[geoffers]

Originally Posted by meldrewreborn

@geoffers

I have a solar thermal panel so although my boiler is on in the summer months it only operates on cloudy days when insufficient radiation has reached the panels....

This has set my mind thinking - as a kid we used to have a h/w tank with 2 heat-exchanger coils - 1 from the fire back-boiler, and 1 from the c/h boiler.

There are plenty of videos of people living off grid making their own solar heat exchangers eg https://youtu.be/Sc78nueDQ64 so it would be a pretty simple task to build your own

... In the winter your regime is costing you money, not saving it.

Actually not true:- as Scotty said ..."you can't change the laws of physics" & create energy from nothing.

I appreciate what you're trying to say ie without the tank being warm my c/h would have to work harder, but with the tank being warm the c/h would not need to work so hard, but the tank still needs energy input. So the net energy input and cost would be identical.

[retrotecchie]

@geoffers

I had an off-grid set up a while back where I needed a ready supply of hot water. Not vast amounts but just enough to wash up a couple of mugs and spoons in the office.

I 'acquired' an old OSO undersink hot water heater that had a 10 litre tank and a 2kW immersion heater. I found a blanking plug the same size as the immersion boss and made a couple of loops of 10mm microbore and used that to make a thermal heat exchanger.

With an old radiator painted black as a thermal collector, a Grundfoss circulator pump powered from the solar PV pumping the primary circuit, I had ample hot water in the sink for nine months of the year.

I even fitted the collector and tank with temperature sensors, built a differential pump controller and wrote some software to log performance on my laptop.

All good fun!








The water supply came from rainwater harvesting, filtered through a slow sand filter and then a reverse osmosis water filter to render it potable. With a 100 litre storage tank, 10 litre solar thermal system, and 250VA of solar PV it was plenty enough for me to sit in the office all day, brew up and wash up and run the laptop and charge the power tools. With a composting lavvy, I could be completely off grid if it wasn't for the CAT5E coming down from the house 100m away for the phone and broadband, although I did eventually replace that with a microwave link.

The office did have 'shore power' for heavy duty power tools and the kettle, but I usually brewed up on a Camping Gaz stove!

[meldrewreborn]

@geoffers

Gas is much cheaper than electricity.

A 6 minute shower with a 10 kw shower uses 1 kWh costing around 35p.My gas saving in the summer covers two very leisurely showers per day.

In the winter your combined bill for gas and electricity would be lower using gas to heat the water. I'll not argue the point any longer though.as facts don't seem to matter.

For anybody thinking of a DIY solar thermal panel, please note to use only mechanical tattings, and not copper with soldered joints. The temperature of my panel has been as high as 150 degrees centigrade which exceeds the melting point of soldered joints. An expansion vessel to accommodate the circulating pressure changes is recommended and an antifreeze circulating solution is also required.

[geoffers]

Originally Posted by meldrewreborn

@geoffers

Gas is much cheaper than electricity.

A 6 minute shower with a 10 kw shower uses 1 kWh costing around 35p.My gas saving in the summer covers two very leisurely showers per day.

In the winter your combined bill for gas and electricity would be lower using gas to heat the water. I'll not argue the point any longer though.as facts don't seem to matter.

...

Just for the sake of completeness to get "the facts" I ran some tests to get the true cost of my savings by not using the hot water tank - clearly if the tank is not used at all, the cost is zero

Starting with the water in the tank from cold, and setting the gas to run for 1 hour used 4.64kWh of energy @7.4p cost = 34p

However, starting from cold, and setting the 3kW immersion heater to run for 1 hour used 2.08kWh of energy (i.e. reached temperature in 40mins), so on my overnight rate of 9.5p cost ~= 20p

With the daytime rate of 32.835p it would have cost ~= 68p (So sensibly I should set the immersion to run for an hour after midnight to benefit from the cheaper rate)

The 8kw shower for 5 mins would take about 0.67kWh, so again if I shower 1^st thing in the morning on the 9.5p rate would cost ~=6p , and on the daytime rate of 32.835p would cost 22p

I appreciate that everyone's situation is different, but I'm sticking with a 6p shower in the morning and zero cost hot water, though may use the 3kW electric immersion on the cheaper tariff to give me a tank of hot water for 20p, rather than using the gas at 34p

[geoffers]

Originally Posted by geoffers

TBQH: For the past year I've not bothered with the hot water, summer or winter. I've got an electric shower; dish washer maybe every 3rd day; can boil a kettle for washing up etc etc

Seems daft to keep the tank hot 24/7 for just a few minutes of convenience per day.

If i want a bit of luxury ie a hot bath after a cold bike ride for instance, I can get the tank from zero to hot in ½hr with both gas boiler & 3kW immersion heater: that may cost say 60p or so, but I bet that's cheaper than running it all the time.

Just following on from my above post, with an idea for anyone else on the Next Drive tariff with a "regular" boiler and a hot water tank ...

I've now fitted a "smart" switch into the immersion heater circuit which turns the (3kw) immersion on for ¼hr at 6:45am.

This gives enough warm water for comfortable hand washing etc, which lasts all day for a cost of about 8 pence.

Your requirements might differ, but this works for me as it seemed an unnecessary cost keeping the tank heated all day using the gas boiler.