No good with phone screenshots and webpage seems different but here are my figures from the phone for june
pv prod 1250.5
to load+batt 351.7
to grid 898.8
self consump 28%
load consump 347.6
from pv +batt 340.8
from grid 6.8
self suff 98%
Here is my image for the month of June
I calculate (as does your ROI sheet you should have been given) from the bottom two values
PV Production 1250.50 kWh (772.40 kWh)
To Load & Battery 351.70 kWh (384.60 kWh)
To Grid 898.80 kWh (387.80 kWh)
To Load and Battery 351.70 kWh @£0.2443 import cost using my rates = £85.92 (£93.96)
To Grid 898.80 kWh @£0.12 export at flat rate Octopus export = £107.86 (£46.54)
Totals £193.78 (£140.50)
I suspect you are going to do well with your system, and smash £1200pa.
My first year ROI was given as £1195, and I achieved £1243.42
I calculate (as does your ROI sheet you should have been given) from the bottom two values
PV Production 1250.50 kWh (772.40 kWh)
To Load & Battery 351.70 kWh (384.60 kWh)
To Grid 898.80 kWh (387.80 kWh)
To Load and Battery 351.70 kWh @£0.2443 import cost using my rates = £85.92 (£93.96)
To Grid 898.80 kWh @£0.12 export at flat rate Octopus export = £107.86 (£46.54)
Totals £193.78 (£140.50)
I suspect you are going to do well with your system, and smash £1200pa.
My first year ROI was given as £1195, and I achieved £1243.42
A bit cheeky of me (sorry team if this is) for adding my personal link
But you could supplement your income to help your ROI by joining Axle energy.
You get £25 by signing up, and at least £10pm minimum, so you gain £120pa at the very least.*
https://vpp.axle.energy/landing?ref=R-ZIFGMMKO
Here is a thread from Archy de Berker CTO of Axle Energy
viewtopic.php?p=10789#p10789
* Even if you had to buy your electric in to top your battery up @30p kWh, you can sell each back for £1 kWh and you get your export rate from energy supplier on top.
But you could supplement your income to help your ROI by joining Axle energy.
You get £25 by signing up, and at least £10pm minimum, so you gain £120pa at the very least.*
https://vpp.axle.energy/landing?ref=R-ZIFGMMKO
Here is a thread from Archy de Berker CTO of Axle Energy
viewtopic.php?p=10789#p10789
* Even if you had to buy your electric in to top your battery up @30p kWh, you can sell each back for £1 kWh and you get your export rate from energy supplier on top.
Do you still get your suppliers export tariff in addition to the £1/KW from Axle?
Yes anything you get from Axle is on top of your export from energy company. Octopus have just launched a similar product for customers by the way.
Since April I've made £62 from Axle. My export is limited to 5kW.
7.36kWp solar array made of 16x Jinko Tiger Neo 460w panels. 8 ESE, 8 WNW facing, Fox EVO 10kWh with 10kW inverter. Installed April 2026. Running ModBus via Elfin EW11A, learning Home Assistant
As mentioned by MattyS, it's on top of your export rate.
So £1.12 per kWh if you are on fixed export, it's hard to go wrong, and a minimum of £10 pcm if you don't get sessions.
If you had to charge battery by grid, it's still going to make a profit for you.
They email you shortly after a session finishes, just to remind you to check that you have been 'released' and system is running as normal.
Just to add to this thread.
My install has been in operation 9 months.
The forecast by the installers was 6MWh per year and it’s virtually bang on.
So far in 9 months generated 4.3MWh and exported 3.3MWh
I don’t do anything fancy, just let the solar meet house and battery demand and export the rest, fill the car off peak on IOG never from solar.
Once a month in the summer have drained the battery to 10% SOC.
Savings have been in front of estimate, compared with the previous year, in the 9 months I’ve made a saving of £830.
With July, Aug & Sep to go for the first year should be around £1150 to 1200.
