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Xringer · 12-22-11, 03:56 PM

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.
www.skyfireenergy.com/downloads/CS6P.pdf

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!

12-22-11, 03:56 PM	#1
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	DHW from PV still working 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. www.skyfireenergy.com/downloads/CS6P.pdf 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! __________________ My hobby is installing & trying to repair mini-splits EPA 608 Type 1 Technician Certification ~ 5 lbs or less..