Having proven the cash and carbon benefits of solar, battery and EV set up in 2020, we spent 2021 planning an installing a major upgrade to the system, to really push the limits on carbon reduction, and to enable larger financial savings. In short we added some more solar panels, doubled our battery storage capacity, and added an Air Source Heat Pump to replace the oil boiler that previously supplied our central heating and hot water.

On 01 January 2022 the upgraded system went live, and the financial and carbon savings really started rolling in. Two very important elements which drive the savings are our Evergreen Energy heat pump, which eliminates heating oil, and our Octopus Energy smart grid tariff, which enables us to charge our total 168 kWh of both domestic and EV batteries at cheap off-peak rates. Click the images below to visit our suppliers’ websites for more information.

The two infographics below present, in ultra-summary form, the overall cost & benefit of the upgraded system for the first half of 2022 from 01 January to 30 June.

To see the detailed monthly reports please click the link below. Otherwise just scroll down to read more.

Where our electricity came from & where it went

The first graphic is pretty self explanatory. The inner circle shows where our electricity came from. The outer ring shows where it went. As you’ll see, a pretty substantial slug of it came from ‘home brew’ solar generation, for which we paid £0. The split between solar, off-peak and peak electricity gives us a ‘blended average’ price for the electricity we used.

This second graphic takes this input-output energy mix and the resulting blended average price per kWh as its starting point, and shows the cash and carbon benefits we’ve captured from the operation of our Smart Energy system. If you click the image, you’ll see a copy of the full Year To Date report in PDF.

What our electricity cost & how much cash and carbon we saved

  • The red ‘bullseye’ in the middle is total cost we have paid to date for grid electricity imports – we pay nothing for solar. This powers everything: heating, hot water, all at-home charging of our EVs, normal domestic use, as well as firing Anne’s pottery kiln several times a month.
  • The middle circle shows the savings we’ve made:
    • by using electricity to power our EVs and not buying petrol;
    • by using electricity to power our heat pump and not buying heating oil;
    • by using electricity at the blended average prices our solar & grid mix generates, instead of paying for standard rate electricity at the current price cap rate per kWh;
    • by receiving the minor ‘Feed In Tariff’ (FIT) incentive for some of our solar generation;
    • by receiving the ‘Renewable Heat Initiative’ (RHI) incentive for our heat pump.
  • The outer circle shows how many kg of CO2 emissions we have removed from the atmosphere:
    • by driving EVs instead of petrol/diesel cars;
    • by heating our home and hot water with an Air Source Heat Pump not an oil-fired boiler;
    • by using our solar generated electricity and our energy supplier’s 100% renewably-generated electricity to power everything, as opposed to the UK average emissions per kWh for electricity suppliers.

We’re publishing monthly blog posts with performance data in this thread. We have also updated the financial payback calculations to reflect the upgraded system and present an overview here.

The remainder of this post gives a summary of the main items we focussed on for the 2021/22 system upgrade to effectively turn our home into a ‘Smart Energy Island’

