After three months of winter heating, it seemed like a good point to assess how the new heating and hot water system was performing compared to the old gas combi boiler. Because of the changes in solar panels and tariffs a direct comparison in terms of monthly cost might be difficult, so initially a comparison in terms of kWh hours would seem more useful. The amount of gas used in 2022 was used to provide heating and hot water, with a small amount used for cooking on a gas hob. The gas hob was replaced with an induction hob and I wasnt monitoring how much electricity was being used by that, so could not account for it. However the effect would be small.
Ignoring that difference, the number of kWh used between the two systems was profound, with the new system using between 28%-53% of the gas figure. The wide variation in the size of the reduction was a little confusing, but I think this is down to several factors between the two years, including:
I know from my monitoring system , that my heat pump is running at a COP of between 4.6 and 3.6 during the winter so far. The lowest COP occuring during a cold snap where the temperature dropped to about 5 degrees C. I fully expected that the heat pump would be more expensive to run in very cold weather, than gas heating. However I also expected that in the shoulder seasons and summer this effect would reverse. Removing gas from my property, meant that I no longer had to pay a standing charge for it and getting an Electric Vehicle enabled me to access much cheaper off peak tariffs and these factors have helped with reducing my electricity bill. In addition my extra solar panels would also reduce bills and provide an income in the summer. So far comparing my total energy bill with 2022 (adjusting for inflation), I had saved £109.31 for the period Oct-Dec. A modest difference and not enough on its own to justify the costs of the improvements made. However I expect this to improve as the the newer EV tariff starts to kick in and solar export starts to increase.
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We finally decided that the time was right to purchase an Electric Vehicle. Second hand prices are very low at the moment and the availability of charging points is getting better. We settled on ordering a 2020 BMW i3.
Having an EV opens up a new range of electricity tariffs available from Octopus and crunching the numbers shows some quite surprising results. Currently on Octopus Cosy and Fixed Octopus Export, I had already picked up on the fact that the cheap rate electricity price and the export price were getting very close (16p v 15p). This meant that there wasnt a great deal of financial difference whether I heated my hot water tank with excess solar via my Eddi PV diverter or did it during the cheap rate periods. One of the new tariffs I could now access with an EV is Intelligent Octopus Go. This tariff is still compatible with Octopus Fixed Export, so I could still get 15p per kWh exporting my excess solar. The idea behind this new tariff is that you hand over the control of charging your EV overnight to Octopus. You just tell them how much you want the car charged and when it needs to be done by. As a reward for this you only pay 7.5p per kWh. This price is a game changer! If I switched to this tariff, then I would obviously get very cheap electricity for my car, but it also meant that I would not get the second cheap rate period in the early afternoon that I currently have when I recharge my 5kWh house battery. Therfore if I assumed that I fully recharged my battery twice on the Cosy tariff, this would currently cost (5 x 2 x 18.13p) £1.81. If I switched to Intelligent Go this would now cost (5 x 7.5 + 5 x 30.52) £1.90. No big change. However heating my domestic hot water now becomes much more attractive during the cheap overnight period, rather than using diverted solar which could be exported instead. If I assume I use 4 kWh of hot water a day, this currently costs (4 x 15p) 60p per day in lost export. If I switched to heating it at night, it would cost (4 x 7.5p) 30p per day. This equates to about £12 per month in savings! As well as saving, I am also helping the grid stay clean by providing my green energy to them in the day when it is needed and using green energy from the grid at night when it isnt needed. So the question is, what is the point of my £500+ solar diverter now? I suppose the pricing of electricity could change in the future and it might make more sense to use my own solar again, but that seems unlikely to me. Perhaps I should look to sell it on to someone who doesnt have an EV? So with the heat pump now working well it was time to get the Mixergy cylinder installed in the same small cupboard. Since it had been sitting around since last year for various reasons, I was keen to finally get it in and working. Since there were no official Mixergy installers in my area, I convinced a local plumber to have a go under the proviso that I would do all the electrical and internet connection work. Everything went smoothly and by the afternoon of the second day, the combi boiler had gone, gas was capped off and the cylinder was in and charging from the Myenergi Eddi PV Diverter for free. As it was a sunny afternoon, we had two welcome showers and a full tank of hot water from the electricity I would have previously exported.
Initially I had decided to just heat the cylinder via an immersion heater, while this is nowhere near as efficient as using the heat pump, I estimated that I only needed about 3 kWh of hot water each day and this could be supplied from my excess PV, certainly for most of the year. I was going to monitor this and if it occured that I was having to import a lot to do this, then I would reassess buying the heat exchanger needed to hook up the heat pump for domestic hot water heating. It was pointed out to me by a couple of people, that I might need to get access to my pump and other plumbing once the tank was installed. This would be difficult because of the lack of room in my cupboard. The solution was to raise the tank off the floor so I could access things from below it.
A quick mental calculation guestimated that the shelf would need to support approaching 200kg and would need to be pretty meaty, so some timber, concrete screws and a couple of hours produced the following result! Having read around the subject and previously fitting a thermal store to my last house, I decided that this time I would plumb for a pressurised cylinder instead (pun intended). My reasoning for this was that although the thermal store worked well, I needed to heat a larger volume of water to a higher temperature to get the same result as a pressurised cylinder. The downside was that I couldnt fit the cylinder myself and it would need an annual service. I had been looking at a Mixergy cylinder which cleverly heats the water from the top down and therefore less water needs to be heated. I reasoned that I might be able to supply my hot water needs (estimated at about 3 Kwh/day) using a solar diverter. I bit the bullet and ordered a 120 litre Mixergy cylinder and a MyEnergy Eddi diverter. The cylinder has the option of adding a heat exchanger to the side so that it can accept input from a heat pump. I wasnt sure if I needed that option yet but it was good to have it there in case I fitted the Eddi myself, but unfortunately finding a plumber who was willing to fit the cylinder proved problematic, so both the diverter and cylinder sat unused in the cupboard. An additional problem was that the indoor stopcock was in the way of the cylinder and I couldnt find the external stopcock anywhere.
Since the house was still unmetered for water, I contacted the Welsh Water and asked them to fit a meter, that way I would get an external stopcock fitted at the same time. |
AuthorEx Radiographer, Information Analyst, Teacher and Self-builder. Now retired Archives
December 2023
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