Major upgrade to our GreenTech

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 from 01 January 2022 to date (we’ll update these images roughly monthly).

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.

Annual Performance Report

So we’ve finally got a full 12 months of data. And we’re very pleased with the results.

Around £5,000 in financial savings.

Over 6 tonnes CO2 emissions avoided.

Over 16,000 miles range charged into our electric cars at home.

Click the image below for the full report, available to view or download as a PDF (16MB)

Annual Performance Summary

If you wish to indulge your inner ElectroGeek, you may be interested in the fully detailed month by month performance reports. We have published this level of detail roughly every month on these blog pages. We have now collated the information into a single PDF, which is available to view or download here. Beware, it’s a large file (c. 55MB) so it may take some time to appear.

September 2020 Performance Report

Finally reached Month 12 of detailed data collection. So now we’ve got a full year’s worth of information on:

  • Consumption: total kWh slurped down by the house and Anne’s electron-munching pottery kiln.
  • Consumption: total kWh ‘fuelled’ into the two EVs.
  • Self-generation: total kWh generated by the 7.5 kWp solar panel installation on the roof.
  • Grid imports: total kWh imported from National Grid, using the 100% renewable Octopus Go smart tariff which provides dirt cheap electricity between 00:30 and 04:30 every night and a slightly below-average cost at all other times.
  • Storage input: total kWh charged into the domestic storage battery, using a mix of only solar generation and off-peak grid electricity.
  • Storage output: total kWh discharged from the domestic storage battery at peak times, avoiding grid imports.
  • Total financial savings from smart electricity generation, storage and discharge over the year’s domestic and pottery kiln consumption.
  • Total mileage charged into EVs, using solar and off-peak electricity.
  • Total financial savings from use of EVs charged on this electricity mix, versus the cost of petrol which would have been required to cover the same mileage in Internal Combustion Engine (ICE) cars.
  • Total tonnes emissions avoided from domestic energy optimisation.
  • Total tonnes emissions avoided by EV use.

You can see or download a PDF summary of the whole year’s data (14MB) by clicking the image below.

Annual Performance Report

Below is the final performance report for the data collection year, September 2020.

It was not a bad month weather-wise, with the Met Office reporting a decent 151 hours of sunshine in our area. The key results are tabulated below.

ItemResult
Solar production524 kWh
Off-peak grid energy imported725 kWh
Peak grid energy imported169 kWh
Peak grid imports avoided by using stored energy from Powerwall battery484 kWh
Total energy consumed (domestic consumption and EV charging)1,418 kWh
Net cost of grid energy, incl standing charge, net of Govt payments for solar£39.88
Cost of 1,162 kWh at UK ‘Big 6’ average rate per kWh£219.75
Saving on 1,162.6 kWh vs UK Big 6 average rate£179.87
Total range charged to EVs, from solar and off-peak grid imports1,194 miles
Actual cost of solar + off-peak grid energy to charge 1,185 miles£15.14
Fuel costs to drive an ICE car 1,185 miles using @35mpg & £1.32/litre£252.55
Saving on 1,185 miles vs cost of motor fuel for same mileage£237.41
Electricity and motor fuel savings in month£417.28
CO2 savings on domestic energy by using solar & 100% renewable grid energy255.2 kg
CO2 savings on 1,185 emissions-free miles versus ICE @ 125.1 g/km240.4 kg
Total CO2 emissions avoided in month495.6 kg
September 2020 Performance Data

The usual monthly calcographic is available for download here or by clicking the image below.

September 2020 Calcographic

August 2020 Performance Report

August 2020 was pretty dull. Coronavirus was still doing its (dull and boring) thing. And the sun only bothered to shine for 136.3 hours in the North East of England. So that meant, inevitably, a pretty dull and underproductive month for our solar micro-generation. However, the Tesla Powerwall domestic battery enabled substantial savings by ‘peak-shifting’. Additionally, the gradual easing of lockdown meant we drove more miles in the EVs. The table below summarises the data.

