Solar Panels As Back-up Power Supply

I don't have specifics, but there are systems out there which will do it.
My understanding is that it's a safety issue, if the grid is down and you are generating power it could energise parts of the grid which are being worked on and thus be a hazard.
You would need a way of disconnecting it from the grid and something for it to synchronise to maybe an inverter.
The simple alternative would be to have grid power and the solar/ back up systems totally separate... mind that would be a pain and there would still be the possibility of accidental cross connection.
This is just how I understand it so don't take it as solid fact...
Hopefully someone with detailed knowledge will step in.
Del
(I reserve the right to be wrong!)

Presumably the 15-year finance scheme includes a certain amount of interest.

Is the monthly payment fixed? What does the interest rate work out at? Is the bank rate likely to increase significantly over the next 15 years? Would your energy bill (without the solar) be likely to increase significantly over the 15 years?

So many unknowns - it's all a bit of a gamble on the financial side (sorry I'm not addressing your question - just some idle thoughts).

As far as I know, power converters for solar panels are designed to extract the maximum power. Therefore, they need a load that can absorb all the generated power, such as the grid.

If you want to use it as a backup, you will need to either use the extra power on something (heating water for no reason), or extracting only part of the power from the sun.

I would recommend buying a generator and waiting. Solar panels have hit that part of the technology cycle where prices drop and technology improves quickly. If you wait 3-5 years you may find the panels are much more effective/cheap. Ironically by waiting to purchase you may find you get to break even faster.

Does your utility allow Net-Metering? If it does, I wouldn't bother with the Enphase batteries. Lots of expense for no reason.

I would need the batteries for power at night.

Then, contrary to what the sales individual says, the arrangement is fulfilling the function of a standby generator while on battery. The question needs to be asked, though, why is there a need for so much power at night?

Maybe he likes to sleep during the (hot, humid) days, and work in his shop at night when it is cooler...

Looking at the Enphase website, it states that their batteries are not usable for backup should the utility power be lost.

If you need backup power while utility power is not there, find some other means of storing and using it. Others have suggested generators (lowest cost), other batteries and inverters (most convenient, but expensive) and other methods. Look around there probably is a solution for you.

Indeed. The batteries then fulfil the role of a standby generator. GA

If these solar panels need to be connected to the grid side of the meter. Which I beleive all the utility companies require them to be. Why is the salesman selling you batteries? Everything you produce will go out on the grid. These batteries do nothing for you. Unless the service to the home is so small that at peak the wires will not handle the load.

The government mandated that the utility companies buy this alternative power that the home owner could provide. But they never said how. So the utility companies have it placed on the grid side. So all you get is the going rate they would have to pay to produce the power. Lets them still hit you up for all the fees. Like peak usesage fee. If you had your solar panels on the home side of the meter that fee would be greatly reduced. Also some of taxes would be reduced.

What you say is true. However, I want backup for four months (my time for nearly worse scenario). ICE generators running continuously for 4 months isn't very desirable. There would be fuel problems and potential breakdowns. The fifteen year payout with the back-up would be fine for me. There's a 25 year guarantee on the panels and 10 year guarantee on the batteries. Of course, these guarantees are worthless if the companies go out of business.

Are you expecting ERCOT to be down for 4 months? I don't think so...

What's wrong with a generator running for 4 months? I have seen countless small gen set unit like the one used construction site light plants with 20 - 30,000+ hours (30+ months) run time on them on all stock original engines and generator heads.

I've heard of many that were way higher than that that were used in fixed lighting application for remote areas as well.

Also where in texas do you live that has stable enough utility power to make for a $158 a month bill yet has 4 month long power outages?

There are places down-state where they do have severe flooding from time to time. Maybe that is how they can have extended outages.

To my knowledge most places that can get flooded out for 4 months at a time on a regular basis tend to be rezoned as uninhabitable wetland areas.

Mostly I am just not buying the 4 month standby power requirement. Even out here in the sparsely populated prairie region of the country a 4 day outage is a extremely rare event.

I know, heck we seldom have outage that even lasts an hour in Lubbock.

I am out in the middle of nowhere as well.

I have a 10kw propane connected whole house generator.

Hurricane Matthew took out our power for 4 days.

We had AC and all the fixins....that's my vote.

Yes, the home NG gen-sets are the berries! The only problem with NG units is if it is a high probability earthquake zone, or sitting on/near a fault line, such that gas service could and would be interrupted.

That is why a propane selector kit is needed, along with a fairly large back up propane tank, IMHO.

Back in 1999 I went through the whole "because I need/want it" excuse game with way more people getting prepped for the Y2K nonsense they were sure was going to happen.

#1 thing was they need the capability to run 24/7 for 3 month to 2 years and the excuses for it in every case were total BS dreamland fantasy stuff. Worse was the bill for fuel to run as normal American household what way.

Buying a tank system that could hold 10,000 - 50,000+ gallons plus the fuel was totally outside of their budgets. Same with a solar and or wind plus battery bank system to do it as well.

