this post was submitted on 17 Mar 2026
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What to do with surplus solar power in an island solution? (lemy.lol)
submitted 5 days ago by greenbelt@lemy.lol to c/asklemmy@lemmy.ml
27 comments fedilink hide all child comments
 

What happens if the sun shines onto your solar panels, and you have too much power. I guess you could cover the panels with a blanket in such a case, but that would be manual intervention ....

Do you need to consume all electric power you generate? Ways of wasting power include ... heating water or electrostatics.

Most people would put surplus power they produce into the grid, but this is connected to government / cooperate regulations and paperwork, some would like to avoid that.

An island solution with solar panels is not connected to the power grid at all...

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[–] MajorMajormajormajor@lemmy.ca 31 points 5 days ago (1 children)

Nothing happens, the controller will open the circuit and prevent the current from flowing.

Optimal solution is biting the bullet and getting batteries, the controller will prevent them from being overcharged, and you will need stored energy on an island.

You could try gravity storage like the other person mentioned but it's less efficient. During the day the solar panels power a pump/motor to move water/heavy object up high, and at night the water/object moves back down and powers a generator. There's a lot more loss since you're going:

solar energy>electrical energy>rotational energy>hydraulic energy/potential energy>rotational energy>electrical energy

and each transition will have losses due to friction and heat.

[–] daannii@lemmy.world 4 points 5 days ago* (last edited 5 days ago) (3 children)

I heard of an interesting green battery.

So you get an elevated water tank.

Excess energy is used to pump water into the tank.

This stores the energy as gravity force.

When you need more electricity than the panels are providing, water is allowed to run down into a ground level tank that rotates turbines on its way down.

A battery that won't ever go bad or lose its capacity.

Turbines and pump will likely need maintenance at some point though. But they won't be using rare minerals or lithium.

I imagine it a bit like those old wooden water wheel mills.

Almost like we had good simple methods a long time ago. They just need a little updating.

[–] itsprobablyfine@sh.itjust.works 9 points 4 days ago

Google pumped storage. This is what most grid scale energy storage is. It's the concept behind hydroelectric dams as well

[–] Xavienth@lemmygrad.ml 3 points 4 days ago

You don't actually get that much storage doing this unless you increase the scale by a couple order of magnitude. At which point you're basically describing building a dam in practical terms.

[–] ObM@lemmy.world 2 points 4 days ago* (last edited 4 days ago) (1 children)

It’s a nice idea but impractical. Energy = mass x gravity x height

Say 10 tonnes of water pumped into a massive 20m high tower… E =10000x9.8x20 Joules. ≈ 2 mega joules.

Theres 3600 joules to a watt hour so divide that and you get:

≈ 550 watt hours (0.55kWh) of storage (assuming perfect efficiency of the turbines). About the same a half a dozen big cordless tool battery packs.

[–] daannii@lemmy.world 3 points 4 days ago

You only use excess energy that would otherwise go nowhere. I'm sure there are ways to make it as efficient as possible. But even if it's not highly efficient, it's a low carbon footprint method that is more sustainable than lithium batteries.

But yeah there might be other ways of storing energy. Maybe winding mechanics. Idk.

[–] hansolo@lemmy.today 13 points 5 days ago

IRL, when commercial solar plants produce more than demand, they ground out the surplus. Just shoot it into the ground. Commercial plants don't have easy ways to store power.

The easiest option for you is to pump water uphill into a tank.

[–] PonyOfWar@pawb.social 17 points 5 days ago (1 children)

Have a battery that stores the surplus electricity for later use. That's pretty standard for solar installations.

[–] greenbelt@lemy.lol -1 points 5 days ago (2 children)

what if i dont want to pay for expensive batteries?

[–] Shimitar@downonthestreet.eu 18 points 5 days ago (1 children)

An island solar system without batteries make little sense.

[–] greenbelt@lemy.lol 4 points 5 days ago (1 children)

What to do if the batteries are fully charged? The charge controller will save the batteries? But how, what happens with the power, is it converted to heat?

