Solar System Repair Help

Sorry this is a little OT, but thought somone here might ave a good recomendation.

Hello,

I have a 9.3Kw solar electric system on my house. It is 8 years old and I have 3 Xantrex inverters (12v). Well one of them has died and another one is dying. Xantrex does not support them anymore - I have to replace them with high voltage units.

So I have some PV Powered 2500w inverters and am looking for help to re-wire the system. Any of the solar companies I have talked to are not interested, since they did not install the system (I did, with help from an electrician friend who moved away).

Any ideas of someone or ome company that would be interested in converting my system. The panels are SP-150's and they are hard wired - no mc connectors.....

Thanks!

Josh

Josh,

How are your panels wired? I assume three independent groups that each feed one inverter?

Correct - 3 independent groups of 18 that power one inverter for each group. There is a total of 3 inverters.

Yes, first re-wire the panels to 18 in-series instead of in-parallel.

Assuming that each panel already has a "bypass" diode, each panel will have two wires connecting to your 200-amp buss wires, a "plus" and a "minus".

A possible "rewiring", use these instructions only as a guide, they might not apply to your actual configuration. Use at your own risk:

SUGGESTION: Adding and using the modern, weather-proof, SAFER connectors is MUCH BETTER than the "hack" below!!!

CAUTION: In daylight, dangerous DC voltages will be present!!! Dangerous AC voltages might be present as well.

WARNING: If you are not competent to work safely with LIVE high-voltage wiring, or otherwise do this kind of work, DO NOT attempt to do this work yourself.

STRONG SUGGESTION: Get a competent electrician to do this work for you.

1. Turn off the AC disconnect, turn off any DC disconnects, turn off all the inverters. Then, disconnect the DC string from the old inverter and remove the inverter. Leave the "furthest" panel connected to both of the thick buss wires (the Minus Buss and the Plus Buss)
2. at all the 17 remaining panels in the "string" of 18, cut the panel's "minus" wire (do not cut the plus-wire by mistake) off of the "Minus Buss", right near the thicker minus-buss wire.
3. go back to the furthest panel, then
4. advance to the next closest panel, and cover any bare wire remaining on the "minus buss". Note that the "minus buss" remains intact, all the way to the new inverter.
5. cut the thick "Plus Buss" wire NEAR this panel, between this panel's plus-wire connection to the Plus Buss and the "previous" panel.
6. reconnect this panel's minus connection to the end of the "Plus Buss" wire that comes from the previous panel. Cover and weatherproof this connection.
7. Cover the remaining "bare" exposed end of the Plus Buss wire
8. go back to instruction 4 to rewire the next-closest panel, if any remain in this string of 18.

Then, re-check all connections, and you should have DANGEROUS high voltage DC ready to connect to the new inverter's DC shutoff.

Repeat as needed for the other strings of 18 panels.

Edit: added above re-wiring steps.

Then, it should be easy, one DC string (Plus Buss and the corresponding Minus Buss) and a common "Ground" to each inverter's DC input.

The AC output of all three inverters (and AC ground, and possibly the AC neutral), PROBABLY get hooked together, wired through a two-pole "disconnect" switch, and through a 40-amp breaker into your service panel.

PM if you need to chat about it.

Ok, I've looked into this for you and the good news is, most likely reconfiguring of the DC circuits will be unnecessary - and if that is the case, a local electrician should have no trouble installing replacement inverters. You could get a Sunnyboy 3000 to replace each bad inverter. It would almost be a drop-in replacement since the input voltage ratings are similar (no rewiring of the solar array will be necessary).

The other option would be one inverter for everything. Fronius makes a 10KW inverter that would work. It would make for a really neat, clean arrangement with just one inverter. On the other hand, the advantage of having three inverters is that when one fails, you're still generating at 2/3 power. Also, if you get partial shading, that is a factor to weigh in favor of having three inverters. I'm in the solar business and could sell you the inverters (the cost is similar either way you go - $1,795 for each Sunnyboy or $5,640 for the Fronius) but I don't do installs outside Tulare County at this time. However I do think this will be an easy retrofit.

Hope this helps.

I was under the impression that I had to rewire all the panels into a higher voltage. The way they are now, they are low voltage 12v. the PVPowered inverters (which I have) need high voltage.

Putting up the inverters should be pretty easy, its the rewiring that is more complex.

The PV Powered inverter requires a 140-450V input voltage, so you can be sure that your solar panels are already wired in series for high voltage. This is a typical range for most grid tie inverters. The Sunnyboy is 200-400V. So I don't think you'll need to have them rewired.

