Science

The Solar Burn, Part 2: The Nuts and Bolts of Sunshine

This is Part 2 of a multi-part series about my attempt to install solar panels on my house. For the previous installation, CLICK THIS LINK. For the next installation, CLICK THIS LINK. Thanks for reading!

The Nuts and Bolts of Sunshine

If you really want to burn your brain cells out from the Sun, try studying the technical aspects of solar power. There’s a lot to the nuts and bolts of sunshine. I could write a whole book, but by the time I finished my brain would look like a pile of ashes.

If you’re as nerdy as me, you can go online and find some good books on solar energy that will turn you into a true know-it-all expert. You know, the kind that leaves professionals rolling their eyes, because you know too much, while not being familiar with the practical aspects of the subject.

I really hate those eye rolls.

I found lots of info online, from Wikipedia and many other sources. I also found a pretty good book entitled, Power From the Sun, by Dan Chiras. The copyright is 2017, so the information is somewhat dated, but I found Chiras’ easy-to-understand explanations very helpful.

There are technical terms that are nice to know, so you can look cool while speaking solar language with the solar pros. One of the most basic terms is, “solar array.”

A solar array is what lay people often call a “solar system.” But I always feel funny referring to a solar array as a solar system. Solar professionals build solar arrays. Whoever builds solar systems is a matter of theological debate.

A solar array, in its simplest form, consists of solar panels (technically known as modules), one or more inverters, and perhaps some power optimizers. It’s the whole system that you buy and have installed, which generates electricity from the Sun. It’s also known as a PV array, with PV standing for “photovoltaic.”

A rooftop solar array.

Solar panels are those big, black photovoltaic rectangles that affix to your roof, and that absorb the Sun’s rays, converting them into electricity. They’ve come a long way these past few years. About five years ago, the best panels for residential use produced 300 watts under optimal conditions. But nowadays the best panels produce 400 or more watts. In fact, the panels I’m buying produce 410 watts each.

“What?! What’s a watt?” you may ask. One watt is a tiny amount of electrical power. One-thousand watts is a lot more power, and is called a kilowatt. If you use one kilowatt for one hour, you’ll use one kilowatt-hour (kWh) of power. A typical home uses 20 to 30 kilowatt hours (kWh) of power every single day. At 30-cents per kWh (which is what our utility charges), that’s $7.80 per day for 26 kWh (which is what my household averages), or $234 per month. That amounts to $2,808 per year.

A solar array can be expected to last at least 25 years, but probably much longer. That’s longer than my wife and I expect to live, since we’re already approaching fossil age. 25 years, times $2,808 per year, amounts to $70,200 in electric bills. But we’ve been quoted $21,000, before the 30% federal tax credit, to have an array installed. So as you may be able to tell, while sliding the beads on your abacus, this deal could save us a lot of money.

But maybe not, as we’ll discuss later.

It helps to do your homework before contacting a solar installer. Get your prior year’s utility bills together, along with a calculator. They’ll need to know how much electricity you use in a year, to design the right-sized system to meet your needs. This will help them determine the correct amount of panels, and size of inverters, so that you can avoid The Solar Burn.

An inverter, by the way, converts the direct current (DC) electricity provided by your solar panels, into the alternating current (AC) electricity that your house uses. There are two different types of inverters. A microinverter installs directly behind each solar panel. But a string inverter accepts DC current from all your solar panels, and converts it to AC. If you go with microinverters, you’ll need one for each panel. But if you go with a string inverter, you’ll only need one.

Microinverters are less expensive than a string inverter, until you add them all up. Then they’re more expensive. But they’re typically warranted for 25 years, while a string inverter is typically warranted for only 10 or 12 years. To replace a worn-out string inverter, it will cost you a few thousand dollars.

The size of the system you’ll need depends on a lot of different, mind-boggling variables. Latitude is one. How far north do you live? The further north, the more panels you’ll need. Can you imagine what the roof of Santa’s house looks like?

Cloudy climates are also a big factor. You’ll need a lot more panels if you live in Seattle, than if you live in Spokane. Tilt and azimuth are important factors, too. The tilt of the panels is generally determined by the slope angle of your roof. The azimuth is the direction your panels will be pointed. 180-degrees due south is always the best azimuth for power production.

But shade is the big granddaddy of all variables.

Ever have someone throw some shade at you? Not a pleasant experience, is it? And when some offending tree, building, or other object throws shade at your solar panels, it’s also not a pleasant experience. Power output will plummet to near zero. You’ll want your panels placed where they won’t get much shade. So you might want to chop down all the trees around your house.

Your solar installer will probably input all the variables, including the shade around your house, into a computer program, that will calculate the size of the system you need. The National Renewable Energy Laboratory offers such a program online, called the PVWatts Calculator, at https://pvwatts.nrel.gov/pvwatts.php. It seems pretty accurate, because when I used it, it gave me a similar number to the one my solar installer got. Which is 4.9 kW. I’m very impressed that our government has produced something that actually works.

Our solar installer has designed our system to include 12 solar panels rated at 410 watts each. 12 times 410 equals 4,920 watts, or 4.92 kW. That means the array will have the potential of producing up to 4.92 kW at any given point in time. But usually it will produce less, since the 4.92 kW can only be produced under the very best, absolutely, positively optimal conditions.

Real-world conditions are hardly ever that optimal. So, the PVWatts Calculator factors in expected inefficiencies. Based upon this, it calculates that our 4.92 kW array will produce about 9,500 kWh of energy, per year. This is enough to meet about 100% of our electrical needs.

And yet how can this be, since the Sun only shines by day, and we use electricity at night? I’ll answer that very important question in a later post.

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50 replies »

  1. I am learning a lot more than I thought I needed to know. Thanks for the lesson you learned. In some ways, this reinforces my joy in NOT being a homeowner. I am most certainly at fossil age (68), and wouldn’t enjoy having to improve my home at this point. I am happily living in a one bedroom apartment with many amenities (washer/dryer/dishwasher/ac/heat, and an indoor pool for year round use) along with a garage (teeny, but helpful for extra storage). We have nice people to call for fixing things, and take care of the landscaping/snow removal. My electrical rates are not offensive for me.

    Liked by 1 person

    • That’s great, but home improvement can be quite a joy. There’s nothing more fun than to look a contractor in his shifty eyes, while trying to figure out how honest he is.

      But if your electric rates are not very high, then there’s no good economical reason to go solar. Better to stick with what you have.

      Liked by 1 person

  2. So much information here youโ€™ve given us. My brain feels sunburned. But I canโ€™t wait to use the terms youโ€™ve provided when chatting with my kids about their new PV array. And are you sure PV doesnโ€™t stand for Puerto Vallarta?

    Liked by 1 person

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