We have a 4kw system installed and a device that heats our immersion heater for the hot water.

Return on the system has been good, but now considering a Tesla 14kw storage battery.
We also have an EV car, Nissan Leaf, which could then use any stored electricity etc.

Thestorage battery is currently around £5k,can’t seem to find any return on investment calculations online, but the money in the bank is earning next to nothing in interest.

Any help, discuss.

From what I’ve read the price of battery storage is coming down all the time and realistically now might not be the smartest time to buy.

That said, your money…. fill your boots!

Probably lots of much better info on this available on the Navitron web site

The number you need is the TOTAL energy exchange capability of the battery before it is considered ‘dead’

EV batteries age as current is pushed in and out of the battery, as the charge carriers eventually loose their mobility and the effective capacity of the battery is reduced. Effects such as temperature and peak current all have differing effects on life time.

Typically, an EV battery is spec’d to last 8 to 10 years of typical usage. Lets say 50% discharge, 5 times a week (the larger the battery, the smaller the DoD used, because typical daily trips are actually quite short)

So for a 20kWh battery, that’s a total energy exchange per week of 20 X 0.5 X 5 = 50kWh, which on todays ‘lecy market is worth around £5, or £260 a year, or £2600 over 10 years.

The complication comes in the fact that a battery used for domestic storage is likely to be much much less stressed than the same battery in an EV (which pulls up to 1000 Amps when you floor it off the lights!) and likely to be kept at a more constant temperature. So, does the power wall come with a battery life estimate?

IME, currently, in pure financial terms, domestic battery storage is not worth it. But if ‘lecy prices climb then it could become worth it in a few short years (of course, you may wish to do it for environmental protection reasons, as well as pure financial ones)

I have had a reply from the original company that installed the current system, see below.

Our total electric usage for the whole household is around 6600 kwh for a year.

Didn’t know about the tarfiff changes , looks like this could force my hand to get cheaper tariff rates overnight, especially in the winter months.

…

Lots of options out for battery storage. The best by a mile is the Tesla Powerwall 2 which will launch this month the 17th. We have 14 pre orders to install as this battery was delayed by six month after the Powerwall 1.

The Powerwall 2 is 14kwh battery at 120Kg in weight, it can be mounted outside and looks very attractive. If you compare any other make the Tesla is actually the cheapest per Kwh and the tech is far beyond its competitors.

Install price for the Powerwall 2 would be approx. £7,000. Not cheap i know but she is a beast of a battery and has very long life cycle so expect over 20 years trouble free charging and discharging.

There is a new tariff coming this year which is aimed at battery storage. the tariff will be 4.99 pence per kwh form 11pm to 7am…….12 pence per kwh for 7am to 4pm…… 24 pence per kwh form 4pm to 6pm….. then 12 pence per kwh form 6pm to 11pm.

The Tesla Powerwall can be charged form the grid as well as solar so you can charge the battery on the low rate to have full battery ready for next morning. Very handy in the winter months when solar is not doing much. this make the battery usable all year round.

It would be nice to find a means to charge a battery from wind power which very often is stronger at night in the winter, but do you think I can find anyone to provide it. I’ve been running a battery for 18 months, not a particularly good brand, when I installed it the Tesla wasn’t available, but something I reasoned was better than nothing.

The Tesla however cannot be charged by many inverters, it needs a particular type, the Solar Edge I believe it’s called, lots of installations are wired in series and the solar edge has a means to sort of wire the panels in parallel, I believe.

The powerwall 2 can be charged AC aswell, so any inverter can be used. although a loss of efficiency can be expected.

£5000 buys me over 20 years of electricity at current rates. If you consume more electricity the first investments would be to reduce consumption:

Solar water pre-heating and a built-in heat pump for top up when needed.
LEDs everywhere.
Master switches to reduce things on standby.
Economical appliances – we cut the oven by better than 60% and found a fridge that cut consumption significiantly.

The time to really make savings is when there is high demand, training the family will do as much good as a battery storage. How much embedded energy is there in a Telsa power wall? And how much lithium? Justified in your car but hard to justify when water can be pumped up hill to store energy.

We have the solar edge panels already installed.

The main driver for the battery is to store and then use the electricity produced by the panels on the roof.

