Emergency Grid-Tie Usage

[billvon]

OK thanks for giving a detailed answer. Did you see my edit in the last post? The panels I'm considering are 36V. I'd think wiring directly from those would solve all of these problems.

So you are going to switch from a ~250 volt system to a 36 volt system by throwing a bunch of switches? Might work but that is a lot of wire and a lot of switches - and they have to be rated for the higher voltage.

Maybe instead of a DPDT switch, Anderson pole connectors just underneath each panel. Then I could re-arrange things in an extended outage as I see fit.

Again, you still have the problem of disconnecting under load. There has to be no load when you disconnect those panels - and unless you break both sides the potentials will still be there. Anderson powerpoles are rated for 600 volts but I'd be pretty uncomfortable working on them live - especially a connector that has been exposed to the elements for a few years (which they are not rated for.)

If you really want to do this I'd suggest the following:

-Use connectors rated for outdoor usage. MC4 connectors (which many panels come with) are an example.
-Break BOTH sides of the circuit. You can do this with a three phase safety switch. For example I use a three phase Square-D disconnect rated for 30 amps 600 volts DC. Get a disconnect like this and switch both positive and negative sides of the string. That will reduce your risk of electrocution.
-Follow the usual rule of not paralleling more than two strings without a fuse.

This will allow you to rewire for a lower voltage but again I'd be very careful assuming that you can just use an AC appliance with a DC source. It might blow the hidden accessory transformer. Or it might look like it works great - right until the time you try to turn it off. You flip the switch, the DC creates an arc across the contacts, and the switch burns while the power remains on. (There are plenty of Youtube videos of people trying to use AC switches to break a DC circuit. They are sometimes pretty exciting.)

To a battery charger, or inverter, or DC appliances, or whatever. I can't see any reason that wouldn't work; I'd be completely disconnecting the grid-tie and bypassing for a different circuit. The biggest concern at that point is whether it's just better/cheaper to get a generator and a lot of gas. However, I already have a generator and gas, and this is plan B, or plan A if the outage lasts long enough.

Why not just get a SMA inverter with the secure power supply? Then there's no rewiring issues at all; you just get 1500 watts at 120 volts AC and don't have to worry about DC side wiring or compatibility issues.

[cdevidal]

Even fancy Anderson connectors are not rated to connect/disconnect while powered, and will show you close up how an arc welder works. (ok, maybe they have an rated model, and I don't know it.).

Grin. So, I'd do what everyone does when disconnecting panels. I suppose that people either work at night or cover with a blanket.

[Mike90250]

Even fancy Anderson connectors are not rated to connect/disconnect while powered, and will show you close up how an arc welder works. (ok, maybe they have an rated model, and I don't know it.).

[cdevidal]

It might. Problems:

1) If you unplug something you could get some pretty nasty arcs. (Think - fire, electrocution hazard.) Same if you try to use a switch that's not rated for (say) 400 volts DC.
2) It's only 250vdc nominal. If it's cold out it could be 300vdc, and your devices might not be very happy about that.
3) It's going to be intermittent due to clouds, shadows etc. Not all loads can tolerate a varying DC supply.
4) Hard to know what's going to work and what's not going to work beforehand. If the thing has a transformer in it you'll blow the appliance fuse (best case) or smoke the transformer.
5) Few off grid inverters will work at 250 volts, and they are definitely not going to like the varying voltages.

OK thanks for giving a detailed answer. Did you see my edit in the last post? The panels I'm considering are 36V. I'd think wiring directly from those would solve all of these problems.

Maybe instead of a DPDT switch, Anderson pole connectors just underneath each panel. Then I could re-arrange things in an extended outage as I see fit. To a battery charger, or inverter, or DC appliances, or whatever. I can't see any reason that wouldn't work; I'd be completely disconnecting the grid-tie and bypassing for a different circuit. The biggest concern at that point is whether it's just better/cheaper to get a generator and a lot of gas. However, I already have a generator and gas, and this is plan B, or plan A if the outage lasts long enough.

Thoughts? Has this been tried?

[cdevidal]

What he is showing should never be done for numerous reasons.

Please elaborate.

Stay away from posting loony land links!

Gladly. I have no interest in posting "loony land" links, whatever those are, if I can identify what they are before posting them. I didn't know this was a "loony land" idea. I'm just a newbie. Sorry if it offended you.

[billvon]

That got me to thinking, why couldn't this work? I could then plug inverters, battery chargers, DC appliances and even xxxxxxxxxxxxxxxxxxxxxxxxdirectly into the panels.

It might. Problems:

1) If you unplug something you could get some pretty nasty arcs. (Think - fire, electrocution hazard.) Same if you try to use a switch that's not rated for (say) 400 volts DC.
2) It's only 250vdc nominal. If it's cold out it could be 300vdc, and your devices might not be very happy about that.
3) It's going to be intermittent due to clouds, shadows etc. Not all loads can tolerate a varying DC supply.
4) Hard to know what's going to work and what's not going to work beforehand. If the thing has a transformer in it you'll blow the appliance fuse (best case) or smoke the transformer.
5) Few off grid inverters will work at 250 volts, and they are definitely not going to like the varying voltages.

