Hot water heating

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Derek Neve

May 26, 2021, 5:59:55 PMMay 26
to electrodacus

I'm looking for help on how to set up about 1-2kW of solar panels to heat a hot water tank of 250 Litres using (probably) a 24V or 48V 600W heating element. (I'm in New Zealand, South Island, so I wont be getting all that much bright sunshine.)

Please can you point me to somewhere on the website that explains the simplest and cheapest way to set up a controller to work at the array's maximum power point and limit voltage to 24V or 48V at the output? At this stage, I'm not thinking of charging batteries as well, so don't need any overflow system to divert surplus energy to the heating element. I've been thinking of using a normal lead acid battery charge controller and setting absorption and float voltages to 24V or 48V, but wonder how the charge controller would behave when set up like that, since the heating element would not behave like a battery nearing full charge.

Your home page says "If all you need is to heat a bit of water with the excess from your small (less than 3kWh) PV array then that can be done with SBMS and some external SSR." Is there somewhere on the website that expands on that idea?

Derek Neve

Dacian Todea

May 26, 2021, 9:48:22 PMMay 26
to electrodacus

If you will be using 60 cell solar panels then ideally you will want a 36V heating elements those are usually 1200W rated with two parallel 600W elements and each element can be connected to two 60 cell solar panels in parallel so 4 solar panels in total.
Then all you need is a solid state relay controlled by the thermostat or just use two DSSR20's controlled by your thermostat.
250 liters of water heated from 25C to 55C that is a delta of 30C will require 250L * 30C * 1.16 = 8.7kWh of energy so with say 4x 300W panels you will need a very good and long sunny day it may only be able to heat the water by 20C delta.
So you may need two 1200W heating elements and 8x 60 cell panels to be sure you can heat all those 250 liters in a sunny day.
If that water is not pressurized just an open tank and it not a problem if it gets to hot to say boiling point then you do not need anything other than the heating elements and solar panels directly connected.

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