Solar#2: Solar Panels Investment Case

Introduction

 

For anyone new to this blog, my focus is improving the energy efficiency of a house in the UK. So this post focuses on the investment case for solar panels in a domestic application in the UK.

 

This would be a much bigger investment than other energy saving investments (such as insulating the attic) and needed a bit more thought. In addition, the other investments, on the whole, brought the benefit of increased comfort...

...if solar panels worked well then we would not notice them, other than a smaller electricity bill, ie the only benefit is financial and a nice warm fuzzy feeling that we are helping the environment.

 

Baseline Return on Investment

Having recently retired the obvious comparison is the annual return on pension investments (I have a defined contribution pension):

• 4.5% - my calculation of the long term return from my pension pot over the last approx. 30years (ie the difference between the final pot value Vs what I paid in converted to annual %age compound interest)
• Published data is available from pension providers, such as Hargreaves Lansdown & People's Pension giving average annual growth over the last 5 years. Picking a couple of funds:
• High performing/high risk (& a Boring Money popularity winner) - HL Fidelity Index World: 13.1% - risk level 96 of 100
• More balanced (equity and bonds) & perhaps more typical performance - People's Pension Global Investments (up to 60% shares): 4.6% - "medium risk".

 

So how does investing in solar panels compare to these investment funds? Both for rate of return and risk.

 

The pension investment risk is interesting. Fidelity uses FErisk scores - a comparison to the FTSE 100. A .pdf booklet from People's Pension has a riskregister and it explains the risks and how they are mitigated. My take is that much of the pensions industry mixes up risk with volatility (eg https://www.aviva.co.uk/retirement/fund-centre/investment-funds/risk-ratings/) and that what we get is a volatility score relative to other financial investments.

 

Pension literature often highlights the need for diversification:

• https://www.vanguardinvestor.co.uk/articles/latest-thoughts/investing-success/The-importance-of-diversification
• How to Fund the Life You Want by Robin Powell and Jonathan Hollow.

However, this is typically a mix of equity & bonds; I have not seen mention of buying solar panels as part of the investment mix!

 

So, given that I can now access my pension pot, should I invest part of this in solar panels or should I keep it all in more typical investment funds in a SIPP? How does the return on investment compare and what is the risk? Does it give better diversity?

 

Return on Investment

Taking the Energy Saving Trusts example of £605 saving with a £7,000 investment then the ROI is 8.6% (see post "Our House is Not Suited to SolarPanels?"). They also suggest that I should factor in £600 for a new inverter at around year 12.

 

However, there are some differences to investments funds. For example, with the investment funds, my capital is still an asset that I hope to get back (but the small print does highlight that it is at risk of falling in value). If I invest in solar panels, then it is not practical to sell the panels and get my money back. At some point they will stop working, so I need to include depreciation and maintenance. In this calculation I have assumed that, as well as a new inverter at year 12, the solar panels have no value after 25 years (ie they stop working). Differences to this assumption are included in the risks.

 

The return from the solar panels is also peculiar because it is index linked. We know that energy prices don't go up each year by exactly the rate of inflation, so I have modelled this as inflation of 2.5% every year (my financial advisor suggested this figure for my pension calculations) and then I have considered differences to this average rate in the risks (downside and upside).

 

Finally, the pension investments come with small fund and platform charges (eg 0.25% for Hargreaves Lansdown platform for funds of <£1,000,000, 0.12% for the Fidelity fund, 0.50% total for the People's Pension fund).

 

Putting all of this together gave me a total ROI, based on today's prices, after 25years, from £7,000 investment:

• Solar Panels: £15,000
• HL Fidelity World Index: £80,000
• People's Pension Global Investments (up to 60% shares): £10,000

For the 2 investment funds the above includes the return of the original £7,000 investment and the headline growth is reduced by inflation and the charges. For solar panels I don't get back the £7,000, but there is no inflation erosion of the return on investment and, while there are no fund charges, I have assumed the new inverter mid-way through the 25years.

