Talk Morgan Forums Community The Malvern Arms Off grid and power walls etc

"In all honesty I didn’t think about payback, at the time of ordering interest rates were rock bottom and I couldn’t think of a better annual return on £17k."

Forgive my slowness but I don't understand this bit. This isn't 17k you've invested.. isn't it 17k you've spent. So it takes ten years to recoup the expenditure and then you get a return? So 17k invested at ,say, 4% for ten years is, say, 25k. So at 2k a year "return" you've another 3 years to wait to break even? So at least 13 years?

Am I being dim here, genuine question
Nick

Hi Nick,
4% interest is pretty new, certainly wasn’t the case when I bought the systems.
At interest rates closer to zero and given I’m not a gambler and I am a pensioner then reducing my cost of living meant either spending the 17k on “living” or reducing my exposure to spiralling energy costs, which have gone up 300% from last year.

I’m pretty comfortable that this is an investment in protection from future economic shocks due to electrical price surges.

I did put in an earlier post that the increases in interest rates had muddied the waters. However if the government removes its support and prices continue to rise (as they surely will) I think I’m on a winner. If it happens to be13 years “payback” it doesn’t really worry me, I’m enjoying annual electricity bills right now of circa £300 rather than £2000 - £3000.

Also the kit is getting more expensive so getting in as early as possible is an important factor. I could probably sell my Tesla battery for a profit right now.

One other thing about the Tesla Powerwall is that I can run completely off grid during power cuts, which is a nice feature.

Couple of questions...
What size PV system do you have? 4 kWp I would assume at that price?
Where does the 12p come from in your savings calculations?

One other thing about the Tesla Powerwall is that I can run completely off grid during power cuts, which is a nice feature.
I see it says about 4 hours worth of energy using light appliances? Have you tested it?

Still find it hard to justify a battery set up - the longevity of the battery is of course another issue to consider with predicted life cycles of circa 10 years...whereas the Solar PV system longevity is of course not an issue other than inverter lifespan.

More reason to go off grid. My energy supplier has decided that as I have been in credit on my last two bills. (Sept & March) that they will refund the credit nearly £200. AND up my direct debit by £75. Each month. ( am on fixed tariff til Aug 31)
Guess they are trying to cover those who are in arrears. ‘‘Twas and interesting conversation this morning, can’t be changed. (We will see) They could not answer why if my present DD is placing me in credit over the winter period. (Credit was increasing) Increasing the DD during the summer will correct the issue. Of interest I do have 5 PV panels.

The panels are 6.4kW and the inverter is 6kW.

You can set the reserve power (the lowest the battery will discharge to in normal use) in the Tesla between 0 and 100%. The Tesla max output rate appears to be 5kW. I have it at 10% reserve just to avoid short term blips. If the battery was fully charged when the outage happened, it would have 13kWh available to run off grid if there was no solar input. I also have a 3kW generator wired to a switch box as back up, we have a lot of overhead power lines and trees in our area. My kids call me a “doomsday prepper” so, yes I have tested it, there’s an “off grid” feature on the app. There’s also a nice feature called “storm watch” where depending on local weather forecasts the battery will automatically top up ahead of the event,

The 12p is the Octopus Go tariff between 0030 and 0430.

These posts are timely.
We have a 4kw panel and a 2.7kw pythontech battery.
We buy power from Octopus: they are very flexible, i'm significantly in debt to them, so far their position is "it should even out in the spring". Octopus customers remain in total control of their direct debit, both when and how much per month.

Earlier this week I had a conversation with a technical representative from the Renewable Heat Partnership.Long story short the advice was to increase the battery capacity to 4 x 2.7kw = 10.8kw, which is enough to run the house for 24 hours in winter
and a couple or 3 days when the PV panels are working. The batteries would be charged from off peak power and/or the PV panels. Our gas boiler is getting old, though it still works well. To go to an air source heat pump would involve a nett outlay of £10k, so we should aim to keep the gas as long as possible and might consider a new gas boiler in 2024, rather than a heat pump, but if grant support goes up to, £10k then er should jump. There is noise about increasing the grant as heat pump uptake isn't enough to meet Government targets..... so watch and wait.

A refreshing, factual conversation by someone who wasn't selling anything.

I'm having an EPC Plus survey & report done this week, having lived at this particular house 18 years and gradually done many upgrades to insulate & save energy it will be interesting to hear what the professionals recommend

Interesting info - I think that your being a bit hopeful on your grid consumption/cost over the course of the year but would be interested as to the actual year figures especially as your basing it on off peak kwh rate when in reality you will use an amount of peak kwh rate.
Also the cost of replacing the batteries at the end of their life I feel should also be factored in to give a true reflection of any battery benefit.
Ref generator - make sure you turn off the Solar PV system if generator connected in as it doesn't do the PV inverter or the generator any good unless its specifically designed to be able to handle the generator input such as a SMA Sunny Island.

Personally - Seems like the PV/battery system you have is a suits your requirements well - unfortunately for me we are 3 phase with 15 kWp of Solar PV and we still consume average 30 kwh per day in winter. Trouble is that in summer I have grid consumption of only 10 kwh per day (80% night usage) so battery energy usage would be minimal vs capacity.

I'd need 3 x Powerwall's to cover winter (1 per phase which is Tesla requirement) so circa 39 kwh @ £36k at current prices!

There are other battery storage systems available that I can install at a cost of around £18k for 30 kwh of storage which I'm looking at which will output across all 3 phases but still not convinced its worthwhile.
That's still a large financial outlay for a product that might have a lifetime of 10-15 years....

Peter I guess have off peak cheaper power makes that pay. Whilst we do fill the 2 x 2.4 kWh batteries we have from our 3.6kW array on some days in winter on most we don't. We have had off grid days but not many.
Today for example all the PV is going into demand. The 2.4 kWh batteries are roughly £1k a go , so your concept would cost me another £2k.
I can't see the payback in that as we don't have economy 7. What we have cost just over £3k & since installing on 21/11/22 has saved us 292 kW. The power imported was 500 kW. The crude payback today is running at 9.4 years & falling.

Only if you plan to replace them. After 20 years our batteries should still have 50 or 60% of capacity which will be fine as we'll be dead by then.