2024

January

Mid way through the month we got the myenergi car charger on line so we can see exactly how much electricity we are using for the cars. We are also now registered with Octopus for the export tariff so we get paid for the exported electricity and crucially can see how much is exported. As we know how much is generated, we can then work out what is used directly in the house. That came on line in terms of data on Friday 27th January.

The figures are still a bit flaky as I'm not totally convinced that the data on the Octopus app is fully reflecting gas use. I think it is under reporting because the smart meter seems to have days off. So with that caveat, here is January's report. We generated 416kWh and used 74kWh of which 26kWh was for the cars. So a net import of 48 kWh. The export meter only came on line for last few days. It looks like we export about 95% of generation so I will discount the net generation to 325kWh net export.

On gas, with the caveat of poor data, we used 751kWh.

RESTATED: On my net zero at the meter basis, this means January ends with a negative balance of 474 kWh. We shall see how things go when we have real people in the house, using more energy with hot water and cooking. Remember we are heating the house to 21 degrees C most of the time and keeping the MVHR running.

February

It was a pretty dreary month in terms of weather - not much chance to use the BBQ. I'm not counting the gas usage of that by the way!

It was relatively mild but a lot of cloud and rain. Despite this the PV had a reasonable month with two days over 30kWh generation and another five over 20kWh. Overall we generated 372kWh.

With the Octopus Export system up and running (although not yet actually paying the 15p/kWh export tariff) we have the export data and that was 313kWh exported. A further 99kWh was pulled in from the grid. No electric car charging in February.

On the gas usage, with again the caveat of flaky smart meter data, Octopus reported that we used 748kWh of gas. I think there are four missing days so I will add pro rata and that means an extra 120kWh to make 868kWh of gas.

RESTATED: Therefore we imported 99 kWh of electricity plus 868kWh of gas making 967 kWh at the meters. We exported 313 kWh so a negative balance for February of 654kWh.

Add that to the January of 474 kWh and we are at a year to date of 1128 kWh

March

The house was occupied for 28 out of 31 days so quite busy. Looking at the temperature data, some guests were running the house at 24 degrees Celsius during the day so quite warm!

Looking at the data, we had a reasonable month on PV generation with a gross total of 696 kWh. Of that, 493 kWh was exported

RESTATED: We also pulled in 359 kWh from the grid of which 171 kWh was for car charging, so a net grid import of 188 kWh during March.

On gas, and again we have blank days with the Octopus "smart" meter, we have a headline figure of 912 kWh. However there are two blank days so we will increase that pro-rata to 975 kWh.

So we imported 188 kWh of electricity plus 975 kWh of gas making 1163 kWh. We exported 493 kWh so a negative balance of 670 kWh. Add that to the previous and we have 1798 kWh negative year to date.

Here's hoping warmer weather, no heating and plenty of sun for the PV will begin to get us back on track!

April

The sunshine finally arrived, albeit with cold winds and occasional wet days. At last the photovoltaic roof had a chance to show what it was capable of.

The basic numbers then: The house was occupied for 21 days with a mixture of family and paying guests.

RESTATED: We generated 889 kWh of which 724 kWh was exported. We imported 220 kWh of electricity with 61 kWh of car charging, a net of 159 kWh.

On gas, the Octopus gas smart meter seems to be behaving better and we have a full month's data, which shows 422kWh used. So overall, 159 plus 422 makes 581 kWh imported and 724 kWh exported - a positive balance for the month of 143 kWh.

That reduces the Q1 negative balance of 1798 kWh to negative 1655 kWh

We are pondering a change to a heat pump as the Octopus deal is tempting. It would cut the heating and hot water kWh by two thirds. Plus it could help reduce overheating in the utility and lobby area due to the boiler giving off unwanted heat. We are also about to fit smart TRVs on the towel rails to help with control of bathroom temperatures.

May

May was a spectacular sunny month in terms of energy generation and this is despite an issue with the local grid capacity. More of that later. The overall generation was 1120kWh and of that 940kWh was exported. We imported 352kWh and used 259kWh on car charging. So in same format as last month, that's 180 kWh used from the PV plus 93kWh from the grid excluding car charging making 273kWh of electricity used.

On the gas, we are having real issues with the management of the system when guests leave. Whilst guests are in the house it is absolutely their choice as to temperatures, hot water use and the like. However, when they leave and the house is empty we need things brought back to 20 degrees Celsius and hot water off. Unfortunately this isn't happening on a consistent basis. So we are wasting gas heating an empty house 28 degrees or more and plus hot water.

Anyway, the gas use in May was 466kWh which is high. We have installed some Tado smart TRVs on the towel rails but for some reason they are not shutting the radiators off. One to investigate.

RESTATED: The net kWh usage for the house in May was 93 kWh of electricity imported plus 466kWh of gas making 559 kWh of import. We generated 1120kWh and exported 940 kWh so a positive balance of 381kWh for the month. Add that to the previous negative balance of 1655 and we have a new negative balance of 1274 kWh.

The other issue is that on sunny days we are seeing the PV inverter shutting the system down for periods as there is not capacity to shove our electrons into the local grid. Our neighbours who have battery storage aren't suffering as much as us because they can fill the batteries during these time. Looks like battery storage is on the list for 2025 improvements....

June

June was another reasonable month despite the rain and the ongoing issue with the PV shutting down, the latter now having been solved we hope by SSE turning down the voltage of their estate transformer.

