Water heating with DC PV

[Tom ibex]

Hello,
I am thinking of making a water heating system with 8 PV panels of ±2kWp, a 500l electric water tank and a suitably sized water heater with a pump to circulate hot water between the tank and the radiator. I am thinking of manually connecting the panels connected in series with the resistances of the balloon during cold periods. In hot weather I would unplug the panels. The DC current from the panels would be used directly by the tank resistors. The tank thermostat would be shunted. The tank would be independent of the house's water system and vented through a tube in the roof to release excess pressure and steam in the event of boiling.
Apart from the adequacy between the power of the panels and the resistances, one of the other questions that I ask myself is the possibility of disconnecting the solar panels in charge with a simple isolated plug. Thanks.
So long

[sicetaitsimple]

Hello,
I am thinking of making a water heating system with 8 PV panels of ±2kWp, a 500l electric water tank and a suitably sized water heater with a pump to circulate hot water between the tank and the radiator. I am thinking of manually connecting the panels connected in series with the resistances of the balloon during cold periods. In hot weather I would unplug the panels. The DC current from the panels would be used directly by the tank resistors. The tank thermostat would be shunted. The tank would be independent of the house's water system and vented through a tube in the roof to release excess pressure and steam in the event of boiling.
Apart from the adequacy between the power of the panels and the resistances, one of the other questions that I ask myself is the possibility of disconnecting the solar panels in charge with a simple isolated plug. Thanks.
So long

Not understood... A small diagram with the summer/winter configuration would certainly help.

[Remundo]

connecting panels directly to a Joule effect does not usually work well

It is better to go through a solar charge controller. Or simply inject everything into the 220V network and stupidly connect your water heater to it.

if you want to do without it, the operating point of the PV field must be at 220V and the amperage provided by the resistor.

For example if P = 1000 W, U = 220V and I = 5-6A

and again it will only work well if the PV field is in direct sunlight. If not, it will give less power, and lose yet performance because the operating point (I, U) with the resistance will be non-optimal.

[phil59]

Some, rewind a resistance, with iron wire, and put only one panel to heat the ball, resistance steatite ....

I can't find the tutorial. Possibly, 2 panels no more, without anything else, without electronics.

[sicetaitsimple]

one of the other questions I have is the possibility of disconnecting the solar panels under load with a simple insulated plug.

That said and to answer the question, if you unplug them at night (or after covering the panels) it shouldn't be a big problem. There must also be contactors or circuit breakers provided for that, do not joke especially in direct current.

[phil59]

Above 50V, it can be fatal.

There are PV circuit breakers, fortunately, but a single panel, or 2 n //, is rarely going to exceed 50V.

[izentrop]

In hot weather I would unplug the panels. The DC current from the panels would be used directly by the tank resistors. The tank thermostat would be shunted.

Hello,
if the voltage of the PVs is close to 230 V, I assume that you have provided an independent thermostat and a contactor suitable for direct current, as here

[phil59]

It's much simpler than that to do.

[PVresistif]

An info on my experience .... installation in operation since 2018 without any pb, no maintenance
I am worried when I read that it would be necessary to shunt the thermostat ..... in any case !!!! a main security cannot be bypassed, it is dangerous!!
the std double thermostat of the water heater does the job very well if the breaking capacity is sufficient (to be checked, in my case 230 W under 30 V or 7.6 A there is a margin ......)
Ohm's law, nothing but ohm's law...
see my website: http://osenon.free.fr/4%20PV%20resistif ... sistif.htm

[phil59]

This is exactly what I was looking for !