Using solar panel DC output to feed immersion heater?

[bluenorw]

Just an idle thought - has anyone any experience of using the DC output of solar panels to directly feed an immersion heater, to avoid the expense and losses associated with an inverter? Evidently, a changeover relay would be required to utilise the usual 240V AC supply at times of low or zero solar output.

 

[EddieB]

I'm not sure if this is a trick question but surely the DC output is just that DC, that's why an inverter is required

 

[Avo Mk8]

I'm not sure if this is a trick question but surely the DC output is just that DC, that's why an inverter is required

But an immersion heater element is a resistive load, so in principle it doesn't matter if it's fed with DC or AC. Other than perhaps the behaviour of the contact materials in the thermostat and cutout.
Maybe more of an issue is obtaining the right voltage at enough current.

 

[EddieB]

But an immersion heater element is a resistive load, so in principle it doesn't matter if it's fed with DC or AC. Other than perhaps the behaviour of the contact materials in the thermostat and cutout.
Maybe more of an issue is obtaining the right voltage at enough current.

Yep, a 24v/48v dc supply would need a different element fitted to the immersion

 

[Avo Mk8]

Yep, a 24v/48v dc supply would need a different element fitted to the immersion

But a 48V immersion would require about 60 Amps to match the performance of a normal 240V mains one, and a 24V one twice that!
You're better off having a 450 Volt immersion surely.

 

[EddieB]

But a 48V immersion would require about 60 Amps to match the performance of a normal 240V mains one, and a 24V one twice that!

There lies the rub mate, put an inverter in.....

 

[bluenorw]

But an immersion heater element is a resistive load, so in principle it doesn't matter if it's fed with DC or AC. Other than perhaps the behaviour of the contact materials in the thermostat and cutout.
Maybe more of an issue is obtaining the right voltage at enough current.

Good point regarding the thermostat contact rating; DC would be more onerous. Presumably solar panels could be connected in series to provide a higher voltage. I think I'll stick with the original idea of using solar water pre-heat of the feed to the hot water tank and forget the PV approach.