Solar panels and how useful they are?


I wrote a few articles about solar energy and decided to open a can of worms on the subject of Solar energy devises.


Let's start from a statement: Sun has enormous amount of energy and capable to provide enough energy for human kind for basic needs.


Obviously it might not be enough to make 1megatone explosions to obliterate a megalopolis with about 100km of radius, but if human kind is willing to go little humble, 1-2 KWatt per hour energy for each house-hold on earth, it is easy job for our gracious Sun.


Also we are not going to talk about someone else junk for 50 cents from ebay because the owner wanted to clean his house from used stuff.


Here we going to discuss practical sides of using solar energy.


Start from example: I had this "solar battery", which came from junk because it had a dead lithium battery and did not do anything. I cracked it open and first thing I did - exchanged dead lithium battery cell to "a" lithium battery



I decided to check how much energy produced by solar panel.


Direct sun light at 90 deg with short circuit condition it produced 15mA (each) . Two of them 30mA. Each panel 5V open circuit. Allegedly by "Chinese accounts" this is 150mW. In normal accounts this is 8mAx4V=32mW.


I rewired his whole contraption to series solar panel connection. Allegedly they are 6V each, so it become 12V  open circuit solar battery.


I can't believe when I measured only 5mA charging current in indirect light and decided to double check with a simple resistor 5.6 ohm in series to solar panels wires, which shows 60mV drop of voltage, thus this is 10.7mA current and  therefore both panels produce about 40mW of power.


I can't believe my eyes as my trusty solar calculator here: https://visbis.com/newsinfo/solar-and-angles-for-panel.html

tells me at 4.5cm x 6cm and two of them it suppose to be 2.8Wx2=0.81W!!! and here we have 20 times less!

Also think about this: 40mW! It is worthless. For example 1 very dim LED flash ligh 3vx 20mA= 60mW. If you try to power one LED diode with this useless panel, it won't be enough.

Needless to say, it is not going to power even radio: 3vx50mA=150mW or modern cell phone with need of 4V x 1A= 4Watt!!! Never ever even for 10 seconds!

Then I stood amazed at this totally useless thing and sun light reveled to me the reason:



So called "solar panel" or "solar battery"  consist of many silicone strips and they are spread-out.

So here is the reality:4mm x 20 mm and 22pcs on each panel = 1760mm = 17.6cm2 per each or 35.3cm2 for two or 0.0035m2

Thus, from this solar calculator it is 0.5W.

I would take this 0.5W but the reality is different.

Useful "device"? Probably not, even it i comes for free. The only things inside are useful: dc-dc converter, charger, li-battery. Possibly solar panels, but only in a simple 1 led device to illuminate keyhole on the door.

Another example:


This is allegedly 240 Watt panel I have with 10A short circuit current on direct Utah sun and 18.7V open circuit.

Let's assume it is 120W, even though many companies sell around 2m2 panels as 240W.

I check numbers on solar calculator and came to around the same numbers.

Let's presume it is good and 120W/hr solar panel normally claimed to be 240W panel and on ebay around 140USD + 50USD shipping= 190..200USD for actual 120W power.

Many Chinese retailers (alibaba etc)  has ads for $0.5/Watt. Let's presume it is $0.9/watt with shipping.

Without any serious usage like kitchen or washing machine, I have a test how much energy needed for lights and 10in tablet+ cell phone and a router.

It came to an average 500W per day. Thus with around 8hrs sun light or 10hours of hazy day, I will need 90 watt panel or around mentioned above investment + solar controller + battery= 300USD

Not much on most people accounts. But let's calculate what if we pay it to City power. About 15cent/KW gives us around 10 cent per day and therefore we need 3USD per month or 36USD per year to cover our basic needs for information and communication.

How does this compared to 300USD or possibly 400USD with all installation problems and help? 10years without too much thinking if snow covered your panel? Or 10 years of thinking that "I'm autonomous and no one could cut my power off"?

There are many points of view on this.

Story is not finished.

Example 3:

Solar heater



Investment is 250 for a small, 2mx 1m stand full of tubes (about 8 or so) and another 100USD worth of pipes + 100USD for water tank with spiral tubing inside, which is commonly used for gas or wood heating water.

Total around 450USD. This can produce around 500Watt equivalent of power. In this case our usefulness increased 3-4 times and we can declare we start making money in 3 years.

If you are a hill-billy like myself and look for cheaper ways to produce energy, you could come up with the project I've done last summer:

or worst than that:

which was my second revision of solar heater, made out from $5 metal scrap, which use to be a house hold water radiator, you could be more serios about your money.

Then you are in business: $25 worth of parts, including super expensive $3 temperature controller and $6 DC pump and scrap 12Vdc power supply.

Those two produced around 400W per hour solar power and all that power was ether used for water heater or for heating concrete floor in the house and thus pumping energy in to earth underneath the house.


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