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.

Solar #7: Interim ROI Figures - 1st 6 months

Introduction

In a previous post I reviewed our solar and battery system after 6 months of use and, at that point, I was awaiting bills from Octopus Energy for the whole 6 months & so could not calculate the Return on Investment (ROI)...

 

...I now have the electricity bills covering the period 1st March to the end of September - a net payment to me of £157.84.

 

 July Import and Export estimates from the Octopus App.

Both graphs show £'s, but the vertical scales are different!

Note that the  Import Costs Don't include the Standing charge

(approx £0.5/day or £15 over the month)

 

But what does this mean in terms of an ROI:

• What do I expect the winter ROI to be?
• What was I paying before for electricity?
• What would I have paid for electricity without a solar system?
• Compare this ROI to what?

 

An important point: this post is just my views on investments and is not intended as investment advice.

 

ROI Comparison and Assumptions

For solar systems I often see 'payback period' quoted, eg 'investment of £7,000 paid back in 8 years from savings in electricity bills'. While this is interesting and makes a nice headline it is not very useful. If I have £7,000 am I better off investing my money in a solar system, or should I put it in a high interest savings account or what about an ISA and put the money in stocks and shares?

 

For me the most useful comparison is my pension (a SIPP). I am recently retired and withdrew £16,220 from my SIPP to invest in the solar system. Would I have been better leaving it in an investment fund (eg FTSE250 Tracker Fund or the more 'sporty' S&P 500 Index fund). There are some key differences that I have allowed for to make this comparison:

• I am told that my solar system will last for 25 years. In reality I am sure that it will not suddenly conk at exactly 25 years after installation, but for the model I assume that its value drops to £0 at 25 years. For an investment fund, while 'the value of an investment can go down as well as up', I might anticipate an average return of a few % each year and hope that my capital is intact after 25 years.
• The investment fund will not necessarily rise with inflation. I am now drawing down on my pension pot. My financial advisor modeled this to give me a regular income and the pot of money running out when I reach 99 years old. He modeled 2.5% inflation (ie my annual pension rise) over the period of my retirement - ie the average return of the funds that I am invested in needs to beat 2.5% just to stand still. In the case of the solar system then the return on investment rises as the price of electricity rises. In this model I assume that the price of electricity rises in line with inflation at 2.5% each year. There are more notes on inflation below.
• I paid for an 'in roof' installation for my solar panels. This added £2,573 to the price and gave us the benefit of a new half roof. However, my roof, while it is working well at present (ie it protects us from the Lancashire rain), it is, apparently, at the end of its 50 year design life. For me £2,500 was a necessary part of the solar investment, but you could argue that if I invested the money in a fund then I would be still be paying to replace the roof in the next 25 years. I have modeled with and without the 'in roof' cost.
• Investment fund costs: an investment fund manager (eg Legal and General) and the provider (eg Hargreaves Lansdown) will have charges - I have assumed 0.5% as being pretty typical total charge (ie fund + provider). The solar system has no equivalent charge.
• Inverter and battery replacement. I am told that inverters and batteries have a life of around 10 years. To make the maths easy I have assumed that at year 12 a new inverter & battery must be purchased. I have used current prices for direct replacements (£5,050, based on battery at £3,600 and inverter at £1,450). Of course there will be an installation charge, but I have assumed that this is wrapped up in the £3,600 battery option price that I was charged for the original installation.
• I still don't know how my solar investment will perform from October to March. Clearly much less sunshine. However, the battery lets me buy electricity at around 15p per kWh, that otherwise I would pay about 25p per kWh. So this saves me something like £1 per day (see my post Solar#6: 6 Months Post Install) or £180 for 6 months; on top of this there will be some solar production - even in Lancashire there will be some sunlight. In the end I took winter ROI to be 50% of summer ROI and have also modeled two cases of +£100 and -£100 to test the sensitivity.
• If I had put my £16,220 into an investment fund then I assume that I would have stayed with a regular tariff. I have found it hard to find alternative non-solar tariffs & so I have just used the mid-point tariff that I am charged with Octopus Flux. With no solar system I would also not need to pay for the electricity to power the inverter and battery. I have used our mid-point consumption over a year prior to the solar system being installed (10.18kWh per day). This has been reasonably static over the last 3 years (from 2021, 9.66kWh to 10.69 kWh daily average over a 12 month period). This is probably a little pessimistic for this summer analysis as we use a little less electricity in the summer, but should should come out in the wash over a full year.

