As we moved into autumn solar generation from our 3.6kWp system will start to drop from the highs of the summer months.
Our Monthly Solar Performance
September 2023
Generation this month was 399kWh. It was 17% higher than the expected estimated monthly solar generation of 340kWh. That's much better than I was expecting but its clear solar generation is dropping off as it was the lowest monthly generation in the last six months.
Our self consumption decreased to 22% of total consumption.This was lower than previous months in the spring and summer. There are two reasons for this low consumption, I charged the EV less often from excess solar generation less often as only 38kWh of solar generation went into the EV. The second reason was because I had started to charge the home storage batteries overnight meaning much less room for storing solar generation during the day. I'd started to charge the batteries overnight from around mid September because the daily solar generation was varying greatly by this point of the month. Our import rate was slightly lower than the export rate so there wasn't really a cost penalty to do this. Any extra electricity imported into the battery would be covered by the extra solar generation that was exported instead of being stored.
60% of solar generation (399kWh) was exported this month, producing a SEG export payment of £52.04.
Generation per day over the month of September was a mixed bag. There were only four days over 20kWh and 66 days below 10kWh. Our highest daily generation was 4th September with 22kWh. Our lowest was 3.7kWh on 20th September. There was a 3 day period between 16th & 18th September where no data was recorded due to internet issues (our broadband cable was damaged during driveway work).
By the end of September our solar panels had generated 3.6MWh since installation. That's exactly the same as the total yearly estimated generation figure. That means any further solar generation will be above the estimated generation figure for our solar system.
October 2023
Compared to September October was definitely the start of the solar generation decline. October's generation was 271 kWh. that was much lower than the previous month, but it was higher than the expected 236 kWh.estimated generation.
Our self consumption this month decreased to 9%. Due to the lower self consumption we exported 78% (211.6 kWh) of the overall solar generation. The reason for the lower self consumption was due to recharging the home battery overnight in the low cost period. I've also stopped charging the EV off solar because I can now export solar generation at a higher rate (15p per kWh) than I can charge the EV overnight (7.5p per kWh) due to a changing to Intelligent Octopus Go.
Generation started off well in the first half of the month with 10 days over 10kWh generation in the first 15 days of the month. The second half of the month was opposite with only 3 days over 10kWh generation. The highest daily generation was 18.2kWh on 15th October.
The change away from Octopus Flux to an EV tariff, and charging the home battery overnight has changed the amount of electricity we imported. The EV consumed 520 kWh of imported electricity. The home consumed 97 kWh of imported electricity. This was all imported at an average unit rate of 9p per kWh, which cost £56 for the month. When compared to Octopus Flux import we would have spent £115.50.
The downside of the EV tariffs was our export rate averaged 9.6p per kWh, giving a SEG export revenue of £20.00. Octopus Flux would have given a higher SEG export revenue of £45.79.
When I compare the costs of Octopus Flux to Octopus EV tariff's it worked out a good choice to make the tariff change early.
Octopus Flux = £115.50 - £45.79 = £69.71
Octopus EV tariffs = £56 - £20.10 = £35.90
Going forward now we are on Intelligent Octopus Go we shouldn't need to change electricity import and export tariffs again. Intelligent Octopus Go will allow us to charge the EV at a great rate whilst also getting a great SEG export rate too.
NOVEMBER 2023
November's generation showed we are getting into winter. The actual generation of 190kWh was actually higher than the expected 162kWh, although generation in winter is a fraction of the glorious days of summer.
The highest daily generation was 13.4kWh on both 6th and 11th November. There were 8 days over 10kWh generation. There were 13 days under 5kWh.
Our self use consumption was just 5% 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 it requires as the smart charging isn't time limited like Octopus Flux and Octopus Go. Our highest import was 45kWh on 17th November and 46kWh on 18th November. I couldn't charge the EV with that amount of electricity on any other Octopus tariff as that's nearly 13 hours of charging, and all at just 7.5p per kWh.
We've been charging our home battery overnight too. The actual electricity used to charge the home battery is a fraction of the electricity used by the EV.
In November we have hardly imported any electricity outside of the low cost period (98%), which means we are averaging 8p per kWh.
Generation Performance
Generation performance in September started very well as there was a mini heatwave at the start of September. Overall generation (399kWh) was 17% over the expected estimated generation (340kWh).