  • Although our existing 24 panel, solar array, rated at 7.5 kWp (kilowatt peak – that’s the standard measure of solar performance under ideal conditions) generated a healthy 5.77 MWh over a year, it was now time to get the final eight panels installed, to complete the planned 10 kWp, 32 panel, array. That had to wait until Anne’s ceramics studio could be built. COVID delayed that by a whole year. The image above shows the completed array: the new bit is on the left, on the studio building with the built-in greenhouse.
  • The 8 final panels are built ‘roof integrated’ actually into studio roof, rather than ‘roof mounted’ on top of it. The panels effectively are the roof of the studio, which handily saves the cost and weight of the slates which would otherwise have been used. Happily, because this ‘solar roof’ sits at a helpful angle facing between the morning and midday sun, a 25% expansion of the solar array is producing about 30% more electricity.
  • Some of that solar production is going into the same to EVs as before: a 100kWh Tesla Model X, and a 30 kWh Nissan Leaf. No change there.
  • The major initial benefit of expanding our solar production was to have more solar surplus energy to store in the two 13.6 kWh Tesla Powerwall batteries we have now installed.
  • But we thought we could probably do more, so we sat down and really thought about it. We did a detailed Cost:Benefit analysis of potentially integrating a major new element into our Smart Energy solution for the home. That element would have to enable us to tackle the really tricky bit of carbon reduction: domestic heating and hot water. We had already done the easy bit by switching to EVs, but we knew that if we really wanted to make a difference we’d have to decarbonise our home’s heating system. And it’s not just us: it’s probably the biggest single challenge the UK faces if we are to achieve Net Zero Carbon by 2050. Just how do we to keep households warm, whilst simultaneously eliminating the 85% of typical household carbon emissions that domestic heating causes?
  • Carbon-wise that led us to the real biggie. We took the plunge and binned our oil fired central heating and replaced it with an Air Source Heat Pump (ASHP) system from Evergreen Energy. We were burning an average of 4,967 litres of heating oil a year. Each litre of heating oil burned emits 2.96 kg of CO2. Because we’re now heating the home and our hot water with 100% renewably-generated electricity instead (our solar and Octopus 100% green grid import on the Go Faster tariff), that’s 14.70 tonnes of carbon dioxide emissions we’ll be taking out every year. That’s in addition to the six tonnes a year we were already saving by using 100% green electricity to ‘fuel’ our EVs and by avoiding grid electricity suppliers who don’t supply exclusively renewably-generated power.
  • Money-wise the fuel cost savings are significant too. Those 4,967 litres of oil cost of £2,640 a year, assuming our the three year average cost of £0.53/litre. In the post-Ukraine world oil is now over £1.00 a litre, so our cost-of-oil-not-purchased savings have doubled. Timing is everything!  We predict a cost saving of around £5,000 a year at mid-2022 prices by replacing our oil-fired central heating and domestic hot water boiler with the heat pump.  That’s just for the heating and hot water, not counting the money we save by driving electric cars and filling domestic storage batteries with solar and cheap off-peak electricity for use at times when electricity is expensive.     
  • And speaking of timing, we squeezed the ASHP in before the abolition of the Government’s Renewable Heat Incentive (RHI) programme in 2021, although the economics would still have worked on oil cost savings alone – all the more so post-Ukraine. If we were installing it in 2022, we’d be using the replacement support scheme, a £5,000 Government grant for eligible ASHP installations.
  • Although heat pumps are at their most efficient when coupled to underfloor heating systems in heavily insulated modern houses, we simply couldn’t rip out 25 radiators in our Victorian-era home without massive disruption. So we accepted a degree of inefficiency and used the ASHP to heat those radiators. But we compensated for this by comprehensively upgrading each radiator with a Smart Thermostatic Radiator Valve (TRV), which we control with Apple HomeKit, to ± 0.5 degrees celsius precision. This enables us to ‘zone’ the house on a room-by-room basis, basically avoiding heating unoccupied space.
  • Finally, all this GreenTech was pushing the limits of what the standard single phase grid supply could safely provide. It is likely that our two EVs and two batteries will all start charing at the same time, particularly in winter, when they’re programmed to switch on at the start of the off-peak super-cheap window for importing grid energy. If Anne’s pottery kiln fires up at the same time, and the heat pump switches itself on, then we’d be overloading our grid connection and could blow the fuse. The solution was to upgrade from a single phase to a polyphase supply. In most of the UK that would be to a three phase connection; in our rural Northumberland location our local Distribution Network Operator (DNO, Northern Powergrid in our case) could only provide a two phase supply.
  • Having gone through the DNO supply upgrade process, we then had to ensure our electricity supplier (Octopus, in our case) upgraded the single phase smart meter to a polyphase unit. This is essential to continue to receive the ‘smart’ Time Of Use Tariff on which much of the cost-saving economics depend.

The time-lapse below shows the installation of the roof-integrated solar panels into the studio roof. They’re exactly the same panels as the eight on the garage roof in the background of the picture at the top of this post. The only difference is that they form an integral part of the roof, rather than sitting on top of it.

One comment on “Major upgrade to our GreenTech

  • Nik Elliot

    Love your setup! We are in the process of doing something similar! We have the Powerwall 2 installed and have built a “shed” to put the 10Kw of solar onto! ASHP, 14Kw EcoDan got installed under the RHI scheme last year. We also went wireless TRVs with the Honeywell system. Car is Tesla Model S being charged with Zappi 2. DNO giving us grief about export limiting, can you advise which device you used please?

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