[–] thenextguy@lemmy.world 10 points 5 days ago (2 children)

Nothing happens. All you have is voltage. No current. No power.

[–] kn33@lemmy.world 1 points 5 days ago (1 children)

I think their question makes sense. The light is hitting the solar panel regardless of whether there's current flowing or not. Where does that light energy go?

As far as I know, it gets converted to heat in the panel and vented off, but maybe there's something else to it.

[–] thenextguy@lemmy.world 3 points 5 days ago (2 children)

There's only so much voltage that will ever get created in each cell by exposure to light. Only so many electrons that get knocked free. Once that level is hit, nothing else happens that wouldn't also happen to a stone, or your skin. Electrical energy doesn't build up.

Yes, most likely the light is just converted to heat. But that's not special.

[–] xthexder@l.sw0.com 2 points 5 days ago* (last edited 5 days ago)

The critical part is that the electrons moving consumes energy from the incoming light, reducing the heat being generated while current is flowing. A disconnected solar panel will heat up a bit more than a connected one, but the difference in Watts per area is low enough the panel can just dissipate the extra unused heat to the surrounding air without any issues (unless you're in the desert, maybe it's possible they could overheat there, but this would likely be an issue even when generating power).

Modern solar panels are only about 20% efficient, so the panel would only heat up an extra 20% if disconnected in direct sun

[–] kn33@lemmy.world 1 points 5 days ago

It's not "special", but it is what they're asking

[–] greenbelt@lemy.lol 1 points 5 days ago (2 children)

electric potential? is the solar circuit a giant capacitor with a stored charge then?

[–] davad@lemmy.world 4 points 5 days ago

Maybe you could think of it that way, but I don't think PV cells store much charge, so they'd make pretty crappy capacitors.

[–] polotype@lemmy.ml 3 points 5 days ago* (last edited 4 days ago)

This is a bit complicated, but basically, energy is power×time and power is intensity×tension. Now if you have too much power, because you can't affect the flow of time (sad), you either change tension or intensity. The easiest is to just lower intensity (or cut it out entirely). If you just open your circuit, your intensity falls to 0. So your power falls to 0 and everything is fine. Just like how when you stop a windmill rotating it doesn't produce any power.

[–] Valarie@lemmygrad.ml 1 points 4 days ago

You can get them used for cheap but the capacity and lifespan may be a bit worse depending on prior application.

[–] hanrahan@slrpnk.net 9 points 5 days ago

i lived off grid for a decade, when my battery was charged the panels are just shade.

On a sunny day the batteries were charged at 11am

[–] Shimitar@downonthestreet.eu 12 points 5 days ago

Setup a gravitational battery. Use extra power to lift rocks/weights that you will then lower, generating power, when not enough sun.

Not common, but proven solution.

Better and more efficient: have batteries.

[–] evasive_chimpanzee@lemmy.world 9 points 5 days ago

I've asked the same question before for small scale at home surplus.

For a small/medium grid like a whole island, it's easier. You generally know ahead of time when there is going to end up being a surplus, so you can let storage get low preemptively. This includes batteries, pumped hydro, heating water, heating/cooling homes, etc.

If that's not enough, you can run some high energy cost things that dont have to run all the time like desalination or electrolysis.

[–] Retro_unlimited@lemmy.world 2 points 3 days ago

No reason to cover the panels. Your battery gets full then you use power and it charges again. It’s not waited, it just waits for when the battery needs to charge again.

You can use extra power to charge things, run appliances or tools, or whatever. It doesn’t matter.

[–] AntiOutsideAktion@lemmy.ml 1 points 3 days ago

Sounds like one of those good problems

[–] NigelFrobisher@aussie.zone 3 points 4 days ago

Take your island mobile.

[–] BarneyPiccolo@lemmy.today 2 points 4 days ago

Seems like using that extra juice to run the water heater is a good use of it. I'd have all sorts of electronic gadgets running all the time, like pumps in a water feature, mood lighting, landscape lighting, etc. Get electric everything (tools, lawnmower, car, etc ), and keep it all charged, all the time.