 

Risks

Given that this blog is about energy, below I have focused on the risks that I see with solar panels:

 

• Additional costs of breakdown and repair
• They do not last for 25 years (downside) or they last longer than 25years (upside)
• The sun does not shine. I am assuming that this will average out over time and that the average is accounted for in the Energy Savings Trust estimates, but I guess that climate change could change the average for better or worse (eg more cloud)
• Inaccurate estimates from the Energy Savings Trust and from installer quotes. My understanding is that these are deliberately slightly pessimistic (ie I should get slightly better generation than quoted).
• Panels degrade over time - apparently this will happen, but to what extent?
• Decision to move house before 25years. My guess is that there will be some increase in house value because it has solar panels. Quite a few websites offer opinions on how solar panels affect the value of a house:
• https://www.thisismoney.co.uk/money/bills/article-12277789/Sales-hotting-solar-panels-add-value-house.html
• https://www.yopa.co.uk/homeowners-hub/how-much-do-solar-panels-add-to-the-value-of-your-house/
• https://www.bettermove.co.uk/blog/increase-home-value-with-residential-solar-panels/
• https://www.theecoexperts.co.uk/solar-panels/property-value
• https://solarfast.co.uk/blog/do-solar-panels-increase-your-house-value/
• https://www.moneysavingexpert.com/utilities/free-solar-panels/

We have no plans to sell our house in the next 25years, but we might want to and it is clearly a risk that we will not get back the residual value of the solar panels. Money Saving Expert seems to give the most balanced view of the above and my opinion is that the affect on house price value will be in the range of £0 to £not very much!

• Electricity prices go down (or up): This is an odd one as:

• Electricity unit prices go down: the ROI is reduced and the return is less. However, (assuming that I still have to buy some electricity) then my energy bills also go down (which is good!). 
• Electricity unit prices go up, above inflation, then the ROI is better, but I am paying more.

Is it good or bad if energy prices fall or rise? My take is that we will be happy if energy prices fall (we have lower electricity bills) and feel smug if energy prices rise (electricity bills go up but people without solar panels are paying even more!)

 

• Change in government/regulator policy: this is really about pricing, but with a subtle difference. The whole price framework could change:
• This happened with the recent April '24 price cap change; the regulator shifted a little of the cost from the unit price to the standing charge. The view expressed in the Guardian (https://www.theguardian.com/money/2024/mar/30/energy-bills-standing-charges-are-not-standing-still) is that this is specifically so that "affluent households, who could afford to install things such as solar panels, would still pay their share."
• Over the next 25 years you can imagine all sorts of regulatory changes to encourage different behaviour:
• Reduce standing charge/increase unit cost to encourage domestic investment in energy saving (or vice versa as above)
• Reduce electricity unit pricing to shift costs from electricity to gas to encourage use of (green) electricity (eg encourage heat pump uptake)
• Increase electricity unit pricing to replace taxation on petrol/diesel as large numbers of people switch to electric vehicles.
• In the end this is another risk - something not in my control and almost impossible to predict.
• Death within the 25years. I guess that if our children inherit the house with solar panels then there will be limited additional value, but they would inherit my pension pot, complete with the original capital in the funds.

 

Conclusion

My take on the above is that:

• The return on investment in solar panels is the range of that from other pension investments.
• There are risks but these are very different to regular financial products and, in my view, a 'medium' order of magnitude, but this is very subjective.
• Investment in solar panels is a good idea as part of a diversified portfolio of investments
• And gives a nice warm fuzzing feeling of being good for the environment.

 

Next steps - get some quotes and confirm that the above conclusion still holds and another question...

...is solar with a battery a good idea?

Solar#1: Our House is Not Suited to Solar Panels?

Our house has two main roof surfaces - one faces roughly East and the other roughly West; my assumption had been that you need a South facing roof to make solar panels worthwhile.

 

Roll on energy price rises in 2022 and I started to wonder if this was true...

