Viability of direct PV HW heating - 42 Lat., Wall mounted Array.

I am running some tests and trying to estimate the viability of direct PV HW heating. Planning to use a solar HW MPPT controller, but testing a simple direct connection for now.

Current setup is a 55Gal dual element HWH with direct DC from the PV array connected only to the 5500/240v lower element, measuring 10.3 Ohms.

The system is based on Suntech 200W, 26 Vmp, 7.6 Imp panels. I could use either 8 (4S2P) or 9 (3S3P) panels. In all cases, they will be moderately shaded and mounted on a south facing wall. I am at 42 latitude with 4.6 solar hours.

Actual test of 3S2P, 6 panels, temporary mounted in the proposed location give a metered peak output of around 4 Amps and 45 Volts. Most of the day the output ranges from 1 to 2.5 Amps.

I expect more power once all 9 panels are mounted & positioned higher up on the wall (1 to 5 degree tilt might be possible), but I don't expect a dramatic increase - probably peaking around 5.5 amps and 65 Volts.

I can vary the HW heating element, but not much else in the setup and can not reduce shading from tall tree trunks all around.

I don't have enough experience to determine whether, based on the results so far, this is a potentially viable setup, even once an MPPT HW controller is in the mix. What do you guys think?

BLUF: Don’t think its enough, but there are some calculations you can do to find out.

I use 1 kWh to heat 6 gallons of water. Try to get solar production for your area based off a calculator like in my signature block. I think you menton up to 1800 watts of panels.

If at all possible, would benefit you to do a power audit on the heater, but if you don’t have a 55 gallon electric heater, that is nearly impossible.

My gut tells me 1800 watts of panels is not enough to heat 55 gallons of watter based off my trial on a 6 gallon water heater. My winter low production is about 6 kWh and summer could probably reach 20 kWh for 2550 watts of panels. I also think if you did make enough energy, most of it would be used up but he hot water heater. I call 1 kWh 10% not my energy, but that depends on production and actual usage. I am at 32 north, and you are even farther north which should be worst.

chrisski said:

I use 1 kWh to heat 6 gallons of water.

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>>I use 1 kWh to heat 6 gallons of water.

What is your element resistance? PV array specs? MPPT controlled or not?

CitroM said:

>>I use 1 kWh to heat 6 gallons of water.

What is your element resistance? PV array specs? MPPT controlled or not?

Click to expand...

I don’t know the element resistance. It’s an average RV heater. Specs are in the link above.


PV array specs won’t change the total kWh needed to heat a system, but in my signature block is a link to my build with all the components.