Possibly your impression that your panels are wired IN PARALLEL is correct, if your OLD inverters had 12v (low voltage input).

Since your NEW inverters are high-voltage units, the panels will need rewiring, as you believe.

Be VERY careful of the DC wires, because, whenever it is light out, they will be electrically "hot".

One SunnyBoy (SMA) 7000 Watt inverter (which can take input from up to 4 strings of panels) would also work well.

Edited: Original string is parallel, not series.

garygid said:

Probably your impression that your panels are wired IN SERIES is correct.

That they are 12v nominal is possible, but very unlikely that they are wired IN PARALLEL.

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Gary - I think you missed that his array is wired to feed three inverters with 12VDC inputs. Yes - panels in parallel to increase current while continuing to feed 12VDC nominal.

If he connects his three DC feeds in series he'll only have a nominal 36V input - and the current model grid tie inverters need about 155V to start.

Josh - it might be worth the trouble of rewiring if for no other reason than being able to use a more modern inverter with better efficiency, but you already know that. It'll be a 'fun' job pulling the panels, then rewiring/reinstalling. How are your panels mounted on the roof? Sorry for the challenge! Andy

AndyH said:

garygid said:

How are your panels mounted on the roof? Andy

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Click to expand...

They are on rack.

I don't think it is too complex, but have to pull up every panel, rewire (maybe put MC connectors on?) and re attach. I think my runs from the roof to the inverters don't have to be changed.

good luck on your project. to be honest with ya, i came here prepared for a lively discussion on the environment and our universe

YES, I WAS WRONG.
His panels are apparently wired in parallel to feed his OLD low-voltage inverters.

I corrected my posts above, and added "example" rewiring instructions. However, there might be some Building Code or Permit regulations for how the high-voltage wiring should be done. If so, best to add and use the "modern" (much safer) connectors.

Josh, I misunderstood - sorry. (I thought you said you had PVPowered 2500W inverters that needed replacement.) So, you have three Xantrex 12V inverters that are going out so you bought some PVPowered inverters to replace them - but of course you need the panels rewired for the high voltage required by the new inverters.

This is going to be a tough job, as the solar panels are hard-wired and the system will need to be rewired. Depending on the wiring configuration that was used, it might be possible to do this within the combiner boxes. If not, it will likely involve some dismantling of the array. Good luck finding a solar contractor who's willing to rewire the system if you go that route. You might be better off simply replacing the old 12V inverters with new 12V inverters.

I have a VERY hard time believing that it's wired in parallel. In fact, I'd even bet a pizza on it.

3 groups of 18 - 48 panels total. Panels are SP-150 (appears to be made by Siemens? Would be nice to have a spec sheet) - the optimal operating voltage is around 34V so they'll push about 4.5A in optimal conditions.

18 of these in parallel is 80A. You would need some HUGE wire (4GA min) to carry that current down from the roof. You simply do not build systems like this.

Current would be almost 3x higher if they're 12V panels. Absolutely not done this way - you'd need wire the size of your thumb running down from the roof and a huge, heavy duty combiner box near the roof where each panel is wired and fused.

(BTW - something doesn't add up - 48 150W panels is only 7.2 kW, not 9.3 kW - perhaps 9.3 kW is the inverter nameplate capacity?)

Not quite sure how 18 of these would be wired up if they are 34V panels - possibly 2 strings of 9 in paralleled for a nominal DC voltage around 300V would be my guess - this would carry a max of about 9A which is completely reasonable.

To really give good advice here we really need to know exact specs of existing equipment and how they are wired - like others suggested, it's very likely that you can simply swap in a new inverter which any electrician should be able to handle.

Thank you everyone for your advice so far - I know this has definitely been OT, but i thought you might be a good resource.

I am going to go out there with a meter and look at the voltage on the individual runs from the panels. When it was installed, I did the grunt work and the electrician did the electrical part. The wires are definitely not 4GA.

You are correct the system is 7.2Kw, I have a separate independent 2Kw system in addition to this system.

josh said:

I am going to go out there with a meter and look at the voltage on the individual runs from the panels. When it was installed, I did the grunt work and the electrician did the electrical part. The wires are definitely not 4GA.

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All your permit docs should outline every little detail of the system. For example, when pulling a permit for a PV system it's typical to require a single-line diagram, a site layout diagram, spec/cut sheets for the panels, inverters and often rack hardware, too. Hopefully you still have a copy.

I would be extremely cautious probing around with a voltmeter - it's likely you're dealing with hundreds of volts and thousands of watts when the sun is shining...

While you're investigating things - snap some pics. They will go a long ways towards explaining what you've got going on there.