Now I do know of several people who do live 100% off grid year round because where they live dictates it and even at that it's bare minimal convinces with a crazy high price tag per usable KWH in both actual financial outlay to keep the system up and running plus the amount of physical labor and general inconvenience involved in making up for every other convenience that we normally just assign to electricity to do manually.

From everything I have seen of their lifestyles running your modern life on bare minimal electrical power is not for the weak, old, cheap, or lazy. Especially if you live where you need high levels of air conditioning and or heat for large parts of the year.

The heat part is not as hard to come by in most areas, although distribution of that heat to all rooms is a challenge.

A/C seems to be a must in Texas, although our ancestors had ways to deal with summer swelter, even in the Texas Republic days, basically two sections of the house, with a shaded "dog-run" breeze way between.

We don't have piped gas where I live so I have my own tank that's good for about a week.

During the 04 hurricanes, we lost power for nine days. Still not a problem because a recharge truck is only a phone call away (this assumes I call before the gas is gone).

And assuming the road from the depot to your place is still there, and the driver is alive, and the truck is not upside down in a pool of water.

That's 17,700no. 12V batteries rated 80Ah!

Haven't looked at the sums, but presumably that's a nuclear winter projection?

ROFLMAO! But I think yur right! Maybe this is all about NK getting away with wholesale murder.

What a thoughtful and well-prepared answer. And in a direction no one saw coming!

Just a small word of warning. If you do decide to go for the panels: get the bird protection fitted at the time the panels are installed, otherwise you end up with a cleaning bill and higher costs to install the protection because the access to the roof needs to be re-established.

You just need a lot of batteries to last several hours, then you are set to go. You can compute the energy used in your home, say 12 hours running on 5kW power.

You could size your inverter at 5kW plus 50%

Just do the math conversion and match it with the Ah of your battery.

Without any cost consideration, damn its doable.

"So, it would take me 15 years to realize any savings."...I'd check the manufacturers panel data sheets (did they specify the brand/model of the solar panels?)...you may find that the useful life, MTBF, warranty may be 10, 15 or 20yrs. So by the time you pay them off, they may need replacing. Just check!!!

do we know, of course we do, living in a "Developing Country" in Africa with plenty of power outages and lots of sun. You can buy really nice programmable inverters, the best ones seem to work off 24 volt battery systems; you can programme how much you draw off the grid based on the power that remains in the batteries - when the batteries are low draw more off the grid. Our electricity bills have a sliding scale where you pay a higher price per unit the more you use so you can buy PV modules over time using the savings. The first step is energy management, go solar water heaters and gas stoves (if they are cheaper to run), LED bulbs etc. and then rewire to critical processes; in other words when you have a power cut perhaps you don't need to run your refrigerator or use the microwave so these are taken off your PV. On costs, you have to replace batteries over time which is an additional expense. I am looking forward to solar development on the Stirling engine; like using solar geysers to heat thermal oil and a system to melt salt (instead of using batteries)which you use to heat the thermal oil when there is no sun - I think I would rather like to have a silent Stirling engine generator.

Maybe you need a UBattery - underground SMR - I understand the UK will be exporting those in the 10 MW_th, 4 MW_e range in the not distant future. Actually, that might be 14 MW_th, since the 10 is the left-over heat available for co-generation district heating.

OK, you might need a community of 2000 people living off this.

At US$158 per month (good grief!) one ought to be looking for economies before investing in solar. As before:

Timeswitches.

High efficiency lighting.

Occupancy detectors.

Turn off and unplug.

Etc.

Go for solar after all the simple stuff has been done, such as banishing the tungsten filament. It will make the solar installation that supports it smaller, and the investment easier to justify.

...and temperature switches.

Check out the Tesla Powerwall.

Yep - that thing might just be his ticket to bliss.

I have been installing solar for 10 years+ and have used the Solar Edge units on most. They just added an inverter that gives the advantage of both grid tie and battery backup.

https://www.solaredge.com/solutions/self-consumption#/

https://www.solaredge.com/solutions/self-consumption#/

I just turned your link into an active link, by using the link tool in the text editor bar.

Unfortunately, the link shows up for a brief instant, then gives the "page not found" error.

I would talk to a different salesman. In the UK, at any rate, you can find a controller with an inverter to supply the domestic requirement, which monitors the surplus being fed back into the grid and which charges batteries for the event of supply failure

I tried to read through all the replies just to make sure no one else covered this point but didn't see it covered. You don't want to be connected to the grid necessarily but would prefer to have a solar system as a "back-up" supply". My question is, are you going to cover the panels 24 hours a day until you need them as a back-up unit otherwise those panels will be generating electricity all day long as it gets sun and the electricity will have nowhere to go once you've fully charged the batteries. That is probably why the utility and the solar installer says it should be connected to the grid. For the $28,000, assuming you have natural gas or propane available, you could buy a stand-by generator probably for less than $10,000 installed and meet all your needs. Use the remaining $18,000 for a vacation elsewhere should there be a long term blackout there.

