Photovoltaic Hot Water production

How I do to use the surplus of energy produced by My Photovoltaic Off-grid System

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My Off-grid Solar system produces a lot of energy currently. I cannot store the surplus, so it is getting lost. I plan to install an 200 L Hot Water tank in order to produce sanitary hot water for my house. This tank would use up to 10 KWh daily, reduce fossil energy consumption and my gas bill.

See my other project "My Off-grid Solar System Monitoring".

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ardenuf100 wrote 10/19/2014 at 23:02 point
If you can accurately measure the available surplus power, you can control an AC to AC converter to precisely deliver that power to your heating element. You would need an element with a mechanical (not electronic) thermostat as the voltage will vary. If you intend to feed the heated water in to a gas boiler, you will need to know the maximum supported inlet temperature.

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Michel Kuenemann wrote 10/21/2014 at 07:32 point

Thank you a lot for your interesting contribution.

Yes I can accurately and continuously compute the available power. The 2000 Watts heating element will be simply controlled by a Triac. The firing angle of this triac is managed by the microcontroller. Depending on this firing angle, more more or less power will be fed to the heating element. A LEM current sensor and an RMS (Root Mean Square) algorithm compute the actual absorbed power. A numerical PI (Proportional + Integral) controller manages the regulation loop so that the absorbed power is always very close to the set point.

This already works very fine on my prototype and I will publish the circuit soon.

Yes, The max. temperature of the water is controlled by the built-in safety thermostat of the tank. For obvious safety reasons, I will not make any changes to this part.

I guess that the input temperature of my gas boiler tank can be rather high because it is its job to heat water... I will check nevertheless.


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Bruce Land wrote 08/20/2014 at 13:59 point
heat pump

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Michel Kuenemann wrote 08/20/2014 at 15:05 point
Hi Bruce,

I have equipped my house with an Off-grid PV system and I have currently a lot of unused power. My plan is to heat a 200L water tank with the surplus of electrical energy.

See the log called "What comes next ?" of my project :


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