PV panels to immersion queries?

[David in the UK]

Relative newbie here, I have searched through the threads that seem to cover this topic but still need some assistance.

I have a grid-tied system consisting of 19 panels (7.2KW) with batteries. This I wish to be left undisturbed as it was installed by a company a few months back and don't want any issues in case of warranty.

I have 2 water tanks, one I wish to have an immersion element connected to a new set of panels solely for this purpose. It will not be grid-tied nor go through the consumer unit (so totally stand-alone).

I want to keep it simple, the immersion element in the tank is rated at 3000w/ 230volts, and my multimeter shows a resistance of 18.9ohms. It would be tricky to replace this immersion as it is a bit unusual with 2 thermostat pockets (1 for the element, 1 for the gas boiler) also it is quite recessed and of an odd design shape.

I can fit 4 of the panels below onto the roof (a total of 1820w). If connected in series it should give 169V at 10.7A, this should (I think) should power the immersion OK, albeit not at full power but I can accept that.

Is this the most efficient method of getting the most power from the panels into the element? I don't think it would be advantageous to go through an inverter as this could lead to some losses? Also, it would mean the additional cost of an invertor.

I understand I would need a suitable DC-rated relay for the thermostat switching.

What have I missed?


The data from the 4 panels I have in mind:

Nominal capacity 455 Wp
MPP current 10.77 A
MPP voltage 42.26 V
Short circuit current 11.38 A
Open circuit voltage 49.45

 

[David in the UK]

Bump. Surely some people will have some opinions and ideas?

 

[efficientPV]

Direct connect isn't efficient but you don't have many commercial options for a dedicated power point heater control which are realistic in price. China should be selling these by the thousands for less than $99. That resistance match is a good choice.

 

[newbostonconst]

Water takes a lot of power to heat. 50 gallons can only store under 9kWh, guessing you are using plastic tanks which will take even less temp increase of the water. If you add real hot water tanks the cost is going to be close to what DIY batteries cost for the same power. Just add batteries.

If your inverter has excess power it is easiest to use 240vac....The elements are rated at certain voltage and when you use lower voltage DC the output drops a lot. Using AC will also allow you to use cheaper and easier AC relays and switches to turn it off on and on. They make a DC controller but it doesn't look to me like it will last and add to the cost.