Solar power backup battery

[ramjet]

So there is this massive push in Australia to get everyone to move away from gas and to go all electric.

We put solar panels on our house a while back. I was not aware that it looks like these have a lifespan as well though.

Anyway, I am wondering if anyone in the know on here can tell me whether a battery connected to the panels that is then used at night is worth it?

Is it only any good if your daytime use is less than the your panel output so that the excess power goes to the battery?

I doubt we have ever made our money back on the panel investment as the rebate for supplying excess power back to the grid has decreased basically every year so the $ figure used in calculations is no longer relevant.

Oh yeah. there is also a push on for EVs but there is a lot of reluctance on the part of Aussies to move to them.

[Bibs]

How much power are you using over night? I can't imagine it's very much. 

If your panels are over producing during the day, that's the time to get the white goods working but I can't imagine the cost of a battery will be covered just to run the fridge freezer overnight. 

[exeterjeep]

8 hours ago, ramjet said:

a battery connected to the panels that is then used at night is worth it

may be if you had a EV on charge at night it could then use the 'free' energy stored during the day?

[C8RKH]

It's like anything really, do the research to understand if it's viable to you, or don't waste your money buying something you don't understand.

You need to work out how much energy you are generating versus how much you use. 

You then need to look at when you generate versus when you use.

The deltas will tell you how much excess electricity you are generating and when, and when you are drawing energy from grid and not producing 

The goal is to balance your generation and use so that in a typical 24 hour period you NEVER draw from the grid. It will always cost more to buy from the grid, than to sell back to the grid. So self sufficiency is key.

Once you understand your generation and consumption, and providing you have more generation than consumption during the day (as this is typically when PV generates) then you know how much spare capacity you have to charge a battery and therefore a good indicator of the battery size to buy.

Hope this makes sense @ramjet

[ramjet]

Thanks for the answers guys. I am aware of the maths and am going to go through the past bills to work out the usage vs generation.

I suppose the question should really have been whether with the life expectancy of a Li-Ion battery being circa 8~10 years, will the saving on your panels to battery system vs grid cost be more than the price of a replacement battery?

[exeterjeep]

Also how good you feel saving the planet.

[snowrx]

Depends on your use case. For me my rural electric company has frequent service interruptions, so I look at my battery as a whole house Uninterruptable Power System, with a subpanel that  feeds my lights, home office and entertainment. I can go a couple days of conservative use without starting the generator, and if I'm in the middle of work or a movie when the power goes, I don't even notice. 

I never looked at the economics of the system, (or my Lotus) I just wanted to offset my grid use as much as I could and have some independence when the grid went down. But extra expense, complexity with a grid-tied system and maintenance needs need to be considered before adding a battery. In my case I was adding the grid to my battery...

 

 

[Escape]

There's also a big difference in the numbers depending on time of year, weather etc. You need to find a balance between peak power generation and average usage for a battery to be cost effective.

[snowrx]

Interesting how we who will drop tens of thousands on a car that almost surely will not cover cost of ownership, are getting the pencils out for solar. Here in the states, barring a reluctant utility or a adversarial state government, a simple grid tie system is now generally cheaper than an economy car, and more durable. 

I figure it's my carbon offset for when my Esprit goes to 11.9:1 AFR on boost! 

[Escape]

Because we chose that car because we like it, we follow our hearts for whatever reason.

The push for solar panels is mainly greenwashing, manufacturing is far from environmentally friendly and economy is often debatable. If I ever decide to install them, it will be for financial reasons only. I have considered, but couldn't make the numbers work. I'd much prefer our government (and others) had allowed/ encouraged investments in nuclear power to ensure cheap, clean and reliable power. Failing that, as @snowrx explained, it might become necessary to have some form of independent power supply, just to ensure uninterrupted power.

[ramjet]

I have done some looking into the power bills for our place and we average about 10.7kWh/day. About 6.7kWh at night.

The suggest battery from one of those online calculator thingamajigs was a 7kW battery which would take 15.8 years to pay for itself, but I presume you would have had to replace it before then, so I would never make the money back.

So there's another electrical goodie out the window.

I was also looking at the heat pump which everyone is pushing over here in Oz. Nope to that as well.

[Escape]

I'm surprised to read the battery takes so long to pay itself back. I do think in the bigger picture a battery is a necessity to make the system viable. And not just to cover the average night consumption, but to guarantee self sufficiency for at least 80% of the nights. Otherwise the more solar panels are installed, the harder it becomes for the grid to keep up with varying demand, and the more expense electricity will become. With more likelihood of brownouts and even blackouts if solar production drops for a longer period.

Not saying you should get a battery, we all look at our own situation and try to make the best decision with what we have and know. But subsidising solar panels without factoring in the ramifications is not proper policy.  

[C8RKH]

I think that what it does tell us @Escape is that the economics around batteries as a storage medium is just not proven, which maybe also explains partially why EV's are more expensive and dare I say not that efficient, don't you think?

 

[Bibs]