2024 Data Analysis

Introduction

While 2023/24 sees a small nudge up in both our electricity and gas consumption, analysis over a longer timeline indicates that weather compensation could be saving as much as £800. I discuss below the key changes:

• Full Year of my retirement
• Weather compensation installed on the boiler
• Solar installed in the Spring

Note: This analysis covers consumption in the home as opposed to solar generation, I have also updated the tariff used to convert energy to £s. For both of these see details below.

Impact of My Retirement

During the pandemic I worked from home for almost two years. The years on my chart above are dictated by my imperfect records of meter readings and I do my best to cover close to a 365day period for each year, but mostly I have gone from late summer (Sept/Oct).

 

For the above chart I was working at home as follows:

• 2019/20: March 2020 onward
• 2020/21: full year working at home
• 2021/22: until 9th Jan 2022

Clearly, being at home in the winter has the biggest potential to increase energy costs.

 

In summer 2023 I finally retired, but for the year 2022/23 above this would have had minimal impact on heating, as this was off until around September.

 

The charts for 2019/20, 2020/21 and 2021/22 neatly track my time at home (in the winter). Clearly, my wife has been much better than me at keeping the heating costs down - she has been retired throughout this period.

 

2023/24 does show an uptick in gas/heating costs, about £80, but compared  to 2020/21, the last full year I spent at home/out of the office, where the difference is around £1,150, consumption has gone down dramatically.

 

Impact of Weather Compensation

In my September '24 post I reviewed one year living with weather compensation installed on our gas boiler.  In summary, weather compensation involves an external temperature probe, attached to the boiler. The boiler then regulates the temperature of the water flowing to heat the radiators and the hot water tank (or 'flow temperature') as follows:

• Hot water on: 80degC (to both radiators and hot water tank)
• Hot water off: flow temperature depends on outside temperature - typically, the boiler display shows a range of 45degC to 55degC.
• Otherwise the boiler works as usual, with the boiler firing up when the room thermostat (Evohome in my case) senses that the room is too cold.

 

Note on flow "Room Temperature Set point" on the boiler: I still have the same graph setting as per my post weather compensation (ie the "22" graph). So in theory the flow temperature should be around 65degC when it is 0degC outside and 40degC when it is 16degC outside warmer outside. In practice the flow temperature display shows slightly lower temperatures at this setting (eg 58degC when 2degC outside); however, this is not too critical as I have simply chosen the "22" setting because it keeps our home comfortable, as opposed to some complex analysis of the graph and our home's thermal characteristics.

 

In my September 2024 post I promised results on savings for the weather compensation system and was optimistic given the academic studies showing significant savings (eg Salford University ~12%). I must admit to being disappointed that I have not seen a similar drop from gas consumption from the previous year - in fact had an increase in consumption of ~6%. I have two opposing theories:

 

• Weather compensation and low flow temperatures do not save any money
• Weather compensation does work and has in fact saved me £1,070. If I had been at home without weather compensation then I would have seen an increase of £1,150 (as in 2020/21), but I only saw an £80 increase.

 

I suspect that the truth lies somewhere between the two theories. After 2020/21 I have also:

• Insulated central heating pipes in the garage (saving "£35+/-£15") - see Insulating Pipes in the Garage post
• Added loft insulation (saving "£200 +/- £100") - See Insulate the Attic post

Cost saving figures above from post 2023Data Analysis.

 

Superficially then weather compensation has saved:

£1,150	(gas usage decrease from 2020/21 to 2022/23)
-£80	(2023/24 gas usage increase from 2022/23)
-£200	(saving from loft insulation)
-£35	(saving from insulating central heating pipes)
£835	Total

I must admit that I do not believe this figure either, but it does indicate that weather compensation has made a substantial reduction in heating costs.

 

The 12% figure quoted by the University of Salford is for an 80degC to 60degC drop in flow temperature. The drop in this case was from 70degC to around 50 to 55degC (on typical cold days). So a similar order of magnitude drop, but the drop below 60degC might potentially have the biggest impact as we get closer to a condensing temperature of 55degC (as quoted by Viessmann). However 12% is the only figure that I have, so this amounts to £150 to £300 depending on if I use the 2020/21 as the baseline or 2022/23 as the baseline.

 

My take is that weather compensation does offer a substantial saving. I suspect not £800 per year, but £200 might be a realistic assumption. Over the coming weeks I will see if the data that I have will help in deducing the truth and, failing that, next year's consumption figures should also help in confirming if this reduction is a one off (eg due to weather) or a consistent saving.

 

Given the uncertainty of the savings an accurate payback time for the installation is not possible. I calculated the cost of the installation as ~£200 (see post installation), so very (very) roughly the payback period could be as little as 1 year or even less.

 

There are other effects of weather compensation that I mention in the post on installation:

• The temperature in the house is more consistent
• The house takes longer to warm up:
• If we go out for the day and I turn the heating off then best to allow 2 or 3 hours for it to warm up
• If we go on holiday and the heating is off for a few days then best to allow 24hours to fully warm the house
• If we forget (or the heating system fails) to restart before we get home then we suffer while the house takes a few hours to warm up eg we had a low pressure error on the boiler while away in Dec '24 . When I got home this was easy to remedy with a top up to the system water, but could not be done remotely. Without weather compensation and higher flow temperatures, then the house warms up faster (but not instantly).

