As we moved into our second winter solar generation from our 3.69kWp system will again start to drop.
Our Monthly Solar Performance
December 2023
Generation this month was just 78kWh. This was 61% of the expected estimated monthly solar generation of 127kWh. That's the worst month of generation we've ever had.
Our self consumption was just 2% of total consumption 792.4kWh. This was low because we don't charge the EV from solar generated power as its worth more to export it, and secondly because we now charge the home battery overnight at 7.5p/kWh. This means if there is any solar generation its generally exported during the day rather than stored in the home battery.
56% of solar generation (78kWh) was exported (44.06kWh) this month. SEG export was actually £9.20 as a total of 61.34kWh was actually exported due to grid charged electricity stored in the home battery was exported during saving sessions.
Our overall consumption was a huge 792.43kWh. This was at a cost of just £64.35 at an average unit rate of 8.3p/kWh. That's a huge savings of 70% compared to a standard variable tariff unit rate of 27p per kWh.
Rewards from Saving Session hugely increased export revenue in December by nearly 5:1 compared to SEG export. Six Saving Sessions gave a reward of £45.81 from exporting just 17.28kWh of electricity stored in the home battery. This gave a total export revenue of £55.01 for December 2023.
Generation per day over the month of December was pretty poor due to quite a wet but mild month. There were only five days over 5kWh. Our highest daily generation was 1st December with 10.2kWh. Our lowest was 0.3kWh on 27th December.
January 2024
Compared to December January was a much better month for solar. January's generation was 165 kWh. that was much higher than December, and also it was higher than the expected 137 kWh estimated generation.
Our self consumption this month decreased to 5% of our overall consumption. Due to the lower self consumption we exported 75% (124.4kWh) of the overall solar generation with a revenue of £18.66. There was only one saving session in January which provided an additional revenue of £6.01.
Once again charging the home batteries overnight in the low cost period has lowered our self consumption of our solar generation. We've not charged the EV from solar as firstly solar generation is often below the 1.4kW minimum needed to initiate a charge, but also because Intelligent Octopus Go lets us charge the EV overnight at a cheaper rate and export at a higher rate.
Generation didn't start off so well in the first half of the month, but it started to increase with a period of good weather from 9th January onwards. We ended up with 7 days over 10kWh generation which is quite good considering it was January.
Our consumption from the grid in January was one of our highest ever with a total of 808.3kWh imported. The main reason our consumption was so high was due to charging the EV (656kWh) as we covered 1821 miles in January. That works out at 2.8 miles per kWh efficiency at a cost of 2.8p per mile from home charging (note this EV efficiency includes the charging losses too). I expected our imported grid consumption to increase in January as EV efficiency decreases in the colder winter weather (i.e. it takes more kWh's to go the same distance).
By charging the home batteries and the EV we imported 98.4% at the low rate electricity, averaging 7.9p per kWh. Our electricity bill excluding standing charges was £63.67 for 808kWh. On a standard variable tariff with a unit rate of 27p/kWh it would have cost £218.16!
The Intelligent Octopus Go tariff is making home EV charging very easy as I can charge the EV every night and always have 80% battery in the morning. If we were on Octopus Go we would only be able to put 28kWh per night into the EV on the low cost rate. On Octopus Flux that would have been just 21kWh.
We had an issue with our home batteries as the cold weather meant the temperature in our garage dropped to 2.9C (I'd installed a temperature sensor as I was worried about the temperature in there during the winter months so I wanted to keep an eye on it to see if I needed to look at garage door insulation). We received a BMS (battery management system) low temperature alarm at 08:45 on 18th January saying our home batteries we offline. We had to wait two days for the outside temperature to increase to 7C before I could restart the inverter and home batteries. We have decided we are going to separate half the garage off so it will a utility room with heating (central heating radiator). This will mean the batteries would be inside the house so temperature won't drop as low again, but also it should help keep our little bedroom warm as it will have a heated room beneath rather than a cold garage.
February 2024
February's generation was slightly better than January's 165kWh.The actual February generation of 176kWh was lower than the expected 189kWh. The wet mild February weather hasn't been great for solar generation.
The highest daily generation was 15.4kWh on 12th February. There were 6 days over 10kWh generation. There were 12 days under 5kWh.
Our self use consumption was just 6% as a percentage of total consumption. This was due to two reasons, firstly we were recharging the home battery every night. Secondly solar self use by the EV was practically zero. This is because the change to Intelligent Octopus Go meant it was cheaper to charge the EV at 7.5p per kWh and than use any excess solar generation, which we could now export at 15p per kWh.
Our daily electricity use still varies due to the EV. Intelligent Octopus Go means we can recharge the EV each night with whatever charge amount is requires as the smart charging isn't time limited like Octopus Flux and Octopus Go. Our highest import was 50.6kWh on 3rd February. We also charged the EV with 45.8kWh on 2nd February. That's a total over 96.2kWh over two nights which is circa 14 hours. There's no other Octopus tariff that would allow that amount of charging and all at just 7.5p per kWh.
