If you had a moderate sized trolling motor battery, it might hold 60 amp hours. In theory, you can take a battery like that down 60 % or so, about 40 amp hours, and in one good sunny day, the panel should be able to just recharge it. A new battery loses about 5% in charging, an older one could be closer to 20%, so 42 amp hours might equate to around 36 amp hours in the battery.

Not knowing exactly what you are trying to set up, I can’t suggest a number of panels, but this gives you an idea. Golf cart batteries are used frequently in solar/battery applications, they only come in 6 volts, so you have to buy them in pairs, but they typically hold 220 amp hours. Two wired in series would give you 12 volts, but still the same 220 amp hours. So you could take a pair of them like we do in our cabin, use maybe 80 or 100 amp hours out of them all night, then you have to put back in maybe 120 amp hours the next day. That would require at least 3 of the 125 watt panels, and you would need good sun. Where most people fall down here is they forget that they also need to run the house during the day. This might be a lesser amount of power, no lighting, but other items have to be accounted for. So if you are using your solar power during the day for laptops, radios, TV’s and refrigeration, that amount of power cannot also be used to recharge the batteries for the next night. So in this case, you might now need 5 or so panels. Also, none of this accounts for the cloudy day, rain and so forth. You can see that it might be difficult to do the math. Most people in remote applications will have a small generator they run once or twice a week for a few hours. The nice thing about solar is you can buy 4 panels today, and add 2 more to them next year. This is not the case for batteries, you need to figure how many you need, maybe add in a little for good measure, and buy them all at one time. If you add batteries later, the new ones will fight with the old ones because they have different charge voltage curves.

If this sounds like a lot to understand, I suggest doing some reading online and getting a few publications, it will be worth the small expense and time. I’ll list some sources below. We did the same thing 12 years ago, today our home is completely powered by the wind and sun. There is a lot to learn, take your time with it and don’t rush into any purchases after just asking a few questions here online, lots of people do and end up with a system that does not fulfill their needs. Try to get to one of the energy fairs listed in Home Power Magazine, it’s the best, fastest way to get up to speed. Take care, Rudydoo

A 125 watt panel generates about 125 watts when fully illuminated by the sun. If you fully illuminate it for an hour, you get 125 watt hours. If you get 12 hours of sunlight a day, that would seem to imply that I need 67000 watt hours/125 watts /12 hours=45 panels.

But for most of the day, the sun isn’t hitting the panel fully, so it isn’t going to generate the full 125 watts. When the sun is 45 degrees to the side, you only get about 70%. When the sun is 60 deg to the side, you only get 50%. And what do you do on cloudy days? And the shorter days in the winter? To make up for this, you have to increase the number of panels to make up for the loss. So in reality, I might need double this number of panels, for realiable solar power throughout the year. That works out to about 90 panels, or 11,250 watts worth for my house.

As to how large a system or how much it will cost, you would call a professional to size your system and give a quote. You can always say no if the numbers don’t work out.

A house requires 1 kW at a minimum, and 2 to 5 kW at peaks. You can do the division, 5000/125 = 40.

Plus, solar panels operate only 4 to 8 hours a day in the winter, so you need to multiply that number by about at least 6 to allow for the dark hours.

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2)The next thing you are going to need is a battery. While you may be tempted to go big or go home on this one, a smaller yet rechargeable battery is your best bet.
A 12 volt lead or acid battery will do the trick. The type you are looking for here is a deep cell battery as they are built the best for constant and continuous use.

3)In order to build your solar panel safely you will also want to purchase a battery box. This will offer protection from the battery and the power it exudes in case you are working in small quarters or have small children running around in the area.

There are also many 12 volt appliances as well. You can even convert some of those "all in one" stereo systems to operate on 12 volts by eliminating the power supply. You will actually use less power by doing so. You will not be able to blow the shingles off the roof unless you add a Class D amplifier to the output, but for most listening, the output is adequate. Some small TV’s these days can be run from 12 volt sources, if not directly, then with a buckboost inverter for a laptop. The small TVs only draw about 30 to 45 Watts. Skip the idea of using an inverter, they are not efficient at small loads, and represent additional load on the system.

So with a little bit of planning, you can run a lot from that 60 Watt system. You can at least take some bite out of the electric bill for mundane lighting.

You can also use them to keep power up on a battery system for lighting in a remote barn. The uses are only limited by your imagination and creativity.

60 watts at 12 volts is 6 watts at 120 volts with 100% conversion.
MOST inverters are only 30-60% efficient, plus battery losses. (Batteries are required to "balance" load and for when sun is NOT shining.)

MOST TV’s draw 120 volts at about 500 watts

MOST homes these days are wired for 100 amps at 240 volts which is 24,000 watts although they seldom draw this much at any given time.
A single standard home circuit is usually 15amps at 120 volts or about 1,800 watts MAXIMUM.