Good answer. However, I don't know why you would cover the panels. If the panels are making more power than is being used, wouldn't it be simpler to just waste the excess since it's free, anyway.

One of the reasons for a solar panels backup system is that there are fewer parts to fail. I believe there are going to be solar contractors that will install systems that can be used as back-ups because it's such a sensible way to have a backup. And, of course, when the system is paid for, a big savings on your electrical bill.

Most systems are connected to the grid to insure that you would have sufficient power in the event your use exceeds the solar capacity and also so you can sell any excess power you generate to the utility, i.e. you're away from home and need less power. This "income" helps shorten your ROI. Not sure I understand your use of "One of the reasons for a solar panels backup system is that there are fewer parts to fail." If your intent is only to use the system as back-up and not everyday use to cut your electrical bill, then your ROI is much longer than your estimate. You are only paying yourself back when you are using the generated power of the system to offset your power bill. Just did some checking and it appears that the consensus is that you do not have to cover the panels when there is no load connected. Like a rotating generator, it will only generate what the load connected to it requires.

I think he meant "Fewer parts to fail than a DG system has".

We don't have a facility to sell back to the grid so if that had been in the equation we may have done it differently. Not drawing the power from the panels is not a factor in our set up - we never generate more than we need because the excess goes to the batteries for night time use. The nicest aspect is that the supply to the critical path is uninterrupted so you don't crash your computer or have to scratch around in the dark for the change-over switch and to start the generator (which you forgot to fill up with fuel). You only realize there is a power cut if you try and use something that is not on your chosen critical path. My advice is go conservative initially, just buy the bare minimum - you can add more panels over time. Something I did forget to mention is make sure you set the panels to the optimum angle for your latitude, angle calculators are free off the internet; I am sorry if this is teaching grandma to suck eggs but it’s amazing how many people get this wrong.

I completely agree with your assessment and use and sizing. What was confusing to me was PAPADOC's desire to only use his system as a "back-up". Did a little research and the consensus seemed to be that no power was actually generated by the panels until a load was hooked up to it therefore there is no need to cover the panels. Just like a turbine-generator unit only supplies the output demanded of it regardless of its rating.

The system would only be a back-up when the power fails. Otherwise, it would provide power to lower the electric bill.

Do you have regular 4 month long power outages and if so why and if not then what the justification for thinking you need it?

I justify it because that is what I want. I realize I wouldn't have full power with the batteries. But I could run a deep freeze and refrigerator, lights, etc. I couldn't run a central air conditioning unit. During the day, I could get the batteries charged with the panels. And, as time goes on, I could acquire more batteries and may be able to get off the grid all together and still run everything.

Does anyone know a solar contractor that will install a system that can be used as a back-up system when the power fails?

That's exactly why we did it, a power cut at 7pm if its dark is unpleasant, having a system using free sun that keeps you comfortable such that you don't even really notice the power cut is great. A plus side is there are not many things you buy that are free to run. The deep cycle batteries are expensive and don't last forever unfortunately. Another plus in my mind is not being too dependent on big brother; taking for granted supply from the grid that is out of one's control makes me feel vulnerable especially as our big brother is nasty. My advice don't buy a back-up system for when the power fails but a system where you can programme how much you draw off the grid based on how much current is left in the batteries (uses only solar until the low level is reached when the grid kicks in). That way you can optimize the free sun and don't even notice the power cut (you dont need to switch anything over). The tricky bit with the deep freeze and refrigerator is the starting current - especially if they both come on at the same time. Instead of air conditioners evaporator coolers don't use much power. We installed the system ourselves, it wasn't that difficult.

I thank you are zeroing in on what I want. It doesn't have to automatically kick in when there's a power failure, but that would be nice.

If I could find someone that could install these systems, I'd sell them myself. What could be better than a system that provides power from the sun and stores it in a battery for back-up and recharges the back-up?

<...It doesn't have to automatically kick in when there's a power failure, but that would be nice...> The facility already exists with battery storage. Why on earth would one design it out (rhetorical question - NNTR)?

One thing that would be better is the same system "selling" power to your service panel (net metering) every day the grid is not down. Check with your local power provider, they will either have an interconnection agreement or a blank stare when you ask for one.

The part of TX he lives in sux to be without HVAC unit that is 100% up.

you are right I looked it up. Looks like a nice place to visit though. Double glazing helps, that is something one should do anyway. If its just for a short while whilst the power grid is out you can put ice cubes into evaporative coolers when the humidity is a problem. If that doesn't pan out HVAC will have to be included in the "critical path" I guess.

Do you think for hot places like that part of TX solar powered Stirling engine generators will eventually replace PV? That development is possibly still way into the future but if you are using solar heat for the power source instead of PV, the hotter it is the more fuel for the genny so perhaps running the air cons is not a biggy.