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:
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.
