Tesla to unveil home storage batteries

Martyn1981

baldelectrician wrote: »

What about the possibility of charging the batteries during the winter from off peak energy?


The basic arithmetic means you can buy power at 8p per Kwh and sue it to save you during the winter months when you don't make much...


discuss

For me, I don't think it works yet. The lifetime of the battery depends on the number (and depth) of cycles, so we can calculate a cost per kWh.

Let's say the battery part of one of these installs is £3k for 7kWh of storage, and for arguments sake, say the whole 7kWh is useable.

Next let's take the 10yr warranty and assume the batt is used fully every day, so 10yrs x 365 days x 7kWh, that gives us 25,550kWh of 'use'.

£3k / 25,550kWh = 11.74p/kWh in storage costs, to be added to the cost of leccy. So the winter E7 leccy actually cost you 20p/kWh if you include the cost of the kit.

Hopefully the batts will last longer and run more cycles, but I've included an unrealistic level of depth of discharge.

If batts get down to £1k, say £2k all in for the kit and install, then it starts to look promising, especially if we assume that each time you need to replace the batts, their cost and power will have improved.

Mart.

Martyn1981

Just a thought on E7 with PV and especially PV with batts.

Can't explain what I'm thinking, so will use numbers instead:-

Choosing easy numbers to use, let's assume a household with 3,600kWh of demand, split 1,200 during E7 period and 2,400 during 'normal' period.

Before PV

Without E7 3,600kWh @ 14p = £504
With E7 1,200 @ 8p + 2,400 @ 17p = £504

After PV

Without E7 2,400kWh @ 14p = £336
With E7 1,200 @ 8p + 1,200 @ 17p = £300 (£36 better)

After PV and batts (assuming an extra 600kWh of leccy savings again split 1/3:2/3)

Without E7 1,800kWh @ 14p = £252
With E7 1,000 @ 8p + 800 @ 17p = £216 (£36 better).


Regardless of using batts to charge up on E7, in this example (with cherry picked numbers) E7 looks like a good decision as import goes down.

I guess it all depends on the actual prices and each household import figures and time of import. But certainly worth a ponder/investigation.

Mart.

baldelectrician

You also have E10 in some areas which charge ALL electricity at the cheaper rate - and with E10 you get cheap power during the day (1pm-4pm) as well as other times


Combine the cheap leccy in the afternoon with the power you are generating you could save without storage (eg you could be making 13p per Kwh and buying at 8 p), whilst you put your hungry appliances on.
Many appliances have timers to utilise off peak periods

zeupater

baldelectrician wrote: »

.... Combine the cheap leccy in the afternoon with the power you are generating you could save without storage (eg you could be making 13p per Kwh and buying at 8 p), whilst you put your hungry appliances on ....

Hi

:think: .... ????? ... Don't really follow that ...

If you have microgeneration and export is on a deemed basis then whether you use the power or not, you're paid for it, in addition, the FiT payment is purely based on generation.

Most of us with demand-side microgeneration technologies would look to match 'hungry appliance' afternoon use to generating conditions whenever possible, therefore there's absolutely no need to have a cheap afternoon tariff as the power we use is effectively 'free' ....

HTH
Z

baldelectrician

The use is only 'free' when you don't draw from the grid.
If you go over you are charged, but if you are on a lower tariff then you pay less

zeupater

baldelectrician wrote: »

The use is only 'free' when you don't draw from the grid.
If you go over you are charged, but if you are on a lower tariff then you pay less

Hi

I know, I've had pv for years .... but that's not what you were describing in "you could be making 13p per Kwh and buying at 8 p"...

A further consideration is the relative costs of single and dual tariff offerings. Normally, to offset some of the costs of supplying cheap rate electricity overnight, the daytime electricity is more expensive. In a case where the majority of the energy being used by 'hungry appliances' is from self consumption with the grid providing a top-up, the issue then revolves around the proportion of the usage cycle where you'll be importing and what the net import power level would be ... this would give the net imported energy. At this point it's simply a case of comparing the value of the 'hungry appliance' net import saving against the increased value of imports during the rest of the day, taking particular account to dark and low-light morning, evening and winter periods ...

HTH
Z

michaels

Martyn1981 wrote: »

Just a thought on E7 with PV and especially PV with batts.

Can't explain what I'm thinking, so will use numbers instead:-

Choosing easy numbers to use, let's assume a household with 3,600kWh of demand, split 1,200 during E7 period and 2,400 during 'normal' period.

Before PV

Without E7 3,600kWh @ 14p = £504
With E7 1,200 @ 8p + 2,400 @ 17p = £504

After PV

Without E7 2,400kWh @ 14p = £336
With E7 1,200 @ 8p + 1,200 @ 17p = £300 (£36 better)

After PV and batts (assuming an extra 600kWh of leccy savings again split 1/3:2/3)

Without E7 1,800kWh @ 14p = £252
With E7 1,000 @ 8p + 800 @ 17p = £216 (£36 better).


Regardless of using batts to charge up on E7, in this example (with cherry picked numbers) E7 looks like a good decision as import goes down.

I guess it all depends on the actual prices and each household import figures and time of import. But certainly worth a ponder/investigation.

Mart.

I have EV which I can charge in the day plus iBoost - I was wondering whther I could have E7 in the winter and standard tariff in the summer....

tunnel

michaels wrote: »

I have EV which I can charge in the day plus iBoost - I was wondering whther I could have E7 in the winter and standard tariff in the summer....

Or for winter there's this tariff https://www.britishgas.co.uk/products-and-services/gas-and-electricity/free-electricity-tariff.html

Martyn1981

michaels wrote: »

I have EV which I can charge in the day plus iBoost - I was wondering whther I could have E7 in the winter and standard tariff in the summer....

Wouldn't E7 still work in the summer? Our summer import gets down to about 2kWh/day now, and most of that is during the night. So even if daytime leccy was more expensive, how much of it would you actually be buying?

Can you set your EV to take a low draw from the system during the day, so as not to exceed PV generation, then top it up at night on cheaper E7?

Mart.

Martyn1981

tunnel wrote: »

Or for winter there's this tariff https://www.britishgas.co.uk/products-and-services/gas-and-electricity/free-electricity-tariff.html

Hiya T. Confession, I've lifted this from Navitron, but someone went through the T&C's and found an anti-social clause that mentions watching consumption for excessive use during the 'free' period.

It also mentions that they'd normally expect 11% of weekly consumption to be used during the free 9-5 day, so whilst they expect actual demand to be higher, they will be watching out "if you start to do all the washing for the whole street".

Kind of shoots down my first thought, which was charge up an EV, do all the household washing, and charge up a massive 50kWh lead acid batt on 'freeday'.

Mart.