Average Energy Consumption

As I may have already mentioned, I hoping to get Planning consent to extend the little bungalow, and will be aiming to greatly improve its energy efficiency.

It currently has oil-fired central heating and mains electricity.

The Energy Rating is presently E (46) so there is plenty of scope for improvement.

Although improving the insulation, and changing the heating are ‘no-brainers’ the electricity side is more interesting, and I would welcome a ‘sanity check’

I am paying £55 per month, Direct Debit to Shell Energy, and my account is increasingly in credit. … consumption in the period from 04-Aug-2022 to 04-Aug-2023 was a mere 658 units, which covers Lighting, Cooking, Fridge-Freezer, Washing Machine, Domestic Appliances, Shower.

To my surprise, that only averages a little over 0.075 units per hour

When I lose the oil burner; heating and water-heating will both need to be electric: But by incorporating good insulation and high thermal mass in the extension, and appropriate air-circulation throughout the dwelling, I am guessing that my consumption might only double [or perhaps triple] and that a Solar PV array will provide much of that.

This all sounds too easy … so what have I missed ?

MichaelG.

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P.S. __ The present enthusiasm for heat-pumps seems unconvincing when we look at the time needed to amortise their cost [see my comment on another recent thread]

https://www.model-engineer.co.uk/forums/postings.asp?th=188049&p=3

Edited By Michael Gilligan on 27/09/2023 13:49:15

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A significant contributing factor to any ‘guesstimating’ is that the cost of electrickery includes a daily standing charge … so, the more you use the cheaper it gets … and in my case [currently using 1.8 units per day] the ratio is certainly non-trivial

Unit Rate = 30.650p per kWh

Standing Charge = 60.93p per day

MichaelG.

Our electricity consumption for the last month was £55.89, including the daily charge, (useful things, smart meters!), for the same usage as yours, for two adults - except our shower uses gas heated water from the tank. So I might be looking carefully at other providers soon, since we are obviously paying a little too much !

Your comment about heat pumps is possibly valid today - and puts me off as well - but will we think the same when the price of gas or oil has gone up 3 fold or whatever, as governments around the World attempt to wean us off fossil fuels to meet emissions requirements ?

I think part of the very high price of heat pumps is that those quotes assume that not only the boiler is changed - the entire heating system is ripped out and new 'everything' is installed:- underfloor heating, or larger radiators, larger super-insulated hot water storage tank etc. I heard that tanks in the loft also need to be put back in, many having been taken out when converting to condensing boilers, but am not sure why this would be.

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Edited By John Doe 2 on 27/09/2023 14:49:12

Michael,

Have recently been looking at heat pumps - a lot of mixed messages out there.

I'm comparing a 30+ year old mains gas boiler (non-condensing) with a new heat pump. Combining relatively low efficiency of current boiler with projected COP of new heat pump, the gas kWh that could be backed out could be replaced by roughly 1/4 of the amount of kWh of electricity. As 1kWh electricity is about 4 times the price of 1 kWh gas - there is little or no cost saving on the energy used. Figures might look a bit different if comparing against oil.

There is potentially some indirect saving as I could do away with the gas supply and the associated standing charge. If you have solar PV (and especially if supplemented by battery storage) things can look a bit better because the heat pump can help you to use more of the PV generated energy. Choosing best tariff to maximise benefit of the PV can help a bit too.

In broads terms, heat pumps still aren't a great financial investment - but in right circumstances can cut CO2 emissions (depends on how the electricity is generated).

Solar PV - shop around and ask awkward questions! A lot will depend on size and orientation of the array, we found that most providers wanted to just supply a small Inverter and avoid the paperwork of consulting the network operator. For our roof (16 panel array, facing almost due South with no shading issues) a larger inverter made sense. The inverters proposed by most providers wouldn't have made good use of the available energy, either for our use or for export.

You need a hot water storage tank with heat pump ad it can't do instant hot water like combo boiler. You might also need bigger radiators as the temperature of the heating water is lower. I'm not sure why they don't use hot air heating with new builds, then the lower temp wouldn't matter as much. Difficult to back fit unless you have a bungalow in which case the ducting could be in the loft. You could then incorporate a heat exchanger and bleed some of the circulating air to the outside, reducing humidity and do condensation in the house.

Edited By duncan webster on 27/09/2023 15:01:31

I seem to remember reading somewhere there is a government scheme for replacing boilers with heat pumps and a grant of up to £7500, worth looking into…..

Boiler Upgrade Scheme | Daikin

Thanks for the comments

Just to be clear … the heat-pump device that I mentioned on the other thread is a self-contained system that heats a tank of water to 55°C using solar. Details are linked there.

They [predictably enough] tell a good story about it, but as the cost looks to be upwards of £5k and the estimated savings were, according to energysavingtrust, about £65 per year … I thought better of it.

My estimated 100year amortisation of the cost was probably too short, given that even the tank is only guaranteed for 25years.

My ambition is to have everything as ‘passive’ as it reasonably can be … to avoid noise-pollution and maintenance.

Solar PV with a battery, underfloor electric heating in the extension, and an ‘instantaneous’ electric heater for tap water. … It should be possible to get the floor slab and the high-mass internal leaf of the walls up to a reasonable temperature, and then trickle-heat with solar. The battery can supply boost heating of air as necessary.