ItemResult
Solar production564 kWh
Off-peak grid energy imported509 kWh
Peak grid energy imported89 kWh
Peak grid imports avoided by using stored energy from Powerwall battery423 kWh
Total energy consumed (domestic consumption and EV charging)1,162 kWh
Net cost of grid energy, incl standing charge, net of Govt payments for solar£17.26
Cost of 1,162 kWh at UK ‘Big 6’ average rate per kWh£180.21
Saving on 1,162.6 kWh vs UK Big 6 average rate£162.95
Total range charged to EVs, from solar and off-peak grid imports1,185 miles
Actual cost of solar + off-peak grid energy to charge 1,185 miles£13.65
Fuel costs to drive an ICE car 1,185 miles using @35mpg & £1.32/litre£248.97
Saving on 1,185 miles vs cost of motor fuel for same mileage£235.07
Electricity and motor fuel savings in month£398.02
CO2 savings on domestic energy by using solar & 100% renewable grid energy209.3 kg
CO2 savings on 1,185 emissions-free miles versus ICE @ 125.1 g/km238.7 kg
Total CO2 emissions avoided in month448.0 kg
August 2020 Summary

Here’s the link for detailed monthly performance report in PDF format. You can also get the report by clicking the calcographic below.

Follow this link to view the in-month and cumulative impact of August 2020 on payback of the capital costs of our solar, battery and EV charging installation

July 2020 Performance Report

July was a pretty good summer month, by North East England standards. Key results are as follows:

  • 1,215 kWh total energy consumption.
  • 816 kWh solar
  • 314 kWh off-peak grid (100% renewable supplier)
  • 86 kWh peak grid (100% renewable supplier).

Taking into account the minor Government subsidy we receive for solar generation, we once again had a negative net cost of energy, paying minus £5.36 for the month’s electricity.

We fuelled our two EVs (and a Renault Zoe we had on test for the first half of the month) for a total of 758 miles in the month. The ‘fuel mix’ going into the EV batteries was 360 kWh solar and 97 kWh off-peak electricity. This blend produced a total electricity cost for 792 miles of EV motoring of £4.84, or 0.6 pence per mile. Using our normal comparison with a 35mpg OldTech car fuelled at the long-term average of £1.32 per litre, we saved £262 fuel costs in month.

The total net financial benefit in July was £384.93, made up of these £262.08 fuel savings and the £122.86 difference between the price we would have paid for 758 kWh of domestic energy at ‘Big 6’ utility company rates (£117.50) and the net minus £5.36 we actually paid.

Emissions avoided in the month by the combination of solar generation, 100% renewably sourced grid supply, and 792 miles of zero emissions driving totalled 378 kg.

Click the graphic below to download the full report in PDF format.

July 2020 energy input blend and usage

Here comes the sun, here comes the sun, and I say it’s alright…(June 2020)

Other than the ongoing mass death virus thingy and associated economic implosion, June 2020 was an exceptionally pleasant month in the UK. As anyone with solar panels will tell you, it was very, very sunny indeed towards the end of the month, although the MetOffice recorded only about 165 hours of bright sunshine in June in our region, compared to the positively Arabian 269 hours which had beaten down on us in May.

Whatever the Bracknell stats geeks say, we ended up with enough sunshine to produce another month with negative cost of energy. As the calcographic below shows, although we consumed nearly a megawatt of electricity for domestic use and charging EVs during this (still a bit lockdowny) month, we actually ended up £12.19 better off in net terms at the end of the period.

The £36.12 Government payment for 740 kWh of solar generation was more than the £23.93 cost of importing the meagre 225 kWh of grid electricity we did not generate ourselves in the month, which includes £7.50 of ‘standing charge’ fixed fee for grid connection at £0.25/day.

Our two EVs were charged roughly 70% with solar (195kW), plus 30% (82kWh) with zero carbon off-peak energy supplied at only 5p/kWh on the Octopus Go tariff overnight rate. Coronavirus ensured that June 2020 was still a very travel-restricted period, so we only covered 593 miles. However, even over this relatively small mileage, that still added up to fuel savings versus petrol/diesel ICE cars of £160.40. The electric ‘fuel’ for the EVs cost us just £4.10 in the month, which works out at only 0.7 pence per mile! It would have cost us £164.49 to travel the same distance in ICE cars, using our standard mpg calculations.

We also won big-time on our 719 kWh domestic consumption. 76% (545 kWh) was solar, including 374 kWh which was stored in the Powerwall stationery battery during the sunshine hours and used in the evenings. The remaining 24% (173 kWh) was zero carbon source grid electricity from Octopus. And over half of the grid imports were stored during the super-cheapo off-peak hours into the Powerwall and discharged at zero additional cost to us during the peak period.

Taking into account the solar generation payment we received from Government, our 719 kWh of domestic energy cost us minus 1.7 pence per kWh, making minus £12.19 net. If we had bought those kWh at UK ‘Big 6’ average rates, we would have paid £111.37. So that’s a net financial benefit of £123.56 for domestic energy consumption.

