Friday, August 1, 2014

Talked To My Electrician

This is the guy who wired the house when it was built and installed the backup generator.  He confirms that because the backup generator already has a transfer switch to prevent its output from feeding back into Idaho Power's grid in the event of power failure, we have no need for any additional hardware.  He said to get a 220V inverter so that it can connect to the bus and provide power to all circuits.  That connection is simple and he can do it in an hour or so.

Things to do:

1. Get my roofing guy up to replace a few shingles that were blown away in the last windstorms.

2. Figure out how these mounting brackets work to hold the panels in place.

3. Buy the panels, inverter, cables, and brackets.

4. Install them.

5. Run the power cable down to the panel.

6. Call electrician.

A frustration: there are a lot of 220V inverters ou there, but few of them are 60 Hz, and most seem to be Chinese-made.  That may be the only realistic choice, but when the packaging is written in incompetent English, it doesn't bode well for warranty issues.

Over at Wholesale Solar, I see American-made panels with nominal outputs of 275 watts, priced at $295 (plus shipping, which is not going to be trivial).  I also see that the 220V, 60 Hz inverters that they sell typically are 24V/48V input--not 12V.  There are some efficiency advantages to using higher voltage solar panels.  But these are expensive inverters, primarily because they are very high capacity.  I really need something like 500W.

UPDATE: And here's something unexpected: solar panel and microinverter combined so that you have a 225W 240VAC output.  Total Harmonic Distortion advertised as below 5%, so pure sine wave.  These are $466.50 each, so roughly equivalent in price to the 400W kit that I saw on Amazon.  Another attractive aspect is that each panel is separate.  You could buy one this month, install it, plug it in, do the same thing next month, and repeat, without worrying about obsoleting inverters.  This appears to be the same panel at $409 each.

UPDATE 2: The downside of the combined unit is that if I wanted to set up a battery array at some point to store electricity for night or long winter periods, I would then to have convert the 240VAC output back to 12VDC, store it, then have an inverter to convert it back.  That would be very inefficient.  Of course, if Idaho Power goes away and I am relying on a battery bank for power, then only having electricity a few hours a day would be the least of my concerns.


  1. Though I did laugh at this:

    "No high voltage DC means safe installation and ownership"

    As if 240VAC weren't a shock hazard....

    On an actually serious note: these are spec'd as 240VAC, but do they have a center tap? And if so, how do they do when 100% of the load is on one side of the 240V center-tapped output?

  2. IIRC if you've got a high-voltage inverter, you can just tie the panels together in parallel to feed the inverter the higher voltage.

  3. Ran across a piece about an older engineer-type who went heavy on solar, but he didn't put the panels on the roof - he mounted them on ground-level frames. The idea was keep everything at a level where it can be reached for repair and maintenance. I've since modified my house plans to include a south facing covered patio - covered with solar panels (the plans call for a standing seam metal roof, and I've never been thrilled about the idea of putting holes in it, no matter how well they're sealed).

  4. Nosomo: I am not sure how the brackets work that hold the panels to the roof. I need to find out. Drilling holes in the roof is not attractive, and I have lots of room on the slope above the house.

    Rick C: Are you saying to take 110VAC outputs and feed them into an inverter that produces 220VAC?

  5. Clayton, no, I was saying as far as I can remember, you can tie two or four 12V panels together to feed a 24 or 48V inverter.

  6. I think Rick means if your inverter requires 24V, then connect pairs of panels in series (not parallel) to get the required input voltage.

  7. Yes, that's what I meant. It's been a long time since I worked with circuitry, and I couldn't remember whether it was series or parallel.

  8. The other problem with mounting the panels on the roof is you have to take them off when you need to repair the roof.

  9. Clayton / Rhonda, heard of your news on Sebastian's site.

    Anything I can help with, feel free to call.

  10. I had solar panels for water heating, not electricity, on a metal roof and it was a bad deal. I finally replaced the roof after removing them. The installer had done a lousy job sealing the holes. He used rubber boots that sun rotted. Expensive lesson.

  11. Heard about your heart attack && stroke.

    Best wishes mate.