[russ]

I deleted the links. This fool is using plug type inverters - has a jury rigged setup 100% - has his panels sitting on the ground?

You can find any kind of trash you want on the web if you look hard enough.

What he is showing should never be done for numerous reasons.

Stay away from posting loony land links!

[cdevidal]

But what about this?

I've been wondering the same. I came across this picture onxxxxxxxxxxxxxxxxxx



That got me to thinking, why couldn't this work? I could then plug inverters, battery chargers, DC appliances and even xxxxxxxxxxxxxxxxxxxxxxxxdirectly into the panels. I can't think of any reason this wouldn't work, but you're the experts. Before you reply that it can't be done, xxxxxxxxxxxxxxxxxxx. The piece he's missing though is the DPDT switch but that's so straightforward I can't see why that would be a problem. Now on to find a DC switch that can handle the arcing...

EDIT: Oh, the voltage regulator might not be needed after all. And probably I wouldn't wire every panel this way.xxxxxxxxxxxxxxxxxxxx are actually 36V and I might find that a whole lot easier to work with.

[mooseofterror]

most grid tie inverter systems use 300- 600VDC from the panels to the inverter. There are a couple 600VDC charge controllers for consumer use, but they are pretty expensive. And then you have the batteries sitting in float, getting old every day. And a 2nd inverter. And a transfer switch. So, it's possible, but very expensive, and you just use it for a couple hours a year, generally. If you are somewhere plagued by ice storms or tornados that knock power out for weeks, it looks more feasible, but how do you insure the PV panels survive the foul weather or flying lawn chairs ?

I was thinking more along the lines of removing my 3 deep cycle batteries from my boat and charging them using the solar panels in an EMERGENCY, but I guess it would be easier to buy a smaller panel, inverter and charge control to charge the batteries. I also have 600w of panels on my pool house for the DC pool pump that is not tied to the grid, so I might be able use this set-up for what I want to accomplish.

Thanks for everyone's help!

[inetdog]

Best explanation I've read , thanks for the insight! I'll rethink my efforts...

You are quite welcome!

Please float your ideas here as you proceed with your rethinking. It will make the learning process smoother.

[Mike90250]

most grid tie inverter systems use 300- 600VDC from the panels to the inverter. There are a couple 600VDC charge controllers for consumer use, but they are pretty expensive. And then you have the batteries sitting in float, getting old every day. And a 2nd inverter. And a transfer switch. So, it's possible, but very expensive, and you just use it for a couple hours a year, generally. If you are somewhere plagued by ice storms or tornados that knock power out for weeks, it looks more feasible, but how do you insure the PV panels survive the foul weather or flying lawn chairs ?

[Sunking]

As in a gas generator?

No Sir, no one would gasoline for a whole house emergency generator. For residential either LPG or NG if have NG service at your house. Larger installations demand Diesel.

[mooseofterror]

Best explanation I've read , thanks for the insight! I'll rethink my efforts...

Hey Moose,

To expand a bit on what Sunking offered, using batteries with solar charging for infrequent power failures is waste of money, since your batteries will need maintenance and will lose life just sitting there.
It is really painful to see the panels just sitting there unused during the day when the power is off, but as a practical matter there are currently no good solutions to that except to understand why and ignore the pain.

There is one maker of grid tie inverters (SMA) which offers a few models that contain what they call a Secure Power Supply. But that is limited to about 14 amps at 120 volts and cannot deliver more power than the panels are producing at a given moment.
Not good for motor starting, for example, even if the running load is within its range.

If you are talking about weeks of outage, then a generator fueled with LPG and a large tank will do the job.
If you are talking about an SHTF outage, then you start another thread on that topic and wait for the fur to fly from both sides.

BTW, the idea of DIY panels and emergency backup in the event of power outage is sort of a contradiction in terms, since DIY panels will never have the reliability needed for that kind of use. IMHO, of course.

[inetdog]

Hey Moose,

To expand a bit on what Sunking offered, using batteries with solar charging for infrequent power failures is waste of money, since your batteries will need maintenance and will lose life just sitting there.
It is really painful to see the panels just sitting there unused during the day when the power is off, but as a practical matter there are currently no good solutions to that except to understand why and ignore the pain.

There is one maker of grid tie inverters (SMA) which offers a few models that contain what they call a Secure Power Supply. But that is limited to about 14 amps at 120 volts and cannot deliver more power than the panels are producing at a given moment.
Not good for motor starting, for example, even if the running load is within its range.

If you are talking about weeks of outage, then a generator fueled with LPG and a large tank will do the job.
If you are talking about an SHTF outage, then you start another thread on that topic and wait for the fur to fly from both sides.

BTW, the idea of DIY panels and emergency backup in the event of power outage is sort of a contradiction in terms, since DIY panels will never have the reliability needed for that kind of use. IMHO, of course.

[mooseofterror]

As in a gas generator? I have one of those as well, but I'm not talking about a thunderstorm power outage. Thanks though...