 

...in Summer 2023 I was researching the topic more seriously and came across this website:

 

https://www.snugg.com/

 

You enter a few details about your property and it gives you an energy efficiency plan. In writing this post I looked again at the website and it looks more sophisticated now, but even then it gave some useful pointers including a link to this website:

 

https://energysavingtrust.org.uk/tool/solar-energy-calculator/

 

 

After adding a few details you get a simple investment case for solar panels:

• How many panels you can fit on the roof (you can also pick from 1 of 4 standard house sizes - that's what I did)
• Roof pitch (our house has a shallow pitched roof, so I went for 30degrees - it turns out to be 26degrees)
• Direction - there is a really cool tool that shows a Google Maps image of your postcode. You can pick your house and adjust the direction (I later found out that mine is -74degrees from South, ie 16degrees from East, but you don't need to know this to use the tool)

• Estimate of shading (we have none - you can pick from 4 levels)
• You add a little bit on what electrical appliances you have and your lifestyle and then you get the answer.
• For me this initial feedback was:
• Solar is suitable
• Suggesting 12 panels
• Annual savings of £605
• Estimated install cost of £7,000
• Payback of 13years, including for inverter replacement at 12 years.
• One nice feature of the calculator is that you can go back and try out different examples (eg I tried out a South facing house and it did not make that much difference)
• Out of interest I retried this just now with 25degrees roof pitch and the annual savings are now £615 and payback 11 years (I guess that their model has the inverter failing just after the system has paid for itself!).

 

 

This spiked my interest, enough to give two more tasks:

• Investment case - is it worth doing with a payback period of 10 to 15 years?
• Get some supplier quotes - what is the real cost and complexity?

...and more blog posts

2023 Data Analysis

Introduction:

So one year on, how does our gas and electricity consumption compare to previous years?

 

At the end of the summer 2022 we added loft insulation (increasing from 100mm to 300mm - see post: "Insulate the Attic". We also reduced the central heating flow temperature and dropped the room temperature by about 1degC (not everywhere - we sneaked it back up in some rooms!)

 

The result:

 

 

A reduction in gas consumption of £325 per year (19%) - comparing year ending October '23 to year ending October '22

 

Lifestyle changes in the year: I retired in the summer of 2023. The year end for this data is 12th Oct 2023, so this would have had limited impact as we only put our heating on during September. We also added weather compensation to control the central heating flow temperature. This was added in mid-August, so again would have had little impact.

 

Potential Sources of Error:

My aim is to get down to purely the impact of energy saving measures. Sources off error might come from:

 

Weather in the time period	I did make some attempt to look at annual average temperatures, but it is more complex than that - eg day Vs night (when heating is mostly off). I am also unsure how much impact windchill (windy day Vs calm day) will have. These results do not take account of variations in weather from year to year, other than 2009 to 2016 should be much better given the 7 year time period.
Life style	My wife's retirement in 2019 and then my retirement in 2023 (data still to be shared) seem to make little impact.
Pandemic	The impact of my working from home and being locked down seems to have caused a big rise in energy consumption, unless there is some other big difference that year.
Energy prices	I have removed the impact of this by recording actual energy used (kWh) and then using just one rate (usage and standing charge) across the whole time period.
Inconsistent time period	I have not measured energy usage on the same date every year, so the period for each 'year' was up to 27days from the 'perfect' 365days. My estimate is that this has made a <2% error in each year's energy usage data.

 

I would be very interested in feedback suggesting any other potential causes of error.

 

My view, from the above and now seeing 2 years of post-pandemic data is that 2020/21 (ie the pandemic lockdowns) is an outlier

 

Discussion:

 

In my post: "Insulate the Attic" I stated that I thought most of this saving was due to the attic insulation. However, reading this article from University College London (https://www.ucl.ac.uk/news/2022/dec/analysis-energy-bills-how-much-money-does-turning-down-thermostat-actually-save) their model from research of 13,000 homes is £1.1 saving per year per degC temp drop per m2. For our house (186m2) this gives £205/year saving for a 1degC temperature drop.

