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Ask Solarman: Your Solar Guide [1]

['This Content Is Not Subject To Review Daily Kos Staff Prior To Publication.']

Date: 2023-09-26  

The gap between my last article and this one was filled with caregiving for my wife, who got listed for a liver transplant by The Mayo Clinic in Scottsdale AZ; relocating there and achieving the transplant; then remaining there for another month for observation & healing. It was quite successful. And very odd, because we were living in the hottest summer on record. My messages to friends started with Greetings from the second plane of hell. It was also a demonstration of what a true universal single-payer system can do, thanks to Medicare covering nearly every cost of a nearly million dollar surgery.

I wrote last time about getting energy efficiency done first. An energy audit can show you more. The two technologies I wrote about are LEDs for all lighting and a power conditioner to make you electrical system work efficiently. The combo can reduce usage by about 20%. So, you’ll need a 20% smaller solar PV system to cover the rest. Even the batteries can be commensurately smaller. The energy efficiency steps pay for themselves immediately, and then some.

And Now, PV 101

Put simplistically, solar cells convert solar radiation into electrons. The cells are wired together on a rigid sheet and into a frame, with a small control board, making a solar panel. How much power they produce depends on the voltage characteristics of the solar cells. The resultant electricity production depends largely on your location, which dictates how much atmosphere sunlight has to go through to reach the solar panels. Clouds, particulates in the air and other atmospheric phenomena occlude sunlight, causing less to reach the surface, or the solar panels one your roof.

Some of solar radiation even reaches the Earth at night. I’ve seen a tiny amount of production from a solar system I developed, on the Visitor Center at the Denver Botanic Gardens, from moonlight.

Below you’ll find out where that power the solar system produces goes and how it benefits you.

Costs and Incentives Help Make the Economics Work

Two decades ago, solar panels were expensive. They and the other equipment to build a system cost so much the only way they made economic sense is if you face them roughly Southeast to Southwest to maximize power production (in the mainland US anyway; latitude changes this a lot). Getting full sun from dawn to dusk was The Way. The electric utility serving Denver wouldn’t even give permission to interconnect a solar PV system to the Grid if they weren’t oriented SE to SW or if the shade on the array from neighboring trees and buildings was more than 10% annual.

Even with optimal orientation and little shading the systems were still expensive and took a long time to pay for themselves. In 2005 the Energy Policy Act created a federal Investment Tax Credit (ITC) of 30% for anyone who put solar on their home or business, and right up to any utility building acres of systems. This launched the steady, slow boom in solar. In Colorado we passed the first voter-mandated carbon reductions, forcing the utilities to offer cash rebates for residential and commercial solar.

Federal and state incentives encouraged people purchasing solar and the industry boomed. The increased sales benefitted the manufacturers, who increased production to keep up. Costs began to fall. Solar panels themselves fell 85% in five years. The incentives worked.

However, until this year’s implementation of the Inflation Reduction Act fossil fuels industry got seven times the federal incentives that renewables got. The IRA reduced that to two times.

Grid Connections

Home solar projects either connect to the electric Grid or don’t. If they do it’ll be under rules called Net Metering (NEM). About 40 states have NEM laws.

https://en.wikipedia.org/wiki/Net_metering

Your solar photovoltaic system generates electricity, supplying your electrical panel. You use this power instead of buying it from the utility. If your system produces more than your home needs, on a moment-to-moment basis, the rest flows to the Grid and you get credited. Normal Net Metering credits you for each kilowatt hour (kWh). You bank the extra kWh and use those credits later. If you produce as much as you use annually then you’ve zeroed out you bill, except the fee to have a meter and be connected to the Grid. Easy peasy.

NEM is getting attacked by utilities across the country. Seems they don’t like losing sales. It is nearly eliminated in California as of 4/15/23. Those kWh you were banking are protected through your multi-year interconnection agreement, but anyone who gets solar now has different rules. The NEM’d kWh get discounted.

Solar PV systems that don‘t have batteries are called Grid Tied. Any daytime overproduction gets sold to the Grid per the above. This avoids the cost of batteries. But when the Grid is down the inverter, which converts DC to AC useable kilowatt hours, doesn’t turn on.

Solar PV systems with Battery Backup have an inverter that takes its startup power from the batteries not the Grid. So it operates when the Grid is down. This system fills a relatively small battery– any size you want but for economy’s sake it’s usually relatively small.

Charting Solar Production

Solar production is charted monthly and annually on a web site that the National Renewable Energy Labs runs. This source data comes from NREL’s web tool PVWatts.

pvwatts.nrel.gov/…

(Outside the US projects start with NASA’s site is power.larc.nasa.gov/...)

The combined ground and satellite data NREL takes the average of the past 30 years of solar radiation at site, which includes all atmospheric conditions. Type in an address and it’ll calculate latitude and longitude. Type in roof orientation and slope (I’ll tell you how to derive those if you want). These are the basic data points to get annual production in Year 1.

I use an app called Sketchup. It’s more complicated than most but I like the flexibility to make design changes as a project evolves. But I’m weird. Or at least an outlier. The online apps are reasonably good.

Here’s a project drawn with this app. Note the WNW facing roof gets its own calculation and both roofs also need a shading measurement, adjusting the production, due to the neighboring trees.

Here's the PVWatts production calc for the SE facing roof. I always chart what one kilowatt of solar panels can produce. Then I can increase or reduce the project size as needed.

Grid Backup is Now, and The Future

The style I started using a decade ago, when some homeowners could afford it and really didn’t want to sign a contract with their utility, is called Grid Backup. You keep your electric meter for backup power. Match the solar PV system output on a daily basis with energy-use monitoring with batteries to catch all the daytime overproduction year-round. This means a fairly robust battery with smart software called the Battery Management System or BMS. The combo manages home power usage, solar production and storage capacity.

Happily, the cost of the battery equipment has come down a lot. But the batteries could double the cost of the system. If you can spring for them, they’re quite useful. But you could still just get a Grid Tied, Net Metered system. The national Grid is fairly reliable, though as we’ve seen California’s climate fires have caused a lot of Grid shutdowns. Texas’ horrible mismanagement t of their independent Grid has caused numerous long shutdowns that have damaged many buildings, harmed and killed people, and resulted in fine print clauses in the rules the utilities follow that allow them to gouge the consumers they failed with massive overcharges.

The immediate benefit of Grid Backup systems comes with the destruction of Net Metered kWh values, led by utilities in California.

This wraps up the basics. It’s time for your questions!

I’ve had a lot of feedback and smart topics addressed in the comments from my last article. And my comments on other solar-related articles. I will compile them and make my next article.

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