Many of my friends say, “I want solar, but where do I start?” So I’ve been thinking about how to teach them what I learned when shopping for solar panels. Let’s start with some basic knowledge about the electricity for powering your home.
Speaking of Watts (W). Watts are a unit of power, and a function of both voltage (V) and current (A). Don’t run away screaming yet. This part is just to help you understand the difference between “watts” and “kilowatt-hours” (KWh) because “watts” are what you use, and “kilowatt-hours” is how they bill you! First of all, kilowatts are just thousands of watts, just like kilometers are thousands of meters. It makes things easier to understand if the numbers are not too big … imagine having to write 900,000 W instead of 900 KW. But the solar panels will be rated in watts, not in kilowatts, so you have to know that. If each solar panel is rated at 250 W, then it’ll take four of them to make 1000 W, or 1 KW.
So what about the “hours” part? Well, all your appliances use a certain number of watts. Like the microwave uses maybe 1200 W, your hair dryer 1800 W (1.8 KW, remember?). Well that’s how much it’s using every instant that it’s on. So the total amount of power your hair dryer uses depends on how long it’s running. Duh, right? So to figure out how much electricity it used when you ran it for 12 minutes (which is .2 hours), you just multiply the kilowatts times the number of hours, and get .9 KWh. So just running that one item for that long just cost you about $.30.
Now the electric meter just keeps track of the whole house at once; it can’t itemize your electric use. So it samples the amount of watts being used at regular intervals (say, once per second) and averages that over a certain amount of time (say, maybe 12 minutes) to keep track of the KWh that you’re using. It may not be exact but it’s close enough. And then all those KWh are added up for the month and the electric company goes through some complicated and incomprehensible tiered rate system and squirts out your bill at the end. And you say, “Holy SHIT, electricity is EXPENSIVE. I really want to go solar!”
2. Photovoltaic Solar Power Generation
Photovoltaic (PV) simply refers to “voltage created by light” and so without getting into what goes on inside the panel, this is the big difference between solar power generation and solar pool heating. A system for heating pool water makes hot water; the PV kind makes electricity.
First, one important assumption. The following information is for a grid-tied system. That means that you don’t store any of the electricity. At any given moment, if you are generating more than you’re using, your meter runs backward as you put electricity on the electric company grid. Importantly, it also means that if the power goes out, you lose power too. Your system won’t keep your house running. This is a critical safety aspect for the electric company—because otherwise, the men making repairs on the power lines could be electrocuted by home-solar-generated power.
A system that is not grid-tied has to have a bunch of big ol’ batteries to provide your house with electric power when it’s dark out, which is a headache and carries risk of explosion if not well-maintained. If you live in the Outback of Australia, that’s probably your only choice, but for most of us, it’s an advantage to be grid-tied.
Solar panels are rated in watts, but that figure is only good for new panels. The power generation drops slowly over the years, too, but you can still expect something like 80% of the rated power after 20 years. The wattage rating on those panels is the PEAK—you know, noontime, no clouds, perfect angle to the sun. So over the course of a perfect day for a 300 W panel, you’ll get something like 2.3 KWh. On one panel, on June 21, assuming a perfect peak of 300 W at noon. You won’t really get that. (By the way, the calculation I used was (panel rating in watts) x 7.64, which is based on a 12 hour length of daylight.) Bottom line is that a 300 W panel, even when new, will not produce 300 W for you, but it’s hard to say what your peak generation will be without knowing exactly where you live.
Your power generation will of course vary as the day goes by, peaking at noon; and by season, with the greatest generated in the summer and the least in the winter. Another factor determining how much electricity you can generate is whether you live in a sunny or rainy climate. Very little power is generated on a cloudy day. Seattle is probably not a great place for generating solar power from your rooftop. You probably already have some idea if your area is sunny enough to make solar power generation a cost-effective option by watching your neighbors rush to install theirs.
3. How many panels do I need?
This is a painfully personal process, which is why you have to do it yourself or trust the salesman. Most of us want to be able to tell if the salesman is in the ballpark of what WE think we need. I have heard some wildly erroneous estimates, and I just wouldn’t skip this.
