Low Voltage Low Power Solar Panels

System · August 2007

Hi,

I am looking for sources of small solar panels in the Voc of roughly 5 - 6V and power of 0.5 - 2 W range. They need to be weather proof. I have found some on Siliconsolar.com. Anyone know of other places with decent quality and prices?

I plan to use them to charge AA NiMH batteries.

Thanks!

BB. · August 2007

Re: Low Voltage Low Power Solar Panels

Don't have any good info on the solar panels--but if you are trying to make a very simple solar charger with AA batteries, you may wish to look into NiCAD cells.

NiCADs are generally, much better at handling the kind of charge/discharge cycles that one or two series connected cells might experience in a simple solar power system. NiCADs can be "overcharged" and discharged flat without too many problems. NiMH batteries should be protected from over charging and over discharging as they can quickly fail if not managed correctly.

Of course, you may have issues with Europe (and other places) with NiCAD cells (because of the cadmium being a highly toxic heavy metal).

Another rechargeable battery that I have heard good things about is a NiMH hybrid type cell--Sanyo "Eneloops" have some pretty good reviews floating around--much lower self discharge than the typical NiMH (~85% of capacity after storage at room temperature over 1 year).

Battery specifications:
AA - http://www.eneloopusa.com/pdf/HR-3UTG_Spec-eneloop.pdf
AAA - http://www.eneloopusa.com/pdf/HR-4UT...eneloopAAA.pdf

I just purchased some AA's and AAA's to give them a try.

Obviously, I don't know your needs--but hope this may give you some ideas.

-Bill

Vic · August 2007

Re: Low Voltage Low Power Solar Panels

eller..

This link is not exactly what you are looking for, but these items are low in cost. You would need to do the waterproofing yourself.

Also, the solar yard lights are getting less and less expensive. You may be able to rob the solar cells from new lights from your hardware store or home improvement store.

The company in the link, below is a good solid company. I am only a coustomer and have no interest in the company:

http://www.allelectronics.com/cgi-bin/category/565/Solar_Panels_and_Photovoltaics.html

Also this: http://www.allelectronics.com/cgi-bin/item/SPL-08/search/SOLAR-POWERED_DEVICE_W__WHITE_LEDS_.html

Good Luck Vic

niel · August 2007

Re: Low Voltage Low Power Solar Panels

ellerbro,
following more closely into the link vic has given shows a cheap battery charger. for under $4 who would really care if one of the batteries is no longer good.
http://www.allelectronics.com/cgi-bin/item/SPL-08/565/SOLAR-POWERED_DEVICE_W__WHITE_LEDS_.html
if you pick it up, let us know how well it performs for you. the cost of the solar cells and white leds alone make this a decent buy, but i think you are getting a charge circuit too though i'm not sure.

System2 · August 2007

Re: Low Voltage Low Power Solar Panels

Thanks for the leads and info. I'll definitely look into those products.

I'm trying to come up with the simplest and cheapest way to put together low-power (0.1W to 1W) LED lighting systems for use in off-grid areas, primarily in poor countries. Ideally, rechargeable batteries would be used in order to reduce long-term cost and waste, but if the system is too expensive then it would be unaffordable to most.

The design I'm considering at this point is:

Solar Panel -> Blocking Diode -> 3 x 1.2V Batteries -> Switch -> Resistor -> White LED

The most expensive part of the system is the power source for the batteries. I've looked for hand-crank and pull-cord generators but they seem to be scarce and a bit pricey. Solar panels look like they might be more viable at this point.

Thanks again,
Jared

niel · August 2007

Re: Low Voltage Low Power Solar Panels

ellerbro,
do click that link for the one i pointed out as it sounds made to order for you. some of what it says is:
this device features a solar cell, rechargeable 3.6V NiMH battery pack and four ultra-bright white LEDs. LED indicators for Power and Charging. DC power jack.
there may be others like it as i didn't go farther than this one.

