Your Questions About Solar Panel Efficiency

Ruth asks…

Laptop Solar Panel Charger Help Please?

I found this solar panel charger for laptops:
Does anybody know what its efficiency conversion rate is? Also, how long would it take to charge an Asus K40AB VX003?
Many thanks

ssadmin answers:

Its only a 2 watt panel, it will take quite a few hours to charge anything from flat, and that assumes constant bright sunshine which we dont get in the UK

Betty asks…

cleaning solar panels?

Do roof top solar panels that get dirty have reduced efficiency? If so, can the homeowner scrub them clean or is it best to hire a certified solar panel person?

ssadmin answers:

Some windex and paper towels should do the trick. Or a plastic scrub brush and soap and water.

Susan asks…

why does green light no give me a good power output for a solar panel compared to red and blue?

i carried out an experiment using different coloured solutions to see the affect of wavelength on power output from a silicon photovoltaic solar panel. I was expecting to see a peak where the efficiency of the wavelength and the energy of the photons were optimum. However instead i found that from wavelength in the blue region it was a fairly high power output which then decreased towards the green region and then increased even higher in the red region. I have made sure i kept the intensities of the different wavelengths constant. What could be the cause for this dip in the green wavelength region?

ssadmin answers:

Silicon solar panels have their greatest sensitivity at the red end of the visible spectrum and in the near infrared. By contrast, the human eye is relatively more sensitive to the green part of the spectrum. Neither silicon nor human eyes are especially sensitive to the relatively short blue wavelengths, but your blue solution may also transmit a significant amount of red or infrared light, giving a comparatively high reading for the silicon's “blue” sensitivity.

Chris asks…

Solar panel question about energy in the U.S.?

Total electrical energy usage in the U.S. per day is on average approximately 2.7 x 10^9 kwh. What total land area of solar panels would be required to satisfy this demand? Assume the panels are placed in the sunny southwest, and overall conversion efficiency of sunlight to electricity is 10%


ssadmin answers:

I don't know the approximate area but…

Energy from the sun is abundantly available all over the earth and will not run out for millions of years. The solar energy striking the earth in one year is almost 1,500 times all of man’s annual energy needs! Solar energy does not have to be mined, drilled for, refined, or transported around the world. Solar power is a form of distributed generation – making energy where it is needed, rather than transmitting power from large central power plants.

James asks…

Solar Panel (70W), Deep Cycle Marine Battery, Inverter for my Conversion Van; Most Efficient Set Up?

Double Checking My Work and would Appreciate any additional input for efficiency. I just bought a conversion van with the normal one battery set up.

My project:

Add one or two Deep Cycle Marine Batteries and attach it as a series, to keep it at 12 V, to the original van battery with a 6ga to 10ga wire( not sure which one, I'm assuming the thicker the better so I'm thinking of the 6ga.).
– My plan is to have the extra Marine batteries in the back of the van, so I guess I'm going to need a pretty damn long wire, but the results will be worth it.

I currently have a Siemens' 70 Watt Solar panel and plan to attach that to one of the Marine Batteries, via charge controller. Eventually I will add another (I'm guessing)-at least 70 Watt Solar Panel to the other Marine Battery if I go with the Two Marine Battery Set Up.

(I noticed my solar panel and charge controller looks like it has 18 ga wires: I would think if I use thicker wires of 10ga to 14ga, I would get more efficient charging through the batteries.

What do you think?

INVERTER: I will then attach a decent inverter to the Marine battery set up to get my power for my products in my van.

Again, any additional input and advise and/or tips would be great!
By the way, what would be the best battery for this application? I've heard Optima Deep Cycles are good, but man they're expensive. If you know of another source, please advise.

ssadmin answers:

Now, someone is coming right down my alley!

It all depends upon what all you intend to run with this
system as to how much of what you will need. You
have an excellent start with the solar panel, and two
batteries. However, do not think that marine batteries
are really a true deep cycle battery. They are not!

What the difference is with a marine battery, or even any
regular car battery is the amount of discharge it should
have allowed by use before recharge. To drop the
battery state of charge below the allowable percentage
will damage the battery so that it will not soon be able
to take the recharges. Most marine batteries are not
designed to drop below a 10% discharge before recharging.
Actually, car batteries are about the same. The only
difference between them is the difference between the
cranking amps versus the reserve capacity.

Reasonable batteries can be found where you can drop
about 25% charge before recharge, but most of those
you can get at places such as Farm and Fleet, and
similar companies, will not be listed with cold crank amps
at all, and a very low crank amps. They are designed
merely with a much higher reserve capacity.

For a true deep cycle battery you would have to get
an actual battery designed for solar recharge. These
batteries can be had in all sizes, and different capacities.
Their drawback is the price. It can run as high as $600 to
$800 each! (Not economically feasible for the casual user
of solar energy.) However, the life span of these batteries
being used for solar charge, and running an inverter system
for power is many years. I have seen some in use that
have been in operation for over 30 years now.

Another thing about batteries. You should get them all
about the same time, and all of the exact same type.
To get one, or two now, and another one or two to add
later is not good. Get what you need to take care of
your maximum use all withing a two to four week time

Next it about your wire sizes.
The cables between the batteries, and the inverter must be
able to carry whatever load is demanded. The best way to
think on this is to use regular battery cables, and keep the
distance short. If there is a great distance (over just a very
few feet) you would have to get cables much larger. You can
have a remote switch to turn on the inverter, and that does
not require any special wire just to work that switch. It can
be regular lamp cord wire if you like. All it is doing is to
extend the switch on the inverter to another location away
from the inverter.

As for the wire from the solar panels you don't need any
wire larger than what is on them to begin with. It is almost
always a small wire about 14 ga or less. Many come
from the factory with 18 ga. The reason for this is that
you are only transferring a maximum wattage of the
solar panel. You use a whole lot more than that with a
toaster, and it doesn't use a wire larger than 14 ga at most.
Even a speaker wire is large enough to run a 100 watt light.

For the length of wire from the inverter to the loads you
demand from it you can use any normal wire that you
would use on those appliances. If you have four outlets
on the inverter, but need six circuits you would use the
size wire to the converter needed for the amount of load
of both the circuits you have split into from the one outlet
on the inverter. The size wire for each of the circuits
need not be any larger than the load on that circuit. In
other words, you can use a large wire to an outlet box
where you would plug in the other two circuits, but
regular wire that can handle the load to each separate

As to your batteries for the volts, and current you should
use as series, parallel system wit more batteries. You can
stay at the 12 volts, but increase the available amps.
Many large systems use a 24 volt inverter to run the 110 AC
since it is easier to gain more amps with this system.

Now, it would seem that the one 70 watt panel would be
more than enough to handle what you might need in a
mobile unit such as a van. Unless you are going to live
outside a home where you would need a lot going each
day, two batteries can run a TV, and a bunch of lights
for several hours without running out of juice, and if you
are running during the day your system is being charged
with the sunlight while you are using the power from the
batteries to run your inverter system.

I don't know what model of panel you have, but the
efficiency of it could be one of the low ones, or high.
As for the charge controller, I don't know what you have
so I can't tell just how dependable it is for your need.
Of course, I don't even know your use needs to calculate
what you might need anyway.

The whole idea of anyone using solar is excellent! In
reality solar is the best resource.

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