 

I feel an experiment coming on here. We did decrease the temperature in a 'lived in' rooms in late summer 2022. However, later in the Winter we moved this back up in some rooms (for more comfort). We had also made no change in the little used rooms - these account for perhaps 50% of the external surface area of our house. So my very rough estimate would be to halve the £205 and attribute £100 for saving due to reducing the temperature.

 

I still don't believe that a reduction from 70degC to 65degC of flow temperature has much impact (eg https://www.viessmann.co.uk/en/heating-advice/boilers/what-temperature-to-set-condensing-boiler.html give the dew point  of 55degC as the maximum water flow temperature to maintain boiler efficiency. However, I have not been able to find a graph or data to tell me the benefit of the drop from 70degC to 65degC.

 

Ignore 2020/21:

Now that I have 2 years of post lockdown/pandemic data I think that 2020/21 was an outlier, most likely we were in the house for much more time and just wanted it warmer.

 

So now the comparison is:

 

Year	Gas Usage	%age Saving on previous year	Energy saving measures taken early in that year
2019/20	£2,100	baseline
2020/21	£2,690	ignore
2021/22	£1,710	19%	Smart Heating Controls (Aug) and garage central heating pipes insulated (Dec)
2022/23	£1,387	19%	Oct: attic insulation, set flow temp to 65degC, drop CH temp by 1degC
n/a	£205	12%	UCL theoretical saving for 1degC temp drop

 

Difference between 2019/20 and 2021/22 is 19% with the main changes being smart heating controls and insulating central heating pipes. Using my calculation in my post on insulating pipes in the garage, £35/year or 2%1, then a whopping 17% is down the smart heating controls.

Drop from 2022 to 2023 is temp reduction (but negated because we nudged it up during the winter, so perhaps half the UCL findings, ie £100. Leaves £200 down to loft insulation.

All the is very rough an ready. I have not accounted for weather or other more subtle lifestyle changes, so my very (very) rough summary of savings is:

 

My Current Estimate of Impact of Different Energy Saving Measures:

 

Change	Installation cost	Approx annual saving	Approx payback period
Smart Heating Controls	£1,800	£2901 +02 / -100	6-11years
Insulate Central Heating pipes in Garage	£120	£35 +/- £15	2-6years
Loft Insulation from 100 to 300mm	£1,160	£200 +/-£100	4-10years
Flow temperature from 70degC to 65degC	£0	£25 +/-£25	Instant
Reduce room temp by 1degC for some of the winter in some rooms	£0 - less comfort	£100 +/-£50	Instant

 

Notes:

1. I have used the 2021/22 gas usage of £1,710 for converting between %ages and £s so that the sequence of the changes does not bias the result.
2. While the calculation gives me 17% saving for smart heating controls I think that this is probably on the high side.

 

Oct 2024 should help confirm if 2020/21 is an outlier that can be ignored and may give more clarity to other conclusions, but also adds two new factors: I retire and the addition of weather compensation to the boiler...

...look out for a future post.

 

Smart Heating Controls - My Experience with Honeywell Evohome - Part 2: More Technical Points

During lockdown in 2020 it seemed like a good idea to get better control of our heating. My focus was better comfort, but saving energy would also be good. We had Evohome installed in September 2020.

 

So, with the perspective of 3.5 years after installation (March 2024), how has the system performed?

 

This is part 2 of this review. I posted part 1 in January, targetting user experience and this Part 2 is focussed on more technical points.

 

Selection & Installation

• The Automatic Bypass Valve (ABV) allows all radiators to have Evohome TRVs. It is a short copper pipe and valve added close to the boiler to allow for pressure release when the last radiator turns off and allow time for the boiler to turn off).

Automatic Bypass Valve (ABV) installed just under the boiler.