That’s the theory anyway

MichaelG.

Thanks for the link, Juddy … but I will probably fall at the first hurdle

There is no practical way that I could do the requisite insulation upgrade until I have built the extension !

The place is a small detached dormer bungalow and the ‘loft-space’ currently has no access … there are wardrobes (sic) under the eaves, and no loft hatch …. I dare not even look until I have a big extension in which to put the contents of those two small rooms.

This is not the first ‘financial loss’ on this project, and I am sure it won’t be the last

MichaelG.

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Extract from my EPC

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Edited By Michael Gilligan on 27/09/2023 16:09:14

If you go for solar pv on the roof you might be wise to ensure birds cannot get underneath. Several houses nearby have had panels for years without problems. Then about two years ago the local pigeons started nesting beneath two of them. One had scaffolding up to clean and fix netting, the other has clumps of twigs blocking the gutters. Suspect the scaffolding cost will have badly dented any savings.

Still discussing roof structures … but it will [hopefully] be a 5m wide x 7m long mono-pitch at just over 10° so we are currently looking at ‘raised-seam’ steel covering, possibly with thin solar panels bonded on … alternatively, I need to find out if there is anything like the Marley ‘solar tile’ idea can work with such panels.

Keep it coming chaps … sometime soon I will need to decide how to spend the last of my hard-eared cash.

MichaelG.

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https://www.lindab.com/product/in-focus/solarroof/

https://www.marley.co.uk/solar-roof-tiles/solartile

Edited By Michael Gilligan on 27/09/2023 16:26:31

For anyone interested in sustainable energy it's worth reading the book Sustainable Energy - without the hot air .

Link is to online version free to read.

Written by the late Professor Sir David McKay of Cambridge university. It might be a little out of date now but the logic and simple maths are still very relevent.

Russell

Thanks for that, Russell

… I have downloaded the PDF

MichaelG.

If anyone with a UK electricity bill wants to invest in renewable power without the hassle of modifying their house or dealing with future maintanenance then consider the community ownership scheme from Ripple Energy.

Financially I have no idea whether it will work out - relies on too many long term assumptions - but I'm hopeful as generation infrastructure tends to work better at scale.

My house/workshop has been off-grid since Dec 2022 reliant on PV solar energy. Monthly usage averaged 1300KW over winter, with 2500KW generated. The excess is exported to the Electricity supplier at 60% consumption value.

I have hot water underfloor heating, which used to run from a solar heated water system, heating a 6000liter insulated water tank, buried in the ground. That heated water ( around 30degC in winter end of day) fed a 3phase 14KW boiler, and then into the pipes in the floors. The boiler was used during many low/no-sun days in winter.

In winter my floor heating energy used was around 50KW/24hour period - I did not run the boiler during day time, since electricity costs are almost double between 10H00 and 18H00. So the floors cooled during the day, and extra energy was needed at night to re-heat.

When I fitted the PV system ( 3phase, 28KW PV capacity) I fitted a Stiebel Eltron heat pump - a 3phase pump, with a variable speed compressor, to heat the floors.. The pump is capable of 12KW output, and is an Air extraction pump.

Since I heat the floor water to 35deg C max, and the floor water return temp is never below 20degC, the delta the heat pump sees is a max of 15deg, at start of heating, with the delta reducing as the floor heats up to 25deg setpoint.

All that gives me a pump COP of 10 (!) and I run day and night, so the floors don't cool in the day. That returns a daily heat output of around 33KW, with a consumption of around 3KW...

My monthly usage for floors in now around 100KW, instead of 1500KW - and THAT ticks all the boxes - energy cost, carbon footprint, comfort....

Lower COP's are to be expected if the water heating temp differential is higher, such as heating water for showers, etc ( 50degC plus..) - but this heat pump delivers a COP of 4 to 5 when doing that...

The heat pump did cost around 8K British Pounds...but is better than sliced bread.

I'd certainly investigate other suppliers, mine is currently 29.684p per kW/h and 48.34p per day guaranteed for the next 14 months.

Rob

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Incidentally … I forgot to mention; If mine is anything to go by these certificates are near-useless

It is however, interesting to dig a little deeper into the drop-down details for your own property, on the web-page

**LINK** https://www.gov.uk/find-energy-certificate

Some of the estimated savings look hardly worth the disruption they would cause

… perhaps that’s why people in the U.K. haven’t prioritised energy-efficiency until quite recently.

MichaelG.

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When I moved here, mid-2022, there was no option to swap suppliers … none of them were taking-on new customers

… even my previous supplier wouldn’t move my contract to another property

We have lived through some interesting times recently !!

MichaelG.

Electricity

Standing Charge Per Day - 51.48

Night - 16.31 p/kwh

Day - 35.33 p/kwh

Gas

Standing Charge Per Day 26.16 p/kwh

Dy/Night = 7.24 p/kwh

Mchael

The annual consuption you state appears to me to be incorrect, I believe either you have a very slow meter or you may have got the dates wrong, 658 kWh for a year !!!

If the figures you stated are correct don't request a meter change.

Emgee