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15w Solar Panel

Samuel Said:

Why are my batteries failing in my solar setup?

We Answered:

You have at least two problems:

1. your solar array is too small, especially for short winter days, it may only be pumping in a total of 150watt hours per day.

2. your inverter is probably draining too much power when idling, maybe just 10 watts per hour, but in a day that is more than your array puts in.

for quick solutions, get a second solar array and parallel the original, also turn your inverter off when not in use.

Other things to do are to get a good Soneil charger to start your batteries off with a good full charge, and make sure you have no other loads on your battery and inverter.

A trickle charger on a 64ah battery bank would be useless, you need to be hitting each battery with about 3 amps apiece to bring them back up.

Nicholas Said:

What solar watt would work to charge a dump trailer battery?

We Answered:

Since it's recharging the battery and not simply maintaining it, you'll need the highest wattage you can get in a recharger..the more you pay, the better it will work..

Leona Said:

How to tell if solar panel can work with inverter?

We Answered:

Hey Mso, Gintable has some good data, but I'm afraid this setup is simply not going to work without a battery. You actually have two problems there. First, you have to think of a solar panel like a boat, you have a choice of anchoring, or tieing up to the dock, but if you do neither, the boat will drift. The solar panels output voltage is not self regulating, and any power inverter needs voltage input in a small envelope all the time. This is why there are two types of inverters, battery based or utlity intertie. In the second case, the grid acts as the dock, or in the first, the battery is the anchor. When the sun shines on the solar panel, it will force whatever is available out into whatever it is connected to until it reaches its open circuit voltage, then it won't do anything. Unless the inverter and its load is exactly balanced to the panels output, your circuit will have wild voltage swings, and the inverter will simply shut down to protect itself. The little LED that lit up when you hooked it to your panel was likely an overvolt or undervolt indication, so it wasn't putting out AC power anyway.

If you had a small battery to let that panel feed into, then you could connect any size inverter to the battery you wanted as long as the battery could carry its load that was running. Then when the inverter was shut down or not carrying a load, the panel could recharge the battery. The charge controller will not help out either, it is not a voltage regulater, it is a CHARGE controller, it needs a battery to anchor the circuit voltage also, so it can Control the Charge. Utility intertie systems don't use charge controllers because the grid voltage is already regulated by the power company.

The second problem is that panel is designed to keep a car battery at float voltage all the time, with nothing turned on. At 300ma, it can barely run an LED flashlight on its own, so trying to get enough watts out of it for even a radio won't happen. You're basically trying to heat the kitchen with a candle. You might be able to heat one can of soup up with that candle, but it would take all morning. The same is true of your radio. If you ran the radio on the battery for an hour, then in a few days with good sun, that 5w panel might put that small amount of usage back into the battery. All the data you're looking at as far as an inverter using 50ma or 300 ma is its idle load, how much amperage is required to keep the inverter on with nothing running on it. Again, even if you balanced the panel output with the inverter idle load and managed to get it to idle on a sunny day, as soon as you plug in a night light, the balance would be lost, the voltage would sag and the inverter would shut down.

Don't let this information turn you off to your idea though, If you have a small 12 volt battery hanging around, either one from a car or lawn tractor, or a smaller hobby type rechargeable, like you might find in an RC car or a DeWalt rechargeable drill, it will charge on the panel just fine, and it will run a small inverter or radio or light, even when the sun goes behind a cloud momentarily. Try it and see. We did the same thing here 12 years ago, and for a year or two, we ran our 12 volt under cabinet lights on a couple golf cart batteries and one 50 watt panel. Today our entire home is solar powered from our 1.4 kw array. It's been fun and rewarding. Good luck and take care, Rudydoo

Francisco Said:

Do I need a new battery for my solar setup?

We Answered:

Hey Brandon, Mike is probably right, but it's possible the charger you are using, the AC powered one, is not raising the battery voltage adequately either. As long as you have this stuff, here's what I would do. Charge it up with the AC charger one more time, then unhook it and hook the panel up, then leave the panel in the sun for several days, checking the voltage once in a while. It should eventually get up past 14 during charging, then stay above 12.6 all night after a few days of sun. Don't worry about overcharging the battery, with that little panel, it won't be a problem. There is a rule of thumb on lead acid batteries that if the charging source amperage, in your case 1.2 amps, is less than 2% of the battery amp hour capacity, you do not need a charge controller, so let that panel run as long as you can stand it, and don't put any load on the battery for a few days and see what happens. You've got nothing to lose. If the voltage stays up past 12.6 overnight, then it simply means the battery was not being fully charged by the AC charger. It likely will not hold the 115 AH it did originally, but it might still work for some small loads.