 

Early installation issues fixed by the installer during September and October:

• A couple of the TRVs did not operate correctly to start with - not sure why (maybe sprocket not engaged with the valve on one?)
• Hot water tank thermostat incorrectly installed (it turns out that the recommended installer had so far installed just 6 Evohome systems and that ours was their first with a thermostat for the hot water tank) - this was also fixed in a couple of visits.
• We had a pre-existing wiring fault; this took more extensive diagnostic work and much head scratching from Mike the installation engineer. He stuck with it and found the cause; a broken cable core between hot water tank and boiler.  I laid in a replacement cable (floor boards up, hole in the ceiling, etc) and he connected the cable at each end.

Installation result:

• From the installation starting in mid-September and finishing at the end of October we had a stable system ready for winter:
• Without the existing wiring fault I would not have needed the installer to return more than a couple of times.
• There were gremlins with the system, over the September/October period, that I fixed myself (eg valves that lost their calibration/off position).
• I agreed with the installer a fair split in costs for the extra work that was not included in the fixed price (the broken cable core was our cost, the rest was theirs)

 

Lessons learned (more technical points)

• The Honeywell documentation is OK for a working system but very limited on fault diagnosis and resolution. There is limited 3rd party material available online. So, learn what you can when the installer is on site.
• Testing the system can be frustrating. The time lag from changing a temperature setting can be from a few seconds to a few minutes as the change ripples through from TRV to app (or app to TRV) and then to boiler. This has never been an issue in day to day operation, but means that testing can take a long time and needs much patience . I am sure that there were a number of times I suspected a fault, but waiting a little longer would have proven that everything was working (see above on knocked confidence).
• I would recommend having a simple test script - eg
1. start with central heating off.
2. Check all radiators cold
3. Turn all radiators to target temperatures above the actual room temperature (eg +2deg) using the app, so that all radiators should come on:
• Wait 20mins (this probably only needs to be 5mins, but you want to be certain that it is not a time lag issue)
• Check each TRV has the new target temperature reading
• Check each radiator is warming up
• If the TRV has the right target temperature but the radiator is cold you can check the actual demand on each TRV on 'system summary' on the handheld display (press 'settings' for a few seconds and you get the option to go to the 'configuration' menu).
4. Turn all radiators off from the app:
• Test as above, but this time you have to wait longer for the radiators to cool down.
• A test script is useful because:
• You quickly identify faults with high level of certainty.
• It helps in removing any gremlins early.
• If there is a fault you can be very specific with the installer on what is wrong and confidently replicate the issue when they visit and then test that the fix has worked.

 

Evohome Software - Deficiencies and Recommendations for Honeywell

While software is pretty easy to use it does have a few (minor) deficiencies/frustrations:

• I have not seen any software updates. In writing this piece I have googled this point and I see that there has been an 'application software' update (mine is v02.00.17.03 and a May 2023 posting on the manufacturer's website has v02.00.19.33 - see https://resideo.my.site.com/ensupport/s/article/How-to-check-the-firmware-on-the-evohome-WIFI-controller?language=en_US). There is very little written about what the update does, other than it 'works on heat pumps' and has 'smart weather features'. I had registered my e-mail address, but Honeywell did not bother to contact me to tell me about the update. Apparently the update should be automatic, but you can also send your MAC address to Honeywell (now Resideo) and they will update the firmware (I have just tried this and the webform kept crashing - I will keep trying in the coming days and update this article if I get a result)...

...so perhaps all that follows is now out of date with the new version of software!

• While programming a new schedule is reasonably simple, it is also a little fiddly. It is Perhaps hard to see how to make it less fiddly on the Evohome controller with such a small display. Perhaps there is a case for a PC / iPad version of the software with a simpler drag and drop scheduling interface (there is a web interface - this seems like a simplified version of the hand controller and does not include a schedule editor)
• The handset and phone apps have different interfaces. Not sure why Honeywell went to the effort of developing 2 interfaces and putting all of their users to the added effort.