Putting domestic energy savings and motor fuel savings together, net financial benefit was £283.96 in the month of June. And the planet was 298.6 kg of CO2 emissions better off too.

Please click the image below for a downloadable PDF of the detailed monthly report. The impact of this month on financial payback of system costs is here.

Covid 19 : Carbon Dioxide Nil (May 2020)

This entire post is available as a downloadable PDF here, if you prefer.

There have been some memorable scorelines over the years.  The two most important of all time being, of course, Nottingham Forest 1 : Malmö 0 and Nottingham Forest 1 : Hamburg 0, to win the 1979 and 1980 European Cup finals.  And, yes, I’d really like East Fife 4 : Forfar 5 to actually happen (and not on penalties, 22/07/2018 doesn’t count).

Another result that really matters occurred in May 2020.  A couple of things came together.  The sunniest spring on record in the UK, with May’s MetOffice stats confirming a stonking 269.6 hours of bright sunshine in East and North East England, our area.  But, on the downside, the Global Zombie Apocalypse Megadeath coronavirus pandemic continued to do its thing.

So, whilst global megadeath was an unreservedly bad thing, on the brighter side, May 2020 gave UK (and the rest of the world) a glimpse of how a low carbon future will look, painting in even more vibrant colours the picture that had begun to emerge in April, the first full lockdown month. 

Pandemic meant pandemonium for the economy.  And that meant massively lower demand for energy due to shutdowns for business and lockdowns for the people. By consequence, that also meant massively less mileage driven on the roads.  

Unless, when it came to driving, you were in the minority which thought might be a good plan to drive a car load of infected people 200+ plus miles from London to County Durham, and then take a 50 mile round trip ‘to test your eyesight’ before driving back to London to lend your moral authority and public credibility to the Government’s campaign imploring citizens to act responsibly.  Honestly?  You couldn’t make it up for a satirical show.  

Now, come to think of it, where’s Malcolm Tucker when you need him? I can barely imagine the weapons-grade Glaswegian invective that would have eviscerated any Downing Street adviser who had decided, erm, to drive a car load of infected people 200+ miles… You get the picture.  Over to you, Armando.

 Simultaneously with massively lower demand, the sun helpfully shone and the wind generously blew, which led, at 12:20 on 24 June, to a record low carbon generation mix of only 60 g CO2 per kWh) at National Grid level.  You can get the Grid Carbon app here.

A tip of the hat to Patrick Erwin for spotting this and posting on LinkedIn.  Responding on that platform, it occurred to me that this was a very clear view of the COVID/Carbon connection in action. 

How curious it is that something as ruthlessly fatal to humans is actually brilliant for the health of humankind’s home planet. 

Basic message: if everybody and everything slows down, the generation mix goes supergreen. 

The real, structural, challenge will be keeping it green when the economy re-ignites.

So how did May 2020 play out at domestic level?  The calcographic below summarises how it went for us.  We hope you like the new graphic style.  Click the image to get a zoomable high resolution PDF.

For those who prefer narrative to calcographics, the main highlights of the month’s performance are summarised below:  

  • We used 1,231 kWh used in total, of which 960 kWh (78%) was solar.  The remaining 194 kWh were grid supplies using Octopus Energy’s ‘Octopus Go’ tariff, which incentivises consumption of dirt-cheap ultra off-peak energy for recharging our Tesla Powerwall and two EVs between 00:30 and 04:30 in the small hours period of very low grid demand.  The month included seven energy-intensive kiln firings for Anne’s ceramics business, which we timed to soak up solar surplus and energy stored in the Powerwall.
  • We only drove 439 miles in the EVs in the month, due to lockdown.  100% of those miles were fuelled with our own solar energy plus (a tiny) 16 kWh of zero carbon grid energy that Octopus actually paid us to use in order to keep renewable generators switched on during the record low demand at 05:00 – 07:00 on Bank Holiday Sunday morning.   
  • Including the small quantity of ‘get paid to use’ kWh over the Bank Holiday, and the minor Government subsidy for solar generation, the results were as follows.
    • Domestic consumption actually cost minus 2.192 pence per kWh, giving a negative cost for domestic energy consumption of minus £26.98 in the month.  If the same kWh had been purchased at the UK average cost per kWh, we would have paid £190.74.  Hence the saving versus UK average for domestic consumption is £217.71.
    • The 439 EV miles actually cost us minus 79p in electricity in total (-£0.79).  Using our standard calculations, the petrol cost of those 439 miles would have been £75.14 in total.  Hence the overall financial saving versus a conventional car was £75.93.