Weather compensation suits a set up with the heating is on all day (ours is programmed to switch on at 6-00am and goes off at 10pm). If we are out for several hours then I will sometimes put the heating into Eco mode (3degC reduction) and if we go away for 2+ days I will usually turn the heating off (ie 5degC for the Evohome system) and, usually, the heating switches back on before we get home and the house is nice and warm when we get back.

 

Finally, low flow temperatures, and so cost savings, do rely on good insulation. So, probably, the savings from weather compensation are improved by loft insulation and central heating pipe insulation as an even lower flow temperature can be used while still maintaining a comfortable home.

 

Impact of Solar System

First I must emphasize that this post is not an analysis of the savings from the solar system (see post for preliminary analysis of solar production return on investment), it considers the consumption of the house from both the grid and the solar/battery system. However, the only place that I found to get this data is from the inverter and this includes consumption by the inverter/battery itself (see note below).

 

The increased electricity consumption in the last 12 months has been the equivalent of £50 (4%), but again almost £240 or 17% reduction from my last full year at home in 2020/21. In this period we have not done much in terms of home electrical energy saving (eg most of our light bulbs were LED by 2020).

 

In terms of energy use the increase over the previous year is from an average of 10.25kWh per day to 10.5kWh per day since before the solar system was installed. This surprises me as I was expecting to see more:

• Solar system consumes approximately an average of 1.2kWh per day (this is the difference between energy in and energy out, eg to charge the 9.5kWh battery each day)
• Some of our other behaviour changes, while reducing cost, have actually increased consumption, eg we run our dishwasher each night at cheap rate, rather than waiting for it to fill up - we probably run the dishwasher more often, at about 2kWh per run.

 

A couple of possible explanations for this are:

• The solar system does give much better data on instantaneous consumption (eg better than a regular smart meter In House Display (IHD) and much better than a smart meter that will not communicate). This visibility has made some savings more obvious eg reducing house power consumption while we are on holiday (devices like the TV, printer, etc unplugged, etc). However, we have not done too much of this - the objective of the solar system was to make comfortable living less costly, not to make us uncomfortable.
• We do sometimes use fan heaters to quickly boost the temperature in a room. The more consistent temperature in the house (from all the changes like insulation, smart controls and weather compensation) mean that this is now a rare event.

 

However, I am not really convinced by either of these explanations.

 

Conclusions

 

Weather compensation has very likely been a very significant driver behind a larger than £1000 saving in our gas bill, over the previous period when both me and my wife were both at home 'full time'. My guess is probably somewhere over £200 per year is attributable to weather compensation, but this is hard to isolate based on  the available data:

• Weather compensation is probably has the fastest payback of any of the significant energy saving measures that we have taken, and also improves the comfort of our home
• The energy saving from weather compensation does depend on having good insulation 

 

Solar Power does consume about 1.2kWh/day of electrical power to run the inverter and battery. However, there is a much smaller increase in consumption from the grid than I was expecting. I do not properly understand this; my best explanation is the data provided by the solar inverter app allows some energy saving, without any significant cost to comfort.

 

Notes on Tariff

In previous posts (Introduction, 2023Data Analysis) I showed similar graphs to the above. However, these show higher columns (more £s) as they have been calculated with different tariffs:

 

Post	Data to	Tariff	Electricity per kWh	Electricity standing charge	Gas per kWh	Gas Standing charge
Introduction	Oct 2022	24 Aug 23 (Octopus - "Coop Loyal 12month fixed")	28.02p	49.77p	7.05p	27.47p
2023 Data Analysis	Oct 2023	24 Aug 23 (Octopus - "Coop Loyal 12month fixed")	28.02p	49.77p	7.05p	27.47p
2024 Data Analysis (this post)	Sept 2024	1 Oct 2024 Electricity: "Octopus Flux Import", "Day" and Gas: "Loyal Octopus 12M Fixed"	25.012	49.983p	6.71p	26.16p

 

My objective has been to compare energy consumption, as opposed to provide actual costs. It is to be expected that tariffs will go up and down; however, what should remain true over time, is that reducing energy consumption will reduce costs. I made the decision to update the rates in this post because they seem to have somewhat stabilised after the pandemic. However, as each chart uses one tariff for the whole period from 2009 to the present, it is not too important to be accurate as the numbers only get used in rough order of magnitude return on investment calculations. Most important is a year to year comparison.

 

Notes on Treatment of Solar Generation

After installing the solar system the smart meter gives consumption by the house and also the solar inverter, eg when it is charging the battery at cheap rate. The battery discharges to both the house and also back to the grid (at peak rate). The smart meter readings for import from the grid and export to the grid are pretty close to those on the GivEnergy app (<2.5% error - see post Solar#6: 6 months post install).

 

Therefore since April 2024. I have used the GivEnergy app's home consumption figure in place of the smart meter consumption figures from before the solar installation.

 

The GivEnergy app gives 6 figures:

• Home consumption (inverter output)
• Solar production (inverter input)
• Battery in (inverter output)
• Battery out (inverter input)
• Grid import (inverter input) - matches smart meter import within 2.5%
• Grid export (inverter output) - matches smart meter export within 2.5%

If you add all the inputs and outputs to/from the inverter then you see a difference. This varies day to day and I have not been able to work out the pattern/causes. However, it does average around 1.2kWh per day and working this back it is part of  the "home" consumption figure provided by the app.