ROI at this rate will be 6.5 years.
Could make more with pushing out more export or fancy tariffs but really can’t be bothered.
Total solar and battery convert here
8 East, 8 West 450w panels
6KW inverter
1 x 10kw EP11
My install has been in operation 9 months.
The forecast by the installers was 6MWh per year and it’s virtually bang on.
So far in 9 months generated 4.3MWh and exported 3.3MWh
I don’t do anything fancy, just let the solar meet house and battery demand and export the rest, fill the car off peak on IOG never from solar.
Once a month in the summer have drained the battery to 10% SOC.
Savings have been in front of estimate, compared with the previous year, in the 9 months I’ve made a saving of £830.
With July, Aug & Sep to go for the first year should be around £1150 to 1200.
ROI at this rate will be 6.5 years.
Could make more with pushing out more export or fancy tariffs but really can’t be bothered.
Total solar and battery convert here
8 East, 8 West 450w panels
6KW inverter
1 x 10kw EP11
My point further back though was in my case, the system itself uses about 4KW per day so these numbers should be deducted from your return because you are counting a saving on something you would never previously would've paid out for.CDubbs wrote: ↑Sun Jul 26, 2026 10:25 am Savings have been in front of estimate, compared with the previous year, in the 9 months I’ve made a saving of £830.
With July, Aug & Sep to go for the first year should be around £1150 to 1200.
ROI at this rate will be 6.5 years.
Could make more with pushing out more export or fancy tariffs but really can’t be bothered.
Total solar and battery convert here
8 East, 8 West 450w panels
6KW inverter
1 x 10kw EP11
I'm not saying the return won't be good, I just believe the figures provided are a bit misleading.
I downloaded a full month of data from Octopus pre-install.
Averaged 15.06 kWh daily
After install according to Fox
Averaged 16.56 kWh daily
~10% difference, which does seem around average for DC->AC (and back from DC->AC when discharging battery)
I am sure that MCS calculations have a 10% loss baked into them, be poor if they didn't.
I do not know why your system is reporting 4kWh extra use, though often people do consume more because they have solar and rinse it.
Averaged 15.06 kWh daily
After install according to Fox
Averaged 16.56 kWh daily
~10% difference, which does seem around average for DC->AC (and back from DC->AC when discharging battery)
I am sure that MCS calculations have a 10% loss baked into them, be poor if they didn't.
I do not know why your system is reporting 4kWh extra use, though often people do consume more because they have solar and rinse it.
When you say "according to fox" where do you get that reading?
If I take 1 day at random (18/6/26) and total up all of the "total load" column from the daily download sheet and divide by 12 (because it reports usage as kw/hour and the reads are at 5 min intervals) I get my daily usage as being 8.35KW.
This is an indicative figure because it is not a real time read of the system but snapshots at 5 min intervals but should be somewhat close to an actual usage because of the number of data points.
If however I look in the app, the reported load consumption for this day is 11.0 KW. That difference is 2.65KW. I was told by my supplier that the app displays post system consumption which is clearly wrong but it does appear that the downloads only include what you use in your home and don't include the system usage. It seems fair to say that the difference between those figures is what the system has consumed.
Someone also advised using the energy stats app which for the above date shows my inverter consumption as 3.0KW.
I had fox monitor the system a few weeks back and they couldn't find anything wrong but I've still not had them explain to me how much the system should use.
If I take 1 day at random (18/6/26) and total up all of the "total load" column from the daily download sheet and divide by 12 (because it reports usage as kw/hour and the reads are at 5 min intervals) I get my daily usage as being 8.35KW.
This is an indicative figure because it is not a real time read of the system but snapshots at 5 min intervals but should be somewhat close to an actual usage because of the number of data points.
If however I look in the app, the reported load consumption for this day is 11.0 KW. That difference is 2.65KW. I was told by my supplier that the app displays post system consumption which is clearly wrong but it does appear that the downloads only include what you use in your home and don't include the system usage. It seems fair to say that the difference between those figures is what the system has consumed.
