kWh for hot water gas vs Electricity

[Ken]

In energy terms measured by that which comes in to your house then leccy is more efficient than gas so that 5:1 fig must be referring to something else.

I wonder if you are using 80C as measured at the top of the tank because you have just the standard kind of length immersion element when in best solar PV practice you need a longer one say 3ft.

[nowty]

I have always thought gas combi's were a bit dodgy in terms of efficiency for hot water, especially in Summer and I do remember that Energy Savings Trust report on combi's and it was not good.

I have a well insulated 300 litre pre-heat tank running into my combi. I can heat the pre-heat tank with either a heatpump (up to 50 degrees) and / or use the twin immersions to heat up to 60 degrees.

From April to Sept / Oct the gas combi is now completely turned off and I only heat my water with free renewable leccy, either direct from the PV or from what's stored in the home battery. If its generally sunny I just use the immersions via the immersun diverters, but if its cloudy I first use the heat pump up to 50 degrees, then top up with an immersun boost as its more efficient.

My gas usage has dramatically dropped so much in summer that my gas supplier keeps refusing to believe my readings.

[Oliver90owner]

My gas usage has dramatically dropped so much in summer that my gas supplier keeps refusing to believe my readings.

We basically only use gas during the winter months. The gas meter sometimes does not change from one monthly reading to the next during a good summer as it is only recording cooker hob usage.

This may change since, recently, when I invested in a BergHOFF Eurocast Non-Stick Teppanyaki Plate - the plain flat version - on July 23rd. My wife had checked their displays and decided there was nothing she wanted or needed, but I fancied the idea of the thing, so bought one.

It has been used on most days - more than 15 - so is rather popular with the ‘Domestic Mistress’, it seems. As cooking the main meal of the day was previously mostly cooked in the electric oven, I expect we are rather better off, but might see the increase in gas usage this month.

[Joeboy]

I like the sound of the Teriyaki plate. Shall have a look. We recently bought a non stick deep pan electric cooking element with lid and it has been great. We have great fun trying to avoid the Smeg 5 gas burner. Much the same April to Oct on gas use (very little). If I can.prove that the water heater gas side is as inefficient as I suspect 5gas to 1equiv electric I will once onto Go utilise switchbot thru the night to heat the HWT. Might be worth doing regardless if output from Ripple is high. Ken, immersion coil is at bottom of tank as is its built in sensor. Will bear in mind coil length for eventual failure.

On reflection we had a number of almost zero pv days in July. Certainly not enough coming in to activate the iboost. I shall check those days on gas meter info against the low low day on solaredge graph when we get home and should be able to get close to the gas vol used across a month solely for HW. This will give me a foundation to adjust from going forward.

[Bugtownboy]

Joe, if you’re looking at alternatives to the gas hob that you can run from your PV, check out Remoska cookers. Relatively low energy, very flexible and practical.

https://www.remoska.eu/en

I think they’re originally a Czechoslovak design, but they were popular in Eastern Europe - MiL is Hungarian and swears by them.

[Joeboy]

Thanks BTB, on a 1st pass it looks as if we burn 19kWh gas extra per day on the zero iboost days. Thats going on month of June compared to July where we had 4 no boost days. Compared to 12kWh electric and getting up to 80 deg rather than 65 deg with gas. Direct heat from the element is the clear winner on a efficiency if not cost basis. Take into account the FF side of things and the output from Ripple on a Go contract it's clearly the way to go. I can't do day to day comp as my meter has been tits up since Feb. Nonetheless, a strong indicator of the way forward. I'm away for a dip in the pool. Heid's overheating!

Noted on the Hob, thank you.

I'll do an average HW use day when home and force gas use with an accurate count. Already and without a calculator or more precise figures 40% efficiency looks possible with gas.

[Joeboy]

Assuming direct electic in tank element to be 100% efficient in OSO super insulated tank then taking into account temperature gained for power used then gas side for heating hot water is only 51.35% efficient in comparison. That's poor.

[Ken]

Not sure the Energy Saving Trust would agree with you. That figure is about right for the non GCH particularly because of the high temp being used and that the boiler is not condensing at those temps.

200L (water) x 60 (temp increase) x 0.00168 = 20.1kWh required to heat the water although in practice not heating all the tank.

When i wanted to investigate this question i just hard wired a OWL(?) meter to the immersion and left it on and also left it on whilst going on a long holiday to give a reading for heat losses. I guess you could also do the same for the gas.

[Joeboy]

We'll see. I'm confident in my figures for a first pass on a rough 24hr cycle at our home. All inputs appreciated, truly thanks Lads.