12vman · August 2007

Re: Low Voltage Low Power Solar Panels

Ellerbro..

What "Type" of lighting do you want? (Portable, Area, Spot, Reading..) I've built and revamped all kinds of normal battery light fixtures to solar..

http://img211.imageshack.us/img211/4126/20060415chargelites00012cz.jpg

http://img88.imageshack.us/img88/1426/20060415chargelites00024ia.jpg

I've built a few hybrid fluorscent/LED fixtures that operate on 12 v.d.c. The LED's and the fluorescents operate independent of each other. They provide a nice soft light with the LED's and if you want some decent area lighting, just turn on the fluorescents..

http://img250.imageshack.us/img250/7795/20050708newlts00019ae.jpg

http://img243.imageshack.us/img243/3149/20050708newlts00026tr.jpg

I find it easier to work with 12 v.d.c. and reduce the voltage to the needed level. You can find many small, inexpensive 12 volt panels that you can work with. Small, cheap controllers are plentiful. (In some situations, you may not need one) Voltage regulators like the LM7806 or LM7809 are cheap and will provide a well regulated 1 amp supply to work with. You can run a bunch of LED's with 1 amp!

I believe you would save some money on batteries by using small flooded lead acid type or sealed lead acid. This would depend on what kind of application you desire..

Just some food for thought..
Don

BB. · August 2007

Re: Low Voltage Low Power Solar Panels

Possibly, your best bet would be NiCAD's and a ~0.8-3.0 VDC boost converter. The reason I say this is that rechargeable batteries are pretty much killed if they suffer polarity reversal (several batteries in parallel, 1 weaker than the rest--Light is run until the weak cell hits zero volts--but the other cells continue to power and and cause the weak cell polarity reversal and attempt to "charged").

I believe that two NiCAD cells in series (and certainly, cells in parallel cannot), will not suffer damaging polarity reversal. Any more cells in a string, that is always a possibility--and for a rugged design, should have a cutoff circuit to prevent this.

But, instead, you can design a simple boost (and inexpensive) converter (regulated or unregulated, with several power settings, if needed), and have a very nice light that will be very difficult to damage (over/under charging, left on when dead, etc.--and there will be no need for a voltage protection circuit--and you can put the "money" towards a boost converter).

A buck converter would be more efficient--but it would also need a battery protection circuit too.

I am sure that you are familiar with the BoGo Light (Buy one, Give one) that is trying something similar (inexpensive, rugged light for rural use).

There is an "all things flashlights" forum were I (and a couple others here) hang out (and how I found Wind-Sun). It is the Candle Power Forums. There are lots of hobbyists, home builders, and even a few that have turned into manufacturers--as well as distributors and manufacturers of components thru complete lights (domestic and international participation on all levels).

There are folks there that sell small converters (from simple on/off to multi levels and modes) and other items to build your own lights--or can help you with more complex designs.

Good Luck!
-Bill

niel · August 2007

Re: Low Voltage Low Power Solar Panels

bill,
have you run into brock over there? i looked at that site and wow just clicking into one area there was a whole page of subjects all with current posts for the day. i'd get lost there or at least lost in the shuffle. maybe you could direct him to a good thread on the subject, but most in remote poorer countries have difficulty in obtaining parts for stuff unless it would be like from here or japan, etc. so assembled would most likely please him better and take away the possibility of having to send to multiple sources.

BB. · August 2007

Re: Low Voltage Low Power Solar Panels

Niel,

Just checked--Brock has not posted for 3+ weeks... Perhaps taking some time off.

It is kind of handy to have the IP Addresses posted, I check them before I reply when the posters are asking questions that may be location specific. For "Ellerbro", it appears that the IP is out of the Northwest US--So, I assumed that, at least for a start, they would be able to use US vendors for now.

I have seen websites where folks use LED's (for example), but finish up with locally available materials (bamboo flashlight anyone?).

I will let Ellerbro tells us what is needed--there is not much (that I remember) on CPF regarding specifically third world flashlights--but there is a lot to read about and specific questions.

