Our energy use has changed over the last year since we installed solar and moved to an EV. The most obvious change is that the amount of electricity we import has increased massively since changing the petrol car to an EV, but the amount of electricity we use at home seems to have changed too.
Home use
Our solar panels were installed mid December 2022. We moved to Octopus Energy the same day. This means we don't have any smart meter data before this date as we didn't have an app with Utility Warehouse.
Firstly we need to understand how a solar and home battery system works. Solar generation will first be consumed by any house loads. If there is an excess solar generation it within be used to recharge the home battery. Once the home battery is full it will be exported to the national grid.
Over 2023 our home consumption has varied. During there winter months like many in the UK due to the high energy prices we we're very careful with our energy consumption. I'd estimate our annual electricity consumption for the home during the first five months was circa 110-120kWh a month (1300-1500kWh per year).
At the end of April we moved to an EV. This is the reason for the high consumption (460kWh) abnormally in May.. The reason for this is att first we didn't have a 7kW EV charger installed so we were charging from 3 pin plug charger in the garage. As this is a normal plug socket it was seen as home consumption by the hybrid inverter.
Since June 2023 our home consumption has been pretty consistent averaging 175kWh per month. That would be a consumption of circa 2100kWh per year. The only months that have generally been lower than 175kWh were June and October. We were away from home for a week each of these months hence the lower home consumption.
I'd say the reasons why our electricity consumption has increased since the home battery was installed in May is two fold:
1. The solar hybrid inverter consumes electricity 24/7. It isn't a massive amount but it's a constant load as the inverter is always on.
2. The solar system has lowered our overall monthly bill we are now less concerned about the overall cost of our electricity consumption.
You can see in the graph below over the summer months solar provided a large percentage of our electricity use. We used little imported electricity for home use in July and August. Imported electricity for home use mainly occurred when the home battery was 'switched off' to avoid it draining when the EV was being charged overnight.
Since September we have been charging the home battery overnight. This has increased the amount of imported electricity used by the home. As its charged overnight it's charged at a much lower cost of 7.5p to 9p/kWh compared to standard rate electricity.
If you compare August and November it has swapped from mostly solar generation self use in August to mostly imported electricity use in November. This would tie in with solar generation across the seasons.
It will be interesting to see how charging the home battery overnight during the higher solar generation months during spring and summer in 2024 will compare with 2023. Even though solar generation would easily cover battery charging and home use in the summer months it will still make sense to recharge the home battery at 7.5p/kWh overnight, rather than recharge it using solar generation as that could be exported at a higher rate of 15p/kWh. It just makes sense from a financial point of view, even once battery charging losses are factored in.
EV Use
As mentioned earlier we initially charged the EV via a 3 pin plug charger whilst we were waiting the Myenergi Zappi being installed. Once the Zappi had been installed from July to November the electricity consumption from charging the EV has been quite consistent at around 500kWh per month which provides circa 1800 miles per month.
The Zappi captures data on where the electricity comes from. Initially we tried to transfer any excess solar generation to the EV during good solar days. as shown by solar self use during June to September. The reason for this was the short 3 hour low cost window of Octopus Flux import tariff meant it was difficult to recharge the EV sufficiently in this short time period. Using solar generation was cheaper than importing at the day rate of 35p/kWh.
Once we moved to an EV tariff in September once solar generation was declining the extra hour of Octopus Go meant there was less need to charge form excess solar. Also solar generation was declining so there were fewer period where there was sufficient excess solar generation available to charge the EV.
Once we moved to the Intelligent Octopus Go EV tariff at the end of October there was now no need to transfer excess solar to the EV as we could recharge the EV at a low cost of 7.5p/kWh, and we weren't limited by charge time as addition smart charging periods are provided if you need more than the standard 6 hour window. Another point is exported solar is worth 15p/kWh compared to 7.5p/kWh imported so it makes no sense to transfer excess solar generation to the EV during the day.
Going forward into 2024 we will likely stay on Intelligent Octopus Go as its the best compromise for use for solar and EV use. We will still avoid transferring any excess solar to the EV. the difference between import and export rates means we are better exporting all solar and later reimporting it at half the cost.
Unit Rate changes
One of the biggest changes from installing solar and moving to an EV is the utilisation of smart tariffs. For 14 years we had stayed with the same supplier, Utility Warehouse, on their standard variable tariff. SEG export rates were the reason we moved to Octopus Energy. Their SEG rate at the time was just much better than the SEG rate Utility Warehouse would other customers.
Initially we stayed on the standard Flexible Octopus tariff. As a single day rate tariff of 35p/kWh the only savings possible were found solar self use reducing the amount of electricity we imported each month.
