Best way to use "surplus" grid tie panels?

[jflorey2]

For a single panel, my spec shows 37.6V open circuit. Would that be a problem for a converter with a 9-36V range?

Yes it would. 37.6 volts might work, but in cold weather that voltage will be much higher. I would use a 36-72 volt converter in such a case. Better yet, a 20-72 volt converter.
(The real range you want is from about 28 to 40 volts.)

If so, would a diode in series do the trick?

You'd need a lot of diodes and they would get very hot if you used them to drop much voltage at moderate currents.

How would I go about shopping for a capacitor bank? I do understand what it would be used for, but searching on the term at digikey doesn't produce what I (think I) am looking for; and a quick Google shows yooge ones like you might see at a sub-station...

Figure out your max voltage, then get a large screw terminal electrolytic at a voltage higher than your max.

[bcroe]

Since you are "tapping into" the damaged panel wiring, you could wire up to just 2 of the bypass diodes instead of all 3 to get
a lower voltage that a $2 Eb*y converter can tolerate. It will be very educational, if you follow up on why some ideas don't
function. I don't see a very large cap as very useful here, it would discharge in less than a second. Bruce Roe

[jflorey2]

I don't see a very large cap as very useful here, it would discharge in less than a second. Bruce Roe

Large caps allow transient loads on the outputs (fan starting up, incandescent light coming on) without collapsing the voltage.

[bcroe]

Large caps allow transient loads on the outputs (fan starting up, incandescent light coming on) without collapsing the voltage.

Yes they do, and might succeed turning on an incandescent light. I think calculations will show storing enough energy to get
a motor running is entirely impractical.

Suppose you charge to 30V and allow 2 seconds at 10A to rev a motor with 3A run, dropping to 28V. The cap would need to
be on the order of 10,000,000 mfd. Bruce Roe

[tastewar]

Thanks for the ideas!

[Raul]

Taste war , I had your dilemma of using spare panels. I end up from time to time with various panel sizes and can't use them together because of differences . Went to my local scrap yard and bought 2 truck batteries £10 each and when they done I can sell them back for the same or wathever the price of lead at the time. I spent £20 more on 2 Chinese Controler and rigged to systems that provide all the outside lighting , front and back garden and few paving lights in the driveway. So far almost a year the batteries are still OK as the draw of few LEDs is about 1/10 of the capacity and the panels cover c/5 so still covers for short winter days. Total investment £40 .

[tastewar]

Cool idea. Thanks, Raul.

[jflorey2]

Suppose you charge to 30V and allow 2 seconds at 10A to rev a motor with 3A run, dropping to 28V. The cap would need to
be on the order of 10,000,000 mfd

Well, 2 farads. But I don't know of any motor that takes 3x power for a full 2 seconds. (Maybe a large A/C compressor, but you're not going to drive a ten ton central A/C with this system.) You size the cap for your load; for things like small motors and incandescent lamps, you can get a .25 farad 35 volt cap for about $20.

[bcroe]

Well, 2 farads. But I don't know of any motor that takes 3x power for a full 2 seconds. (Maybe a large A/C compressor, but you're not going to drive a ten ton central A/C with this system.) You size the cap for your load; for things like small motors and incandescent lamps, you can get a .25 farad 35 volt cap for about $20.

OK there is a price point, thanks; your situation may vary. Thats not high enough voltage to cover discussions above, and
0.25F won't spin up a big flywheel, so it would be easy to spend a lot more. But the results might justify it. Bruce Roe

[Mike90250]

Problem with using caps for surge alleviation, you can only use the top 2-5% of the cap, after the voltage sags below the inverter DC cutoff, the cap is useless. And you need low impedance flat braid to get the most out of the cap.