Someone also advised using the energy stats app which for the above date shows my inverter consumption as 3.0KW.
I had fox monitor the system a few weeks back and they couldn't find anything wrong but I've still not had them explain to me how much the system should use.
I've just done the above for a total of 56 days since the install.
Consumption as measured from the download = 429.5KW = 7.67KW/day
Load consumption as measured by the fox app = 654.4Kw = 11.69KW/day
Difference = 4.02KW/day.
Consumption as measured from the download = 429.5KW = 7.67KW/day
Load consumption as measured by the fox app = 654.4Kw = 11.69KW/day
Difference = 4.02KW/day.
My ROI will be calculated as what I am physically paid by my energy supplier for export plus what I have used (as per the download sheet) x difference between my import and export cost (so about 11p per KW) or ~84p per day based on my 7.67KW per day average currently.
Edit, thinking about it it should be the full amount, not difference for home usage so about 23p x 7.67 or ~ £1.76 per day.
Edit, thinking about it it should be the full amount, not difference for home usage so about 23p x 7.67 or ~ £1.76 per day.
If you take the post at the top of this page for your June figures, can you show your working out, and see how it would compare to mine?spiral wrote: ↑Sun Jul 26, 2026 7:39 pm My ROI will be calculated as what I am physically paid by my energy supplier for export plus what I have used (as per the download sheet) x difference between my import and export cost (so about 11p per KW) or ~84p per day based on my 7.67KW per day average currently.
Edit, thinking about it it should be the full amount, not difference for home usage so about 23p x 7.67 or ~ £1.76 per day.
So a full ROI calc for June's figures if you can please.
Unfortunately I can’t do my full figures for June in the way that I want to calculate because I wasn’t passed for export to the grid until 12/6 so can only do the maths using that date onwards as my supplier has no data for scrutiny before this point.
For June my usage as per spreadsheet totalled 146.52KW (7.71 per day). Multiply this by 25p (import cost) = £36.63
Export total was 683.69KW (22.79 per day) . Multiply by 12p (export price) = £82.04
Both added together = £118.67
If I use my June app figures from 12/6 I get:
Export total = 672.9 x12p = £80.75
Load consumption = 226.6 x 25p = £56.65
Both added together = £137.40
Export figures in both the app and the actual payment are pretty close. Where I see a massive difference is in the way they report consumption to include that used by the system when in reality it is lost energy in that without the solar system you would never have had to use that energy.
An analogy would be petrol costs 160p per litre where you live but there is a garage 50 miles away selling it for 100p per litre. It may still be beneficial to do the 100 mile round trip to buy it but your benefit is not 60p per litre because you’re consuming additional petrol to get it.
For June my usage as per spreadsheet totalled 146.52KW (7.71 per day). Multiply this by 25p (import cost) = £36.63
Export total was 683.69KW (22.79 per day) . Multiply by 12p (export price) = £82.04
Both added together = £118.67
If I use my June app figures from 12/6 I get:
Export total = 672.9 x12p = £80.75
Load consumption = 226.6 x 25p = £56.65
Both added together = £137.40
Export figures in both the app and the actual payment are pretty close. Where I see a massive difference is in the way they report consumption to include that used by the system when in reality it is lost energy in that without the solar system you would never have had to use that energy.
An analogy would be petrol costs 160p per litre where you live but there is a garage 50 miles away selling it for 100p per litre. It may still be beneficial to do the 100 mile round trip to buy it but your benefit is not 60p per litre because you’re consuming additional petrol to get it.
I put your full June figures into my spreadsheet to compare (aware your export didn't start until 12th)
So that you can gauge your system ROI to mine.
Mine
Exported: 381.607 kWh (from Octopus) = £45.79
Self-use: 365.4 kWh (from PV & Battery) = £91.35
Total: £137.14
Yours
Exported: 898.8 kWh (from App, Octopus will be close to this) = £107.86
Self-use: 340.8 kWh (from PV & Battery) = £85.20
Total: £193.06
That gives your ~40% higher ROI figure.
