Solar Panels Query

[NorthernRaider]

IIRC 400VDC is the standard FEED IN voltage for supply power from local networks INTO the local grid, To power your home it should pass through an inverter / regular to drop it to 220VAC, or to 13 .something to charge up your batteries.
The Isolator is in place so your system can be isolated from the local grid, theoretically that device should be able to redirect your arrays power to a regulator to supply 13.something to your batteries .

RS there is a darned good little book you can get called DO IT YOURSELF 12 VOLT SOLAR POWER by Michael Daniek ISBN 978-1-85623-072-8 Its an illustrated natty little book on all things 12 volt and solar.

[Nix]

Ok, as I see it, you're getting a series array of 24v solar panels to make up a 3kW system. As we said before, grid tie inverters automatically isolate from the grid when it goes down and you will get nothing from it, it's part of being G83 compliant. I would personally have an isolator to isolate the panels to the inverter and another one between the inverter and the grid for any work to be done on any part of the system. Please note that 400v DC is a dangerous voltage and not to be tampered with.

So, what to do?

Straight off the bat, you may have a problem with that sort of voltage. Most controllers dealing with 400v will be very expensive. The small ones start at 12/24v then they go up to handling 48v, then 100v, and so on. When you're talking 400v, you're talking high end. You also need to "tap off" or divert that incoming pv with either a two way switch or adaptor. The installers won't help you here cos it will modify their installation and they will be liable for it. Any warranty would be void as well. If you only are charging a couple of batteries, that could be another problem as you're cracking a nut with a sledge hammer! If it's a long haul SHTF scenario then I don't think anyone's going to smack your bottom for accessing the panels for survival but you've got to be aware and competent with the sort of voltages this system is giving out and, no disrespect, but it doesn't sound like you are. You don't want to be found burnt to a crisp!

A temporary measure would be to set up a suitable battery charger to a battery bank. But that's relying on the mains coming back on to replenish the batteries. Not good for a scenario where you need sustained backup over a long period of time.

Difficult this, I know what I would do but for someone like yourself I need to have a ponder...

[Skvez]

(2 September 2013, 12:47)Nix Wrote: Ok, as I see it, you're getting a series array of 24V solar panels ...

I agree with nix that this sounds like 12 panels rated at a nominal 24V each wired in series. Off load this will produce a voltage of around 400V DC.
This is fine for a grid-tie system but much too high a Voltage for a typical battery system.
In a SHTF scenario you would need to re-wire all the solar panels from series to parallel to give you 12 times the current at 24V. Then feeding this Voltage into a charge controller to charge two 12V batteries in series. (Perhaps only useing some of the panels if your charge controller isn't rated to handle the full current of all of them)
I fear the series wiring of the panels will occur on your roof not inside where it's easier to get to.
400V DC will give you a nasty shock, and if you're on the roof at the time even if you survive the shock you may not survive the fall when you let go.

[Lightspeed]

(5 September 2013, 13:51)Skvez Wrote:

(2 September 2013, 12:47)Nix Wrote: Ok, as I see it, you're getting a series array of 24V solar panels ...

I agree with nix that this sounds like 12 panels rated at a nominal 24V each wired in series. Off load this will produce a voltage of around 400V DC.
This is fine for a grid-tie system but much too high a Voltage for a typical battery system.
In a SHTF scenario you would need to re-wire all the solar panels from series to parallel to give you 12 times the current at 24V. Then feeding this Voltage into a charge controller to charge two 12V batteries in series. (Perhaps only useing some of the panels if your charge controller isn't rated to handle the full current of all of them)
I fear the series wiring of the panels will occur on your roof not inside where it's easier to get to.
400V DC will give you a nasty shock, and if you're on the roof at the time even if you survive the shock you may not survive the fall when you let go.

Good point re the wiring being outside of the roof. To rewire them it prob best to work on them at night and from the underside by removing roof tiles into the loft.

What do you think?

[Nix]

Problem with this sort of voltage is that it will be there during daylight hours when you can see but disappear when it's night time when you can't. I really don't want to encourage anyone who isn't familiar with electricity to start messing around with 400v. That's how people can die.

The series connections will most likely be under the panels but on top of the roof using MC4 connectors and adaptors. Trying to reach these connections from the loft will be extremely awkward and you have the added problem of making good the roof again.

If you did get to them and parallel the connections, you'd certainly get your 24v but you'd also get a potential 125 amps! This will melt most controllers on the market, let alone anything else on your circuit. We're talking serious fire risk here.

Each one of these solar panels will be most likely be rated at 250W so each one will be adding nearly 11 amps to the circuit if connected in parallel. If you're only using two 12v batteries in series (as they'd have to be), then even one panel would do a reasonable job but two obviously better depending on your loads/usage. Three panels and you have to start being careful about your wiring (I'd personally use at least 4mm cables with three panels) and the rating of any switches etc.

Now you can see why I'm scratching my head on this one for someone who isn't familiar with electrics and it's risks!

[River Song]

Mmmmmm Sounds to me that I might call in a qualified electrician to fit some of
switching arrangement. Might be worth a couple of hundred

[Nix]

Careful how you arrange this RS, the installers certainly won't want you touching the existing system and it'll give them the perfect excuse if any problems arise to invalidate the warranty. If SHTF, then that doesn't matter so much, I guess, but you still need someone who knows what they're doing.

[Lightspeed]

RS You will be getting free daylight mains electric off the pannels in the here and now.

Use this to charge a bank of 12v deep cycle batteries using a conventional 240v smart charger. Now you will have immediately available 12v power to fall back on as soon as you have power cuts. You can start pulling together lighting and other devices that you want to power from these.

As prep, get a high ampage solar charge controller ( actually get several ) plus cable connectors that match those used by the installers of the original system, plus wires to connect to the charge controller, and from the charge controller to the batteries.

Learn how to disconnect single cells from the installed system. Know which wires to cut and which to leave in place, and where to plug your charge conytroller in. With this knowledge and with the materials listed above you will ready in case of permanent grid down, and will be able to keep your battery bank charged.

It will be a good idea to take lots of pics of the installation and in particular the connectors being used ( try to lose a connector or two while the installation is in progress maybe??) Post some pics here and I bet Skves ot Nix will be able to tell you what you need to do to get a functional grid down solution.

[River Song]

Thank you so much - Thats so useful. I'll take piccys etc when they install which should be around 19th of this month.

meantime, consider that they are also installing a large inverter to take this 400v dc
and convert it into AC to the grid. Why can't I disconnect it from the grid and use the feed from the inverter? Also there is going to be an isolator.

Hmmm

[Lightspeed]

[quote='River Song' pid='69550' dateline='1378450784']
.....Why can't I disconnect it from the grid and use the feed from the inverter?

As the guys have said, you can but cost of an inverter from 400v to 240v / 12v will be high and sourcing one difficult.

Do not risk touching 400v DC. Its VERY dangerous. This why the advice is that when the time comes, only attempt changes to the cell wiring at night when they are not generating any voltage at all.