PV Gap

Bonnie Said:

how do i pick out solar panels to match my battery bank?

We Answered:

Hey Feemind, we have a home that is powered by the wind and sun, and we use L-16's also. Our system has 20 batteries, a 1.4 kw solar array and H-40, 1000 watt wind turbine. I have a couple issues with your calculations. You do have about 14 kwh or storage, but if you are planning on using all of it each night, your electronics and inverter will not have access to all that power. The voltage curve of a lead acid battery drops quite low during the last 30% of discharge, even lower when you draw it all out in less than 20 hours. Batteries of this type are rated on a C-20, or 20 hour rate. Your system will shut down before you get through half of the battery capacity. In addition, even if you could discharge those batteries 80 or 90 % each night, they would be shot in less than 2 years. We only discharge ours 15 to 20 pecent each night, and after 11 years, my batteries are toast. We are replacing them even as I write this. That battery bank can reliable give you about 5 kwh each night, then it will need almost 6 kwh the next day to replenish it. Your array will have to produce the needed 6 kwh during the day, and carry all your loads at the same time, maybe another 8 or 10 kwh for your house. In the end you'll need a large array and a quality charge controller.

Here's the good news, since you selected 12 volts as your nominal system voltage, it doesn't matter what panels you choose. Virtually all panels today are wired for 12 volt charging, and have an open circuit voltage of about 17 or 18 volts. You can buy 3 used Solarex VLX-53 panels this week, then find a great deal on BP-120's next month and add them to the first three, and later wire in some Sharp-210's. Solar panels all get along fine with each other as long as they are all set up for the same nominal charging voltage and wired in parallel to the battery or charge controller, and you can buy more of them over time until your reach nirvana.

There are some great resources to learn more about this sort of thing, I will list them below. Make sure you have DC rated overcurrent devices at all points exiting the battery, when you have over 1000 amp hours of battery storage connected to your homes electrical wiring, you have a tiger by the tail. A short circuit in that DC wiring without a DC rated fuse or circuit breaker can melt through monkey wrenches, catch 4/0 welding cable on fire and cause battery enclosures to explode. Also, try to install those batteries in some kind of plastic tub to catch any acid that gets loose for any reason. Make sure you water those L-16's each month with distilled water too, more often in hot weather. You'll be amazed how much water they go through in a month.

We started down the same road you're looking down now some 12 years ago, the two best things I did back then was subscribe to Home Power Magazine and go to an energy fair. The fairs are all over the place, and most of them are listed in the back of Home Power each issue. You can hear talks on batteries, inverters, panels and wind turbines and buy discounted parts on the spot, that's what we did. Spend some time getting more informed on this subject, it will be well worth it. Good luck Free, and take care, Rudydoo

Nina Said:

How can i know if MPPT is done by inverter or DC-DC Buck converter in solar system?

We Answered:

The Sunny Boy 6000 is a grid-tied inverter - it will not work if it is not tied to the grid.

MPPT is a feature inherent in pretty much all modern inverters of reasonable size. There are certain loading conditions which will extract maximum power from the panels. The inverter adjusts its load to achieve that. It's all done inside the inverter.