Panel wattage and no. of batteries?

[SPIKE]

Is there a limit to how many batteries can be hooked up to a small solar panel?
I though about purchasing the small solar setup that Harbor Freight sells. It is 45 watt.
I really need to start learning more about solar and thought it might be a good learning tool.

SPIKE

[bee_pipes]

Yup, there's a limit. When you have added enough batteries that they never completely recharge ;D

You're getting a charge controller too? Keep us posted on your experiences - may save someone a fried battery down the road, or give someone experiences to imitate.


... really need to start learning more about solar and thought it might be a good learning tool...


An excellent book on the subject is Rex Ewing's "Power with Nature" (ISBN 0965809897). Will tell you the terminology for the components and discuss pro's & con's of a few brands of the components.

Regards,
Pat

[12vman]

Hey Spike.. U Go! ;)

"Is there a limit to how many batteries can be hooked up to a small solar panel?"

Yep.. If you have too much load, (battery) the small panel won't overcome the amount of resistance of the battery(s) to do any good. The big battery will basically just short the little panel out.. :P

In most cases, building a system starts from the expected loads (usage) and worked out towards the panels. In your case, you have a set wattage of panel and this is what you have to work with. Your usage will be limited to the charging ability of the panel. This will also gauge the size of your battery. If you have too much battery, they'll never achieve full charge and eventually be ruined. Gotta work 'um, baby.. ;D

NOTE: Find a battery that has caps on the top so you can check the electrolyte level! If they are charging properly, you will need to add distilled water from time to time..

First thing.. If Harbor Freight hasn't improved their charge controller in that kit, I'll suggest that you look for another one. I'll help ya pick one later..

A short, simple formula that works for me in my area. (Subject to change in different locations)..

A: 4 hrs. of prime charge time during a day with a fixed array, pointed and angled in the right position. (10 am 'till 2 pm) This is the "window" of time that you will design from..

B: Battery size is figured at around 4 times the charge capability of the panel. (max. discharge level of the battery should be kept around 20-25%)

OK.. The meat.. 8)

45 watts of panel can produce around 3.75 amps of charge current during good conditions. (Full Sun) Multiply that times 4. (Ref: "A") That gives you around 15 aHr. max. that can be replaced to the battery. This also tells you the maximum power usage that you can safely use in a 24 hr. period to avoid damage to the battery.

As for the battery, look at the maximum charge potential of the panel. Being that you don't want to discharge the battery any more than 20-25% of its total capacity, multiply the charging potential of the panel in the 4 hr. period by 4. (15 aHr.) (Ref:"B") This gives you a battery size in the neighborhood of 60 aHr. reserve. (see the connection?)

Of course there will be a small amount of charge before 10am and after 2pm but I figure that this just covers the normal internal losses in the battery which is around 20% with a small bonus. This just avoids a lot of brain bending math, IMO..

The math..

45 watts divided by 12 volts = 3.75 amps. (12 volts = the working voltage)..

aHr. (amp hours) is figured by the amount of current (amps) that can be "supplied" to the battery from the panel OR used as "loads" (lights, TV, pumps, ect.) in your situation in a 1 hr. period.

You are limited to a maximum usage to 15 aHr. in a 24hr. period with this set up. With everything figured with the above formula, you shouldn't have any issue with the battery not achieveing full charge within 2-3 days figuring that not all days are clear and perfect. On clear days it should get fully charged as long as you stay within your 15 aHr. limit!

Have fun! ;D

[Anon001]

Spike,

There really isn't anything to add to what 12v said. But, I used an old satellite dish stand for my panels. I built a frame to mount to the stand for the panels to attach to. This allows me to be able to adjust the angle 2 or 3 times a year and also, I can rotate it through the day. At night, I turn it to where it is about halfway between facing the rising sun and the sun position at noon. Then midafternoon, I turn it due west. I get more hours of charge doing this. I find it easy to keep the batteries charged that way. But, I am also home all day every day to be able to do that.

My favorite book is "The Solar Electric Independent Home Book". You can find it on Amazon.com and it may be on half.com as well. This was the book that backwoodssolar.com recommended to me back about 11 or 12 years ago. My copy is ragged now... But, it is an easy to follow, easy to understand book for someone new to solar.

Paul

[SPIKE]

Thanks guys for all the input.
I am an electrician by trade with a bit more knowledge than the average electrician. I actually earned a associates degree in electronics engineering, but at that time the construction money was too good and I never got into electronics full time.
It's funny how "if you do not use it, you loose it". At least that is how it is for me. The knowledge that I retained definately made me a better electrician.

But I have no dealings with solar.

Is the 45 watt panel set up even worth messing with? I hope to get a small building for chickens and a bit of storage built this spring. I was thinking about solar for it and just to help me get started using some solar.

Thanks again,
SPIKE

[12vman]

If you take the potential of the Harbor Freight system and divide it into a 24 hr. period, you could use .62 amps/hour. (15 divided by 24) In 12 hours, 1.25 amps/hr. That's enough for some low level lighting.

What do you plan to use the power for?

[12vman]

This (http://www.affordable-solar.com/xantrex.c12.charge.controller.htm) is the controller I was talking about. The light control make it automatic. Really sweet unit. I use one here for my outdoor lighting. (dusk/dawn feature)

It'll easily handle the Harbor Freight panels and if you ever decide to expand, It will handle up to 12 amps of charge. (around 150 watts of panel)

[SPIKE]

Thanks 12vman for the info on the controller.
I am mainly looking for a way to power some lighting.

SPIKE

[12vman]

That Harbor Freight kit comes with two lights, I believe. You might have to "Goob" the connections a bit if you don't use the supplied controller but it's not a biggie. Just be careful on the polarity.

Paul will tell ya about those cold cathode fluorescent lights I told him about. Nice units! I use them around here. They put out a lot of light for the power they use. They'll light up a chicken coop! They work in the cold too..

[Anon001]

Paul will tell ya about those cold cathode fluorescent lights I told him about. Nice units! I use them around here. They put out a lot of light for the power they use. They'll light up a chicken coop! They work in the cold too..
I actually replaced my 12v CFL's in the house with them. I "built" light fixtures for them out of "white" flashing I had. I just curved them, drilled a couple holes, stuck the "inverter" to the back side and attached them to the ceiling with that little inverter fitting right up into the box. They work great. I have a cornea disease, so I am very sensitive to bright artificial lights, especially flourescents of any type. These cold cathodes don't hurt my eyes. I also have a bathroom medicine cabinet from the 1950's with chrome. It has a light fixture attached to each side of it. I replaced the "bulbs" with the cold cathodes as well. They come with a "switch" for each one. I hid the switches under the medicine cabinet. That allows me turn on both or just one at a time. They are cheap and they only use 3.7 watts.

Yeah, 12v.... I sure do like 'em and I still owe ya! ;D