Hand controller scheduling interface	Hand controller temperature override interface
iPhone scheduling interface	iPhone temperature override interface

• The 'System Summary' screen is pretty useful in diagnosing issues - showing the %age demand on each radiator; it seems odd that it is buried on the configuration menu.
• I have not tried the 'optimum start' and 'optimum stop' features.
• I do think that these are a great idea  - Evohome learns the warm up / cool down profile of your home/room and you schedule the time at target temperature as opposed to the heating off/on times. In other words Evohome turns the heating on early on a cold winter's day so that when you get up the house is warm; on warmer days the heating comes on later saving you money.
• So why not use them? Given the initial 'teething problems' this seemed just another layer of complexity to go wrong; I wanted to build confidence in a stable system. I must admit that during the last couple of years I have pretty much forgotten about Evohome (which is what I wanted) and I have not got around to trying this feature. Writing this has got me interested again (I feel an experiment and another blog post coming).

 

After all the above 'negative points' I reiterate the point from part 1: The Evohome software is easy to use and fine for day to day operation. However, I do think that Honeywell has missed an opportunity and a few extra software features that would improve the value of the system:

• Self guided fault diagnostics / resolution (eg my low cost HP printer has great animations for replacing ink cartridges and all the faults that I have encountered over several years)
• Build in more fault tolerance (eg a monthly automatic TRV calibrate cycle and a proper battery warning on the hot water thermostat would probably eliminate >90% of the issues that I have seen)
• Better controls on going out / turning the heating off/down (Eco mode):
• Resolution of <days><hours><minutes> on when to switch the heating back on
• Include the option of hot water off and a check box to have this on, say, 24hours before the heating is on (I have the hot water scheduled just once per day and want to return from holiday with hot water in the tank)
• Checkbox option for 'optimum start' so that Evohome works out when to put the heating on for my expected return time, even if I am not using optimum start at other times.
• I see that other systems have 'geofencing', so that your mobile phone instructs the system when to turn on based on your phone's location. I have not used such a system, but my view is that this feature would be bad:
• My distance from home is not a good indicator for how long I will be away (eg 5 miles walk to a local pub and a boozy afternoon by a log fire Vs 10 miles to a shop and back in 2 hours)
• How does the system decide how to arbitrate between 2 or more phone? (& not an easy algorithm as my wife often does not carry her phone with her, especially if I have mine).
• If the flow temperature is set low (good for boiler efficiency) then the warm up time, from cold, may be several hours. In other words geofencing would have to work with an 'optimum start' algorithm. If you were away for more than a few hours and you drove home at 70mph then the 'geofence' would need to be set at a few hundred miles away - is this really practical? If you fly home then it relies on the efficiency of your local airport - for me landing at our local airport to home is usually about 2 hours, ie the house would not be warm after a week away in Tenerife in the winter and the geofence was set at the airport.
• 'System Summary' screen is pretty useful in diagnosing issues, this should be more easily available  - I do not understand why this is buried on a hidden page on the hand held display and not available on the phone app.
• The schedule has a limit of 6-temperature changes each day - see part 1 on how we use the system - it would be better to have more.
• PC / Web version of the application software for easier schedule setting.
• Having a few labelled schedules (eg on the PC interface) would probably be useful (holidays, winter, summer, visitors staying, etc) - the system currently allows just one additional stored schedule.
• Data logging:
• good for diagnosing Evohome faults (log target and measured temperature)
• Helping to assess where the heating is working hardest (log target temperature, TRV demand and measured temperature). I think that this would help show where insulation would have the biggest impact and/or if a radiator is undersized.
• Synchronised demand. I have a theory that Evohome is turning the boiler off and on more times than is required and that this is wasting energy. This is just a theory and clearly depends on the boiler and my knowledge of boilers is almost zero...

