Solar Hot Water

[xelasnave]

Has anyone experience with making their hot water via a direct connection from solar panels (the ones that make electricity not units that circulate water) to the electric hot water service. I have obtained info from Rainbow Power company which frankly I dont fully understand in so far as the unit appears to be a switching unit to go from solar to main grid power..I am interested to know if one needs such a unit given there will be no switching to main grid power...moreover any comments on heating via a solar panel and not the water circulation unit would be much appreciated.

Details from Rainbow Power Company site...there is a heater element as well.

.Description
Sun Flux - Hot Water from PV Panels

The Sun Flux can be retro- fitted to an existing electric hot water tank giving the user the ability to switch from PV solar to AC grid if there have been long periods of insufficient sun.

The Sun Flux is an IP65 rated device that can be installed to the lower element of a twin element electric hot water tank with AC grid directly to the upper element. This application will give the user automatic transfer to the grid if there has been long periods of insufficient sun. Or install without the grid connected at all for off grid applications. When installed on a single element tank the user has the ability to switch from solar to mains grid if required.

The Sun Flux requires 4 standard PV solar panels and works with 2.4, 3.0 and 3.6 kilowatt heating elements. No plumbing alterations are required.

Heater unit.... Description
Twin heating element from SunFlux.

500W & 3000W dual water heater, includes control thermostat. Highly recommended for older, single element hot water tanks.

Connect the 3kW heater to your SunFlux, and the 500W element to off-peak or controlled load.
End of description...



In any event it would seem a sensible addition to any city house given hot water makes up a decent part of energy expence...
Alex

[sheeny]

G'Day Alex,


I assume your HW service is 240V? Therefore you'll need an inverter to convert your solar DC voltage to 240V AC. How do you power your HW service now if not from the Grid? Generator?


Now I don't think you can just connect the inverter to your HW heater either. It needs some smarts to tell it when the water is up to temp and to divert the electricity elsewhere, so you aren't boiling water and making steam.


I do exactly this with my solar and HW service, except that I am connected to the grid. To do this I use a Catchpower. It prioritises solar power to household demand first, then to hot water. Once up to temp, the excess power is exported to grid as normal. It allows for manual overide if you haven't had enough sun, and is fully programmable.


Al.

[xelasnave]

Thank you Al for your reply.
The current hot water service is merely a holding tank with no electricity connected and the hot water comes from a wood fueled stove.
When I spoke to Rainbow last year it seemed a good idea...I think the electricity is DC...maybe that is the significance of another element..I dont know that this should be too difficult...it would seem a DC heater element and perhaps a timer in the circuit so it heats only for a determined period...there would be the risk of drawing down on your hot water but perhaps thats better than steam..and any thing that improves the current set up cant be too bad...I dont like seeing her chop the wood...anything I can do to make the life of the girls better I will do...I feel guilty spending on astronomy in part.. .
Alex

[sheeny]

I just had a quick look at the Sun Flux page - the elements are 240VAC. I couldn't find any DC elements. It sounds like the Sun Flux is an alternative to the Catchpower I use, with the exception that you replace the element in the HW service with their element. That may suit you more than a Catchpower if you don't already have an element in your HW tank.


I assume you are using solar power anyway so you have a use for any excess power after the water is to temp?


Al.

[Malewithatail]

Thought that all may like to read the reply.
The element in a hot water unit, be it solar or otherwise, will corrode quickly when supplied with dc as opposed to normal 50 hz (or 60Hz for our USA viewers !) energy. They are not designed for operation on dc, even thought the rating may well be the same and the resistance is suitable. This assumes you have a 240 v dc battery bank.
Our hot water is solar heated, and the backup is the wood stove, with a backup-backup that switches the 3.6 kw element to the 240 v from the inverter either through a manual switch, or when the battery's are fully charged, via a relay from one of the PL60 regulators. It also helps to have 20 kw of installed solar, at 48 volts, a 2,500 amp hr submarine battery bank, plus a 5 kw continuously rated inverter/charger. Yes, that's over 400 amps dc at 48 volts and takes 3 regulators all communicating with each other to keep it under control. The panels are angled to take advantage of different sun angles during the day, so the peak power is around 300 amps in summer in full sun.

[Sunfish]

We used to chop wood for the hot water growing up. Glad I don’t have to do that now.

A heat pump hot water system can be run from PV with inverter if you have excess and often is. That is because a heat pump draws only 1 kw and can run from a 10amp circuit if no booster is used. Some models are designed to be PV connected and have specialised circuits . Old school plumbers do not like heat pumps as there are some shocking cheap ones out there and they can’t be fixed by a plumber but I have had one for 20 years running on 10 amps. My next installation will have the heat pump run on PV.

You would still need enough PV and inverter but this can be done I understand, will not be cheap, and if you are in an area with subzero overnight temperatures your options are limited to models with efficient refrigerants that tolerate sub zero.

I am surprised your fuel stove system does not also include a solar hot water system as my sisters’ house in the country had.

[xelasnave]

Hi Al
Yes using solar and it would be great to dump excess into hot water.


Peter is my neighbour and helper with the observatory and has told me he made his post to also help others besides me..

So thank you Peter it is very thoughtful of you...hope to see you in a couple of days and share other options. I have a five kVA genny so maybe just use it????
Alex
Alex

[xelasnave]

Thanks Ray...the previous owner did not see the need given there are about 10,000 trees here.:)
Alex