kWh for hot water gas vs Electricity

[Joeboy]

Not sure if I've asked this one before. On an average water use day we will run the dishwasher, a couple of showers and then general hot tap for cleaning etc. We will then use between 10 to 12kWh of diverted electric to bring the 200 ltr+ tank back up 80 deg C. Do that for a 30 day month and that's 330kWh electric. From memory that does not corelate with gas use saved. I'm pretty sure that month to month comparison we are around 1,500 to 1,800 kWh less gas use and that doesn't get up to 80 deg C. Wondering if anyone has worked out the ratio for kWh burnt on a GCH system in comparison to direct element heating. I am thinking it's about 5:1 going on figures. Take pity on me I've only got this much solar pv to keep me occupied!

[Mr Gus]

I despise that type of "solar" Joe (apologies) whilst you may have a grip on good operation many who buy that sort don't.

They are too often advertised with overstated capacity & the premise of leaving anything black with a battery attached to superheat in the sun (uk or otherwise) is worrisome by way of result & reputation that solar in general gets as a result.

I have 3 different sized fold open (one with a standing prop) that I can then provide shade to a powerbank or phone, they all work very nicely though aren't "pocketable" & are the sort of thing i'd leave at a holiday home.

However, the difference being I paid around £5 for each as part of one of those shonky review programs for sellers on amazon they are there if you look (places like vipon) but so much price overblown tat nowadays that you still have to be very selective. (leave an honest review if you do it's always nice to see some genuine solar product knowledge, just be prepared for amazon to take it down regardless of quality)

[Joeboy]

This one is 2.5 years old and was excellent on my European tour a couple of years ago. Charged off of van roof pv.or alternator while on move and charged phone many times over when out and about. It's a bit smaller than my note 4 so ok for a cargo pants pocket. Efficiency of the solar side of it? Unlikely but it looks good, flashes lights, has a torch and just maybe has a small solar phone charging capability.

[Joeboy]

I prefer these wee one's only a couplea quid from the shonky shop, good wee bit of kit. I will even admit to using them at home charged off the arrays thru the day to save any power drawn from the battery stack at night.

[Mr Gus]

https://www.amazon.co.uk/gp/product/B01 ... UTF8&psc=1 (the small one)

No faff set up, sits in my backpack mostly, bought in 2016, there was a plethora of them at that time for peanuts, but I tended not to alert " st elsewhere forum folk" due to a few disgruntled folk who used to snipe.

Bought 4 different brand units of various size which we use every uk summer, & in the alps.
I tend to keep a few power banks for this purpose also ...ok 8, typically 10, 15, 20,000 capacity

[Bugtownboy]

Not sure if I've asked this one before. On an average water use day we will run the dishwasher, a couple of showers and then general hot tap for cleaning etc. We will then use between 10 to 12kWh of diverted electric to bring the 200 ltr+ tank back up 80 deg C. Do that for a 30 day month and that's 330kWh electric. From memory that does not corelate with gas use saved. I'm pretty sure that month to month comparison we are around 1,500 to 1,800 kWh less gas use and that doesn't get up to 80 deg C. Wondering if anyone has worked out the ratio for kWh burnt on a GCH system in comparison to direct element heating. I am thinking it's about 5:1 going on figures. Take pity on me I've only got this much solar pv to keep me occupied!

Apologies for not answering the question, Joe, but I’m staggered at the amount of energy you’re using to heat water.

We haven’t got anything fancy - combi boiler for DHW and CH (if used) - cold fill DW and WM. Run the combi in eco mode and tend to wash hands with cold water.

Showers are from the combi, have an occasional bath.

Our annual gas useage, including the Hob, is 1800-2000 kWh. (Heating is from ‘dry’ WBS’s)

In fairness, we do like winter Sun, so we’re away for 6 weeks over winter.

[Stinsy]

To the original point:

Gas typically costs: 2.5p/kWh, whereas you (typically) get 5.5p/kWh for selling the power to the grid. So you're better off selling the electricity than diverting it to your hot water tank. However many combi boilers are woefully inefficient at producing hot water (the impressive numbers on the box are for space-heating), so in reality it is probably a wash.

[Joeboy]

Not sure if I've asked this one before. On an average water use day we will run the dishwasher, a couple of showers and then general hot tap for cleaning etc. We will then use between 10 to 12kWh of diverted electric to bring the 200 ltr+ tank back up 80 deg C. Do that for a 30 day month and that's 330kWh electric. From memory that does not corelate with gas use saved. I'm pretty sure that month to month comparison we are around 1,500 to 1,800 kWh less gas use and that doesn't get up to 80 deg C. Wondering if anyone has worked out the ratio for kWh burnt on a GCH system in comparison to direct element heating. I am thinking it's about 5:1 going on figures. Take pity on me I've only got this much solar pv to keep me occupied!

Apologies for not answering the question, Joe, but I’m staggered at the amount of energy you’re using to heat water.

We haven’t got anything fancy - combi boiler for DHW and CH (if used) - cold fill DW and WM. Run the combi in eco mode and tend to wash hands with cold water.

Showers are from the combi, have an occasional bath.

Our annual gas useage, including the Hob, is 1800-2000 kWh. (Heating is from ‘dry’ WBS’s)

In fairness, we do like winter Sun, so we’re away for 6 weeks over winter.

Well North and both my girls like to shower for about a year at a time, same here but not quite so extreme! House is about 2,500 Sq ft, I haven't unhitched the CH from the figures to any precise degree. Just going from memory on the drop we have seen in comparison pre and post iboost. If I get down to 14MWh of gas this year it will be a win! I've never believed it's a 1:1 on gas vs electric on system boilers for heating water and just wondered if anyone had dug down into it? I'll be having a closer look at figures when we get back home.

[Ken]

10yrs or so ago the energy saving trust did detailed monitoring of gas condensing boilers about 25 in total, in actual use, 2/3 combi 1/3 system.

They measured gas and electrical energy in and water energy out

In the no CHG period no boiler managed more than 50% ish efficiency and some system boilers less than 40%. This is due to stop/start losses and heat losses. So in the no CHG period not a lot between gas and leccy unless you are going to have very long showers with a combi boiler.

In the CHG period the stop/start losses are mostly taken care of if the CHG and DHW are on at the same time.

The OPs figs are off my range of comprehension both in energy used and heating the water to 80C. Whats wrong with heating the water to 50C or less and halving your losses.

My wife and i use 1000kwh/yr ( 2 showers+ dish washing) heated solely by PV but for 20-25 days a yr i need to use the boost button for a few minutes.

Not sure what you are referring to when you say 5:1 nor if i have answered your question.

[Joeboy]

Thanks Ken, the ratio of 5:1
It appears that we are using around 5 kWh of gas for each equivalent kWh of electric to heat our water in a rough side by side comparison. 80 Dec C is the limit on the thermostat of the immersion heater in tank. On an average day we use about 12kWh of electric off of the pv before the iboost signals 'tank hot'. Always going to run that to the max when we can. The 12kWh figure is a worst case and there are days when it's lower but tbh not many.

Thanks for the 40 to 50% efficiency figures on the gas boilers, appreciated. The gas side only brings the water up to around 65 deg C. I have the boiler set at a value of 7 out of a max of 9 to condense. Can't split the CH from the HW setting and swmbo likes her rads toasty so that settles that.

Going on figures from yourself and BTB we are hyper users of HW. That's cool, just how we roll.

Thanks for the info.