...Just say that Evohome switches on radiator A  and the room with radiator B is at temperature and so the TRV is off. This will fire up the boiler. A little later room A gets to temperature and so the TRV on radiator A switches off. The boiler now turns off. A little later, the same happens with radiator B so the boiler is on again. Is there an opportunity to optimise this so that when the boiler fires up because radiator A is demanding more heat then the system checks for any other radiators that will need heat in the next, say, 30 to 60mins and turns on these TRV's (perhaps at a low %age demand) to give (some of) this heat early when the boiler is on anyway. I am not sure if this would save energy and I guess that it all depends on the current Evohome algorithm and boiler efficiency characteristics.

• I think that Evohome has the data to be able to provide a measure of insulation. I have seen figures quoted for insulation quality in terms of 'temperature loss in 5hours from 20degC inside when 0degC outside' (https://www.euronews.com/green/2022/12/09/europes-energy-crisis-in-data-which-countries-have-the-best-and-worst-insulated-homes). Since installing Evohome I have also put in some additional insulation - it would be really cool if Evohome could tell me if this has had an impact and how my home stacks up against others in the UK and elsewhere.

 

My view of Evohome after 3 Years

• Comfort: Evohome gives a much more consistent and controllable temperature through the house than our previous setup (ie thermostat in the hall, programmable timer and mechanical TRVs). The following are minor points in comparison to the previous set up.
• Our Kitchen temperature is not very even across the room; I think because the radiator and thermostat/TRV is behind a breakfast bar & there is limited air circulation with the rest of the room. The fact that we worry about this, & this was the case before we installed Evohome, tells you that we are getting to the finer points of getting good temperature control. I may experiment with a separate Evohome room thermostat, located elsewhere in the Kitchen.
• We have our flow temperature set at 65degC. I understand that a lower flow temperature would make our condensing boiler run more efficiently. However:
• As the boiler also heats our hot water tank we need a 65+degC flow temperature to avoid bacteria growing in the hot water tank.
• Our boiler model can achieve this with a weather compensation add on, but this means that the flow temperature will vary during the day. Question: will the Evohome self learning algorithms cope with an ever changing flow temperature? (see future blog post on weather compensation)
• Reliability:
• After the first couple of months I learnt how to fix the occasional (every few months), and undocumented, TRV fault and I now believe that, outside of battery failure, this is the only TRV fault that I have ever seen:
• TRV and physical valve being out of sync (eg radiator valve is off and the TRV 'thinks' that it has turned it on).
• I have not found any online guide as to how to fix this, but the following is quick and seems to work:
• Turn the TRV to +5degC and wait for the TRV to finish attempting to turn off the radiator (ie after any motor whirr has completed).
• Unlock and remove the Evohome TRV (slider the bottom of the TRV)
• With the TRV removed, manually turn the valve off (black knob/sprocket on top of the valve, that engages with the TRV) until you feel strong resistance, without forcing it)
• Replace the TRV and lock.
• Turn up the TRV to a high (radiator on) target temperature:
• The TRV will start to whirr and switch on demand (within a few seconds)
• Often, but no always, the TRV display then shows "CYCL" and, I think that, this indicates that the TRV is self-calibrating (ie finding the max on and max off end of travel for the valve). After cycling for a while (1 minute?) the TRV then goes to the set temperature.
• Hand held display battery life is a pain, especially when doing fault diagnosis. It would be good to be able to carry the handheld device from radiator to radiator to check demand against radiator temperature. The handheld display battery life does not allow for this, lasting only a few minutes.

 

Final Comments:

I would recommend Evohome if you want to control individual room temperatures and you are not a technophobe. With a few developments and better support materials, I think that Honeywell/Resideo could make this a more robust system suited to a much wider market.

Insulating Pipes in the Garage

We had a new condensing boiler installed in Summer 2017, complete with new radiators and connecting pipes. The new connecting pipes are mostly plastic and, to simplify installation, the garage was used to route some of the pipes. My simplistic take is that the other pipework, mostly in the ground floor ceiling (and a little on internal walls or behind skirting boards), is helping to warm the house and so the fact that it is not insulated does not really cause significant losses. However, the pipework in the garage, was simply raising the temperature of the garage.

