PV Gap

William Said:

How many solar panels, batteries and what size inverter to run 2500 watts at a cottage on the weekend?

We Answered:

Hi Darcy, if there is one thing you can learn from reading through all your answers here, it's that there is a great deal of misinformation out there on solar power. We have a log cabin in the northern great lakes, and we have powered it with solar and wind power for almost 10 years now. Originally, we did the same thing you're trying to do now, generate enough power for the weekends. We had the same problem, finding good information. Tons of people told us horrible stories about having to cover hundreds of acres with solar panels and install a battery bank the size of an RV to run my DVD player. We made lots of mistakes, but our final system today shows the benefits of having learned everything the hard way. Our 1500 square foot cabin generates its own electricity with a solar array that fits nicely on the roof of our one car carport, and a wind turbine just a bit larger than a ceiling fan. The battery bank fits under the workbench in the garage, and our 4000 watt inverter runs everything, washing machine, microwave, TV, stereo and all the lights.

I can only guess at your load situation, at 2500 watts tops, my guess is this only occurs when you are making breakfast with the lights and electronics running, maybe for an hour or two. The rest of the weekend, you have some lights and some electronics, and nothing the rest of the week. You really are in the perfect situation for solar power. A solar array is great at making limited amounts of power all week, which can add up to a healthy amount of power on the weekend. Here are my suggestions.

First, do some research beyond asking hacks like us for information. Get a subscription to Home Power Magazine, the only periodical that gets into the nuts and bolts of what you are trying to do. I will put the link below. Second, if you can get to one of the energy fairs this summer, go to it. It's where we got most of our information and some of our initial parts 10 years ago. Third, try to get a more accurate handle on the loads you're running. Look for a Kill-A-Watt meter online, and plug stuff around the house into it you might be using at your cottage. You'll settle lots of arguments about how much power things use pretty quickly for $35.

Then, when it comes time to design a system, select an inverter that is at least large enough to run most your loads at the same time. There are lots of 2500 watt models around. Put in a larger battery bank then you think you need, and a smaller solar array than you have calculated you'll need. Batteries are finicky devices. Once you buy them, you can't wait 2 years and add more, the old ones fight with the new ones. Panels all get along fine however, you can get 750 watts of panels now, add another 200 next year, and 300 more 2 years after that. Also, if you go with a small enough array, less than 2% of the amp hour capacity of the batteries, you don't need a charge controller initially. Get a book at the library called, "The Complete Battery Book," by Richard Perez, and read about lead acid batteries. The best bang for the dollar is the Trojan T-105 golf cart battery, they hold 220 amp hours at 6 volts, or about 1.2 kwh each. I would suggest maybe 6 or 8 of those batteries, a 2500 watt 12 volt inverter, and maybe 500 watts of solar array to start. That would cost you around $3,000 for all the parts, and you won't need much roof space, it could easily fit on the porch roof. You would just shut down the inverter and DC loads Sunday night, and normally, by Friday, the batteries would be full to start again. Our first system only had 150 watts of solar, it was a little short, but we got by with it for one year and added panels later.

There are some other groups that get into this stuff, I will list names below you can google for their web address. Our cabin was actually featured in Home Power Magazine at one time for our small system, if you subscribe, you can use their search engine and look for, "Small System First," to see what ours looked like. Most of the fairs are listed in the back of Home Power each issue, make one if you can, they are worth the time. Good luck Darcy, and take care, Rudydoo

Daisy Said:

Solar Panels / Batteries Hookup (Parallel, Series)?

We Answered:

It depends on what your needs are. You must have more voltage available than the battery rating. that is,if your storage battery is rated at 12 volts ( like your car), you should have at least 13-14 volts than the battery rating. Most solar cells can produce 1 to 2 volts per cell. In order to get enough voltage you must put the cells in series so it's additive... 2+2 + (etc) until you at least 2 volts more than than the battery you are charging. Then you have tho consider charging current. Here, the panels are connected in Parallel.. parallel combines the current, so 2 milliamp + 2 milliamp = 4 milliamp.so you must parallel to get the current that you need so you feed enough current to charge the battery. Need more info? Check out this website http://tinyurl.com/y8m8rlx

Henry Said:

Which is more affordable batteries or solar panels?

We Answered:

power from your local utility is more affordable.

you need solar panels to charge the batteries, they work together. You will spend as much or more for the panels as you will for the storage and converters.