We've also charged our home battery overnight too. The actual amount of import electricity used to charge the home battery (124.5kWh) is just 21% of our total imported electricity. The EV used 588.3kWh.
For another month running we hardly imported any electricity outside of the low cost period. 98% of our imported electricity was at the low rate which is why we averaged 8p per kWh in February.
Generation Performance
Generation performance in December 2023 was very poor. Overall generation (78kWh) was just 61% of the expected estimated generation (127kWh).
Solar generation in January (165kWh) was 20% over the expected estimated generation (137kWh).
A mild and wet February saw actual generation of 176kWh was slightly lower than the expected 189kWh. This was 7% under the estimated generation.
For the year so far the actual generation (419kWh) is slightly behind the estimated generation of 453kWh. The wet weather in December and February caused solar generation to be lower than expected.
Savings
This year is the first year we are planning to stay on one tariff (Intelligent Octopus Go and Octopus Outgoing export tariff) throughout the whole year.
As our export tariff is 15p/kWh our SEG revenue will likely be lower than last year, but we should be able to save more from imported electricity by charging the home battery overnight.
We exported a total of 316.6kWh back to the national grid during the winter months (some of which was imported electricity stored in our home battery and exported during the saving sessions). Self use consumption accounted for 102.4kWh, the majority (95.2kWh) being consumed by the home. As our daytime export is now higher (15p per kWh) than the cost of overnight import (7.5p per kWh) it effectively doubles the amount of electricity we can import back at the same cost. That means there is less sense to self use the excess solar generation by transferring it to our home battery or EV.
As expected savings our savings this winter were much higher than last winter, partly because we are now being paid for our exported solar. Overall savings over winter was £228.14. That just slightly more than autumn's saving of £227.76. It represents 23% of 2023's overall annual savings. That's quite impressive when winter is considered to be the worst solar season of the year.
The cost breakdown was:
SEG export revenue was £47.49 from the 318.9kWh exported during winter.
By exporting electricity stored in our home battery during ten Saving Sessions provided a total of £63.57.
By lowering our average unit rate of imported electricity to circa 8p/kWh by charging the home battery overnight saved a total of £88.41 compared to the standard variable electricity unit rate.
Self use of solar generation by using solar generation whilst it is generated or by storing it in the home battery saved £26.65. We've tried not to put solar generation into the EV but there have been occasions when the `EV has still been plugged in which has saved £2.02 compared to the daytime unit rate.
One interesting point now it that we now have more avenues of savings compared to last years SEG export and self use savings. As we now have a home battery we can charge the home battery overnight lowering our electricity unit rate. We can also export from the home battery during the saving sessions too.
Total savings in January and February were quite similar at £66.65 and £68.91 respectively. Savings in December were higher at £92.58 due to higher savings from the six Saving Sessions that month.
EV savings
It's difficult to calculate savings from the EV and including them into the savings from solar and our electricfication. Theoretically whilst I could compare the difference in the cost of charging the EV at standard variable rate to charging overnight on Intelligent Octopus Go it doesn't seem to be a fair comparison. The best comparison for an EV would be against the cost of petrol for a similar sized ICE vehicle.
We used 1853kWh to charge the EV at home. At 7.5p/kWh that would have cost £138.98. If we used an average efficiency of 3 miles per kWh this would have provided enough to drive 5559 miles over winter. that would have cost 2.5p per mile.
A similar sized ICE vehicle (Hyundai Tucson) would have an efficiency of circa 50 miles per gallon. At current petrol price of £1.45 per litre (£6.58 per gallon). This would be 13.2p per mile.
For 5559 miles it would have cost £731.56 for petrol whilst home charging the EV cost £138.98. This gives a total petrol saving over winter of £592.58, which is in addition to the savings made from solar.
As our EV is a company car the cost to us is very similar to our previous company car. This means we only have the company car tax rate (BiK) and additional payment to step up a model to an EV to pay. We don't have tax, insurance, buying outlay or maintenance costs to work into the overall cost. Its solely the monthly company car rate which is very similar to the previous company car. This means the savings from petrol running an EV can be used as payback against the solar, home battery and EV charger. It would drastically drop the payback (Return On Investment - ROI) of the £15.5K outlay to around 4-5 years if similar solar and EV savings could be made throughout the year. This is a great use of savings from petrol as we have theoretically invested it in the solar and home battery giving a quicker payback for a system that will operate for up to 20+ years.
Summary
Key Statistics for Winter:
* 419kWh generated
* 316.6kWh exported
* 102.4kWh (4% of overall consumption) self sufficiency from solar
* Solar/Home savings of £228.14
* Petrol saving of £592.58
As this is our second year of having solar we are now much more settled in its operation and how to live with it. Having a home battery and being on the Intelligent Octopus Go tariff should provide a good compromise between solar and EV use for us this year. It will be interesting to see how the year progresses compared to last year in regard to performance and savings.