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My Solar Panels 2021 to 2026

It all began when I bought my first "Plug in" car, a 2018 Toyota Prius. In those days I could charge the car for free at the local supermarket.

Also at that time the government gave grants to fit home chargers. My home charger is only 3.5 kW as the cable from the house to the fuse box in the garage is low power.

Chatting at the charger I found that many folk had solar panels on their property but charged here because it was free.

In February 2021 I contacted Island Renewables who installed 12 panels and a 6 kWh battery array.

Prior to this, my weekly electricity use was about 24 kWh, about 3kWh per day. This was mainly cooking, washing and TV, all space heating was via the gas boiler. Then, with the solar panels my use dropped to only 1 or 2 kWh each week. The energy company I was with then had a fixed tariff with no export facility.

It was time to change suppliers. I chose Octopus Energy because of the range of tariffs on offer. Although Octopus have these initiative tariffs the clever ones do require a smart meter. It took until June that year to fit a smart meter.

All is well now and for the rest of that year I had a income of £173 and outgoings (not including the daily standing charge) of £94.

Here you can see a weekly graph of my electricity use in 2021

This shows the first nine weeks of the year, (no solar) and the last eight weeks back to high consumption, oh dear!

In the winter months I changed some space heating to a fan heater but also the battery would be nearly empty (less than 20%) by the end of the day.

The next year was much the same. In 2023 things changed, I hosted two friends in the Annexe, the energy used obviously increased, I will not try to compare that year.

I now have a fully electric car (EV). I drive about 3,500 each year. In the summer and when the cost of electricity is low or negative I charge at home. In the winter most of the charging is done at the local public charger. This is added to my Octopus bill that I pay monthly.

I did think that extra panels on the South facing roof would be a good investment, it should make the hours of generation longer as well as a 50% increase in potential power.

In October of 2023 I changed the way I managed the system.

The tariff I use is Octopus Agile, this has 48 different price points throughout the day, in the early hours the price per unit can be quite low, after 16:00 hrs the price increases. At times of high wind and / or high solar energy the price can be negative.

In October 2023 I introduced my Early Hours Charging (EHC) scheme. From 01:00 hrs to 04:00, I set the inverter to charge the house battery. This has a number of advantages.

The solar energy is helping me pay for my electricity but the price of gas is sky high, how can I get my gas consumption down? It is coming down a bit

2021/22 __ 17,000 kWh
2023/24 __ 15,000 kWh

In March 2024 I installed an Air to Air heat pump in the lounge, this will provide heat in the winter and cooling in the summer. And as it is powered by electricity it should reduce my gas consumption. I thought it wise to add another 3kWh to the battery array, oh dear more cost.

In October 2025 I installed an Air to Air heat pump on the floor of my bedroom this replaces the radiator, and is the only heating in that room.

Every day I note the maximum and minimum outside temperature and from these, I get what is known as a Degree Day value of coldness.

The cost of these heat pumps was £4,000 it would be good to know if that purchase was worthwhile. I have figures from past years. These cover the period, October to June and measure my gas consumption versus Degree Days.

In June 2026, I asked Gemini to compare two years 2021-22 and 2025-26

Conclusion: "The property's energy performance has been transformed. It now uses less than half the gas to maintain similar comfort levels compared to the 2021-2022 period".

Here is the Gemini report in full it mentions a 52% reduction in gas consumption. In the year 21-22 (October to June) 17,000 kWh of gas was used, half of that is 8,500 which at 5p / kWh is a saving of £425.

Here you can see the graphic showing the data I gave Gemini

This graph shows coldness (Degree Days) in the X axis and gas consumption (m^3) in the Y axis. Each dot represents a week, numbered from 1, first week in October 21, and 37, first week in October 25. Point number 40 was the week the Air to Air heat pump was fitted in my bedroom.

Then a friend asked, “How much more electricity are you using now“ ? The answer was a five fold increase. Which sounds a lot but in all the years after the solar panels were installed the amount earned in export has always exceeded the amount I pay for electricity.

Data

With all these numbers there should be a better way of visualising them, here is one way.

Here you can see the four categories of solar and how they change over the year.

The amount the house uses is fairly constant, with higher use at both ends of the year. This is measured by the inverter.

As the days get longer the amount generated by the solar panels builds to a maximum.

The electricity from the grid for which I have to pay is high in winter but next to nothing otherwise.

Of these four categories I have no control over the amount generated, apart from adding more panels but I am limited here by the size of the inverter. I guess I am happy with the the amount of kWh for which I pay, adding a battery will reduce this.

My EHC policy has increased the amount the house consumes, this will increase this winter due to the use of the Air to Air heat pumps. The question then will be, is the battery big enough? However, it will reduce the amount of gas I use.

Oh dear, I now have the Green v Financial question. In the long term gas will be phased out. Gemini says I saved £425, that's a good start. The price of electricity with Octopus Agile averages, over the year, at 15p/kWh (Max = 20p Min = -2p). The problem here is that I set the time of the EHC and this is not always the cheapest, that day.

I have the software package known as Home Assistant and various sensors in the house. I have written an automation that will turn on a lamp in the lounge if the temperature in the bedroom is less than 18℃. Then if the lamp is on, I turn on the bedroom heat pump manually. Within the software there is also a link to the Octopus Agile prices for the day. So may be I can make the EHC more proactive and charge the house battery at the best time each day.

The price of gas is 5p/kWh but if the COP of the heat pump is 3 or more then the electricity used by the heat pump is cheaper that gas !

The price of the energy I export, this year is 12p/kWh, this will always be less that the price that I pay when importing. So the more you use, the more you save. Last year I exported 3800 kWh at 12p/kWh that is £456.

Here is another article entitled
How Solar panels and a Battery can save you money
With links to some UK tariffs.

The future

This year 2026 I have not used any gas since March 30th, all the space heating has been via the heat pump, the hot water tanks are heated via an immersion heater. One tank has a smart switch which turns the immersion on for 30 minutes each day.

I will have to use the gas boiler in the winter but let's hope for a mild winter with no gas used until mid December !

Terry Rawkins 28 July 2026