Solar Panel: battery ratio

[Jdsk]

Yes. I'd start with:
• Charging the battery in every cheap rate window
• Running washing machine, dishwasher etc during the cheap rate window
and studying the usage once those are in place.

Do you have the note about Octopus's changes to tariffs?

Jonathan

[roubaixtuesday]

Yes. I'd start with:
• Charging the battery in every cheap rate window
• Running washing machine, dishwasher etc during the cheap rate window
and studying the usage once those are in place.

Do you have the note about Octopus's changes to tariffs?

Jonathan

Not seen any note.

The battery roughly matches our daily usage, so I think we don't need to think about timing of demand, we can just rely on the battery.

[al_yrpal]

Your electricity is very expensive, mine from Ecotricity is 22p per KW hr, with a standing charge of 54p pd? Gas 5.2p per KW hr.

Al

[rjb]

Get one of those solar boost devices to heat the water in your immersion tank.
Ours gives us free hot water for 8 months of the year before we put the gas boiler on for the CH.

[roubaixtuesday]

Your electricity is very expensive, mine from Ecotricity is 22p per KW hr, with a standing charge of 54p pd? Gas 5.2p per KW hr.

Al

Thanks! I haven't looked at tariffs much yet, note that's not my current tariff, it's a tariff which allows export. But for sure worth looking elsewhere at some point.

[roubaixtuesday]

Get one of those solar boost devices to heat the water in your immersion tank.
Ours gives us free hot water for 8 months of the year before we put the gas boiler on for the CH.

Decided against, £500 to fit and very limited gain - in fact loss as it's actually more economic to export the leccy and heat the water with gas.

If we want to we can just turn on the immersion heater, which would default to solar anyway.

[roubaixtuesday]

Installation all complete, and bureaucratic hoops to get export permitted duly jumped through.

With wall to wall sunshine this week, we're getting 20kwh daily generation and a substantially negative electric bill, and even including gas for hot water, probably an overall negative total bill.

It varies a lot though, from 2.5kwh on a very dark and wet day to this on sunny days. I'd guess overall zero electric bill on average for March climate, and perhaps over the year as a whole. Obviously will be very seasonal.

The control system (Fox ESS app) leaves a lot to be desired, though improvements are promised; it's both more complicated than it needs to be and lacks ideal functionality on control of batter charging and discharging.

Here's yesterday's chart.

[Jdsk]

Well done.

Did you stick with the 5 kW hr domestic battery?

Jonathan

[Jdsk]

...
The control system (Fox ESS app) leaves a lot to be desired, though improvements are promised; it's both more complicated than it needs to be and lacks ideal functionality on control of batter charging and discharging.
...

Is there a support forum? Official or unofficial?

Jonathan

[PDQ Mobile]

Installation all complete, and bureaucratic hoops to get export permitted duly jumped through.

With wall to wall sunshine this week, we're getting 20kwh daily generation and a substantially negative electric bill, and even including gas for hot water, probably an overall negative total bill.

It varies a lot though, from 2.5kwh on a very dark and wet day to this on sunny days. I'd guess overall zero electric bill on average for March climate, and perhaps over the year as a whole. Obviously will be very seasonal.

The control system (Fox ESS app) leaves a lot to be desired, though improvements are promised; it's both more complicated than it needs to be and lacks ideal functionality on control of batter charging and discharging.

Here's yesterday's chart.

Screenshot 2026-03-19 125554.png

I am interested in your ongoing experience.

One thing, in particular, puzzles me.

Why does the chart show 6.4 "discharged", yet only 5.4 "consumed"?
Plus 0.3 kwh "imported".

[roubaixtuesday]

Installation all complete, and bureaucratic hoops to get export permitted duly jumped through.

With wall to wall sunshine this week, we're getting 20kwh daily generation and a substantially negative electric bill, and even including gas for hot water, probably an overall negative total bill.

It varies a lot though, from 2.5kwh on a very dark and wet day to this on sunny days. I'd guess overall zero electric bill on average for March climate, and perhaps over the year as a whole. Obviously will be very seasonal.

