Solar Storage system

A month ago I built a small solar panel, and it outputs 5V @346mA, for a while Ive been wanting to use the power it gives..But Id have to be outside in order to use that power. I now want to be able to store it. So which battery do I use? To chose from I have:

• NiMH
• Li-Pol (or Lion)
• Sealed Lead Acid

Most likely with my solar panel, Id have to go for 4V Lead Acid Batteries, or 3.7 (Lithium) or 3.6 (NiMh). I already have a controller in mind to charge the Lithium Batteries and the NiMh Batteries. The Sealed Lead Acid shouldn't be hard to charge as long as I log how many hrs of sunlight I get.

Now My Question is not of capacity, but Of longevity and temp range and shelf life. I have read that LiPols and LiOns only have a 2 year shelf life..that seems rather off putting. I can get LiPols for 0.99 cents if I order more than 10 (I planned on ordering 21). The Li-Pols are from a surplus store and are rated at 3.7v at 670mAh and have over and under voltage protection along with over current protection. Is this True that Li-Pols only last 2 years even if you use them or not?

Ive also read that Sealed Lead Acid batteries last 2 to 5 years as well. I have not been able to find Data on the longevity of NiMh Cells.

Now, since this is going to be outside, Ive taken in the temp range of Each of these batteries. Right now in the North east of the US, its spring time, so temp hits around 70F (some days 80) and a low of 50 to 60F. LiPols/Lions have a temp range of 0 to 50C (32F to 122F). Now it never gets that Hot here..but it does get that cold. So Id have to build a box and keep them shaded. Lead Acids on the other hand have a temp range of -60C to 60C (they seem to last a good 5 years in cars with the crazy temps). NiMh Cells can be charged at 0 to +45C (32F to 113F)


Cost Analysis:

4V 10Ah Sealed Lead Acid Battery $15.95+8.58 Shipping = $24.43
21 3.7v 670mAh = $20.79 +$8.00 shipping (estimated) = $28.79.

The SLA will give 40W of power
The Li-Pols will give 52W of Power (all hooked up in parallel) however, Ive been thinking of charging in parallel, using them in series/parallel.

SLA price per watt = $0.61
LiPol price per watt = $0.55


Link to LiPol battery
**broken link removed**

Link to SLA
**broken link removed**

Now Im not lookin to power my house...I really just want a storage element with occasional use. There a slight problem with the LiPols, since their surplus, I dont know how long theyve been in storage, or when they were made, and if theve been there for 2 years they could be dead already. Same with the SLA, I dont know if they top off their battery's and trickle charge them

So to sum up my question, which battery type will be best for storage? Which has the best temp range to stand up to the elements? Which will last the longest? Both SLA and LiPol seem to be around the same price. I do Not plan on leaving the system outside in the rain or snow. It also seems NiMh cells are rather expensive, and for roughly the same price LiPol and SLA batteries seem to be competing against each other. I *did* plan on building a small box to put the batteries in, to keep them sealed from the weather or bugs. I am Really edging towards Li-Pol but I am afraid of them melting because of the hot sun or because of the summer (Summer peaks at around 100F)

I also do have a charger IC in mind for the Li-Poly Batteries, so that is no concern to me. Yes i do realise it will take a while to charge a huge battery, but time is what I have.

add: The LiPoL Cells will also give me more flexibility and allow me the hook them up in series for a higher Voltage, instead of having to use a boost converter to boost up the voltage for use.

True that Li-Pols only last 2 years even if you use them or not

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No absolutely false as any number of cell phone users can atest to. In general the lifepspan of a battery is measured to the point where it only retains 80% of it's original charge. If the battery is treated well I don't see why it couldn't go 5 years. You're buying completely unknown batteries if you're buying surplus though, they could be much older, and possible even arive already dead if their voltage dropped too much in storage.

As far as the environment and the application goes you've left a can of worms in your post. "I don't want to power a house" doesn't tell us anything about what you DO want to do, and occasional is not a measure of time that can be engineered for.

If you want advice you should do more than play 20 questions (bigger the than a breadbox, smaller than a house)
Define SPECIFICALLY what you want this device to power, SPECIFICALLY what environement it will be in, and any other constraints you might have. If you can't name these specifics we can't answer your question because there isn't one to answer.

Sceadwian said:

No absolutely false as any number of cell phone users can atest to. In general the lifepspan of a battery is measured to the point where it only retains 80% of it's original charge. If the battery is treated well I don't see why it couldn't go 5 years. You're buying completely unknown batteries if you're buying surplus though, they could be much older, and possible even arive already dead if their voltage dropped too much in storage.

As far as the environment and the application goes you've left a can of worms in your post. "I don't want to power a house" doesn't tell us anything about what you DO want to do, and occasional is not a measure of time that can be engineered for.

If you want advice you should do more than play 20 questions (bigger the than a breadbox, smaller than a house)
Define SPECIFICALLY what you want this device to power, SPECIFICALLY what environement it will be in, and any other constraints you might have. If you can't name these specifics we can't answer your question because there isn't one to answer.

Click to expand...

Opps, let me re-edit my main post and add that. Thanks for pointing that out.

