Specifications for switch?

Some thoughts ...

Is the solar kit connected to the mains? If so, why change between the two?

Any break before make switch should do, but then you have to consider the earthing arrangement.

I have thought about this for when I get a PV array installed. If, e.g. in the height of the summer, I am generating 4 kW and using very little, it would be better to heat my water cylinder (what else, if not a large battery?) than pass the surplus into the mains. Clearly with gas heating, there must be a break even point when the cost of leccy (PV + mains) and gas are the same. It may in fact be better to have a low-powered immersion heater (do 1 kW examples exist?) to use up a smaller surplus.

I do not think that this is as easy as it seems. I can also see a situation where the PV battery is charged up and the surplus is going into the Grid. Potentially, it could supply the immersion heater for, say, an hour and then charge up again.

Am I thinking along similar lines to your client?

To be honest there appear to be things to check further before committing.

All I know is that there is a 3phase TT supply. One phase feeds the main house and another feeds a heat pump. The heat pump cannot keep up with the demand for hot water, ergo the requirment for a facility to turn on an immersion heater on one of the 2 tanks associated with the heat pump when demand is too high.

When the heat pump was fitted, a tank was supplied which I am guessing is generally heated by a hot water coil from the heat pump unit but there is also an immersion heater present.

Now, what gets complicated is the way the RISC rebate is paid, with a disqualification if the aux immersion is connected to the 'dirty fossil fueled mains side. Since all of this was done, solar panels have been added but I don't know how the solar generated supply is divided up, but the solar folks removed the prewired dirty mains connection to the immersion heater from the heat pump CU and wired it directly to their new solar supply. Problem is, the heat pump cannot keep up with HW demand so am thinking of fitting a change over s/w so that the heater can be fired by the dirty mains for short periods when extra HW is required in a hurry.

So, the idea is one T&E to the immersion heater FCU. One supply in T&E from the mains, and another from the solar, with a change over switch to swap between the two.

I asked about the type of switch because of my ignorance of the regs surrounding the nature and rating of switch contacts related to renewebles and all this nonsense about suff having to be bidirectional. But I suppose that it doesn't matter because the solar supply is I think - must check - coming directly from the inverter already oven baked for 230VAC.

To be honest there appear to be things to check further before committing.

All I know is that there is a 3phase TT supply. One phase feeds the main house and another feeds a heat pump. The heat pump cannot keep up with the demand for hot water, ergo the requirment for a facility to turn on an immersion heater on one of the 2 tanks associated with the heat pump when demand is too high.

When the heat pump was fitted, a tank was supplied which I am guessing is generally heated by a hot water coil from the heat pump unit but there is also an immersion heater present.

Now, what gets complicated is the way the RISC rebate is paid, with a disqualification if the aux immersion is connected to the 'dirty fossil fueled mains side. Since all of this was done, solar panels have been added but I don't know how the solar generated supply is divided up, but the solar folks removed the prewired dirty mains connection to the immersion heater from the heat pump CU and wired it directly to their new solar supply. Problem is, the heat pump cannot keep up with HW demand so am thinking of fitting a change over s/w so that the heater can be fired by the dirty mains for short periods when extra HW is required in a hurry.

So, the idea is one T&E to the immersion heater FCU. One supply in T&E from the mains, and another from the solar, with a change over switch to swap between the two.

I asked about the type of switch because of my ignorance of the regs surrounding the nature and rating of switch contacts related to renewebles and all this nonsense about suff having to be bidirectional. But I suppose that it doesn't matter because the solar supply is I think - must check - coming directly from the inverter already oven baked for 230VAC.

whjohnson said:

Now, what gets complicated is the way the RISC rebate is paid, with a disqualification if the aux immersion is connected to the 'dirty fossil fueled mains side.

I see, but strictly-speaking, the presence of a switch should change nothing.

I do not see any problems doing this with a single appliance, provided that (as I mentioned earlier) the switch is break-before-make so that the two sources can never be connected together.