Hacking Solar Panels during Blackout

[Mgmny]

So, title says most of it. I'm putting in solar panels without a tesla powerwall, and i want to know how to access that clean electricity during a blackout/apocalypse. Right now, when the power goes out, there is an auto turn off as is required for safety of lineworkers.

What i'm hoping to be able to do: create a switch that when the power is off, I can send the electricity from the grid to either an outlet (guessing this is not possible or is prohibitively expensive) or send the DC power to something like a car battery to hold the charge and I can run a AC/DC converter off this battery to small appliances (think cell phone, flashlight, etc).

I don't need to power my hole house, but I'm just thinking it would be really dumb for me to have electricity availability on my roof if the grid goes down for an extended period of time that I can't access - or at least know how/be able to access a backup plan.

I've tried googling this, but to no avail. Any thoughts?

[Cadman]

I believe there's at least one grid-tied inverter on the market today that has a built-in receptacle to allow this. The bigger problem is without a steady-state load (battery bank or grid tie) your generated voltage will exceed safe limits (both high and low) for anything you want to power as the incident light varies (assuming you could somehow force the inverter to continue outputting AC voltage).

Tapping into the panels prior to the inverter will provide you with high voltage DC which still won't do you much good unless you can rectify and regulate it. Arc-flash becomes a genuine concern.

The bottom line is your screwed unless this really is an end-of-days scenario, in which case you could rewire your panels to match a series DC battery bank load.

[Lulee]

Can't RVs use solar panels to charge up batteries/banks of batteries?  They must have something that you could use.  Or a camping supply store might have a simple panel to charge a phone if that's all your interested in doing.

I could be WAY wrong here so check it with someone more knowledgeable of electrical code but if you switch off the main breaker, doesn't that prevent flow from your house back into the grid so then you could power your house with your panels or a generator during an outage?  The code in your area might require something automated to effectively throw the main breaker.  But it seems like I've seen that on This Old House where they've had generators installed that automatically cut in to provide power during outages that it's all automated including the state of the main breaker.

[Wrenchturner]

A transfer switch is the proper tool for this.   It really depends on how "apocalyptic" you're willing to go.  Household ac is just parallel wiring.  Pretty easy to substitute one power source for another.  Lots of unsafe ways too and the power company might notice a loss of continuity.

Also, yes, you will need a big pile of batteries depending on how much energy you want to access in non-charging periods (ie overnight).

Lead acid is great but it makes a lot of H2 gas and requires maintenance, like topping off with distilled water.

[nereo]

As Cadman and others have said, switches exist so that you can take a subset (usually 2 or 4) panels and use them for things like recharging laptop/phone/radio batteries, etc.  But having it serve as a proper backup (including during nighttime and rainy/stormy) events is a serious undertaking.

I'm all about reducing my carbon footprint and finding green energy sources (see my side blog) but the cold honest truth is that if you want a power backup the unquestionably cheapest solution is to buy a small a/c generator that you can tie into your electrical, and to keep some gasoline on hand to power it with (you can cycle it through your car(s) every season to keep it fresh).
That will cost you ~$1,500 and is fairly foolproof and apocolypse resistant*.  All the other solutions (having a battery pack, inverter switch(es)) will cost you 3-5x this amount, and will come with their own carbon footprint, and will require maintenence.

*Keeping enough gasoline on hand to power a generator for a few dozen hours is pretty simple.  During most emergencies you can still get gasoline, though it might require waiting and/or limits.  In true "society has fallen" scenarios your PVs will likely become a target for theft, and at that point you are left with guns and ammo and defend your property type living.

[NorCal]

There are inverters out there that will keep an outlet on in case of a blackout.  They are legal and to code.

This is honestly something you should be asking your solar installer about.  It's doable, but it has to be part of the system design and (I believe) permitting.  I'd also imagine there might be equipment compatibility issues as well.  You might run into a situation where there's an inverter capable of doing this, but it's only compatible with batteries from a certain manufacturer, or something similar.

Please stay away from unpermitted hacks to make this work.  It can pose a real fire danger, as well as a real danger to line-workers if not done correctly.

[Wrenchturner]

So... I have a bad habit of not really reading posts...

If you just want to power flashlights and phones, go the usb route with a single 12v agm battery.  You could tie into the existing solar fairly easily, you wouldn't want a lot of watts pumping into the battery and you wouldn't want to break the bank on a 12v charge controller either.  Not sure how residential solar controllers work but worst case you could just parallel off a panel directly.

