hot water heating.

[native pepper]

Met a bloke at a gig we did over the weekend, who has an interesting approach to hot water heating. He came over during the gig (sunday arvo) to ask if we knew any Johnny Cash songs, so we did Folsom prison blues as it's the only one we could remember, not having played any country music older than 20 years for over a decade. After we did our version of it making up some words as I couldn't remember them all he came over during the next break and thanked us. When he was talking to us another bloke came over and asked him when he was going to do their hot water heating for them, to which he replied do you have the panels and inverter yet.

Being curious asked the bloke if he was off grid and he replied no, still on the grid, and asked what the inverter was going to be used for. Turns out this bloke is a builder and he got sick of his large hot water bills, installed solar hot water but wasn't satisfied with it so pulled it out. Got some cheap solar panels and an inverter, hooked the inverter to the solar panels and then to the hot water tank and during the day the power from the panels heats the hot water, costing zero for hot water and giving them enough hot water to last 3 days, without any sun. He said it works great and even with the amount of hot water his wife and kids use, so far they haven't run out, but come close a few times even with the 440lt hot water tank.

Don't know any more as we went back on and he left as soon as we finished, so not sure whether they were pulling our legs or not. It does seem like a simple cheap solution, but not being a sparky not sure if it's actually feasible or not. If it works, would solve a lot of peoples hot water bills and would seriously think of doing it myself, my solar hot water doesn't work as well as it should. There's been times had to light the fire to heat water, especially when have guests staying.

[Busman]

Don't need the inverter, just take the DC current from the panels and pass it through some DC elements, been doing this as one of the 3 ways to heat water on our coach. Others are via heat exchanger with engine coolant, or use the inverters and a 240 v element.The panels on VP are nominal 24 V so about 39 volts to take care of, just use a 24 volt and a 12 volt element in series, near enough to take care of the 39 volts. # have 3 such pairs and put 2000 watts of solar on the coach through them, while the 1000 watts on the trailer is still charging batteries. Takes about an hour to have our 50 ltrs storage tank steaming hot.

[supersparky]

NP, we heat our home hot water in a similar fashion. We have 3kw of roof top solar on the house and a grid tie inverter. Our HWS runs through a time switch, which is set to heat for about 3-4 hrs a day. We don't use a lot of power on a daily basis and don't have a pool, so our power bill is usually about $350 - 400 a quarter. There is enough solar left over after heating the water to get some feed-in credits. We weren't lucky enough to get on the 40c/kW bandwagon that some people still enjoy, but are pretty happy with that arrangement. The time switch can be set to boost, if the need arises. But it hasn't in the past 5 years.

[Eddy]

just use a 24 volt and a 12 volt element in series, near enough to take care of the 39 volts.

Hi Busman
How have you physically set this up , are both of the elements heating the water ?
Thanks

[T1 Terry]

If you can buy the solar panels cheap, string them together in series and join them to the hot water element. If you can't make up 340vdc (240vac rms is 340v peak to peak or total voltage) normal roof top solar panels are around 40vdc open circuit, so 5 panels in series would be 200vdc open circuit, the voltage under load I'll leave to someone who has more active brain cells this time of day, but it will be slower to heat a full tank than when connected to the mains, but the element is still just a resistive load, sop sort of a controlled short circuit.

You could get fancy and use a cheap solid state relay from evilbay, a 25 amp DC DC one of these https://www.ebay.com.au/itm/26649458524 ... R-Dttr_cYw
or
https://www.ebay.com.au/itm/14526519188 ... R97ttr_cYw

On the 3v -32vdc side, battery positive (12v or 24v) on the + side, the thermostat to the negative side and the other input to the thermostat to the battery negative, or if the hot water cyl doesn't have a thermostat, a 70*C NO one of these https://www.ebay.com.au/itm/28479241332 ... R-70_r_cYw mounted towards the bottom of the cyl to turn the element off if the water gets too hot.

The relay will need a heat sink and mounted somewhere it can get cooling and use heat transfer paste between the relay and the heat sink, and a scrap of aluminium attacked to the cylinder to act as a heat absorbing surface, heat transfer paste on the back of the thermostat and maybe even between the aluminium and the cylinder, and the whole process becomes automated.

T1 Terry

[native pepper]

We'll be playing there at the end of this month, will ask for details. In my bus, when the batteries are full, switch the hot water heater on and run it through the 2000w PSW inverter and that works well. The batteries are normally full within a couple of hrs after sunrise, so hot water isn't a problem. At home when batteries are full on sunny day do the vacuuming, washing and anything else that uses a lot of power, the batteries usually top up before the sun goes down. Proper management of the battery system means even with the small lifepo4 pack have never run out of power and even then can start the gennie to top up.

[pet-els]

I had a heater in my bathroom it was Chip heater. Haha

PeterH

[Busman]

just use a 24 volt and a 12 volt element in series, near enough to take care of the 39 volts.

Hi Busman
How have you physically set this up , are both of the elements heating the water ?
Thanks

Eddy,
We have a relay that takes the 2000 watts from the roof of the coach, puts it through 3 x 70 amp circuit breakers and then to the 3 pairs of elements. Each pair is 1 x 24v and 1 x 12 v makes up same resistance as a 36 v element. I could have had 3 x 36 v elements made up but did not realise it at the time, just used readily available from ebay.I made up a copper tank from 100mm copper pipe, the elements are in that. When the process starts a 24v circulation pump moves water from the storage tank, through the copper tank with elements in it, and back to the storage tank. I have a thermostat on the tank that will stop the process when the water is too hot, I don't bother with it, just flick it on and forget, I have it on a timer so switches off after an hour.That is plenty for the days hot water.

[Eddy]

Thanks Busman

I was wondering how you added extra element position into a commercial unit like a suburban hot water system

But you made your own hot water tank

[Busman]

Yep, not pretty but it works ! Will have to tilt head to left, dunno why.