Now if you take my own annual ROI of £1200, and you use a conservative 25% figure, that means you should get around £1500pa ROI, and potentially more.
If you sign up for a VPP scheme, then you can gain at least another £120 each year with Axle.
Now if your system is using 4kWh a day to power itself, what matters is what flows in/out of your CT clamp for export payments and what you pull from the grid. If you are using 4kWh a day, then it could be your firmware is old, I don't know.
My increase was only ~1.5kWh each day, so maybe this is something to be looked at, as mentioned maybe a bad firmware version or something.
So that you can gauge your system ROI to mine.
Mine
Exported: 381.607 kWh (from Octopus) = £45.79
Self-use: 365.4 kWh (from PV & Battery) = £91.35
Total: £137.14
Yours
Exported: 898.8 kWh (from App, Octopus will be close to this) = £107.86
Self-use: 340.8 kWh (from PV & Battery) = £85.20
Total: £193.06
That gives your ~40% higher ROI figure.
Now if you take my own annual ROI of £1200, and you use a conservative 25% figure, that means you should get around £1500pa ROI, and potentially more.
If you sign up for a VPP scheme, then you can gain at least another £120 each year with Axle.
Now if your system is using 4kWh a day to power itself, what matters is what flows in/out of your CT clamp for export payments and what you pull from the grid. If you are using 4kWh a day, then it could be your firmware is old, I don't know.
My increase was only ~1.5kWh each day, so maybe this is something to be looked at, as mentioned maybe a bad firmware version or something.
When you say your increase was ~1.5KW is this what you see now v what was used before?
Have you tried a spreadsheet comparison of a daily usage download v what the app says was used?
I will definitely get back in touch with the installers but previously when I did this they got fox to monitor the system and tell me nothing was wrong without explaining anything.
Have you tried a spreadsheet comparison of a daily usage download v what the app says was used?
I will definitely get back in touch with the installers but previously when I did this they got fox to monitor the system and tell me nothing was wrong without explaining anything.
Yes this was a before/after install calculation...spiral wrote: ↑Tue Jul 28, 2026 4:45 pm When you say your increase was ~1.5KW is this what you see now v what was used before?
Have you tried a spreadsheet comparison of a daily usage download v what the app says was used?
I will definitely get back in touch with the installers but previously when I did this they got fox to monitor the system and tell me nothing was wrong without explaining anything.
I downloaded a full month of data from Octopus prior to install, and grabbed around 21 days worth of 30 min readings to get a fair average.
I then took a month of data post install from Fox website, and picked 21 days of data.
The 'increase' of Load was an average of 1.5kWh for a day.
I suppose what I really need as a comparison is someone that has the same system as me i.e.
Fox ESS KH 7KW Inverter
Fox ESS EP6 Plus 5.76KW battery.
Fox ESS KH 7KW Inverter
Fox ESS EP6 Plus 5.76KW battery.
Do you use energy stats?
My 3 previous days inverter consumption there are 5.0, 4.1 and 5.0
My 3 previous days inverter consumption there are 5.0, 4.1 and 5.0
I checked energy stats for yesterday, it claims 5.7kWh to run inverter.
I don't personally care still if that is accurate, I am happy to still calculate the ROI based upon PV self-use/export supplied by Fox.
You can grab figures from the energy stats app, and deduct this from your ROI figures if you like in your spreadsheet.
I am not 100% sure, but I think MCS calcs that installers use and supply to you, include a baked in 10% loss.
I don't personally care still if that is accurate, I am happy to still calculate the ROI based upon PV self-use/export supplied by Fox.
You can grab figures from the energy stats app, and deduct this from your ROI figures if you like in your spreadsheet.
I am not 100% sure, but I think MCS calcs that installers use and supply to you, include a baked in 10% loss.