Electric Money Saving Idea?

rjmachin

Hi,
Not sure if this is the right forum, but thought I'd try here as it is a money saving question.
I currently use around 600 kWh per month (around 20 kWh per day), I also have just got a EV which I estimate will add a further 166 kWh per month.
I do not have solar and do not think I will be getting it.
However, I am wondering if it is possible to get a battery storage system, together with something like Octopus Go with the idea to charge up the battery during the night when the electric is a lot cheaper, then use the battery power until it runs out during the day to bring down the cost.
So, octopus go rates in my area are 5p from 00:30-04:30 and 13.72p from 04:30-00:30 including VAT per kWh.  Standing charge is 25p per day.

The EV charging which I will do overnight during the 5p price band would cost £8.30 (5p x 166)

I am not sure what energy is currently used overnight from the fridge, freezer etc.  I could read the meter before going bed and checking again in the morning to get a rough estimate.  Some of the 600 kWh will currently be from overnight usage (3-4 kWh per night maybe?).

Do you know what a rough cost would be for such a system?
I presume there is a range of battery capacities at various prices.

My thoughts are that the initial costs would be:

• Cost of system / package / parts
• Cost of electrician to install system

Then the cost of charging the battery (5p per kWh)
But then there would be the savings of using the battery.  
So would the savings in electricity outweigh the cost of the system and charging costs, and over what period?

Gerry1

Probably about as cost effective as building your own mini Dinorwig !

matelodave

As far as I can see a Tesla 13.5kwh Powerwall will cost in the region of £5.5k and you'll have to add the installation costs say at least £1k, probably more (lots of companies on t'interweb who will quote you). The cost depends on the capacity but I doubt you'll get a lot of change out of £7-8k.
You need to do a lot of careful sums to see whether you could actually charge it within the 5p window (same with the car)  - You've only got three hours at 5p which limits how much you can get into the car (a 7kw charger will only get 21kwh into the car in three hours) and the powerwall would have to fully recharge to 13.5kwh in three hours as well.

Assuming you save 13.5-5p/kwh = 8.5p/kwh and the system cost you £7k then you've got to use at at least 82,353kwh before you break even.

Even if you could save all the energy you need  and then use it all it would take 82353/7200 = 11.4 years but as you probably can't, breakeven will take even longer (although if you put the washing machine, tumble dryer and dishwasher on timers to use during the magic three hours you might be able to reduce it a bit)

Have a look here https://www.solarguide.co.uk/solar-batteries#/

ASavvyBuyer

matelodave said:

 You've only got three hours at 5p

On Octopus Go you get 4 hours @ 5p/kWh.

However, you also need to take into account, when working out the figures, the losses when charging & discharging the battery, which can be as much as 10% each way.

matelodave

In that case you'll get 28kwk into the car at 5p and probably fully charge the powerwall but as you say you need to take into account the charge/discharge efficiency. 

gzoom

We have a PowerWall, Solar PV, and an EV. 

A Tesla PowerWall is close to £10k for a fresh install + gateway 2. It does work well but if you are using 20kWh a day before EV charging your need x2 so atleast £15k+ in up front costs.

There are clearly cheaper options but even those will struggle to make the numbers work, especially without solar PV.

The first thing you should do is look at why you are using so much electricity in the first place. 20kWh is a base load of 800watts for 24hrs, the base load for our 5 bed detached is between 100-200watts max. 

Excluding EV charging we use 10kWh max per day at the weekend, and 5-6kWh weekdays. Cutting back on electricity consumption is by far the most cost effective solution to a high bill .

Oh payback on a £10kish PowerWall install is about 20-25 years if you use the entire 14kWh capacity everyday to load shift from day rate to night rate.

gzoom

I should add though if you can stomach the upfront costs, the impact of solar+battery storage on your electricity bill is quite dramatic.

This is our latest bill, and September wasn't even that sunny. We did a few long trips in the EV, and since about March/April our electricity usage has looked like this. 95% E7 rates, and the standing charge making up a big proportion of the bill.

Our best month was in April this year, agonisingly close to been 'off grid' for a whole month.....Sadly we just don't get that much Sun every month in Summer

AmandaWanda221

So do you think it`s a good idea? I was thinking about it as well.

Cardew

AmandaWanda221 said:

So do you think it`s a good idea? I was thinking about it as well.

As explained in the posts above, the battery idea is a non starter in economic terms.

Also firms introduce cheap tariffs to recruit customers and then increase prices. I would be very surprised if Octopus retain their 5p/kWh price for a long time; so I wouldn’t make any long term calculations based on that price.

Gerry1

When EVs take off the government will no doubt wish to replace the lost fossil fuel taxes, so it's a safe bet that electricity for EVs will be highly taxed.  The apparent low running cost is just bait to get people switching.  It's nearly always like this: the Prius was free from the Congestion Charge, but that was soon scrapped, ditto Tesla's free electricity.  And then there's the cost of coronavirus...

st999

Gerry1 said:

When EVs take off the government will no doubt wish to replace the lost fossil fuel taxes, so it's a safe bet that electricity for EVs will be highly taxed.  The apparent low running cost is just bait to get people switching.  It's nearly always like this: the Prius was free from the Congestion Charge, but that was soon scrapped, ditto Tesla's free electricity.  And then there's the cost of coronavirus...

How will the Government know what proportion of electricity is being used to charge an EV to tax it?
Stupid question, they will just increase the VAT on electricity so we will have one rate of VAT for gas and a higher rate of VAT for electricity