Solar, Battery, TOU tariff a goer?

ASavvyBuyer

There are lots of people on the SpeakEV forum that have switched to GO, or are in the process of switching to it. Most find the 4 hours every night is fine for topping up their EV.

A mentioned elsewhere, the 1000 limit was only for those that wanted a "cheaper" smart Zappi charge point as part of the switch to Octopus Go.

Our average rate for all our electric, is about 7.5p/kWh including VAT, since we switched to Go. We were already an Octopus customer on a fixed electric tariff, so our switch to Go went very smoothly.

thisreallyisme

From what I understand, the Powerwall can now guarantee no export to the grid and so the battery passes the DNO test and is not the problem.

So I am just left with export from the solar panels problem.

Solar Edge do an inverter with export limitation which can be set to an export of say 3.68 or even zero. However, it only operates within an 'up to 5 second' delay before it kicks in and throttles back the inverter. So within that 5 seconds I could be exporting higher that 3.68 with a larger inverter for a couple of seconds causing problems for the grid, hence not allowed by DNO in my area due to export pressure on the grid.

I am pretty sure that I am stuck with 3.68 solar panels. So this is what I have to work with.

thisreallyisme

Ah thank you, ASavvyBuyer, right that makes sense! And 7.5p is very good.

Luckily, I don't need a charger as I don't have an EV but do have a very hungry appliance in the home. They have confirmed to me that I don't have to have an EV to go on to this tariff.

ASavvyBuyer

thisreallyisme wrote: »

Ah thank you, ASavvyBuyer, right that makes sense! And 7.5p is very good.

Luckily, I don't need a charger as I don't have an EV but do have a very hungry appliance in the home. They have confirmed to me that I don't have to have an EV to go on to this tariff.

Currently, during the Winter when we have poor Solar PV generation, just over 70% of our electricity is imported at the 5p/kWh rate.

In the Spring, Summer & Autumn, with the Solar PV system generating more, I am expecting that % to be even higher, as the majority of our daytime electric will be from our Solar PV system.

Regarding a battery, be very careful working out the payback period. Some, battery installers are using very high compounded inflation rates for electricity costs to justify the investment.

Also, for each kWh you put into the battery, you need to add the cost of the battery system divided by how many kWhs you expect to get out of it during it's lifetime. This usully works out as somewhere between 6p-10p extra per kWh depending on the size of the battery.

zeupater

Hi

Here's the predicted position based on a simplistic uplift from 3300 to 8000kWh/year using the variables provided ....

£1295 - standard
£1028 - +5.7kWp
£707 - +13.5kW usable stg (5kWsupp/3.3kWchg/unrestricted CHG%)
£615(312d+303n) - +E7 charging

Predicted charge at 16:55 on 01/12 is 17Wh, so fully depleted.


HTH
Z

thisreallyisme

Thanks Z, could you explain these figures a bit more for me please? I'm not grasping it...

zeupater

thisreallyisme wrote: »

Thanks Z, could you explain these figures a bit more for me please? I'm not grasping it...

Hi

Effectively, on the basis that 8MWh should cost the first number, adding your 5.7kWp system would predict a reduction on you Bill to the second ... adding the PW2 to run only off PV excess results in a further predicted reduction to the third & moving to an E7 supply agreement to utilise cheap rate overnight energy during daylight hours results in the fourth bill projection with the numbers in brackets providing a breakdown of daytime & nighttime unit £billed. Predicted bills include standing charges & VAT.

The figures are based on actual system performances which have been used to predict your described array and inverter capping, an average household appliance/gadget usage profile has been applied & rescaled to 8000kWh (There isn't a dedicated high use profile yet!) ... Unit costs are based on currently typical pricing (I think I used actual figures from a Scottish Power fixed rate offering with E7 cheap rate from 23:30 to 06:30) ... PW2 prediction is based on unrestricted use with limits on charge & discharge being 3300W & 5000W.

HTH
Z

thisreallyisme

Thank you for that, Z.

Very interesting that the cost saving in this calculation increases the % return by adding in a battery (without any subsidy).

The solar and battery costs are around £6500 each, so with solar alone return is 4.1% in first year, add in battery and it's raised to 5.2%.

zeupater

thisreallyisme wrote: »

Thank you for that, Z.

Very interesting that the cost saving in this calculation increases the % return by adding in a battery (without any subsidy).

The solar and battery costs are around £6500 each, so with solar alone return is 4.1% in first year, add in battery and it's raised to 5.2%.

Hi

With the realisation of capital & opportunity loss of course!

Segmenting the project, you're really looking at a basic payback on the storage of 16years (6500/413) before assessing the effect of battery degradation ... I can model that but it simply makes the position worse!

HTH
Z


#edit ... using current economics, after 16 years the incremental saving would be more likely in the range of £368/year if it helps ...

Martyn1981

thisreallyisme wrote: »

From what I understand, the Powerwall can now guarantee no export to the grid and so the battery passes the DNO test and is not the problem.

So I am just left with export from the solar panels problem.

Solar Edge do an inverter with export limitation which can be set to an export of say 3.68 or even zero. However, it only operates within an 'up to 5 second' delay before it kicks in and throttles back the inverter. So within that 5 seconds I could be exporting higher that 3.68 with a larger inverter for a couple of seconds causing problems for the grid, hence not allowed by DNO in my area due to export pressure on the grid.

I am pretty sure that I am stuck with 3.68 solar panels. So this is what I have to work with.

But don't forget, if the battery is on the DC side, then the inverter can direct generation to the battery before the 3.68kW AC limit. EG if you were generating 4.68kW (DC side), then the inverter could charge the batts at 1kW, and also output 3.68kW AC.

This would save you having an additional inverter (like the one in the PWII) and battery losses are less since it only goes from DC to AC once, instead of DC to AC to DC to AC (panels to house to battery to house).