 

See also my April 2024 investment case post - this has more on the risks of investment in solar.

 

Model Construction

My aim is to find what annual percentage growth I should look for in an investment fund to give an income that is equivalent to the electricity bill savings from my solar investment:

• Step #1: solar ROI over 12 months:
• Analyse my bills with solar Vs what I would have been paying with a regular tariff and no solar system - this gives a return on investment of £353.45 in Q2 and £328.39 in Q3 (Octopus change their rates each quarter, so the bills have neat cut offs at the start and end of each quarter). The total for 1st April to 30th September is £680.84.
• I added 50% to this for the winter to give me a complete year return on investment estimate of £1,021.
• Step #2: model equivalent hypothetical investment fund:
• Investment £16,220
• Each year:
• I take out £1,021 as income (eg to pay the higher electricity bills without solar power)
• And the fund grows by x%
• 25 rows in an Excel spreadsheet gives me the remaining capital after 25 years
• By trial and error I set "x"% (the annual growth rate) so that the remaining capital is £0 at 25 years (as per my assumed value of the solar system)
• Step #3: account for inflation and investment fund charges
• Once I have "x" (the equivalent annual growth), I then add:
• 0.5% to cover charges for the investment fund
• 2.5% to cover inflation
• Step #3: Test some variants of this model:
• At year 12 add £5,050 into the fund - what I would have paid to replace the battery and inverter mid-way through the life of the solar system
• Invest only £13,647 at the start, ie no re-roofing - 'on roof' solar system.
• Add and subtract £100 to the annual return on investment (ie test out £1,121 and £921 income each year) - the aim here is to test the sensitivity to differences in performance (eg errors in my winter estimates).

 

Results

My view is that the base case is the on-roof installation (ie £13,647 initial investment) and replacing the inverter and battery after 12 years. This gives an equivalent fund growth of 6.4%.

 

If I take the higher investment then the equivalent investment fund only needs to return 4.9%.

If my inverter and battery lasts the whole 25 years, with the initial investment of £13,647) and nothing added to the fund at year 12 then the fund would have to grow at 8.5% to match the solar system ROI.

If the annual return from the solar system is +/-£100 from my estimates (based on the 1st 6 months) then this adjusts the equivalent investment fund ROI by about +/-1.1%.

 

Discussion

This model includes a large number of assumptions. For some of these I have modeled the sensitivity and this gives a range of 3.8% to 9.6%. Others I have not modeled, eg removing inflation takes out 2.5% from the equivalent fund return, but it might also be reasonable to take 5% as an inflation rate for electricity (see below).

 

In the end 6.4% seems like a reasonable mid-point between the range of assumptions. I guess that for what is, I hope, a low risk investment, then perhaps this is OK.

 

I would also point out that, based on my experience, the extra work that comes with the battery (see post "6 Months Post Install" is far more than comes with a typical SIPP investment. Potentially a solar only installation, with no battery, would compare better for the work required.

 

In my April 2024 investment case post I used an annual return of £605 based on a solar system price of £7,000 based on figures from the Energy Savings Trust. Given that I invested £13,647, then I might expect a pro rata increase in return, ie £1,175 each year. I feel a post is need in April 2025, with 12 months figures to see if I am being overly pessimistic with my annual return estimate or over optimistic with my April 2024 estimates.

