Returns (ROI) doesn't seem correct


I am trying to work out my ROI on my DIY solar and the returns graph just doesn’t seem to add up, I think I am just misunderstanding how it is calculating the ROI.

I have 4 x 260w (1kw) of panels and a few batteries I use to shift my power usage for my agile power tariff but I am using 15.5p in pvoutput as an average p/kwh, I would of said very roughly this would save me around £120 > £160 per year.

Solar was installed end of July last year and I have made some improvements since it went in, bigger batteries and I charge overnight now as well.

So in the nearly 9 months installed I have generated 531kwh x 15.5p has me at £82.31 and the amount generated has improved with the batteries and charging etc so I might get to the £120 ish per year, maybe more.

Total system cost was roughly £500 so I would of thought £500 / £120 would have me around 4 and a bit years ROI, not counting for derate, inflation and deprecation but the returns graph looks like this with my ROI Jun 2035.

You must have zeroed out the Performance Derate, Inflation cost and the Asset Depreciation to still have the system value the original £500.

Normally when the the Net Position minus the System Value has the Returns equal the System cost is when the ROI is zeroed out. Everything after that is Profit.

The monthly FIT credit appears as 0.00

Check that the Average FIT Credit greater than 0, otherwise no export credit is added to the monthly return.

how do I even get here?
I have checked like all the menus and cant find it and even searched through the help menu and still couldn’t.
last resort I changed the web address to roi.jsp and it loads but for the life of me cant work out how to get there any other way.

Your Outputs>MORE>Returns>Calculate

1 Like

Sorry for the late reply.

Just on the FIT credit, I am actually zero export but one of my readings is slightly high/low for consumption vs production so it shows as export. What I have done is set the tariff in the settings to be 15.5p import and 15.5p export as it is all energy saved and used by the house.

Without zeroing anything out and leaving the defaults as below;

I get the following;

I still don’t understand how it is calculated, if you take aug 2020 above it has FIT credit £1.36, Energy Savings £8.70 then month total as £3.18 surly that should be the two together £10.06 but it is only £3.18.

Also if I go back and look at Aug2020 I produced 79.133kWh and exported 15.485kWh so 94.618kWh generated so £14.67 saved.

If I take the avg for the last 280 outputs like the calc it is 2092Wh so if I take this as the average for the year that is 763.58kWh x 15.5p is £118.35 a year.

£500 / 118.35 = 4.22 years

The returns calc has me at nearly 10 years.

Any ideas ?


The Daily Charge of 0.222 needs to be accounted for -

Month Total = FIT Credit + Energy Savings - Daily Charge
= 1.36 + 8.70 - (31*0.222)
= 3.18

The calculation takes the average for all days (280) recorded rather than for that specific month.

The 0.284kWh export per day for all 280 days including months where the system exported close to 0.

Ah ok that is the bit I am missing, thank you for the explanation.