 

Situation before insulation:

Pipework routed through the garage: 

• 13.8m of 28mm  diameter pipework
• 2.3m of 15mm  diameter pipework
• 8.4m of 10mm diameter pipework

When hot water was flowing to these radiators the pipework was hot to touch. 

 

After insulation:

28mm Pipes with Insulation	10mm Pipes with Insulation

 

The external surface of the insulation is very slightly warm to touch when water is flowing to the radiators. I would expect that the radiator temperature is a little warmer now, but I could not detect this by hand.

 

Shopping list:

• 2x 3pack x 2m of 9mm thick insulation for 10mm diameter pipes. Note: most insulation that I found for smaller pipes was thinner than for larger diameter pipes; I am not sure why given that the physics, I think, is the same. I chose the thickest that I could find.
• 13mm thick insulation for 15mm diameter pipes.
• 19mm thick insulation for 28mm diameter pipes.
• Pipe clips (new ones to allow space between pipes & the wall for insulation)
  
• Spacer/washers: the pipe clips for smaller pipes, did not allow enough space for insulation at the back, so spacers were requires so that the pipe sat a few extra mm from the wall).
• Duck tape (to hold smaller pieces of insulation, eg at corners and joins)
• Total Approx £120

 

Doing the work:

This took a total of about 10 hours at the weekends, mostly in replacing the pipe clips to give space for insulation behind the pipes - better insulation and the insulation holds on the pipe without (much) tape.

 

Estimate of saving and payback:

This is hard. This was the only new energy saving measure that I took before the winter of 2021/22 and in 2021/22 we saw a 36% (£980) saving in gas usage over 2020/21. However, I am not convinced that insulating a few pipes gave all of this saving. Perhaps lockdown during the pandemic causes a spike in usage in 2020/21 or 2021/22 is unusually low and usage will rise back up in 2022/23...

...I will analyse the data for 2022/23 and see if I can get a better understanding of the energy saved and payback over a longer period (future blog post). However, given the low cost and the dramatic drop in pipe temperature, I would be surprised if payback is very long.

 

Can I Calculate the Energy Saving?

This website  (https://modbs.co.uk/news/fullstory.php/aid/615/Clear_thinking_on_insulating_plastic_pipes.html>) gives a range for the heat conductivity of plastic pipe of 0.16 to 0.22 W/m.K. I am a little dubious about this as heat loss is surely related to surface area and my pipes range from 28mm diameter down to 10mm diameter, so must have a surface area range of around 3:1. However, using an average of:

• 0.2W/m.K for all pipes (irrespective of diameter)

and assuming:

• Uninsulated: a temperature drop of 60degC across the plastic pipe wall, from flow temperature (set at 70degC) to average room temperature (guessed at 10degC)
• Insulated: zero temperature drop on the plastic pipe wall (ie all the temperature drop is across the insulation)
• Gives a total saving in heat/power loss of ~300W, when the pipes are hot

I mapped this across the year with the following assumptions:

• Heating on from 6am to 10pm = 16 hours (some days we keep it on later, but we also turn it off when out)
• Duty cycle (& this is a real guess) of 50% in winter (4 months), 25% in Spring/Autumn (2months+2months), 10% in summer (4months)

Gives an annual saving of approx. 500kWh, or ~£35, at the £0.07/kWh charge that I am using from August 2023.

Given how hot the pipes were then I can believe the 300W (1/3 of a 1 bar fire). However, given all the assumptions I think that there is quite an error band in this calculation, especially in the average pipe thermal conductivity and the duty cycle that I used to map this onto annual energy savings.

 

And Finally:

In writing this post I have realised that the pipework for the hot water cylinder is all under the 1st floor boards (above the ground floor ceiling). Perhaps there would be a case to insulate these pipes as they heat up the house in summer (a future project and blog entry perhaps).