Solar without batteries

[Yuhjn]

Is it possible to do solar without batteries? Obviously you only have power when the sun is out, but beyond that, are there any other issues?
How about running a well pump to fill a pressure tank with a system like this? Think solar without battery could get to the start voltage without the need for huge numbers of panels?

[StressMan79]

you need some sort of storage medium, this is the grid, batteries or even big old capacitors.
Unless you want to size the PV array to provide the hightest required draw, you will want a battery or 3. Basically a battery bank acts as a buffer to high loads--say you have a load that you run once a week for 20 min that is 400 watt.
A battery can provide that easily (~12 AH), but if you were to size the PV array to do this, you have to have a ~800 watt array for one load that is running for 1/3 hr once per week. a battery is a much better choice.

[loghousenut]

Never argue with a guy who's name may indicate that he could go Poastal on you at any time hahahaah. I suppose I won't argue witha guy who's an engineer also, but to elaborate on the answer to the original question, there are circumstances where solar panels work famously without batteries. One instance would be an attic vent fan that should opperate in the heat of the day. To agree with Peter, for your home power system you will want a nice battery pack that consists of batteries that are the same size and age and perform identically. The 6v Trojan t-105 golf cart batteries are cheap, easy to find, and last a long time with proper care. Nothing wrong with slightly over-sizing your battery pack. You'll appreciate the extra performance and they will last longer, thereby not neccesarily costing more. You can beef up your system by adding more panels at any time but you'll spend a couple of dollars for a bigger charge controller.

[ivanshayka]

I had worked for a lady who owns organic farm, she is completely off the grid. She ran her waterpump directly from pannels, two panels size of 8X10 feet aprox (don't know any more stats on that). It worked great when sun is out, sometimes the pressure seemed to get out of control. Lately she got batteries, huge bank of batteries, but I dont know how it is working out for her now. Just wanted to share that with you. Thanks. Ivan

[jimirwin]

Although it may not be available for a number of years...MIT scientist Dan Nocera and his team discovered a way to split ordinary tap water into hydrogen and oxygen for use in fuel cells, so - you can use a few gallons of tap water instead of a bank of batteries!

The full story and a video can be seen here:

http://web.mit.edu/newsoffice/2008/oxygen-0731.html

[StressMan79]

solar pumping...

you rarely want batteries for a solar pump. a pump motor controller for times when the sun isn't at full bore (swaps current for voltage to run the pump). Anyway, you have a storage media, your tank... picture having no tank and no batteries... you'd never be able to turn the water on at night. in this case, the tank stores the product of the day's solar work.

-Peter

[rreidnauer]

Also a thing to keep in mind is that the standing open voltage of the panels in full sunlight will be 21~22 volts for a 12 volt panel. (perhaps even higher in the cold of winter) As you add loads to the panel, the panel's voltage will drop. You need to consider voltage sensitivity of equipment you are connecting. I'm not sure how something like a TV would like going from say 17 volts to 5 when a cloud passes by.

As mentioned, yes pumps and fans can work well without batteries, however, I don't think I've ever seen a solar only well set up that pumps to a pressure tank. Only ones which pump to a holding tank, then use a demand pump when water is needed.

My solar domestic hot water system runs straight off a small solar panel, running two circulation pumps specifically built for use that way. It's a perfect method, since they only need to pump when the sun is out.