Your Questions About Whole Home Solar Panel System

Henry Dover answers:

Daniel, first, don’t lose heart with solar technology. You might not be aware of this, but very few panels will put out the rated power in varying conditions. I have a dozen KC-120′s here, poly’s. I do not have a “watt” meter here, but I question how it measures this figure. Are the panels connected to a charge controller while you are measuring them? If so, is it an MPPT type controller, or a PWM? Different controllers will back the amperage up on your panel output differently depending on what the panels peak power voltage is, and since a mono has a different peak point than a poly, if they are wired in parallel, they are fighting each other a bit. If you are using a PWM controller, then none of them will be putting out peak power anyway, mine never do, but they still work fine.

The mono panel you have is probably more efficient, meaning it produces more electricity per square foot of surface, not more watts than the same wattage rated poly panel. I’m betting the mono is slightly smaller. I have never worked with that brand panel, but if you want real information, since your panels are all made by the same manufacturer, just contact them and tell them your readings. They will have a tech guy who can explain it better than anyone on this crazy website. We’ve been powering our home with the wind and sun for 13 years now, and teaching solar power in the local schools for about the last 8. I’ve learned there are 2 things in vast supply in solar power, sun, and misinformation. It always amazes me how many people are willing to chime in here with their knowledge on the subject, yet they have never laid a hand on a panel or battery. Try getting a call or enote into Renology, or write a letter to the editor of Home Power Magazine.

The only way I know to actually test the output of any panel is to isolate it from anything else, other panels, batteries and charge controllers, then first test the open circuit voltage, right at the panel junction box, not the other end of the 10 gauge wire, combiner box or anything. Then repeat the test for amps short circuit. Multiply the voltage by the amperage, and you should be in the ball park of watt rating. Higher is normal in the winter time. As always, you mileage may vary. I don’t get the 21 mpg my car manufacturer claimed on the sticker, and I paid a lot more for my car than you did for your panel, but I still own my car. Good luck Daniel, and take care, Rudydoo

Henry Dover answers:

If they use 15kWh a day, then this is (15*365) = 5474 kWh per year.

Now, find the number of kWh generated for each day of the year:

We know that 20% of the year it generates 2kWh, which is 73 days, so do 73*2 = 146kWh.
We know that 35% of the year it generates 10kWh, which is 127.75 days, so do 127.75*10 = 1277.5kWh.
We know that 45% of the year it generates 20kWh, which is 164.25 days, so do 164.25*20 = 3285kWh.

Now, add up all the energy it has generated, and get (146+1277.5+3285) = 4708.5kWh.

Divide this by the total (5474), and you get:

86%.

I did it for the whole year because I don’t know how many days are in this ‘particular month’ so I just did it for 365 days – I think it should be the same.