Heating water

[Eric Bzikot]

Hi! I have an 8 panel system, 340 watt panels in two arrays feeding a 3 kw water heating element in a 200 litre water tank. The steel tank is not insulated as the plan is that it will lose heat at night and warm up the conservatory type room. Save the weeds from freezing. I installed it last fall and although the room doesn’t get very warm, it’s never frozen the plants, so I’m happy. Unfortunately the first heater element only lasted till January when it corroded out. I replaced it and installed a magnesium sacrificial rod, and replaced the same water. But the replacement element has burnt out, not through corrosion. It may have been a faulty element, or is there another reason why it’s eating elements? The volts from the panels on a very sunny, very cold day with snow all round max at 243 volts, open circuit. Voltage is generally lower, with load, and poorer sunshine. A 240 volt rated element should take it? The businesses suggest cyboinverters to convert to AC but they cost $2000 plus and I can’t see why it should be necessary. Can anybody please enlighten me on this thing?

[bcroe]

The voltage looks reasonable, but a standard tank thermostat is incapable of
controlling DC power for many cycles. Solve that problem first, perhaps use
a solid state switch. That ought to be a lot simpler (and more efficient) than
an inverter. good luck, Bruce Roe

[Mike90250]

Heater elements are made to cycle off and on . All the thermal cycling would cause failure in 10 years or so.

Running them ON for 6 hours at a time must be causing something else to happen to kill them in a year. Was there any crust or crud on the failed elements ?
CALROD elements should have a ceramic between the electric and water, not sure how they would corrode

How about the connections to the elements - are they secure? But a bad wire connection would, I expect, char the wire insulation from heat.

[checkthisout]

Pic of elements and what temp is your water hitting and what is the water source? Heavy mineral well water? Any other people in the area with normal a/c heaters to ask how long their elements last?