@batalto, we run at about 500W/hour, but things spike as an average with the dishwasher, dryer and the oven, which really pulls us up and drags us upwards of 20kWh per day. A lot of that, thankfully, is offset on a daily basis via the PV.

As a winter project I’m going to try and work out how much our smart home tech and IT costs to run. We’ve got about 35-50 devices connected to the WiFi at any given point in time and I’m guessing that adds up in a hurry.

Posted by: @derek-m

@atommyk

I think that it could be due to all the 'energy saving' devices that Mars has installed. 😎 

I think you’re right - imagine what our energy consumption would be like without them 😂

Posted by: @majordennisbloodnok

Posted by: @markc

Thanks for all the data and link to PVGIS. The PVGIS spat out figures that were inline with the data from Majordennisbloodnok.

I have a daily average of 16kWh of non ASHP usage. I'm breaking this down to 12kWh in the day and 4kWh at night.

This would mean that without batteries, May, June, July and August would be generating excess electricity that I couldn't use.
These are also the months where the ASHP is not needed.
From the SEG I imagine this to be worth £50 per year. (1209kWh x £0.04)

So the 6kWp system would generate 4791kWh that I could use. At the current price of £0.34 that equates to £1628 saving per year.

A £9k installation therefore would take 5.5 years to pay for itself.

Not sure about the SEG, tbh @markc. We went instead with the Octopus agile outgoing tariff which is a variable export rate. Our May, June, July and August figures as you can see in the spreadsheet equate to Octopus paying us £75, £63, £95 and £89 respectively. By my reckoning those four months alone earned us £322 after we'd used all the solar leccy we could. Given that's already £270 over and above your £50 estimate, I'd guess you'd want to factor that into your ROI calculations.

This does, of course, depend on you not using something like Octopus Go; they don't allow both those tariffs together for obvious reasons.

Although you can't have Octopus Go with Octopus Agile outgoing, there have been users using an EV tariff from other suppliers (e.g. EDF Go Electric) combined with the Octopus Agile Outgoing tariff.

This is difficult if not impossible right now given the mess in the energy market....

Posted by: @markc

Thanks for all the data and link to PVGIS. The PVGIS spat out figures that were inline with the data from Majordennisbloodnok.

I have a daily average of 16kWh of non ASHP usage. I'm breaking this down to 12kWh in the day and 4kWh at night.

This would mean that without batteries, May, June, July and August would be generating excess electricity that I couldn't use.
These are also the months where the ASHP is not needed.
From the SEG I imagine this to be worth £50 per year. (1209kWh x £0.04)

So the 6kWp system would generate 4791kWh that I could use. At the current price of £0.34 that equates to £1628 saving per year.

A £9k installation therefore would take 5.5 years to pay for itself.

I went a bit OTT with my ROI forecasting and downloaded hourly data from PVGIS. I don't suggest that you do the same necessarily, but it's worth noting that because of the peaks and troughs of solar power - which I imagine would be much more pronounced with minutely data - it's not so easy to just take daily or monthly figures. Not only will you generate excess power in May - August, but it's highly likely that with a 6kW array you'll have excess from March - October as well, just on a lower level. Furthermore, since many hours are cloudy but you can't just stop using electricity, you'll also import more electricity than you are predicting. Of course you can affect this with different usage patterns, but just be mindful that your results will be worse than predicted when aggregated to a daily or monthly level.

Also with regards to monetary savings, don't mistake a kWh used to a 34p saving. Yes, you can use a solar diverter to heat up your water tank, but this wouldn't have cost 34p/kWh of heat to do so otherwise because you have a heat pump. Yes, you can run the washing machine and dryer one day because it's got a sunny forecast, but did you need to do a wash load yet? Did you need to use a dryer instead of hanging clothes up? You could overheat your house with the heatpump and not use it at night or some of the next day because it's sunny, but this makes it less efficient and wouldn't have used nearly as much electricity to keep it steady. The true ROI should be done on how much cheaper your bills are. Having a saving figure by means of PV usage of £1628 doesn't mean your electricity bill will drop by £1628, and if it didn't, then did you really save £1628?

I don't mean to discourage you from solar, and I recently paid the deposit on a similar array at a similar cost, I just don't want you to be either discouraged by real world results or misled by simple calculations which was my error when I first started calculating this for myself.

For reference, I'm optimistically forecasting PV production of 5808kWh of which 3520kWh would be exported, and imports of 2030kWh. This gives me a saving of £919 with usage of 4315kWh. However, if I use monthly figures using three quarters of my electricity in the day like you have assumed, then this comes to 2646kWh exported and only 1153kWh of imports which is a saving of £1181, almost 30% larger!

@oswiu get a battery - it smooths out those peaks and troughs as well as covers you over night

@batalto I modelled a battery, but despite it's benefits it increases the time to pay back, possibly up to the lifetime of the battery depending on inflation, although I didn't look at using it with cheap overnight rates. Plus my wife and I agreed to prioritise a heatpump, and we certainly don't have unlimited dosh!

@oswiu my battery accounts for roughly 32% of my total power use. Not sure how you modelled it, but its a solid investment in my view. I've been tracking its benefits for the last 3 years of having one and with a heat pump its basically invaluable. You can see my data below I'm already on track for around £1.5k in savings from having it this year. Frankly that figure is larger now my peak power is 39p vs 15p it was - Winter is coming

As a note, I buy a lot of power because of the heat pump and I have a battery tariff so I fill them on a cheap rate.

For the months I bought power:

Jan 1840

Feb 1060

Mar 895

Apr 574

May 187

Jun 185

July 122

Aug 200

Sept 266

@batalto very interesting real world figures, thanks! It's not that I don't want a battery - and indeed these figures show roughly what I had predicted for our system, it's just that we suffer from infinite wants and a finite bank balance. I'm hoping by the time we get an EV, there will be some vehicle to home/grid options out there