I'm using four 200w panels connected to a 10 ohm load, trying to heat my hotwater storage up a few degrees, when it's sunny.
But, the Max power point voltage for the PV series
array is 115.6 Vdc.
So the 10 ohm load is too low & drops the voltage down to 40-60Vdc.
Typically, I've been seeing 400-450 watts from the panels.
(Higher when conditions are perfect. Real cold and very sunny).
So, it's been working, but not working very well..
But today, I installed a new 6.3 ohm (300w) resistor in series with the 10 ohm load.
Ohmite C300K6R3 6.3 Ohm 300 Watt Power Resistor | eBay
(7 amps squared is 49 x 6.3 Ohm = 309 watts, for the new resistor. So it might not last very long).
When it's all warmed up, the actual total resistance is now about 16.5 ohms.
115.6v / 16.5 ohms = 7 amps! (the rated current for my panels is 6.93A)!
So, next year when the sun comes back, we should see about 115v x 7a = 800 watts!!!!
800w = 2729.713 BTUs per hour!!
When I checked the power before making the mod, it was under 400w.
For a short time today, the PV was up to 100 volts @ 6.72 amps.
Making 672 watts with hazy sunshine is a good sign.
16.5 Ohms seems like the near prefect match for the series array.
These are good panels. We are hoping to see 600-700 watts on the average sunny day.
I'm keeping my fingers crossed!