June's generation was 1100 kWh of which 955 kWh were exported. We imported 113 kWh of electricity, had 59 kWh of car charging and 276 kWh of gas giving import of 475 kWh. So a an export/import balance of plus 625 kWh. Add that to the May to date of negative 1274 kWh and we have a first half negative balance of 649 kWh.

The towel rail saga has been solved by the warm weather and the towel rail circuit being turned off. We have also had Octopus looking at putting an air source heat pump in to replace the boiler. In the end, we felt that the installation, particularly the proposed pipe runs, was not going to be what we wanted. So despite a very attractive price (under £2,000 installed) we have chosen not to go with Octopus at this stage.

The house has performed well in terms of not overheating. Part of this is due to the first floor roof lights that really help get air through, as well as the tempered air via the MVHR system.

July

As mentioned in the News section, we had a two week period of no PV generation whilst Scottish and Southern Electricity monitored the mains voltage at Reflections. Long story short, the local transformer was set too high so at peak generation times the voltage in the estate network exceeded the limits on our PV system which then shut down. SSE turned the voltage down and it seems we are now getting uninterrupted generation. However, we lost nearly half the month.

Even so, we generated 679kWh and exported 532kWh of that. We pulled in 186kWh from the grid, had 44kWh of car charging and also used 438kWh of gas.

That makes an import of 142kWh of electricity for the house plus the 438kWh of gas making 580kWh usage.

RESTATED: The export was 532 kWh so even with two weeks out, we are nearly positive on negative on 48 kWh net import. The year to date balance deteriorates a bit to a deficit of 697 kWh.

We are also seeing holiday guests setting the Zappi to use just the PV generated electricity which is great. Any personal car charging is included in the rental.

August

First an admission of arithmetical incompetence or perhaps logical inconsistency.

I have been inconsistent in my logic for earlier months and have had to restate them. It is a balance of export and import that we are looking at, adjusted for car charging.

This month of August, we generated 1160 kWh and exported 897 kWh. We imported from the grid 229 kWh but had 29kWh of car charging so an adjusted import of 200 kWh. The gas usage was higher than I expected (blame high usage of hot water and the dreaded towel rails) at 568 kWh. So our balance is an import of 768 kWh and an export of 897 kWh so a positive balance of 129 kWh.

That makes a year to date balance, still negative, of 568 kWh.

I will try and tabulate everything and put in a separate "Year to date" table in the next week or so. Hopefully that won't mean I have to edit everything again. Fingers crossed.

September

It is the season of mellow fruitfulness and also a lot less sunshine!

We had 50% of the days booked for holiday guests and as we are learning, guests mean hot water usage rises. As a reminder, we keep the house heated to 21 degrees whether it's occupied or not. So gas usage was 565 kWh. The PV was down a fair bit at 812 kWh and we exported 652 kWh of that. We imported 126 kWh of grid electricity and had 62 kWh of car charging.

From the spreadsheet that gives us a small positive balance of 23 kWh leaving the year to date as a negative balance of 545 kWh.

The Year to Date table is on the House Performance summary page

October

We spent a couple of weeks at Reflections this month. Apart from putting some welding goggles on Pliny - so he is now Pliny the Welder - we explored the countryside a bit more and visited friends and relations. A very pleasant time with some good weather.

In terms of house performance, we generated 602 kWh and exported 463 kWh with 217 kWh of car charging and a net import of 120 kWh of electricity. On gas we used 757 kWh as two other weeks with guests so lots of hot water used. The heating isn't really coming on at all.

However, this makes another negative month of 414 kWh so our year to date is now 959 kWh in the read. Realistically we are not going to recover that in November and December. Full details in the table on the summary page.

November

Along with many others, we suffered from a very gloomy first couple of weeks in November. And then the PV system decided to go AWOL in the last week due to an oversensitive trip switch. I suspect we didn't lose much!

The bare numbers are generation of 215 kWh, export of 180 kWh and 35 kWh used in the house. We imported a further 90 kWh of electricity from the Grid and also 494 kWh of gas. So an overall net import of 404 kWh that increases our debit to 1363 kWh of which gas contributes 6580 kWh.

The heat pump option would probably swap that for about 2200kWh assuming a Coefficient of performance of 3. That would change our negative balance to a positive one of around 2500 kWh or so. We will do the final numbers in 2025.

Finally, we are upgrading our heating and hot water programmer to a "Smart" version so we can make sure hot water, towel rails and pumped hot water are all off when no-one is in the house

December

A quiet end to the year with yet another strange outage on the PV system for a few days at the beginning of the month. That gave us 18 days rather than 31 of generation and we scraped 122 kWh in total and exported 99 kWh There were three days with 15 kWh each but most of the month was pretty low.

No guests at Christmas but a group over the New Year so hot water and heating at full stretch later on. We upgraded the hot water, towel rail and pumped hot water circuit controller. It was an EPH "dumb" system with no remote control so we upgraded to their smart version which allows us to change programs via an app. All seems good so far.

The electricity imports were In terms of energy from the grid, we had 102 kWh of electricity and 702 kWh of gas making a net negative of 705 kWh. That leaves us with an annual deficit of 2068 kWh. So definitely not net zero, even if we add in lost generation from July and December outages of say 500 kWh.

The only way we are going to get to the net zero is with a heat pump. Even with a poor coefficient of performance of 2.5, that would replace the 7282 kWh of gas with 2912 kWh of electricity. That would give us a positive (better than net zero) balance of 2302 kWh for the year. Let's see what 2025 brings in terms of heat pump incentives.