 

Notes on Inflation

Taking the last 25 years (1999 to 2024) then the average UK inflation rate has been 3.2% (ie £10,000 had the purchasing power of £21,719 in today's prices) - see https://www.officialdata.org/UK-inflation.

 

Why have I used 2.5%? It just happens to be the rate that my pension advisor use for modelling my income from my pension pot. So if the last 25 years is a good guide to the next 25 years then perhaps we should add 0.7% to the equivalent pension fund return needed to match the solar system return

 

But what about electricity price rises? If electricity prices rise at a slower rate then my future £ savings will be lower, conversely steep rises in electricity prices will mean that my investment in a solar system is getting a bigger return. Our new government (2024) is promising big investments in renewable energy and so reductions in domestic energy bills. However, over the last 25 years electricity prices have risen much faster than inflation, at 5.4% per year on average (See the report on "Domestic energy prices" from the House of Commons Library: "In April 2024 prices for gas were 270% above their January 2000 level in cash terms, and electricity prices were 350% higher").

 

My view is that inflation is all in the risks of investing in solar power - upside and downside (see Solar#2:Solar Panels Investment Case) & I will stick with 2.5% as the mid-point for inflation, and accept that it could go either way. The really good news is that the risks are very different to my more traditional pension investments and that having a range of different risks, for different pension investments, is often said to be good (see book "How to Fund The Life You Want" by Robin Powell and Jonathan Hollow).

Solar#6: 6 Months Post Install

Introduction

I kept putting off writing a 3 month review of our solar system - I want to write an honest appraisal and I had really wanted to be able to paint a 100% glowing picture of a fantastic investment...

...but, like most things, there is good and bad and the data is ambiguous. So, at last, I have bitten the bullet and written this 6 months review:

 

There are a few points that are not covered and I intend to cover in future posts:

• 6 months Return on Investment (ROI): as I write this, Octopus has resolved my smart meter issue and are just finalising my June through September bill. In this post I discuss energy (kWh) and power (kW), but in the end it all boils down to money (£)! A future post.
• Scheduling: GivEnergy are promising a solution to the firmware issue that, in some cases, means that scheduled discharging is not optimal - I do have a summary of this issue below and I will discuss the scheduling topic in more detail in a future post, once, I hope, the issue is resolved.
• Emergency Power Backup: I have not yet paid the extra for this facility to be installed.

 

I don't want this introduction to sound like I am disappointed with the system, so a few, more positive, points:

• It works - the system is robust and the 6 month performance looks to be on track to beat the 12 months figures in the Lovatts proposal
• GivEnergy software is cool and the overall hardware and installation looks neat, well designed and with solid construction.
• The GivEnergy software does allow the system to be scheduled for the Octopus Flux tariff and, so far, I believe it has been broadly optimal over the course of the spring and summer.

 

Lovatts Installation

All functioning well - solar system and roof.

Installation - My View: It Looks Good

Since the installation I have had not really needed any help from Lovatts and I would certainly recommend them to others. Their one shortfall is their limited knowledge of scheduling the GivEnergy system and they have tried to help here, but are limited by the support & documentation provided by GivEnergy.

 

GivEnergy Hardware

Not much to say here - it still looks good and has not skipped a beat.

 

GivEnergy Software - Phone App

This has great monitoring capabilities; this does help in understanding where energy is consumed and how to make savings - see section below "Consumption Visibility Gives Savings".

 

It took me a while to work out that the scheduling features of the phone app are limited; really a sub-set of the cloud app. Since working this out I have not used the phone app for scheduling. To add to the confusion:

 

• My installer had limited knowledge of how to schedule the system
• The GivEnergy helpdesk, while staffed by very nice and helpful people, do not have knowledge of the scheduling features of the system and they were not aware that the scheduling interface of the iOS app is different to the Android app version described in their documentation.
• The phone app documentation is limited: the more obvious features are fully covered, but not scheduling.

