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rojo's avatar

Realistically, what can a 45 watt solar panel system be used for?

Asked by rojo (24179points) October 2nd, 2014

A national discount chain offers a 45 watt solar panel system for sale.

Some of the things they suggest can be done with it is charging your car battery, charging your laptop, providing electricity at a campsite and having an “off the grid” backup in case of a power outage.

So, what can actually be done with a 45 watt system? How much, or what, could you backup in an outage?

Is this a useful product or an expensive plaything?

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17 Answers

elbanditoroso's avatar

More than I thought…


LuckyGuy's avatar

Let’s do the math…with a little testing first. We bought a solar pack that advertized 100 Watts in bright sun. On a clear day around noon, we aimed it perfectly at the sun and measured. It only put out about 50 Watts. One of our engineers contacted their US engineering department and they admitted the design did not put out the 100 watts. “The new version coming out in early 2015 will provide 100W.”
Let’s say your device is Made in China, like ours, and is really only putting out 22 watts in bright sunlight . Can you use it to charge a car battery? Let’s do the math.
A typical car battery is rated at 42 amp hours at 12 volts That is about 500 Watt hours. That means you can fully charge the battery in 500 watt hrs/22 watt = ~ 24 hours of bright sunlight if aimed at the sun around noon. Figure it would take about a week to charge a car battery with no losses.
A laptop only draws 20–50 watts so it is possible to charge a battery that will run the lap top. You can also charge batteries that will run security lights and cameras.

Let’s figure out how much the electricity is worth. Where I live electricity at the plug costs 13 cents per kW-hr. If you use the device for 4 solid hours perfectly aimed at the sun you will generate 4×22 = 88 Watts hours. Call it 100 watt hrs for easy math. That means in 10 days you will generate 1 kWhr of electricity worth 13 cents. 1.3 cents per day. Use it every day for 2 years and you will have generated ~$8.00 of electricity.

Certainly there are some applications that can use it. I could use one to keep my tractor charged. It could run the bubbler pump in my pond. It could keep the battery for my deer camera charged.

Is it worth the trouble? I’ll leave it up to you to decide.

syz's avatar

Probably one of these

ARE_you_kidding_me's avatar

The ones horrible freight sells?

another thing to keep in mind is that they are very heat sensitive. Once they sit in the mid-day sun and warmup a panel that provides 3 amps when you first put it out will drop down to a couple of tenths of an amp.

45 watts will trickle charge a couple of marine batteries which can be used for quite a bit. small electronics like cell phones and radios can be powered directly through a regulator. It’s best to float it all on a battery. I have a small bank of batteries and a couple of 60w panels for times when the power goes out. It’s come in handy a time or two.

Those kits are not the best value btw. You really want poly or monocrystaline cells. In the same space those panels from the harbour freight take up you could get ~160 watts. The cost has dropped dramatically in the past couple of years.

cookieman's avatar

@LuckyGuy: “deer camera”?!

LuckyGuy's avatar

@cookieman “deer camera” are also called a trail cams or wildlife cams. They are battery operated, motion sensitive, Infrared devices that photograph and also record temperature, pressure, time, phase of moon and location. You set them up in the woods to see the animals moving along the trials. Usually they are in isolated areas with no power. A typical camera uses 8 AA batteries that last about a week or 2. If you connect it to a car battery you can let it run for months. A properly size solar cell can charge the battery so the camera can record indefinitely. Here are a few shots from my land taken with an older camera. (I really should update that blog.)
Hunters use them to scope out the wildlife in new areas and get a feel for the amount of movement and animal size. I use it to photograph the deer, fox, coyote, skunks, racoon, turkey, opossum, and even coywolves that pass through

JLeslie's avatar

@LuckyGuy You just gave me an idea with the solar camera idea. Does it have to be a car battery or can it be double A rechargeable batteries so you don’t use the bulky car battery?

LuckyGuy's avatar

The unit operates on nominally 12 V. but will work fine at 10 Volts. A stack of 8 new AA alkaline batteries (1.5V each) is 12 volts. You can stack rechargables, typically 1.2 Volts and use 10 of them. It might be easier to use a small motorcycle or garden tractor battery. I use what I have around the house and in the barn.
To be honest the “car battery” I use is actually an old car jump start box that has a weak battery. Rather than throw it out I use it for the camera. It has a readout so I know when to charge it.
Many of the deer cameras have solar power options and rechargeable batteries.

JLeslie's avatar

Do you buy the cameras at sporting good stores? Like Bass Pro? Dicks?

LuckyGuy's avatar

I bought mine from Sprotman’s Guide, but, yes, you can buy them at any of the sporting goods stores. Before you do I might have some suggestions depending upon your use. If you plan on using it for security you need to have it be far infrared or “no glow” so there is no visible flash and humans can’t see it – usually in the $120–160 range . You might also want it to have video capability with sound.

It is quite common for people to tie their camera to a tree in the woods with the provided mounting strap, put in a 32GB SD card so it can take 16,000 pictures, hook it to a 12 volt gel cell battery for 2 months of operation. And when they come back in a month, the camera is gone.

JLeslie's avatar

@LuckyGuy Do any of these cameras have the capability to warn you on your phone that they were triggered? Or, does that sort of thing require paying a service?

LuckyGuy's avatar

Remember these are designed to be in the woods for months with no power source, in all kinds of weather, from rain and snow to hot sun. And they will work in all light levels from bright sunlight to total darkness. I do not know of any that automatically connect to wifi. That takes a lot of power and would limit their operating time. My camera typically takes 200 pictures a night!
There are wireless security cameras that will do what you want and work as long as they are within wifi range.

LuckyGuy's avatar

I just did a search and found some. I am not familiar with this product but it does say it uses the cellular system .

ARE_you_kidding_me's avatar

They can be adapted to cellular even if they don’t come that way. It’ll cost and they are highly vulnerable to theft or vandalism. I have a couple systems like this out for work.Most people just get an inexpensive one at walmart or a sporting goods store. A neighbor caught a picture of a black bear nearby with one. They are not supposed to be around here but we are close enough to their habitat for this to happen though.

LuckyGuy's avatar

@ARE_you_kidding_me “black bear…They are not supposed to be around but…” Nice! One picture is worth 1000 opinions. The picture I got of the coywolf scared the crap out of me. They are moving down from Canada and supposedly have reached the PA border about 100 miles south of here. They are 2x larger than coyote, weigh about 50 pounds, are not afraid of humans, and use strategy to hunt in packs. I have not seen them but did hear some awful sounds in the woods one night. Maybe they took down a deer and were calling in the rest of the pack. My neighbor saw a couple along the tree line watching his dog. Yikes!

Time for a solar recharged, battery operated, electric fence?

ARE_you_kidding_me's avatar

Yeah it’s hard to argue with photographic proof. This bear was in a subdivision that was a 2008 victim and grew back up with small trees and blackberry bushes.
I still jog there regularly, just with a can of mace handy.
Wolf hybrids scare me too.

RocketGuy's avatar

Another use for an old jump start battery is to run a car stereo while parked. Doesn’t run down the car battery, so you can blast to your heart’s content.

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