Emergency Grid-Tie Usage

[mooseofterror]

Complete newbie to the forum and solar, really just looking for suggestions. I'm sure the question has been asked before, but I didn't find the answer I was looking for so...

5kW grid-tie system, no batteries installed, want to explore the possibility of using my solar panels in an EMERGENCY. Not looking to power my entire house, just very basic necessities should the need arise. was wondering if it is possible to install a transfer switch between the panels and inverter so I could isolate the panels form the grid-tie inverter and then use a charge controller to charge batteries and run an inverter ? Feasible? another possibility? Do not want to mess with tricking the inverter to think the grid is still alive.

I would not being doing this project myself, but I have access to electrical engineers in my family to make sure it is done correctly. Rural setting, house is off the ground, so I can "hide" the transfer switch, etc easily...

Sorry if I offend anyone and thanks for any help!

[Sunking]

No offense taken and none offered. Only way to have emergency power during outages is to install a whole house generator. Have a nice day.

[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...

[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]

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.

[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.

[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 ?

[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.

[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!

[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.

[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!

[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.

[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.

[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?

[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.).