In Search of a DIY Guide to Rooftop PV
In Search of a DIY Guide to Rooftop PV
Why do so many books provide bad advice on residential energy?
Most new grid-tied photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) systems are installed by solar contractors. Here’s what usually happens: the homeowners call up a few local solar companies; representatives come to the house to make a site assessment; the homeowners choose the contractor whose quote sounds reasonable and sign a contract for the work. The homeowners don’t even have to put up a ladder; all they have to do is sign a check.
Is it possible to do the work yourself? The answer is, “It depends.” In areas of the country with lenient local regulations, homeowners may be able to install their own solar array. But they’ll have to be adept at submitting all the required paperwork, including permits; they’ll probably have to hire an electrician to make some of the electrical connections; and they’ll have to get the system inspected and approved before it can be connected to the grid.
Off-grid systems are an entirely different story. Many off-grid homes are located in remote rural areas beyond the reach of building codes and inspections. In these areas, it’s fairly common for off-grid homeowners to install their own PV systems.
Advice for the DIY crowd
I recently got a copy of a new book called Solar Rooftop DIY. Written by Mike Sullivan, the book aims to be “the homeowners’ guide to installing your own photovoltaic energy system.” There’s a need for such a book — one that is more accessible than a textbook aimed at electricians, but is still technically accurate.
For a homeowner who doesn’t know much about PV systems, Sullivan’s book might be a useful introduction to the topic. The book’s photos can give a homeowner a better idea of what various components look like, and can help a homeowner understand the steps involved in a typical residential installation.
Unfortunately, though, the book is flawed — flawed enough to spark in my mind a silent diatribe against publishers’ love affair with badly written advice books. I’ll return to that topic later; first, let’s assess Sullivan’s book.
Many pages are devoted to irrelevant topics
Sullivan’s writing style is repetitious and sometimes vague. Certain topics get far more attention than they deserve: for example, Sullivan spends several pages discussing the difference between monocrystalline PV modules and polycrystalline PV modules. For the average homeowner, does this distinction matter? No.
Similarly, Sullivan provides an in-depth discussion, several pages long, on the various types of thin-film PV modules. Right now, thin film modules have less than 1% of the residential PV market. For all intents and purposed, thin-film is dead — at least when it comes to residential-scale PV — so the entire discussion is irrelevant.
Sullivan’s advice isn’t always dependable. While it seems to me (and to many observers) that the jury is still out on microinverter dependability, Sullivan praises the advantages of residential PV systems with microinverters. For most homeowners installing a grid-tied PV system, a single wall-mounted inverter probably makes more sense than dozens of roof-mounted microinverters.
Sullivan fills many pages with charts and formulas to allow homeowners to make pencil-and-paper calculations to determine the expected annual electricity production from a proposed PV array. But this type of pencil-and-paper calculation is unnecessary; these days, everyone goes online, enters a few inputs into the PVwatts calculator, and determines the answer in seconds. (On page 102, Sullivan belatedly mentions PVwatts — but only after the exhausted reader has plowed through a dozen pages of sample calculations.)
Energy saving advice
When it comes to a chapter on energy saving tips, Sullivan’s train goes entirely off the rails.
He advises homeowners who install a rooftop PV system to switch from an electric water heater to a gas water heater and to switch from an electric clothes dryer to a gas clothes dryer. But many homeowners who install PV find that their new PV system generates more electricity than the family can use. Since most net-metering contracts are in essence “use it or lose it” contracts — you can’t get paid by the utility if you produce more electricity in a year than you use — homeowners with large PV systems are more likely to swap their gas appliances for electric appliances than the other way around.
Sullivan advises readers that “a solar thermal rooftop water-heating system has a very short payback period.” In fact, the payback period for a typical solar thermal system is 50 or 60 years.
Sullivan makes the following ridiculous claim: “In the case of the United States, ... the conversion of 60 incandescent 60W bulbs … to LED lighting alone could save the residents of a single home about $722 per year.” But since the average American family spends only $150 per year on electricity for lighting, saving $722 per year is (to say the least) highly unlikely.