Step 1. Find out your average monthly electric bill and usage in kilowatt-hours (KWh). For example, before we went solar, our monthly electric usage was about 1300 KWh for a total of $283 average per month.
Step 2. Determine if you want to have all your electric usage covered, or just part. Usually it’s most cost-effective to only cover MOST of the required energy. My plan was to generate about half of the estimated 1300 needed , and my installer agreed that was a good number. It would keep the electric bills very low—I was thinking in the bottom two tiers. But it turns out that’s not a good way to think of it. More about that later.
So, HELLO, come back to Earth! I just want it all!! How many panels is that? OK, now here’s where it gets REALLY personal, because not only does it depend on how much power you want– it also depends on where you live.
To help you, there are some cool online tools out there to help you determine how much power you can expect to get from your general location, on average, for a given wattage system, so you don’t have to go through any painful math to get there . Try this one: http://www.wholesalesolar.com/StartHere/GRIDINTERTIED/GRIDINTCalculator.html
The site above asks, “How Many Sun Hours a Day Do You Get?” –nice and simple. But you might also hear or wish to Google the term “insolation,” meaning how much sunlight you get per square meter, not to be confused with “insulation,” the pink fluff in your attic. The insolation figure can be considered “effective hours of sunlight per day,” and varies depending on who you ask, which really isn’t fair, and is based on historical averages, which in these days of climate change might be pretty worthless. Here in California’s high desert, I’ve been getting about a 6 or 6.5, which may be a reflection of the ongoing drought more than the typical average over years. Our annual generation has been 11 Megawatt-hours when the prediction was 8. So that’s significantly higher than we had any right to expect. The map suggests it should be more like 5 to 5.5, which matches what the installer recommended. So here’s a table you want to keep:
System Sizing Based on Sun Hours
|6.5 Sun Hrs
|6 Sun Hrs
|5.5 Sun Hrs
|5 Sun Hrs
|4.5 Sun Hrs
|4 Sun Hrs
|3.5 Sun Hrs
The installed system was rated 5.75 KW with an estimated annual power generation of 8.2 MWh (Megawatts are 1000 Kilowatts, so that’s 8200 KWh.) That should have covered about half our use. So how many panels is that? Well, nowadays panels are upwards of 315 W each; we could have gotten our 6 KW for 19 panels. As it was, our panels were only 240 W and so 25 of them was 6 KW. You’ll note the system was rated at 5.75, but that’s because some of the panels were facing east, some west, and the rest faced south, the best direction.
So take the number of watts desired (6000) and divide by the number of watts per panel (315) and it’ll tell you how many (19).
Woo-hoo! Now I know how to figure out the size of my system and compute the number of panels.
4. Other considerations
You also want to consider where the panels will be located. If you have enough property, I recommend installation on the ground. Yes, not very pretty … plant a row of shrubs to hide them. But a ground installation means no worrying about the integrity of the roof installation. It also guarantees you can get the most advantageous angle to the sun, whereas on a roof you are at the mercy of your architect. The other thing is that they are much easier to clean if you can reach them easily. (Always clean them when they’re cool.) It probably goes without saying that wherever you put the panels, they need to be in direct sunlight all day if possible, but you might be surprised what some people will forget.
And you’ll also note that we could not get all our panels on the south-facing roof. So we used a new technology to help make that OK.
In the Old Days, solar panels were ganged together like Chrstmas Tree lights, the kind where if one goes out, they all go out. In that kind of arrangement, if one panel had some shade thrown on it, then ALL the panels acted like THEY had shade too. Sort of a cosmic empathy. The lowest-generating panel controlled the total output! That SUCKED. So the industry invented a way to make each panel an individual using little devices called microinverters. So each panel produces what it produces and if one of them is offline, it’s just one panel, not the whole system. The microinverters also got rid of the big inverter panel, allowing all the panels to come together and bring a single wire to feed the meter.
So our system had microinverters and therefore we could have panels on every part of the roof. It took a little more to get the total output needed, but hey, small price!