Whilst solar generation in October was lower than September actual generation (271kWh) was 15% over the expected estimated generation (236kWh).
Solar generation was expected to be lower in. November. Whilst it was low actual generation (190kWh) was slightly better than the expected 162kWh. This was 17% over the estimated generation.
For the year so far the actual generation is still ahead of the estimated generation by 450kWh. This was an increase of 122kWh since the summer.
Savings
Solar savings were expected to dip as we moved into the autumn months as solar generation performance drops from the highs of summer. Due to the expected drop off in solar generation we moved from the Octopus Flux tariff to Octopus Go EV tariff at the end of September. This allowed the home storage battery to be charged overnight at a much lower rate of 9p per kWh compared to the standard 31p per kWh of a standard single rate tariff. It also allowed cost savings from charging the EV at a lower rate during the low cost period. This reduced the cost of charging the EV by 50% (18p per kWh down to 9p per kWh).
The shorter days in September caused the average export rate on Octopus Flux to drop to 19p per kWh. This was because the shorter days meant less solar was exported between 4pm to 7pm. Due to changing to Octopus Go our export rate in October was only 9.6p per kWh in October. This increased to 15p per kWh in November as the Zappi charger was now compatible with Intelligent Octopus so we were able to move back to the Outgoing Octopus SEG tariff.
We exported 601.2kWh back to the national grid during the autumn months. Self use consumption accounted for 258.8kWh, the majority (212.4kWh) being consumed by the home. The lower solar generation meant there were less days where the EV could be charged from excess solar, but also because we've stopped charging the EV by solar as our daytime export is now higher (15p per kWh) than the cost of overnight import (7.5p per kWh).
As expected savings from solar started to drop in autumn. Overall savings in autumn were £227.76. SEG export revenue was £88.27 from the 582.5kWh exported during autumn. Home unit rate import savings increased because the home battery was being recharged overnight at a much lower electricity cost rate.
Changing to an EV tariff and away from Octopus Flux meant the cost to charge the EV during the low cost period rate dropped considerably. Intelligent Octopus made charging only on the low cost rate very easy.
As an example 600kWh imported on Octopus Flux in August would have cost £112.8. 600kWh imported on Intelligent Octopus Go would have cost £48 That's a difference of £64.80..
Exporting 400kWh in August on Octopus Flux would have provided a revenue of £86.4. Exporting 400kWh on Outgoing Octopus would have provided a revenue of £60. That's a difference of £26.40.
Whilst our EV import each month is high it should make sense for us to stay on Intelligent Octopus Go and Outgoing Octopus rather than move back to Octopus Flux in spring 2024.
Overall I'm very impressive with a total savings so far of £999.24. If I were to add in unit cost savings from electricity consumed by the EV overall savings would be around £1438.49. EV unit rate savings by using low rate electricity rather than the higher daytime rate would be over £100 each month.
As expected savings were higher in the spring and summer months.
Due to changing tariffs four times in 2023 and only receiving export revenue from mid February our savings in 2024 should be higher than 2023.
If we stay on Intelligent Octopus Go next year we will likely see lower export revenue during the summer months as the export rate with be lower on Outgoing Octopus. This loss in SEG revenue should be offset slightly by the lower cost of home electricity by charging the home battery at 7.5p kWh. It should also mean we export more next spring/summer as the home battery should be full from overnight charging so excess solar shall be exported earlier. It will of course mean lower costs to charge the EV, which is responsible for majority of our electricity use. The EV has increased our annual consumption from circa 1800kWh per year to circa 7500kWh.
Summary
Key Statistics for Autumn:
* 860kWh generated
* 601.2kWh exported
* 258.8kWh (12% of overall consumption) self sufficiency from solar
* £227.76. saved
* 22kWh (4th September 2023) but only 13.4kWh (6th & 11th November 2023)
Key Statistics for all four seasons
* 4056kWh generated
* 2917kWh exported
* 1138kWh (23% of overall consumption) self sufficiency from solar
* £999.34 saved
* highest ever daily generation - 27kWh (4th June 2023)
This year has been a big learning curve for us regarding solar. Hopefully in 2024 we won't need to swap export and import tariffs as Intelligent Octopus Go and Outgoing Octopus should provide a good compromise between solar and EV use for us.