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The ongoing saga of getting an installer for my air source heat pump, battery storage and solar is continuing but nearly complete. I have now got a price that i can work with but im at the last step of calculating how long it will take to pay back my initial outlay.

I have gone over this a few times and calculated different amounts on each occassion so nothing would surprise me if i had missed something out or calculated something twice.

So below is my calculations based on some facts, some estimates and some prices that can change at any moment.

A couple of facts:-

Total Gas usage per year – 16,500KWh, including hot water and gas hob

Total Electricity usage per year – 5,800Kwh this includes my plug in electric car usage.

Total cost of installation circa £27,000 ….. £10,000 of which is paid by Government grants leaving £17,000 to be paid using the government facility of an interest free loan over 10 years. This works out as £142 per month, £1704 per year.

I have a couple of existing solar array which output 3,000kwh per year

Installation includes:-

3 No 15 kwh home batteries 45kwh total

A 9kwh air source heat pump (no tank as im keeping my combi boiler as back up and for hot water)

17 No. 480W solar panels (still waiting on estimated solar production from the panels)

Estimate –

Assuming my air source heat pump has a COP (coefficient of performance) of 3.0, I estimate total electricity usage for the pump to be 5,000 kwh as …….. 3.0 (COP) x 5,000kwh = 15,000kwh. As noted above my total gas usage is 16500kwh and that includes hot water and gas hob, so taking 15,000 kwh for heating alone is probably to high but better being high than low.

Assuming using Octopus Intelligent Go I estimate i will fill the batteries each night @ 7p per kwh…… so 45kwh x 365 x 0.07 = £1,149.75 total cost of electricity for the year.

Now for the Math

I take 45kwh x 365days = 16,425kwh…….. but i only use (Total Electricity usage per year – 5,800Kwh this includes my plug in electric car usage) + 5,000 kwh estimated for ASHP use…….. 10,800kwh.

16,425 – 10,800 = 5,625kwh which can be sold back to the grid @15p per kwh…….

5,625 x .15 =

.**£843 profit**Similarly i can sell my solar panel output back to the grid for 15p per kwh. I dont have my predicted solar output for the new panels so i have estimated as follows…. 17 No 480W panels = 8,160kwh max output, im assuming 4,500 kwh output from these as some are North West facing, not ideal. Therefore including my existing 3,000kwh output that makes 7,500kwh x .15p =

**£1,125 profit.**So total profit of £843 + £1,125 =

**£1968 per year / £164 per month**Total monthly payment looks like £235

Total monthly income looks like £164

so it looks like i will be paying £71 per month on average over the year but at present im paying £200 per month for gas and electric so could it be that i am making a profit of £129 per month or am i missing something?

(i have not taken into account standing charges and the gas i will continue to use for hot water and gas hob. I have no idea how to calculate the gas usage so i would appreciate any imput on this.)

The only person who got all his work done by Friday was Robinson Crusoe.

Anything i post over three lines long please assume it is an article lol.

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