An added benefit of storing the energy is that we can use the energy to charge the Nissan Leaf.
The ability to top up the battery at 5p kw on low peak times is another big benefit. Can then use the energy from the solar panel production and some stored energy from overnight. This would be a very low cost system in terms of reducing monthly outgoings.

Just the initial outlay cost of the installation really, having said that, could buy a used car for £7000 ish, and it cost money to run, and depreciate at an alarming rate.
Or, leave money in a silly low interest rate ISA and continue with paying a lot for electricity.

I also do feel that we have the means to reduce our monthly energy bill long term, and do the environment some good at the same time.

The chap who installed the original system is coming over to explain the details this week.

I see that though the quoted e-mail talks about 20 years out a Powerwall 2 the warranty is 10 years.

https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall%202_AC_Warranty_Europe_1-2_English.pdf

£7000 installation over 10 years that’s £700 per year. Unlikely to pay for itself in savings I’d have thought. Of course hopefully it would last longer than the warranty period.

Assuming say an average 12kwh* stored then used from the Tesla per day A mix of solar and 5p offpeak. Call it 2p per KWH average. Saves 10p per KWH. 10×12 £1.20 per day. Saves £438 per year.

The £7000 cost would be paid back in 16 years. Worth it? Maybe if you are confident a 16 year old battery will still be performing well enough long past the life cycles it is warranted for. THen that isn’t allowing for the fact that if you are willing to tie up £7000 for 15-20 years a stock market fund would be likely to generate a decent income. Maybe not £438 per year but allowing for the lost investment income the payback period for the Tesla would be extended considerably.

*Assuming capacity drops evenly from 14KWH to warranted 80% at 10 years and drops further as time goes on.

Thanks irc

That helps put some perspective on the money side of things.

However, I would imagine over the next decade that electricity prices will increase, making the purchase of electricity from the grid more expensive. Difficult to factor that in , in payback terms.

As for putting the same £7000 into some shares etc, yes, could well do better, but wouldn’t have the monthly saving benefit of lowering our monthly expenditure.
Having now retired, we are more conscious of the monthly drain on energy bill, community charge, water rates etc.

Lowering the expenditure allows us to budget long term.

Buying a van, which I have considered for purely going to further afield places for mtb’ing, would just see me blowing the same amount of money for no return at all, and cost money to run.

Sometimes the financial argument does have to stack up that well to persuade you, when we bought the solar panel system , the numbers were ok with a payback of about 7 years.
But we are glad we installed them, again with lower outgoings.

Just had the chap out who did the initial install.

Went through the details and prices etc,

Have decided to put a deposit down on the Tesla Powerwall 2 battery.
Demand is high at the moment, will be about 10 weeks until installed.

You can also daisy chain additional batteries in the future, which avoids the initial expensive install costs, and makes some sense further down the line. Battery prices will probably fall in the next two to three years time also.

Maximum drain from the battery to the household is 5kw, and the battery can be controlled from an app regarding the import from the grid.

Should work well with the ev car charging.

I’ve understood you are a retired couple so just two of you. I’m really surprised by your electricity consumption. Now junior has gone we are looking at a yearly consumption of 1550kWh (less than 5kWh a day). Even with junior at home showering twice a day we only got to 1850kWh. We have solar panels and selling to the grid is so profitable we don’t use any of the production ourselves.

The house is all electric with a wood burner and solar thermal to reduce electricity consumption. Roof, floor and walls are all well insulated and there’s triple glazing. The washing machine is fed direct from the solar system on the fill cycle and the solar system is used as a pre-heater for a traditional immersion tank when the water isn’t hot enough for a shower (roughly six months).

The wood burner is used sporadically for three months and most days for three months. We cook on it and get a couple of kettles of hot water from a two-hour burn.

Have you broken down where the electricity goes? When I did that it was clear that solar thermal would save the most electricity and pay for itself in about 11 years.

@edukator –

he mentions running a Nissan leaf – just charging that up once a week is 1500KwH straight off…

if you have any additional roof space, additional panels would make sense, as you will struggle to charge the battery for 6 months of the year. i would anyway.

@leebaxter

Yes, we discussed extra solar panels, the key issue that stopped this from going ahead is the bonus of importing electricity from the grid in the off peak time.

Looking at buying energy at 5p kw between 11pm to 6am.

We still have one child living with us, can’t see him leaving any time soon…..

Shower usage and charging the car are probably where the bulk of the energy consumption comes.