Octopus Go Intelligent Tariff - recent changes

pensionpawn

Just read this..

HalfFull

https://forums.moneysavingexpert.com/discussion/comment/81895080#Comment_81895080

So to continue your comparison and continue to the real cost…

A 39K EV with an 81.5kWhr battery , using 80% depth of discharge over 3000 cycles is..

3900000 pence / (81.4 x 0.8 x 3000)kWhr = 20p / kWhr. Plus the cost of the electricity, which as this is an IOG thread is 7p/kWhr. So V2G costs 27p/kWhr, which doesn't exactly seem like a saving to me?

QrizB

The only potential hole I can see in your calculations is that a 10-year-old EV will still have some value. Probably less than £10k, but value all the same. So you probably don't want to amortize the entire EV cost over those 3000 cycles.

Doing the same sums with the £11.4k 96kWh Fogstar battery / Solis inverter bundle gives a cost of 4.95p/kWh, which (assuming 7p/kWh to buy electricity in the first place) makes 12p/kWh overall. That's probably worth having.

JKenH

These theoretical calculations are interesting but what use will a typical householder have for such large batteries and energy usage? The pence per kWh figures quoted depend on maximising use of the battery everyday. 

If you are on IOG the opportunities for arbitrage are limited. You buy at 7p and sell at the new reduced rate of 12p but that 5p apparent profit in reality is probably less than 4p/kWh after round trip losses. (AC to DC and back to AC). If you are charging and discharging 60kWh per day, that’s more than 20MWh p.a., HMRC will probably treat you as trading and tax you accordingly.

QrizB

... what use will a typical householder have for such large batteries and energy usage?

I have no idea but someone on this thread was suggesting they needed a monster battery and so a large-capacity EV was the only option. Perhaps they have direct electric heating and don't fancy a heat pump?

The same type of calculations can be done for smaller batteries, if that's more generally applicable (noting that the PW3 is more expensive per kWh than the EV and so the resulting price-per-kWh will be larger). But I'm not doing arithmetic at this time of night!

Reed_Richards

I already have a 6.5 kWh battery. In January my average daily consumption of day-rate electricity was 26 kWh. Last June it was 1 kWh per day. So in winter a much bigger battery would save me a lot of money and in summer it would be of almost no benefit. Frankly, I get a bit lost working out what I would need to pay for a bigger battery to make it economic.

JKenH

So far this month I have discharged 302kWh which is an average of 13.1 kWh/day from my PW3. YTD my average has been 11.9 kWh per day. It will be interesting to see what the daily average is for the whole year. Other than when the battery was calibrating I think I have only run out of battery before midnight once this month on the 15th when we had visitors staying and very little solar. I usually time the ASHPs to come on an hour or two before midnight to use up anything left in the battery and sometimes cut it a bit too fine.

I think the PW3 is pretty much the right size for us at about 14kWh. I will say, though, that having a battery has encouraged us to consume more electricity and the reduction in the Octopus export rate will encourage even more self consumption of our generated PV. With an import rate on Go of 8.5p and a lower export rate of 12p, arbitrage is not worth it in terms of wear and tear on the battery. The nominal profit per kWh from arbitrage on Go has reduced from 6.5p to 3.5p and on IOG from 8p to 5p.

I wouldn’t be at all surprised if Octopus find a significant difference in arbitrage activity as a result of the reduction in the export rate. I wonder how that will match up with their modelling of the impact of the export rate change. I have no idea whether the consumer arbitrage is beneficial to them or not. I believe some customers have genuinely tried to reduce pressure on the grid by exporting from their batteries at peak times. That might change now.

matt_drummer

https://forums.moneysavingexpert.com/discussion/comment/81896830#Comment_81896830

I think the plan is to fill the car up with electricity `cheaply' and export at higher rates to make the car pay for itself.

The person considering this cannot make an economic case for buying home battery storage and they feel that the only viable option for them is an ev withe a large battery and bi-directional charging, otherwise neither home battery or ev is on their radar,

That's why we were talking about killing the battery with a heavy charge/discharge use pattern.

JKenH

Let’s have a quick look at some numbers. It costs 7p/kWh to import on IOG which after round trip losses means the cost of import is around 8p/kWh. Let’s say we can charge at 7kW for the full 6 hours of IOG adding 42kWh. A V2G system might discharge at 3KW so in 14 hours we are able to discharge the whole 42KWh earning a net £1.68 (42kWh x 4p).

Assuming we didn’t drive the car at all and charged and discharged every day we would earn £613 p.a. Or ££6130 over 10 years. Let’s say we could buy our EV for £40k, the. The opportunity cost of that money (lost interest) might be around 3.5%  or £1400 p.an and of course over 10 years it might depreciate by 75% to £10k costing a further £3k a year. So buying a car to use purely as a battery on IOG tariff costs us £4,400 p.a. to earn £613 p.a.

We might decide we also want to spread the cost by using it as a car as well but we then have to add in road tax, insurance and maintenance. While we get the benefit of saving petrol, every 3 or so miles we cover reduces the potential for earning by 1kWh or 12p.

I suppose the one upside of reducing the export rate is that the opportunity cost of driving a V2G capable EV (rather than exporting from it to the grid) falls from around 5p to 4p per mile. 

Edit:rather than take this thread further off topic discussing V2G I have stated a separate discussion on page 397 of the EV Discuthread on the green and ethical board. Unfortunately I haven’t worked out how to post a link direct to that page but perhaps someone else can help me out.

Qyburn

Would you anticipate to bank on Octopus continuing to pay full export rates in combination with an EV import tariff? It wasn't that long ago that an EV import tariff would only get a much lower export rate. I could see that being revisited if V2G becomes a reality and customers are pumping 40 or 5050kWh in and out every day.