In March we moved to Octopus Flux tariff due to the higher rate of SEG export. At that point we didn't have a home battery so we were still importing as we used it. The different unit rate periods meant we load shifted some use into the low rate period to offset our use during the evening peak period. This meant our average unit rate was similar to the standard Flexible Octopus tariff rate.
Once we had installed a home battery and moved to an EV we started to shift our electricity import to the lower cost period. This started to drop our average unit rate whilst on Octopus Flux from 32p/kWh to 18p/kWh. That's a unit rate drop of around 40%.
By moving to Intelligent Octopus Go EV tariff we were able to drop the unit rate down from 18p/kWh on Octopus Flux to just 7.5p/kWh on Intelligent Octopus Go.
Due to double the SEG export rate on Intelligent Octopus Go we have started to charge the home battery overnight. This means the battery is recharged early in the morning allowing solar generation to be exported earlier in the day.
In November 2023 our daytime unit rate use was just 1.9% of our 704kWh consumption. A combination of charging the home battery and EV means our average unit rate of 7.9p/kWh is much lower than the standard Flexible Octopus tariff we were initially on at the start of the year.
Compared to the current standard Flexible Octopus tariff unit rate of 28p/kWh the same electricity consumption would have cost £197.19. On Intelligent Octopus Go we paid just £55.99, which is nearly 72% less than the standard single unit rate tariff.
The reason why such a huge unit rate decrease is possible even though we import far more electricity than previously is because we've 'load shifted' outside of the day time and peak periods.
The daily consumption graphs below from January and November both show how solar generation means we don't need to import electricity during the day when there is solar generation.The home battery and EV mean we now only import electricity overnight, and don't use any peak period electricity during the evening.
Also note the EV charge schedule isn't a single block as the EV charging schedule is decided by Octopus Energy using Kraken Tech. This allows the EV to be charged at the cheapest greenest times, saving us money, but also helping to balance the grid at the same time by varying the charging schedule over the night.
Typical consumption over a day in January 2023
Typical consumption over a day in November 2023
How the Home Battery helps
The home battery helps us by storing electricity for the home to use later when there is less solar. its also the reason why our average unit rate is so low for home use.
Each day can be quite different to the last. Some days have great solar generation, others have very little. The home battery allows us to even out the different days and ensure we have sufficient capacity to cover our daily consumption.
Firstly I should say during winter the home battery recharges itself every night between 23:30 and 05:30. the reason for this is to ensure we have sufficient stored power whatever the amount of solar generation iOS available. In the summer we dopant necessarily need to do this, but as solar export is no worth more than the cost to import overnight it will still make sense to recharge the battery overnight even during the summer months.
The graph below shows a good solar day where the battery is recharged overnight and topped back up with solar back to 100% early morning. It stays around 100% until solar generation stops around 4pm. Evening consumption starts to drain the battery down to around 80% before recharging starts again at 23:30.
A graph showing us over a good solar day.
In the above graph you can see the Kraken Tech working its magic managing the EV charge on and off overnight. This shows how Kraken Tech balances the national grid by managing the EV charging rather than a single constant charge period.
The graph below shows a poor solar generation day where there is little solar generation to recharge the home battery during the day. The stored capacity in the home battery provides our home with its electricity without needing to import any power from the grid at daytime unit rate.
You can see on a poor solar day we're relying on the capacity of the home battery to meet our home consumption as the battery capacity was down to 55% by the end of the day compared to 80% on the better solar day graph above.
Having sufficient home battery capacity to cover a full day's consumption helps stop us from importing daytime higher rate electricity. It also helps the national grid by not importing any electricity during peak periods.
Summary
Solar and the EV has changed the way we use electricity at home. Our consumption has definitely increased, mainly due to swapping from buying petrol to home charging the EV. Our annual electricity consumption is circa 8,500kWh (2,100kWh for home use and 6,400 for the EV). The solar and home battery has helped to reduce our monthly energy bills as our unit rate is now much lower now we recharge the home battery on low cost unit rate energy. The solar panels are also generating SEG export payments which would be circa £400-500 next year on Outgoing Octopus. If we export the same amount of solar generation next year our electricity bill including EV home charging and standing charges will likely be circa £30 per month. The savings compared to using petrol to cover 22,000 miles, even in an efficient Toyota Prius, are huge. I'd estimate when also considering petrol savings the cost of installing solar, home battery and EV charger will take circa 5 years to pay off (note we don't have an outlay for the EV as its a company car that costs a similar monthly rate as the previous petrol Toyota Prius did).
Of course we are still using gas for heating and hot water so there is that charge on top. Our next change will be moving away from gas by installing a heat pump. That's something we will look into over the next few years.