I wouldn't, editing a thread at this point is bad. Simply post your updated requirements as a new post in this thread, that way we have refrences to what was before and what is different now. You can't turn back time, but you can restate your objectives =)

Goodpoint


My Purpose For these batteries is to have them for emergency lighting or emergency cooling (ie power a 12V peltier and some 12V fans or to power some larger 12V Fans.) The Charging will be done outside, where temps range from 10F to 90F. The Batteries will be used Inside once charged in a temp range of 50F to 70F. As for the draw, A peltier can use up to 16V at 8 Amps (but 12V is fine)..atleast the one I have, but would limit it to 1amp draw as its only cooling air. The Fans draw around 1W each. This is just an idea, the emergency lighting is probably a "better" idea because one needs light more than cooling. Of Course powering a small inverter to power a 120V Fan is a nice idea as well.

As for emergency lighting. I have quite a few Luxeon V Portable LEDs (5W) that consume up to 700mA each at 6.86V for full brightness. 6 of these are hooked up series/parallel to run at 13.72V at 2.10 amps. Id like to think they would be run for maybe 1 hr or 2 at a time, and probably at reduced current (say 500mA each)

Above all, Id need a boost converter for the lead acid cell. I could also email bgmicro and ask the state of the cells.

If you plan to use the power for cooling only then 346mA boosted to 14V (enough to charge a 12V lead-acid) will be about 100mA. After charging the battery for 8 hours, you could run the 8A Peltier for about six minutes. If you use a pair of LEDs at 6V 500mA, then the energy gathered in a whole day (6V 1600mAh) will run them for about an hour and a half.

This assumes that the solar array provides the stated output. Some solar cell suppliers tell you their output at noon on the Equator. You should check your own solar cells to see what they actually deliver in Connecticut.

What do you need emergency cooling for?

Peltier coolers are less efficient than the traditional phase change cooling, they're just used for camping because they're small, light and cheap.

How often are you going to be using the emergancy lighting?

I have lights in my shed which only get powered once a week for a few minutes. They're two 8W fluorescent tubes powered from 24VDC. A couple of 12V panels are hooked up in series, connected to two 12V 14Ah lead acid batteries via an LM317 regulator. I've forgotten what size the panels are, last time I measured the curent it was only 50mA but that was in early spring. I've had it connected for over a year now, the batteries haven't gone flat and power the lights, whether it's -10°C or 30°C, the minimum and maximum temperature over the last year. I understand your climate is more extreme though?

mneary said:

If you plan to use the power for cooling only then 346mA boosted to 14V (enough to charge a 12V lead-acid) will be about 100mA. After charging the battery for 8 hours, you could run the 8A Peltier for about six minutes. If you use a pair of LEDs at 6V 500mA, then the energy gathered in a whole day (6V 1600mAh) will run them for about an hour and a half.

This assumes that the solar array provides the stated output. Some solar cell suppliers tell you their output at noon on the Equator. You should check your own solar cells to see what they actually deliver in Connecticut.

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Oh, I built the panel myself. So those are the actual measurements on a sunny day when connected to a load. Are you saying it would be easier to boost the solar voltage and just charge a 12V battery instead of charging a battery directly and then boosting it?

Hero999 said:

What do you need emergency cooling for?

Peltier coolers are less efficient than the traditional phase change cooling, they're just used for camping because they're small, light and cheap.

Click to expand...

Yes thats true, their only 10% efficient from what Ive read. Better off powering a swamp cooler then or some fans.

Hero999 said:

How often are you going to be using the emergancy lighting?

I have lights in my shed which only get powered once a week for a few minutes. They're two 8W fluorescent tubes powered from 24VDC. A couple of 12V panels are hooked up in series, connected to two 12V 14Ah lead acid batteries via an LM317 regulator. I've forgotten what size the panels are, last time I measured the curent it was only 50mA but that was in early spring. I've had it connected for over a year now, the batteries haven't gone flat and power the lights, whether it's -10°C or 30°C, the minimum and maximum temperature over the last year. I understand your climate is more extreme though?

Click to expand...

No Actually that temp range is pretty much the same where I live, maybe with a slightly higher high temp. Emergency lighting will probably be used once or twice over the whole year but it would be nice to have for other uses.

So it seems like the answer is the SLA battery

Overclocked said:

Oh, I built the panel myself. So those are the actual measurements on a sunny day when connected to a load. Are you saying it would be easier to boost the solar voltage and just charge a 12V battery instead of charging a battery directly and then boosting it?...................

So it seems like the answer is the SLA battery

Click to expand...

Since you need a charge regulator between the solar and the battery, a regulator of some type will be there anyways. Boosting the solar voltage allows you to have the entire battery capacity when the time comes. But there are a lot of other factors, such as will it have to be converted again for its end use? It makes sense to me that the battery voltage should be chosen for your final usage.

Storing and charging the battery outdoors and then bringing it in and rewiring it for series or parallel when you need it doesn't seem very convenient. You can't run any wires at all? 5V 364mA can use almost anything.

About 1993, I bought a solar charger, which put two nickel-cadmium rechargeable batteries, but largely unrealized charge, the battery was drying quickly broken, I hope the situation has changed now.

You can refer to the introduction of these products.
Travel Solar Battery Chargers