasing, and compare that with a flat loan payment over 15 years. You’re going to find out that you’re spending probably three times as much by renting your power from the utility for the next 30 years as you would spend buying a system today and owning your power.

So buying a PV system takes away that fear factor about rising utility rates.

With a PV system, you know exactly what your electricity cost will be. You’ve already paid it. It gives you immunity from rising energy costs. But the focus on return on investment may be misplaced. When someone buys a Mercedes, are they focused on the return? For most homeowners, buying a PV system is a decision that they make for other reasons. People want to do something with their money that makes a positive difference rather than do something that continues to be part of the problem.

So what does the Solar Pathfinder say about my prospects?

At the center of your roof, you’ve got seven months of about 95 percent sun, and then it starts to degrade in the winter months. The good thing is, you’ve always got some sun during the best hours: Even in the middle of winter, you have five hours of sun starting at 11 a.m. If we walk over here to the east, where the neighbor’s building is taller, it takes out the sun from 1 p.m. on in the winter, so that’s not where we want to go. But if we move farther north on the roof, it gets much better. Bottom line? There’s a viable solar resource here.

There goes one of my biggest excuses.

The fossil-fuel age is ending. The question is, how do we make our homes and other buildings carbon neutral? I’m optimistic it can be done if we have the collective will.