We have a home that is completely powered by the wind and sun, has been for almost 10 years now. We made plenty of mistakes and learned a lot the hard way. My old system was simply 4 golf cart batteries wired for 12 volts at 440 amp hours, and it ran DC lights and electronics with a 150 watts of solar wired directly to it, no controller. It uses a bit of water in the summer when it's near full charge on sunny days, but it has worked that way for years. If you're going to replace the battery in the end, consider using two Trojan T-105 golf cart batteries instead of one from the marine place. They really are designed for that kind of service, will deliver more of their stored power and run longer for you, but definitely keep them charged up. That little panel is designed to keep a car battery charged while you leave the car for a long time, not for running any loads. Even on a sunny day, at 1.2 amps, you might store 6 or 8 amp hours, which translate to 4 or 5 you can draw back out at night, not a lot of power. It would be good for LED lights and maybe a radio, or a small intermittent load, like a drill or laptop.

A really good place to look for more info on all of this is Home Power Magazine. They really get into the nuts and bolts of solar, batteries and such. Our home's small system was even featured in it years ago. If you subscribe online, you would have access to their archived articles for years past, and you could use their search engine to find an article called, "Starting Small." There is also a great book at the library by Richard Perez called, "The Complete Battery Book," that talks all about charging lead acid and other types of batteries, it's worth reading just the lead acid chapters. I will list a few other places below you can google for more info. Good luck with that battery, and take care Brandon, Rudydoo

Edgar Said:

So I have a 15W solar panel, 750W power converter, 300W rice cooker, and a 12V battery...?

We Answered:

You're thinking of running the rice cooker from the solar panel? I'm afraid the news is pretty much all bad.

Assuming everything was 100% efficient (after the solar panel's 15W rating), you would need 20 hours of best sun conditions to get enough energy to charge the battery to run the rice cooker for one hour.

In practice you'll need at least twice that because you can't use the last few WH in a battery charge, so figure 40 hours.

Battery charge and discharge are not 100% efficient and neither is the inverter. These losses will push you to at least 50 hours.

"Best sun conditions" means high noon on a clear blue summer day in the southwest US, or similar. A typical summer day gives the equivalent of maybe seven hours of "best sun conditions" as the sun is only directly overhead for a short time, and even if you aim the panel at the sun the light loses strength at other times because it has to travel through more air. So we're looking at seven days of charging for an hour of cooking.

If a winter day with no clouds, you only get the equivalent of about five or six hours of those "best sun" conditions per day... now you're up to ten days charging per cooking hour.

If the weather is cloudy, more charging time is needed. If you move north, again, more charging time is needed.

Pauline Said:

What do I need to create such solar power to power these appliances?

We Answered:

Your battery storage capacity appears to be adequate assuming that your speaker is relatively low power. You'll probably need a panel 3 or 4 times the size of the one you are contemplating since even at the equator you will not be getting full output from it at all times.

<edit>(in response to additional information) Your proposed 15 watt panel is still the weakest link. Start by adding the wattages of your devices. 2 CFL@11 watts, low power 5.1 speaker setup @10 watts, and the nanostation2 WiFi link@12 watts = 44 watts. Add another 30-60 watts for a small laptop (from your earlier question) and possibly a laptop power inverter and you'll have a current draw somewhere in the 6-10 amp range assuming a nominal 12 volt system. Multiplying by 6 (hours) gives you a requirement of 36-60 amp-hours daily. Using 36ah from a 50ah battery every day will give you a rather short battery service life. A 70ah (or better yet a pair of 70ah) batteries would be a far better chouce.

Even with a nearly perfect charge controller you would be lucky to recharge your battery at a rate of 1 amp with a 15 watt panel that tracks the sun. That means that you would need between 36 and 50 hours of optimum sunlight *each day* just to cover your daily usage. Obviously that is not going to happen so a 15 watt panel isn't going to be enough. </edit>


Felix Said:

Solar Panel Help? Beginners?

We Answered:

The bigger the better, 20w isn't a lot of power, so you might as well get it.

If you have $400, you can build him one or get him the stuff to do so. This would be WAY better than owning a panel already built because he will learn sooo much more about them. I found this site when I was dinking around with solar panels… All the other sites you google/yahoo for will be advertisements. I think the author of this one was a engineering student.

Hope this helps!

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