If you have to have a roof mounted system, make the salesman talk to the details of the installation AND the warranty on the roof. Our installer brought close-up photos of the racks and mounts, and explained exactly how they were installed and how that would prevent leaks. Perfect. Most sales folks not only don’t know that stuff, they don’t care.
5. Cost. COST! Buy or lease?
First, what if you BUY the system?
So you need to know that the panels themselves are not too expensive but like with all construction work, you will pay the big bucks for the labor. Plus there are SO many parts … the racks, rails, microinverters, inspections, permits, etc. By the way—do NOT do this yourself unless you know what you’re doing (like are a licensed electrician.) Edison does not have to approve it if they don’t like it, and it must be permitted, which means plans on file with the city.
I’ve seen estimates of a net cost of $3-$5 per watt not counting “extras.” Our system was about $29,000 ($4.95/W) before rebates and $18,000 after rebates, which is closer to the $3 per watt price. We had two rebates: first, the California Solar Initiative was $3110, and those rebates are almost gone. Then there was a 30% tax rebate on the cost after the state rebate, for almost $8000. But we had to wait until the next year to claim that, which is based on the year of installation. That rebate is still around. But the point is, a typical system should probably NOT cost more than $5 per watt installed.
How to pay for it?? There are lots of loans out there right now just for solar installation. They are low-interest (whatever that means.) If the system costs $25,000 and you get a 5-year, 4% loan, the payments will be something like $450/month. That’s quite a bit more than you’re paying for electric, isn’t it? But your electric bills are going to be Zero or Low. And in 5 years, you’ll still be paying Zero or Low for that electric use. So it’ll take awhile, but if you have the payment space in your budget, it’s better for you than that new car you don’t really need.
Will the purchased system pay for itself, and how long will it take? Well of course it’ll pay for itself, and how long it takes is based on your electric bill and how much you pay for your solar. At this year’s production rate, ours will be paid for in about 5 or six years.
Leasing is great if you just don’t want to OWN the thing—can’t do the payments, can’t pay cash, but want relief on the electric bills. Leasing will not save you as much as an outright purchase but it beats the shit out of paying the electric company and there’s no money out of pocket. You pay the leasing company for your electricity at a much lower rate than the electric company charges. The only thing about leasing that kind of scares me is that the leasing company will peg their rates to the electric company, so your rates may increase over time. Don’t get me wrong, it’s still a great deal. But it’s hard to compute the savings.
6. Your new electric bill
Not like the old bill, that’s for sure. The old bill had five tiers (maybe more) and I based my estimated need for the solar system on trying to keep it within the first two tiers. But when you switch to solar, you also switch (not automatically! Take action! Call the electric company!) rate plans. For homes with PV solar production, you get something called net metering. And with this comes on-peak and off-peak rates. On-peak, as you can imagine, is EXPENSIVE energy. It’s daytime, when the stores and offices are open, running their air conditioning full blast. As the proud owner of a PV system, you are GENERATING extra power during those peak hours, hooray! Those kilowatts are valuable!
On the off-peak (dark) hours, you’re using electricity. But it’s cheap.
So for us, with an average production of 900 kwH, it’s paying for that 1300 or so that we use!! Magic! No, it’s really just that the produced energy is more valuable than the consumed energy. But that also means that all the calculations you might have made based on tiered systems is way wrong.
There’s nothing to keep the electric company from raising their rates, and no one knows how the future will affect solar customers. Southern California Edison already charges about $1.50 a month for delivery fees, which honestly seems fair. That’s your charge for being grid-tied. To make that more convenient for me, I paid upfront about $25 that they can continue to draw on during the year. But in states where they didn’t already have those charges, solar customers have been outraged when the charges began.
The other thing is that although you pay delivery fees monthly, the total charges for electricity are annual. That’s right: one bill a year. Edison keeps a running total so you can see where you are and it’s no surprise at the settlement month, but it took me several months to figure it out. Our first year we owed Edison about $300, the second year they paid us $45—totally unexpected and indicative of an unusually sunny year.
Is it all worth it? In areas like ours, the deserts of southern California, that’s an easy question to answer. OF COURSE.