12v to 5v usb will help your capacity too.  And agm batteries are very low maintenance and they don't risk leaking or venting, Depending on the battery.

Li ion would work well here too.

[lutorm]

It depends on how your installation is hooked up, but our panels are connected in series so the inverter sees about 300V. You really don't want to play around with that. If you want to be able to get power during a blackout, look into the SMA inverters that have a dedicated outlet you can turn on if the grid goes down.

[SwordGuy]

… I don't need to power my hole house, ...

I didn't know we had hobbits on this forum!   You might need a bigger battery to cook 2nd breakfast with. :)

[Mgmny]

Thanks everyone for the input!!

I asked my installer about the SMA inverter last week, i'm waiting to hear back what the price difference is. If it's more than $200, i'm probably better off buying a gasoline generator, it sounds like.

It sounds like hooking up a normal ICE car battery to the panels with a simple "cigarette lighter" converter is out of the question, so i might be SOL.

I sorta figured the solar panels would be "cool" in a "true" apocalypse, but i suppose it probably makes me a target, and I will probably get murdered for them... sigh.

I'll just stick with the clean energy part of them and keep looking into SMA.

[px4shooter]

Look at a dual fuel generator. Gives you options and ethanol free gas is a pain to find around here. You may have better luck, but then you have to still monitor how the fuel is degrading. I like having the option of propane.

[Ripple4]

not sure if hacking something together would be worth it in an emergency, you probably have more pressing issues and other, better ways to get useful electrical power, like a Walmart $40 12v inverter connected to a running car.

To use the solar I hope that you pre-plan. this is because most 60-72 cell panels will be around 30-40volts with the sun shining, and that's not very useful or efficient. If you have an existing solar install it might not be so bad to upgrade to a battery. the very popular Enphase brand (1 inverter per panel) has AC-coupled battery technology, look at their homepage. It may be possible in the future to AC-couple different brands of equipment, and also mix AC and DC coupled batteries in the same system, read up about it, its next level stuff. on the other hand if you have a string inverter (1 inverter for all panels) than adding a large 24/48v deep cycle battery and a charge controller with a matched input voltage to the existing grid-tied inverter, parallel to the existing inverter with a A/B transfer switch might also be relatively easy. as a DIY'er I've only installed off-grid solar, my Ohio-based, off-grid system produced 450KWH this month.

[BDWW]

It'd be pretty trivial to get AC power from your panels.

All you'd need is an MPPT controller, a battery, and a dc-ac converter.

Figure out what the open voltage is on your panels. Compare to the max input voltage on your mppt controller. This will tell you whether you can run some in series or you'll need to run circuits in parallel. Home panels will probably require you to run parallel if you want more power than one panel can supply.

If you panels are run with mc4 connectors, you can simply buy a Y connector, and run a separate - switched- circuit to your mppt controller. Hook the controller to a battery, and the battery to a DC-AC converter, and voila - AC power.

If the power goes out, simply flip the switch/connect the circuit, and you're good to go.

edit: I can go into a lot more detail and come up with a parts list on amazon for you if you're really interested.

[Just Joe]

https://www.backwoodssolar.com/learning-center

Plenty of good reading there.

For occasional power outages - just buy an inverter generator. They are "quiet" and they can throttle up and down depending on load making them more fuel efficient. All the brands make them. Even Harbor freight sells a nice 1600W version for about $500. Do your homework and see what works best. I have a pair of Honda generators at work. One is a "tiny" 1500W and the other 6500W. Both are quite easy to live with. Chain them down so someone doesn't run off with them while you aren't looking.

You could also go DIY solar and charge a couple of batteries with budget solar panels and use an inverter. Would power a few gadgets a few hours per day or LED lights for the whole evening. I have a 1000W inverter that I clip on my car's battery for occasional tasks like running a Sawzall or drill. Works fine. I can even run an electric single cup coffee maker that way. bout four brews and I start getting low voltage warnings. Idle the engine and it'll go forever.

For charging phones we use the batteries from our ebikes. Both have USB ports and can keep a phone charged for a week or more.

At home we have a Kohler home generator. Previous owner installed it. Capable of running all the lighting but it is wired to power the main floor only. Automatic disconnect switch. Runs on propane from a buried tank. Its noisy - sounds just like a lawnmower outside our bedroom window. Keeps the fridge cold, powers the HVAC, on demand hot water, TV. Everything is automatic. Supposedly consumes 1.5 gallon of fuel per hour at half load.