The control system (Fox ESS app) leaves a lot to be desired, though improvements are promised; it's both more complicated than it needs to be and lacks ideal functionality on control of batter charging and discharging.

Here's yesterday's chart.

Screenshot 2026-03-19 125554.png

I am interested in your ongoing experience.

One thing, in particular, puzzles me.

Why does the chart show 6.4 "discharged", yet only 5.4 "consumed"?
Plus 0.3 kwh "imported".

The grid export has used some of the battery storage. The way it goes on a sunny day is:

- solar charges the battery up to full as well as supplying house load
- solar then goes to house load and export to the grid (at cheap rate, 10p/kwhr)
- The battery is then forced to discharge at peak rate (4-7pm, 29p/kwhr)

On this particular day the total battery discharge is higher than the house useage

Hope that makes sense.

The graphs get a bit confusing with multiple overlays, here's the same day with grid export superimposed,

[Jules59]

I have a 6.6kW solar panel array (the max our roof design would allow), 14.5kWh battery and Zappi 7kW car charger.

Octopus are lowering their tariffs in April.

During the 5 hr night time low rate (5.2p/kWh) we will charge the car , charge the battery, heat the hot water and run the washing machine and dish washer if required.

Even in the dark winter the battery is big enough so that we only occasionally import at the high rate (28p/kWh) . In winter the battery will be down to 10% before it recharges whereas in summer it'll be up at around 90% so doesnt need to much to top it up.

Yesterday (a sunny day in late March) we exported 24kWh at 12p/kWh as we were away from home and only a few electrical things were running , including the pumps for the sewage treatment plant. We imported only 3.4Kwh during that 24 hr period.

Our big issue is the heating oil as there is no gas supply in my neck of the woods, and that has more than doubled in price - so we are trying to eke it out until it gets warmer and then not required until next winter.

[Jules59]

We're getting solar via local authority scheme.

Recommendation is for 14 panels, 450W per panel so nominal 6.3kW, and 5kwhr battery.

10 or 15kwhr batteries are available at a price.

We have an immersion heater, so will top up hot water which is another energy store.

We don't currently have an EV but will likely get one when we next change our car (and will get a charge point fitted while we're at it).

Current usage is ~8kwhr per day average

5kWhr battery feels small to me? But maybe another 5 (£1200) isn't worth it.

Any rule of thumb/ experience to offer?

From my limited experience I think the best way to run these systems is to have a battery big enough to cover your average daily consumption. That way in the winter when you have little solar generation you can charge up at night on a cheap rate and run the house on the battery. When solar generation improves with the weather your battery will need less to charge up at night as the solar will be supplying part of the house load. When you hit 100% SOC you can export the solar excess which pays well compared to the cost of charging at the cheap rate .

Our average daily consumption {15kWh) changes little throughout the year as we dont heat the house electrically and so I opted for a similar sized battery.

Ive omitted the BEV from those figures.

[Jules59]

...
The control system (Fox ESS app) leaves a lot to be desired, though improvements are promised; it's both more complicated than it needs to be and lacks ideal functionality on control of batter charging and discharging.
...

Is there a support forum? Official or unofficial?

Jonathan

I have a FoxESS system.

Ive found the phone App better than the desktop dashboard. Both are somewhat unintuitive and Ive needed help from the FoxESS community to understand what Im doing.

Here is what it looks like

https://www.facebook.com/groups/foxessownersgroup

Ive found it very helpful with a lot of knowledgeable people happy to reply to questions both basic and complicated. Its got a little swapped with Australians recently - who have gone mad on solar power as their installations are costing half that in the UK due to Gov assistance. They go for big batteries too as grid failure is a real issue in parts of Oz these days and want EPS backup.

Zappi (BEV charger) Similarly helpful FB group with links to specific issues.

https://www.facebook.com/groups/1473299693471546



I does take a bit of perseverance to get to grips with devices.

[roubaixtuesday]

Well done.

Did you stick with the 5 kW hr domestic battery?

Jonathan

10