 

My view now is that the phone app (iOS and Android) are great as a monitoring tool, but it is best to do the scheduling in the cloud app. This is actually fine if, as I do, you want a set and forget system. It is easy to do a quick check on how the system is running on the phone app, but setting the schedule is a more considered activity, done (I had hoped) just once.

 

GivEnergy Software - Cloud App:

This has similar monitoring features as the phone app and much better scheduling capabilities. The cloud app also has some interesting reporting and data download capabilities that I have only made limited use of. There is no documentation for the cloud app (or none that I could find) and the helpdesk know very little about the scheduling features.

 

Scheduling with the Cloud App: Once I have the GivEnergy firmware bug fix I will report on this in more detail, in a future post. Right now my schedule makes use of the Octopus Flux cheap rate and peak rate periods:

• Timed charge: from 2am to 5am to 100% (Octopus Flux cheap rate)
• Time discharge 2 x 45  mins during the peak rate of 4pm to 7pm. The 2nd discharge finishes at 7pm. Both are set with a 4% minimum battery charge. My aim is to avoid consumption from the grid at peak rate and then to maximise discharge to the grid, without manual intervention.
• Outside of these times I use the ECO mode that works as you would want - ie prioritising home consumption of solar energy, then charging the battery and finally if home consumption is satisfied and, the battery is at 100% charge, it exports to the grid. If the available solar power is not enough for home consumption then the battery is used and, if this is exhausted, then the grid is used. If peak demand in the house exceeds the inverter/battery peak limit (nominally 5kW)  then the grid is used.

So far the battery has not been fully discharged at 7pm, on most evenings, ie we have only had very limited import from the grid at peak times and almost always because we have exceeded the peak capability of the inverter (nominally 5kW). This can happen, eg if the oven, grill and kettle are on at the same time, but actually accounts for very little energy (eg from my Octopus bill for 1st July to 28th Sept peak rate consumption is only 2.0kWh).

 

A bug in the GivEnergy firmware means that if we do not hit the 4pm peak rate window with the battery at 100% charge, and I do not adjust this time based discharge schedule, then we could end up with more peak rate import before 7pm. I think that this is likely to happen now that we are past the Autumn equinox.

 

Performance Numbers:

• Solar energy generation
• The Lovatt's proposals, based on the MCS calculation, states that for a 12 solar panel system we would produce 3,610 kWh each year. I was told to pro-rata this number for the 14 panel system, ie 4,212 kWh each year. After losses of 181 kWh/year (pro rated from the proposal), this gives 4,031 kWh
• For the 6 months from 1st April to the end of Sept the actual generation was 3,362 kWh. From what I can see the Solar generation energy figures given by the GivEnergy app are after losses, so 83% of the full year 4,031kWh in the proposal. It looks like we should exceed the proposal, by a decent margin, unless the winter is really, really gloomy!

 

• Power: The peak power of each solar panel is specified as 400 Watts in the proposal, or 5.6kW for an array of 14.  On 28th June the GivEnergy app showed a peak power generation of 7.257kW. I am a little dubious of this figure as on days with very variable levels of sunlight the peaks were always higher than on days with continuous sunshine. For example, the day with highest energy (36kWh) had a peak power of 5.38kW. I am not sure if this is an artifact of the measurement system of if the system is more efficient when there are only short bursts of high sunlight levels. In any case, given the non-optimal direction of the house, pitch of the roof and location on the globe, even the 5.38kW seems pretty good.

 

• System and Battery losses: I have struggled to make sense of losses - this is what I have worked out from the energy figures provided by the cloud app:
• Grid to home - there are no losses here (& you would not expect any, it does not go via the GivEnergy system).
• Solar: clearly there will be losses in the inverter, but the figures quoted are after losses, so it is not possible to work out (from the energy data) what these losses are.
• Battery in and out: This averaged 11% of the energy input or 1.28kWh per day over the 6 month period. During this time the battery was fully charged on most days, using cheap rate electricity and around 60% was discharged to the grid at peak rate with the remainder discharged to the house. On gloomier/shorter days there were one or more mini-discharge charge cycles. On longer sunnier days then the battery pretty much stayed charged and the house ran off solar/battery from 5am. While there is variability in the daily losses, there was no obvious relationship with the charge/discharge pattern on that day.

