Testing the first solar panel

The final coat of paint went on this morning and I added the blocking diode. This brings the output voltage down to 19.7 VDC but in the direct sun, I can get 2.01 amps from the panel as noted on the Fluke picture below. This was wonderful as it told me that the original calculations for a 35 watt panel were good. I also tried to use the Radio Shack DVM and it has finally given up and retired.


I also found that even a very slight shadow on the panel made a big difference in the output. My original location for taking measurements was next to the house and under a tree with no leaves. I did not think it would matter but I lost almost 900 Ma of current due to these very slight shadows. This prompted me to move to the middle of the back yard and to test the panel on a battery.


I used a 27 amp hr. battery and found that even with a late afternoon sun, I got a steady 1.6 amps at 15 vdc into a partially discharged battery.


The next step is to add the Morningstar solar charger and then hook up the inverter.


The first panel was set in place on the roof and of course the sun was absent for three days. I got the wiring in place, temporarily mounted the inverter and tested it with the TV using 2, 100 amp hour batteries in parallel. All went well and the TV performed without any problems.


I am using a 10 amp Morningstar solar regulator that uses PWM to charge the batteries. I have chosen this over building a simple regulator because of research on the long term effects of charging a battery using a simple charger. The PWM system is reported to rejuvenate batteries that have developed sulfide. My batteries were removed from service because they would not hold a charge.  They were brought back to life using a AC powered PWM charger and it took about four days to accomplish.  Therefore, it looks like a PWM charger is the best choice.


I am also using a low voltage detect circuit  (not yet installed when this picture was taken) that monitors the battery voltage. As the remaining solar panels are not complete and I have not finished the wind turbine, the low voltage detect is used to switch in a AC power battery charger when the batteries are low. The detection circuit will charge for an hour and then recheck the batteries. If they are still low then it charges another hour. This is a temporary solution. In the final configuration the PLC (Programmable Logic Controller) will monitor the battery voltage and compare it against the charge current. If the AC charger is necessary it will stitch it on


Some lessons learned so far :


· The first solar panel, while working better then expected, is much heavier then I originally expected it to be. I will not build another panel using wood for the frame.  - (looks like I have to eat those words) While I have not selected the materials for the second and third panels, I am leaning toward aluminum side rails and Plexiglas which should keep the finished product much lighter than the first one.

· The first panel was too small. I should have used more cells in parallel to get more current. My mounting space on the roof is limited so all future panels will have a higher output then the first panel.

· It is also clear that an MPPT controller will improve system performance. Therefore, I need to make larger panels so I can increase the voltage output.


· The battery system and modified sine wave inverter surprised me. I first used a small 27 amp hour battery to test the inverter with a small TV and compact florescent light for a load. I was pleasantly surprised to find that although I made an initial drop from 13.4 VDC to 12.5  in about 40 minutes, the voltage stabilized for another 35 minutes when in gradually dropped to 11.8 VDC. I stopped the test after about 90 minutes when I was certain that my 400 amp hour batteries would allow me to operate the TV and satellite system using the inverter.

Fluke DVM used during testing

Testing in morning sun

Roof Mounting

First breadboard of system

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