Heat Pump running cost sensitivity analysis.
I now have a years worth of data for my system and have produced a spreadsheet to try to understand the cost drivers and which levers to pull. From the outset I considered the heat pump/solar/storage as an integrated system to make use of the lowest available TOU tariff.
The running costs…
My annual bill last year was £1737 including charges. The TOU tariff is Octopus Cosy for the heating season and then Go in the summer season. This running cost is less than mains gas heating for my UK detached 4 bed Victorian house, mostly well insulated, heated to 19 degrees for 19 hours a day. We do use a lot of hot water which pushed up the all year round baseload to 16kWh a day.
The attached screenshot shows all of the inputs required that affect running cost - it is a long list…
note how the coldest months are £300, a bit of a shock if you do not know that is coming! In the summer the costs are mostly just standing charges. The battery works hardest in winter cycling twice a day so that heating is on continuously at the cheapest rate and never at the peak rate 4pm to 7pm. The average rate over the entire year was 16p/kWh ( the summer go tariff at 8p is used to the maximum when there is no solar).
But what if I just installed a heat pump?…
Had I not installed a battery I would have to resort to scheduling to avoid expensive TOU tariffs. This is difficult to do and still be comfortable, even with triple dip TOU. I assumed you can move 50% of the demand and still keep the comfort. The result is £2883 per annum or 22p/kWh.This is an increase of £1146 over the year, or a 5 year pay back on the solar inverter battery combo.
The most expensive option is the battery storage but the savings are nearly as much as solar and will just get cheaper over the years.
Here is just the 8kWh battery storage option and it gives £2329 annual running costs with a saving of £554. Again a 5 year payback.
My domestic heat pump system is 8kW rated but it can reach 9.5kW, my heat loss is 8.5kW at -1C. It comprises a SamsungHTQ heat pump plus 3.6kW solar panels with hybrid Solis inverter and 10kW Dyness (8kW usable) storage. Solar cost was £2500 partly installed by myself on a ground floor garage roof. The battery would normally be £2500 but I bought used ones for half the price. The Heat pump and pipework was around £6k and again I did most of it myself using an existing DHW tank and did not apply for the grant due to delays and conditions. The grant would probably cover the labour if not doing it all yourself say £17.5k total. I know many people are quoted far more but all properties are different and mine was a straightforward conversion. It replaced an oil fired boiler with annual energy costs of both electric and oil of nearly £3k annually so a no brainer really…
The saving over oil is £1.4k annually making the payback 12 years. There is no payback on mains gas unfortunately but as the above shows if you are paying much more than 22p a unit for electricity on average it may be worth getting battery storage especially if you already have a suitable solar inverter.
The availablity of low cost TOU in the future is always a concern as many consumers take up the option making them more expensive.
It is a very complex subject. My spreadsheet may be wrong and I apologise in advance if it has errors but I would be interested to know if these annual running costs seem plausible from your own experience…