Here is the main CPF thread on the BogoLight.

-Bill

niel · August 2007

Re: Low Voltage Low Power Solar Panels

sorry i made an assumption as to where eller was and didn't check.:roll:

System2 · August 2007

Re: Low Voltage Low Power Solar Panels

I appreciate all your input on this. I've come across the BoGo Light and it looks like it does its job well and for a pretty good price, $25 for two.

12Vman, those are some cool lights you've got rigged up. I can definitely see the advantages of using a 12V system with so many options available, but it would probably be too expensive for most in developing countries. What do you suppose a 1 Watt 12V LED light system (battery, PV panel, LED, etc.) for general room lighting purposes would cost? I know 1W seems way too weak but that's actually brighter than a kerosene lantern which is what many in developing countries use.

I wasn't aware of the reverse polarity issue with batteries. Fortunately, when the voltage to the white LED gets down around 2 or 2.5V little to no current flows so the batteries don't discharge any further. So that shouldn't be an issue.

It looks like there are a number of groups working on solid state lighting for the developing world, each with its own approach. The approach I'm taking is to make some sacrifices for simplicity and cost savings. I'd rather use a current limiting resistor than a constant current driver and forego a charge controller and just use a blocking diode between the PV panel and the batteries. I don't think I'd have to worry about overcharge when using a 0.5W to 1W PV panel would I?

My plan is to come up with simple designs using off-the-shelf parts that would be assembled by someone in the developing country. The parts that are not available in-country would have to be imported somehow.

The three light types I'm thinking of are:

1) Reading Light - Just a 5mm LED running at 20mA with a current limiting resistor and 3 AA batteries. A PV panel and rechargeables could be used for those who can afford it. This basic light can be built for around $1 (without PV panel or rechargeables of course) and lasts for many many hours.

2) Flashlight - A 1W LED with reflector, resistor, and 3 AA or D cells. Again, a PV panel and rechargeables could be used for those who can afford it.

3) General Room Lighting - Providing the same or more light than a kerosene lantern at a lower cost is the goal here. A 1W LED, resistor and disposable batteries would be the cheapest initial cost, but the recurring cost of buying disposables looks to be similar to the recurring cost of buying kerosene. This is where the PV panel plus rechargeables is really needed. From the digging around I've been able to do it looks like this system could cost as little as $15 including PV panel and rechargeables with zero recurring cost, except to replace the batteries when they eventually die. For this system I envision the panel left on the roof with wires running down to the battery pack inside and the LED hanging from the ceiling. The appropriate weather proof PV panel for this system is what originally sparked this thread. The selection of PV panels appropriate for this use seems to be a bit limited.

I'm of the 'use as many local materials as possible' camp ala bamboo flashlight, so the look of the finished lights would depend upon what the local person found to work best, but most likely the electronics wouldn't change much.
I'm presently trying to start up a little pilot project with some contacts in Tanzania and Namibia. I know AA rechargeables are available there but am not sure whether they're NiMH or NiCad. LEDs and probably resistors and PV panels would have to be imported.

I guess that's a pretty good rundown of what I'm up to. Here are a couple pix of a typical reading light and a general room light that I put together. The general room light was just slapped together for testing purposes and I didn't have a PV panel at the time, the finished product would look much different.

Attachment not found.

Attachment not found.

BB. · August 2007

Re: Low Voltage Low Power Solar Panels

I applaud your efforts to create a light (or lights) useful for folks around the world.

I would suggest that you weigh the use of some more efficient (and, of course, probably more expensive) LED's that are just now coming out...

Cree recently came out with a ~3watt LED that is about twice as efficient as the current crop of LED's out there. Twice as efficient implies 1/2 the battery and 1/2 the solar cell (or twice the run-time with the same parts).

