# PV system - is it worth getting a battery?



## Cilar (7 Jul 2019)

Do you think it is still worth getting a house battery with a PV system:
- Announce of introduction of house to the grid payment in next few months/years
- Electric car on driveway with Zappi charger to divert excess PV electricity to EV battery

Pondering whether the investment in battery in a PV system would be worth it?


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## Leo (9 Jul 2019)

Cilar said:


> Pondering whether the investment in battery in a PV system would be worth it?



Try work out the cost and what you think it might save you over time. Bear in mind the battery capacity will consistently fall over time, the rate of fall being determined by the quality of the battery. If you're getting a long pay back period approaching 10 years, it's probably not worth it.


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## Palerider (9 Jul 2019)

Good question, my system is going in shortly, I went with a 6kw  battery and expect a ten year payback.electricity is going up, I don’t know if I am doing the right thing with a battery but  I can store and reuse  electricity without accessing the grid then for me it makes some sense, the battery has a ten year warranty , depends on yourself really.


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## Leo (9 Jul 2019)

Palerider said:


> the battery has a ten year warranty



Does that warranty specify the minimum remaining capacity at that point, or is it just a warranty against complete failure or manufacturing defects?


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## Palerider (9 Jul 2019)

I doubt it,  I suspect like any manufacturer warranty it will be against defects.


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## Leo (9 Jul 2019)

Palerider said:


> I doubt it,  I suspect like any manufacturer warranty it will be against defects.



Fair enough, some of the EV manufacturers are clarifying expectations in this area, I was interested if any of the home battery suppliers were starting to take the same approach.


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## Alkers86 (10 Jul 2019)

Cilar said:


> Do you think it is still worth getting a house battery with a PV system:
> - Announce of introduction of house to the grid payment in next few months/years
> - Electric car on driveway with Zappi charger to divert excess PV electricity to EV battery
> 
> Pondering whether the investment in battery in a PV system would be worth it?


The only financial reason to get a battery currently is to avail of the larger grants available. I would get the smallest battery I can find in that case. If you're not availing of the SEAI grants, it doesn't make financial sense.


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## Laughahalla (10 Jul 2019)

Battery is usually guaranteed to have at least an 80% charge after 10 years.

If you go with a small battery e.g. Pylontech 2.4kwh / 3kwh then the SEAI will give you €1000 towards it so you might as well avail of it.

if the feed in tariff scheme comes in soon and with a good feed in tariff or net metering then it might negate the need for battery storage.
i currently have a diverter to the immersion and a battery and  I still end up giving electricity away to the grid.

without storage (battery or immersion tank  or feed in tariff) you will give away most of your production.


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## Leo (10 Jul 2019)

Laughahalla said:


> Battery is usually guaranteed to have at least an 80% charge after 10 years.



Can you point to a home battery that makes such a claim? I'm finding it difficult to locate much in that area.

A few of the EV manufacturers will only guarantee 60-70% after 8-10 years. Mercedes for example state 70% after 8 years or 100k km, whichever is first and only provided an authorised Mercedes dealer carries out an annual certification. Tesla, although noted for slow degradation make no such capacity guarantee at all.


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## Laughahalla (10 Jul 2019)

Here is a blog that has done some research .. I'm sure there is more information out there.

*Tesla Powerwall 2 Warranty*
Tesla guarantees the Powerwall 2 will be free from defects for 10 years, will have an initial capacity of 13.5kWh at installation, and at 10 years will retain 80% of its capacity










						PylonTech, Powervault, Powerwall 2... What's In the Warranty?
					

Tesla Powerwall 2 (residential solar storage system) offers a much better warranty than Pylontech or Powervault 3. Despite the fact that Pylontech and Powervault 3 are LFP (lithium ferro phosphate), Tesla's Powerwall 2 wins hands down when it comes to aesthetics, simplicity, functionality and...




					blog.spiritenergy.co.uk


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## Leo (11 Jul 2019)

Thanks for that. I also found after that starting with the Model 3, they offer a 70% after 8 year warranty, but go on to state that the warranty will only 'correct defects in the materials or workmanship of any parts manufactured or supplied by Tesla'.  So if your battery falls under 70%, you still have to prove a manufacturing defect for them to act on it! At least the PowerWall warranty doesn't have a similar restriction.


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## thos (15 Jul 2019)

What are you doing for hot water? Have you considered a diverter like an EDDI to use that surplus?

What mode have you got the Zappi in? An EV needs 1.4kw of power to charge, so if you are using Eco+ mode only on Zappi, you may be finding times when you've got solar surplus but not enough to drive the car, so this surplus could still be used elsewhere.


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## Cilar (21 Jul 2019)

EDDI may be an option to divert to hot water when car is not charging - cheaper than getting batteries. That said, hot water is supplied by a heat pump so already very economical (~3-4c per kwh of heat), so difficult to say whether this is worth it. Ideally, a system that would force the heat pump to start when there is energy surplus would be ideal - I suspect that may actually even allow to fully heat water during winter months as 1kwh of electricty results in 3 kwh of heat with heat pump, which is sufficient for our daily needs in dhw. I do not think such a system exists though.


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