 

Solar production Seasonal Observations

Considering the 6 months from 1st April to 20th Sept (the first 6 months period where I have complete monthly data):

• Total production is 3,360 kWh, or on average 20.2kWh per day.
• The month with the highest production was June at 690kWh or, an average of 23kWh
• The month with the lowest production was September at 390kWh or, an average of 13kWh
• The June daily solar production range was 8.82kWh to 36.24kWh
• The September daily solar production range was 1.48kWh to 24.51kWh

It will be interesting to see how solar production fares in the winter months (as I make the final edit of this post, in mid-October, we have just had a miserable truly Lancashire day of  rain and dark grey clouds with only 0.76kWh of solar production for the whole day.

 

The thing that I have been surprised by is the enormous daily variability:

• Over 4:1 best day Vs worst day in the summer
• Over 16:1 around the autumn and spring equinox

Given this variability, then if a tariff requires scheduling to achieve maximum ROI (ie anything other than a flat rate tariff) then I think that the options are:

• Daily manual adjustments depending on expected weather and energy use profile
• A fixed schedule that is robust to a wide range of weather types and usage patterns
• A schedule that automatically adjusts depending on the weather forecast and expected usage patterns.

This topic is something for a future post - suffice it to say that my objective, at present, is the fixed robust schedule, & I think that, other than the bug mentioned above, the GivEnergy system allows this when combined with a tariff like Octopus Flux.

 

Accuracy: GivEnergy Vs Smart Meter Energy Readings

I took grid import and export readings roughly every 2 weeks from the smart meter and the GivEnergy software.  The readings for both import and export were in the range of 0.8% to 2.5% difference, with the smart meter giving slightly higher readings for both import and export. I was pleasantly surprised by how close these figures are and how closely the graphs match over complete days. The biggest deviations that I saw were in a period in September (9th to 20th Sept) where I was running the system to minimise grid import; on days where the import was <1kWh then the error rose above 2.5% - for example

	GivEnergy Cloud app	Octopus App	error (kWh)	error (%age)
11th Sept	0.17	0.30	0.13	43%
18th Sept	0	0.04	0.04	100%
19th Sept	0.29	0.33	0.04	12.1%

I am not sure that there is too much to draw from this other than there is a small error between the two meters that consists of:

• A small gradient error of <2.5%
• A small offset, noticeable at <1kWh/day
  
• A small amount of noise, noticeable at <1kWh/day

The smart electricity meters that I have had have both been labelled as 'class B' and apparently this means within 1% accuracy, according to IEC62053-21/-22 (but I must admit that I have not read this standard).

 

GivEnergy Cloud App May Export	Octopus Phone App May Export

 

GivEnergy Cloud App September Export	Octopus Phone App September Export

 

For both import and export the smart meter has slightly higher readings than the GivEnergy system, so no particular bias in Octopus's favour or mine (Octopus win a little on import, I win a little on export).

 

My view is that, even with these larger %age errors on low readings, the error band is pretty good and not significant in terms of billing.

 

Consumption Visibility Gives Savings

The GivEnergy phone app gives great visibility as to the instantaneous production and consumption in our home. My view is that, in general, I want to live my life without constraints set by energy consumption, but, having said that, if some easy adjustments mean that we save money then I am all for it.