Sullivan advises homeowners who are undertaking renovations to replace older windows with new “double-pane windows” because doing so “can produce substantial energy savings.” Actually, the energy savings will be tiny — and the payback period for this investment can be 100 years or more.
Finally, Sullivan recommends that homeowners pay to have “an insulation contractor inject granular insulation in the spaces between the inside and outside walls.” Granular insulation? I guess that means an insulation material resembling grains of rice. It’s hard to know what he’s talking about here.
Watts per hour
OK, so Sullivan’s energy saving tips are bizarre, and his PV installation advice is undependable. Things get worse: the book is often technically inaccurate.
Sullivan writes that net meteringArrangement through which a homeowner who produces electricity using photovoltaics or wind power can sell excess electricity back to the utility company, running the electric meter backwards. is “called a ‘feed-in tariff’ scheme in many countries.” In fact, net-metering schemes and feed-in tariff schemes are different. While most net-metering schemes credit a homeowner for the retail rate for any excess power exported to the grid, a feed-in tariff scheme usually credits a homeowner at a rate that is more than the retail rate.
In his discussion of off-grid systems, Sullivan always refers to fossil-fuel generators as “diesel generators.” But for off-grid homeowners, gasoline-fueled generators or propane-fueled generators are more common than diesel generators.
Sullivan advises homeowners to look at a year’s worth of electricity bills to determine how many kWh of electricity they consume. He writes, “You can simply record and add up the kilowatt hours (kWh) during the previous 12 months and calculate an average. For most single-family dwellings, this will be in the range of 7,000 to 9,000 kWh per month.” That’s an order-of-magnitude error; in fact, according to the Energy Information Administration, the average American household uses 901 kWh (not 9,000 kWh) per month.
If you care about electrical units, you’ll begin to tear out your hair when Sullivan confuses watts and “watts per hour.” Sullivan notes that many refrigerators consume between “500 to 750 watts per hour.” Later, in a section discussing the power output per square foot of a typical PV module, Sullivan writes, “As a general rule, about 100 square feet [of PV] … will generate roughly one kilowatt per hour.”
By now, you’re holding big clumps of hair in your hand.
The title of Sullivan’s book promises to explain “Solar Rooftop DIY.” So where is the step-by-step installation advice for the do-it-yourselfer?
The advice can be found in a single chapter — Chapter 10. The chapter takes up just 26 pages of this 180-page book. It’s a deeply disappointing chapter. Rather than describing the thought processes and problem-solving skills required to install a residential PV system, the chapter is simply a series of photos (with captions) showing a single PV installation job.
Are there better guides out there?
If any GBAGreenBuildingAdvisor.com readers can recommend a good guide to DIY installation of solar electric systems, I’m eager to hear about it.
Most do-it-yourselfers will probably consult one of the free online guides:
- NABCEP PV Installation Professional Resource Guide
- California Energy Commission: A Guide to Photovoltaic (PV) System Design and Installation
- Solar Electric System Design, Operation and Installation
Time to indulge in a diatribe...
This sloppily written book was published by W.W. Norton, a respected publisher that’s been around since 1923. W.W. Norton has published countless well-reviewed works of fiction and nonfiction, including The Feminine Mystique by Betty Friedan, A Clockwork Orange by Anthony Burgess, Thirteen Days by Robert F. Kennedy, and Liar’s Poker by Michael Lewis. The company has published works by seven Nobel prize winners and 15 Pulitzer prize winners. So how does a respected publishing house end up printing drek like Solar Rooftop DIY? It’s a mystery.
Curious homeowners who are interested in learning more about residential topics turn to a publisher like W.W. Norton in search of authoritative advice. Instead, they are misled.
There’s something about the topic of residential energy that attracts bad writing, bad thinking, and bad fact-checking. In a recent address at a conference in Florida, building scientist William Rose referred to this problem as the problem of “zombie ideas.” (He provided two examples: “you are going to trap moisture” and “a house has to breathe.”)
For some reason, when an apparently intelligent editor with a degree from a top-notch university is assigned to work on a book about residential energy, his or her brain just falls out on the floor. I have no idea why this occurs, but it is distressing.
Martin Holladay’s previous blog: “Slow Progress on New Blowing Agents for Polyiso.”
- Countryman Press / W.W. Norton
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