Also, I would suggest an inexpensive buck (or boost) regulator would also be helpful in extending the brightness of the light... Generally, an LED with just a resistor to limit current puts you in the choice of having a bright light that dims significantly overtime, or a light that starts at the needed level, and gets too dim to use relatively quickly. Although, standard NiCAD and NiMH rechargeable batteries have a much flatter discharge curve (vs Alkaline), so regulators are not as necessary.

You could also use a PWM circuit to adjust light levels too (without the "relatively" expensive inductors that a buck/boost circuit would require). And as you "regulate" the light level down, the battery life goes up proportionally (less wasted power as no series resistor).

But, if you stay with locally supplied materials and labor, the less high-tech you will want to go... Exposed electronics and moisture/mold/corrosion become serious issues.

Perhaps making a "black box" of a potted converter (any reasonable voltage in, use a second switch--or multiple on/off cycles to change levels--probably made in China, India, or etc.) and supply several sizes/types of LED's plus crystalline Solar Panels (recommend avoiding amorphous panels as they fail pretty quickly--sometimes 20% loss of output per 6 months, vs 20% over 20+ years for crystalline panels)--and leave the rest to local suppliers.

-Bill

12vman · August 2007

Re: Low Voltage Low Power Solar Panels

ellerbro..

Would you consider something like this..

http://www.siliconsolar.com/Solar-Cells-by-the-Watt-p-106.html

Getting the batteries charged seems to be the biggest issue. LED's and resistors are rather inexpensive..

Maybe pot luck on what you get but it might be an alternative to buying new. Small chargers could be built on-site. (by a trained person) The cells could be placed (sandwiched) between glass panels with the edges sealed with silicon sealer (or some sort of sealer that won't affect the cells) to keep the weather out..

An inexpensive cell holder can be built with wood, bamboo, or with whatever materials that are available. All you need to do is hold the cells together while they are charging and have contact to the connections from the panel. A friend of mine built a holder using 3/4" PVC pipe. (for AA cells) He placed a spring in an end cap that was connected to the negative lead from the panel. (to provide tension) He then drilled holes every 2" to slide a pin through (connected to the positive lead) to give the positive connection to the top battery. The voltage of the panel was above the voltage of the cells combined being charged (in series) and the current was limited to the output of the panel itself. I improved this idea a bit by building a "V" block configuration. This way, "AA" and "C" cells could be charged with the same fixture being that they are the same length. If small springs for tension reasons aren't available, possibly a wedge of some sort could be implemented..

For the cost of a 1 watt LED, you could build several smaller fixtures and spread them out around a room. What I did with some outdoor lighting was build fixtures that hold 3 LED's connected in series and operate them with 9 v.d.c. from a 12 v.d.c. supply.. (LM7809)

http://img96.imageshack.us/img96/2041/20050621meled00031wj.jpg

I have 4 of these under the eve of my house which is around 6' off of the ground. They provide plenty of light to get from the vehicle to the door. Built very cheaply! I used white cereal bowls purchased at the Dollar Store. The L.E.D. holder in the center is one of those 3 leg thingies that stops the pizza box from stealing the cheese. The L.E.D.'s are hot glued to the holder and the leads are soldered in series..

They throw off a nice light. As you can see, I defracted(sp) the polarized (straight line) light with the cereal bowl. A couple of these in a room would be great and for a lot less money..

I've been running these lights now for 4 years with no issue. I run the L.E.D.'s a little under voltage being the max each one could handle is 3.6 volts for total brightness. The key is.. Don't run them to the max and they will last for years..

Here's a few links that may give you some ideas. Some of the fixtures in one of the sites are pretty cheap and you may get a better price if you go for wholesale status..

http://besthongkong.com/

http://www.ledshoppe.com/

http://ledsupply.com/index.php

Telco · August 2007

Re: Low Voltage Low Power Solar Panels

Very nice, I like that! That looks bright enough as is that you could probably add 6 more LEDs, paint the inside of the bowl with chrome paint, and get enough light to replace an actual fixture in the house.

Hmmm....

Low Voltage Low Power Solar Panels

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