 

Home Screen: instantaneous production and consumption	Power Graph: 3.3kW peak production - not bad for October	Battery Charge Graph

So how has this helped:

• The first quick win was that we saw that the dishwasher uses a little over 2kWh for each run - so we save around 20p each night or £70/year by remembering to run this overnight at cheap rate (it has a built in timer) - and is usually convenient to have clean dishes each morning (of course, this raises another question on whether to run a half full dishwasher over night! - we usually do).
• Anything with a heater is a high consumer - tumble drier, washing machine, iron, oven...
• Peak rate starts at 4pm and we charge the battery overnight at cheap rate. Export before 4pm gives us around 15p per kWh, export after 4pm around 25p per kWh. So if we get to 4pm with a full battery then we can export most of the contents at 25p/kWh. If we get to 4pm with a less than full battery then we might lose some export at 25p/kWh. So, do the washing on a sunny day, in the morning, then it is likely that you still get to 4pm with a full battery, and we have exchanged laundry for exporting at 15p/kWh, but do the washing on a gloomy day and the battery is not fully charged at 4pm and we have exchanged doing the laundry for exporting at 25p/kWh...

...Keep the laundry for sunny days - perhaps saves of 1 to 4 kWh (10p to 40p), or a £few per year.

• Before going on holiday it is possible to drop the background run rate consumption from 200W to 300W, by around 100W, eg by turning off various low consumption devices like the TV, printer, etc at the wall socket. 100W is 2.4kWh per day, so over a week's holiday that is 16.8kWh or around £2.50.

These are just some specific examples of how the visibility to consumption provided by the GivEnergy app is useful; being conscious of instantaneous consumption can be useful but, in my view, is unhealthy as an all consuming lifestyle choice! Spotting the bigger savings is perhaps worth around £100 per year for us.

 

Mature Technology? Where is this Technology on the Market Adoption Curve?

There is a marketing concept for new technology of the adoption curve

The Technology Market Adoption Curve

The concept of the 'chasm' was introduce by Geoffrey Moore in his book "Crossing the Chasm". My summary of the concept is that many technology innovations look like they have made a promising start, but actually it is the early adopters and visionaries who are buying them. Many technology products fail to convince the early majority to buy in - these people are looking for proof from other users whom they know and trust (ie not fancy marketing). There are plenty of people who disagree with this concept for all technology and for specific technologies. For example, for solar energy, does government incentive (eg no VAT) impact on the adoption curve?

 

My view is that the adoption curve is a useful concept, but is not precise and it is often hard to slot each individual buyer into a neat category.

 

Having said that, it is clear that for a technology product to succeed it must be easy to use and be seen be obviously useful if mass adoption is going to happen

 

My experience, after installation and 6 months with this system, is that solar panels, without a battery, are ready for the majority market and, as long as the numbers stack up, and you have a reputable provider, they are probably a reasonable investment.

 

However, add in a battery and the system is, in my view, very firmly in the innovator/early adopter phase. For a battery to reach its potential return on investment (ROI) it requires:

• Scheduling to get the full return on investment
• Flexible electricity tariffs and this needs a working smart meter (see my posts Smart Meter #1: My Journey and Smart Meter #3: My Journey Part #2).

Both scheduling and getting my smart meter to work has taken more time and effort than, I would have thought, the majority of people would want to spend.

 

My take is that I have selected (perhaps more correctly 'stumbled upon') two of the leading suppliers in the field (Octopus and GivEnergy), but it could be that other suppliers have these issues resolved - it would be interesting to get feedback from others on this point.

 

I do think that both of these issues are in the hands of the industry and, perhaps solutions are close at hand, if the players have a desire to resolve the issues. However, until the issues are resolved, my view is that domestic battery systems should only be purchased where the user is prepared for the effort required as an early adopter.

 

Summary:

The system is operating reliably and the software is good, with the exception of the scheduling points above (& more detail in a future post) and the issues with the smart meter (now resolved).

 

I am also coming to the conclusion  that the domestic solar+battery energy industry operates as a 'cottage industry'. It works well for enthusiasts, prepared to invest time and effort and is not really ready for mainstream users...

 

...but it is probably the case that the domestic solar (with no battery) makes life much easier, is a more mature market and is ready for the mainstream.