In total, in May 2020, we met all our domestic electric requirement and drove 439 miles for an actual cost of minus £26.98.  That is to say we were just under £1 a day better off for using energy, whilst causing zero emissions.

The total saving, versus the UK average cost of all electricity used and driving 439 miles in a petrol car, was £293.64.

That energy performance also produced a total saving of 310kg in carbon dioxide emissions versus the carbon impact of using grid energy at UK Grid average carbon intensity and fuelling and internal combustion engine (ICE) car.  It’s worth noting that the emissions saving was lower than usual, due to the lower EV mileage in the month.  This is because it is miles driven in EV, versus the carbon impact of covering those same miles in an ICE, which causes the greatest reduction in CO2.  

So, there you have it; a brilliant result!

Covid 19 : Carbon Dioxide 0

Great sunshine, shame about the virus. (April 2020)

With a superb 223.5 hours of sunshine, April generously bestowed lots of free kWh on the solar panels. But coronavirus ungenerously killed tens of thousands in the UK. Which meant lockdown. Which meant very little driving in the EVs. Which meant the vast majority of our stored energy went into domestic load via the Powerwall.

On the upside, “one permitted exercise a day” meant around 500 miles in early April on the eBike, through the beautiful countryside around home.

River North Tyne, near Wark
eBike on 14th Century byway in Northumberland

All was going brilliantly, until 14 April, when Alan got hit from behind on the back of the helmet by the wing mirror of a delivery van doing that COVID-driving thing; assuming there’ll be nothing else on the road. Long story short: two spinal fractures, two broken hands and face mashed up a bit. And the van driver didn’t stop. Alan found some minutes later unconscious on the road. On the upside: had the odd experience of being the only non-COVID patient in the A&E hospital. 2 consultants and an entire nursing team. On the downside: bike knackered. On the really big upside: one of the A&E consultants said that 8 out of ten cyclists who have that accident end up under the wheels of the vehicle which knocked them off. So, really glad to be alive!

So that’s why April’s performance report is a bit late getting to you folks. Apologies; better late than never.

Key results:

  • 833.3 kWh solar generation; of which
  • 307.3 kWh charged into Powerwall storage battery for domestic use;
  • 526.0 kWh used at time of generation for domestic load or charging EVs.
  • 184.3 kWh off-peak grid electricity consumed; of which
  • 116.7 kWh was charged into Powerwall storage battery.
  • 41.2 kWh peak electricity consumed.
  • Total cost of grid electricity purchased: £22.04
  • Total Government payments for solar generation: £40.63
  • Net overall cost of electricity in month £-18.59 (i.e. negative 1.5p/kWh).
  • Total consumption in month: 1,175 kWh
  • Cost of 1,175 kWh at UK average cost per unit: £182.20
  • Actual cost of electricity, including standing charge, net of Government payments: £-18.59
  • Total savings on electricity costs alone vs UK average: £200.79
  • Total savings, including the cost of petrol saved by driving EVs: £271.26

However, lockdown and injury meant very little driving in month. Only 424 miles. Hence a lower than normal emissions saving of only 297kg carbon dioxide avoided, compared to roughly 3/4 tonne in a typical month. Basically, we didn’t do very much green-powered driving, for which hydrocarbon fuel would otherwise have to be burned. So less planet-saving by us. But there was a huge amount of planet-saving by the coronavirus: kept billions of cars off the road worldwide and grounded global aviation. Silver lining or what?

Now, Mr Corona, thanks for coming in to HR for your performance review. Let’s start with the positives. No question about it, you’ve made the biggest contribution in modern history to solving the climate crisis. So an outstanding A+ on that score. And you might even put Ryanair out of business, so maybe humanity will have another reason to thank you. But, I’m afraid I am going to have to issue you with a formal warning about this global zombie apocalypse megadeath thing you’ve been doing. It’s just not acceptable and you’ll have to stop…

Back in locked down Northumberland, only a tiny fraction of our EV mileage was ‘fuelled’ with overnight cheap rate electricity, for a total cost of £2.29 in the month. The rest was solar, costing £0. So that gave us an overall average fuel cost of £0.005 (half a penny!) per mile.

