MPP solar

[Busman]

So 6 24 volt panels that run at about 39 volts = 240 VDC but the I have to isolate or disconnect the 240 ac supply when the DC is connected and only have eggs in the one basket.

I think I would prefer to run a seperate system as I have done in VP, seperate thermostat run from a plug pack on a timer and it would switch the panel dc to flow until water was hot enough. Leave the 240 ac element in place, leave it connected to the timer, but change the time allowed to later in the day, if water was hot enough no mains current drawn, if not original element could do it's job to top up.

This would make the system totally automatic, plus have redundancy.

[jon_d]

or fit a second element.

[T1 Terry]

So 6 24 volt panels that run at about 39 volts = 240 VDC but the I have to isolate or disconnect the 240 ac supply when the DC is connected and only have eggs in the one basket.

I think I would prefer to run a seperate system as I have done in VP, seperate thermostat run from a plug pack on a timer and it would switch the panel dc to flow until water was hot enough. Leave the 240 ac element in place, leave it connected to the timer, but change the time allowed to later in the day, if water was hot enough no mains current drawn, if not original element could do it's job to top up.

This would make the system totally automatic, plus have redundancy.

Household panels are generally up around the 40v to 50v open circuit voltage. Because a solar panel has no output current when open circuit voltage is measured, the 6 x 50v = 300vdc would be seen across the wires when the solid state relay opened, but not across the element because the resistance load would pull the open circuit voltage down to around the Vmp (Voltage maximum power) or lower, depending on the rating of the element.
As an example, 6 x 250w panels with a Vmp of 40vdc would generate 1500w = 40v x 6 panels = 240vdc @ 6.25 amps. No idea is the water heating capacity of a 1500w element powered with 1500w is equal to a 3600w element powered by 1500w .... I know the voltage would be lower but the current would remain at 6.25 amps ... but as far as the heating potential ...... I'm sure someone would know the formula to do the comparison ... but that's not me I'm afraid ....

T1 Terry