Your Questions About Solar Panel Kits

Mandy asks…

How to select solar panel charger for laptop (basic electricity related questions)?


I have ASUS UL30VT laptop. The text on the battery says 15V, 5600 mAh, 84Wh. The adapter (black box on the cord) is:
Output: 19 V DC, 3.42 A, 65W
Input100~240 V AC, 50/60 Hz universal

I went to ebay and found different solar panels but I am not sure which parameters I need to look for. For example this one
It has a number of specs. Will it work for my laptop? And if not, which parameters indicate that? If yes, how long will it approximately take to charge the battery?

Also I found several other ones
which are way more expensive than the first charger. Why is that? Is it because they seem to provide not only the charger but also the battery? Or is it because the panel is more powerful which leads to faster charge times? Will it work with my laptop?

ssadmin answers:

Your first concern would be damaging the laptop. At the least, you would likely void its warranty. Why do you want to do this? There's no way it's economical if any alternatives (like AC power or car battery) are available. If you are lucky, the first one might charge the battery enough during a day to provide power for about an hour's use. You'd also be very lucky if it lasts a year, or perhaps even works when you get it.

John asks…

Is there any way to tell how much light a solar panel is receiving?

For my science fair project I am building a solar powered BEAM bot from a kit I am going to order online. For my experiment I was going to expose the BEAM bot to three different light sources to see which one worked best. So I just wanted to know if I would be able to determine how much light the solar panel on the BEAM bot is receiving.

ssadmin answers:

Go to your local camera store and buy a light-meter that will read out in lumens per sq ft, or lumens per sq meters. Back in the good old days this is how every photographer set the iris on their camera.

Steven asks…

What are some websites that you can buy Lego kits that have motors, solar panels, etc.?

These sets must have wires, motors, and battery packs at the least.

ssadmin answers:

The best source is Pitsco, I've included the link below. They are very oriented to educational aspects utilizing Lego.
We have bought unique individual parts from them especially for robot building associated with First Lego League competitions.

Chris asks…

is a 40 watt solar battery kit fitted with a battery protection circuit to prevent overcharging of batteries?

Is a 40 watt Solar Panel Battery Charger Kit with a Maximum Power Voltage of 17.5V
Maximum Power Current of 2.29A with Open Circuit Voltage of 21.5V, fitted with a battery protection circuit to prevent overcharging of batteries?
Or is it recommended to have a Solar Power Charge Controller?

ssadmin answers:

Hey Dave, it depends on the, “Kit,” you are speaking of, but generally, no, they do not have a circuit to prevent overcharging batteries. This would be the same as a charge controller. I don't know which kit you are speaking of, most manufacturers make several sizes of them. Kyocera has a 40 watt kit with a panel, mounting hardware, cables and connectors. Most panels today do have something called, “Bypass Diodes” installed. A diode is nothing more than an electrical check valve, allowing current to flow in one direction, toward the battery, but not the other. This prevents the battery from discharging into the panel at night.

There are instances where you do not need a charge controller. In short, if the panels maximum current rating, called short circuit current, in amps, is no more than 2% of the battery banks amp hour capacity, then a charge controller is not needed. We have two installations here that work that way. Our small home system which provides 12 volt power for cabinet lights, garden lights, and some small 12 VDC electronics in the home uses 4 golf cart batteries wired for 12 volts. This gives us an amp hour capacity of 440 amp hours. Since our 3 panels add up to a maximum of 8.2 amps, well below 2% of the 440 AH rating of the battery, we do not use a charge controller. It has worked well for over 11 years now. The only thing we have to do is make sure the batteries are well watered each month, particularly in warm weather.

There is an excellent book on the subject at your local library, called, “The Complete Battery Book,” by Richard Perez. If you pick it up, just pay attention to the chapters on flooded lead acid batteries, which are almost always the type used in solar applications. Richard also happens to be the founder and edtior of Home Power Magazine, a periodical that gets into the nuts and bolts of home grown energy. I recommend subscribing if you are really going to tinker with this technology. You'll find great articles and ads for exactly what you are trying to get into. Some other links are posted below.

Whatever panel you end up with, if it doesn't have diodes or a charge controller, you can get diodes at Radio Shack pretty inexpensively. If the panel is not rated over 4 amps, just get the 6 amp silicone diode, for about 89 cents, and put it right in the junction box on the back of the panel. Make sure the positive output of the panel is first routed through this diode before going to the battery. Hook it up when the sun is out, and see if the battery is getting a charge. If not, you probably have it in backwards, just turn it around. That's all the charge controller we have on our little system, one diode in the back of each panel.

If you do subscribe to Home Power, you can use their online search engine to look up old articles. Back in 2000 they were so taken with our low cost ultra simple system that they ran an article on it. Use the websites search to look for Small System First if you want to check it out. Good luck Dave, and take care, Rudydoo

Joseph asks…

What is a good solar panel to buy?

I am fairly new to the solar panel scene, and am eager to try to set one up myself instead of buying a kit.
I am looking for a solar panel that puts out 100 Watts or more, and can produce more than 20 volts. Thanks

ssadmin answers:

Hey C, the answer is you should buy a panel that meets your needs. A 100 watt panel is pretty easy to find, but I'm curious about the desired voltage. Most panels are designed to charge existing batteries, which normally come in multiples of 6 volts. This is why battery banks of 12, 24 or 48 volts are so common, and large deep cycle batteries of 6 volts each so easy to find. A panel set up to charge a 12 volt battery normally has 36 cells in it, which yields an open circuit voltage of 18 volts DC. A panel for a 24 volt battery will have 72 cells, with a V max of 36 volts. If you're trying to charge a 12 volt battery, 17 or 18 volts will work fine. If you are trying to do something outside the box like directly power your computer (which has a 19 volt power supply) with a 20 volt panel, then you'll run into some problems that might be too numerous to mention here. Mainly, solar panel voltages are unregulated without a battery to anchor them, this is why they never list a nominal voltage on a panel, only its maximum, it might be anyplace between zero and max if hooked directly to a load. The only exception to this is when hooking directly to a utility intertie grade inverter, they are designed for these large ranges in voltage, almost nothing else is.

If you really want to get involved, here is what I would do. First, get a subscription to Home Power Magazine, it's inexpensive and right to the point. Then look for an energy fair near you in the Calendar section of the mag when it arrives. Go to one of the fairs, we did 12 years ago, now our home is completely powered by the wind and sun. In the mean time, check out the sources below and learn what you can. One thing I encourage people to do is build up a small system themselves, with a 12 volt battery, panel, and small inverter. Now you can run your laptop, or other small electronics and lighting with your own power source. You'll have a much better understanding of the entire technology and be more equipped to make decisions. Home Power has great articles about people doing just what you are trying to do, that is why it's so worth the time and expense. Good luck C, and take care, Rudydoo

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