Overall that’s a saving of £70.46, versus the £72.75 cost of fuel to drive an internal combustion engine (ICE) car for the same 424 miles. On that basis, ICE fuel costs would be around £0.17 per mile.

That makes our largely solar-powered miles around 34x cheaper than petrol! So feeling super-smug this month. Will aim for absolute zero fuel costs in May.

As usual, click the image below to download the full monthly report. Payback economics are here.

March 2020 Performance Update

The big news in March 2020 was, of course ‘Black Death 2.0’ (aka COVID-19), bringing death, fear and economic implosion on a worldwide scale.

On the upside, it was an exceptional sunny month! Only March 1929, 1995 and 2003 have produced more hours of sunshine in the North East of England since MetOffice records began (in 1929). So a juicy 521 kWh of free electricity fell out of the sky and into our house, domestic storage battery and two EVs.

And lockdown meant that, in the latter part of the month, we hardly did any mileage in the cars, so we used less off-peak electricity on the exceptionally good value Octopus Go tariff.

Headline summary data (rounded to nearest whole number) is listed below. Click the image at the end of this post for the usual detailed PDF of the month’s performance. And click the banner here for a referral link that will save you (and us) an additional £50 on their dirt-cheap overnight energy.

  • Solar generation: 522 kWh, of which 177 kWh was stored in the Tesla Powerwall domestic battery and discharged during peak hours.
  • Tesla Powerwall discharge of stored electricity: 546 kWh, of which 177 kWh came from solar and 369 kWh from off-peak electricity.
  • Octopus Go off-peak grid supply: 802 kWh, of which 369 kWh went to Powerwall and 433 kWh went to charging the two cars.
  • Peak grid energy consumed: 180 kWh.
  • Total financial benefits in month: £421 including motor fuel saving.
  • Total CO2 emissions savings in month: 570 kg.

This rather helpful month has helped keep the whole system on track for a rapid payback. Running totals are here. However, if the COVID-19 lockdown persists for a prolonged period over the summer months, a rather counter-intuitive effect will become apparent. If we drive very few miles in our EVs, then it is likely that they can be entirely ‘refuelled’ from completely free solar energy. The payback equation subtly alters:

  • Payback to date has been on the basis of reasonably high mileage, which is refuelled using a blend of solar and (quite a lot of) off-peak electricity. There is massive delta between the cost of that electricity blend and the cost of petrol to propel a conventional car over the same mileage.
  • In lockdown, far less miles will be driven, which will mean that this delta does not come into play, as the vast majority of charging is likely to be solar, at £0 cost.
  • Our savings, versus petrol for a given distance, are likely to be less overall. In short driving “a few miles at absolute zero energy cost” is likely to deliver less of an overall benefit than “many miles at a very low blended energy cost.” The effects will play out over the next few months.

During this month, Alan also published an article analysing the major upgrade to the package of tax breaks and other incentives the UK Government is introducing on 6th April 2020 to encourage the uptake of electric vehicles.

February 2020 Performance Report

February 2020 was a month of severe storms (Ciara, Dennis and Jorge) which brought widespread flooding and general misery to much of the North of England. Fortunately, all the solar panels stayed firmly attached to the roof and even managed to generate a bit of electricity on the few sunnier days between the downpours.

So, once again, the bulk of the emissions-reducing and cost-saving contributions came from the Octopus Go tariff, providing dirt cheap, green-sourced, electrons to the two EVs and the Powerwall between 00:30 and 04:30 every night. Click the button below if you’d also like to sign for 5p/kWh electricity sluiced into your EV or domestic storage battery in the small hours.

As usual, the detailed monthly performance report is available by clicking the image at the end of this post. The headlines are as follows.

  • £460 financial benefit in the month. This saving compares the cost we actually paid for all the electricity we used (overwhelmingly during the night on the Octopus Go tariff to charge the cars and the domestic storage battery) versus the cost we would have paid at the UK average rate per kWh. It includes a saving of £232 for the petrol we did not have to buy to drive the 1,545 miles charged to our EVs during the month.
  • 404 kg of CO2 emissions avoided by using only 100% renewably-sourced electricity versus the emissions that would be caused by using electricity produced at the UK average generation mix of renewable and carbon-based sources.
  • 311 kg of CO2 emissions avoided by using only 100% renewably-sourced electricity to power 1,545 miles of motoring in EVs, versus the emissions that would have been caused by covering the same distance at the UK average g/km CO2 emissions rate.