Some rough calculations on solar cells from examples

This was a mail I sent to campers about energy harvesting for charging my cell phone:

Samsung Charging Experiment
i did several more experiments in the nice sleeping week i took, still in the valley of the Loir.

Very important for instance is the amount of energy harvested, for instance with all my solar cells i could produce 50 mA for my telephone- but my adapter produces 700mA and needs 4 hours to charge my telephone. so you can calculate the 50 mA will take at least 60 hours to charge my phone, in which time it uses also energy again……!

charging my samsung at 50-70mA
picture of charging my Samsung at 50-70mA (full Sun) with the LTC3105 IC.
Aniela answered:
With that in mind, how would you explain Pauline van Dongens wearable solar loading up a mobile phone within 2 hours? Has she got so many cells that it will get to the 700mA or put something inbetween to get there?

Some calculations around this dress
Hi Aniela, good question! So a dress that can charge my Samsung at half the time of my adapter which is connected to the mains.

First of all, my cells are the cheapest I could get – a few years ago – there are certainly more powerfull (more expensive) ones. The Sunnybuddy chip LTC3652 of Sparkfun Pauline-Summercamp invested in can do charging at 2A = 2000mA, eg with the solar cells of, which can give 950mA at 8V (meaning more at 5V).  You need at least two to get 2000mA. These costs 50 dollar – we need that in a minute.
(My favorite harvesting IC ltc3105 is more micro harvesting, that is right! Every harvesting IC has its own domain.)



Secondly, from the text of this garment you mentioned
“The coat incorporates 48 rigid solar cells while the dress 72 flexible solar cells. Each of them, if worn in the full sun for an hour, can store enough energy to allow a typical smartphone to be 50% charged.”
50% charged means around 1500 mA, at 5V compared to my Samsung specs.

EDIT:You can also read this text differently: Each meaning: each of the two items coat and dress, not each of the solar cells. Then you can calculatie that all the cells together, with the right direction on the sun (this is a problem eg in tropical regions where the sun is above you, not so much in Holland, where the sun is always low ) can generate this energy mentioned.

So this calculation is done on the “wrong” interpretation of the text on the website:

Meaning around as powerful as the above mentioned solar cell.
So … expensive dress if you do a bit of calculations: these cells are around 50 dollars each (compared to the price of Sparkfun solar cell):

(48 + 72) * 50 dollar = 6000 dollar (estimated) investment on solar cells for the coat and the dress.

Yes! With that amount of investment you are certainly entitled to expect something to happen!!! (Expensive adapter by the way…)

What is important is to understand about energy domains, and being able to do some calculations, big is not equal to small, although both are energy.

By the way: the text says 140 solar cells, EACH of them capable of charging half a battery of a phone in 1 hour…why so many? Well because most of them will be in the shade, or not pointing to the sun most efficiently. So from a harvesting point of view, as far as this text explains it right, this garment is a disaster, if you look at the return on investment and/or efficiency…… If this text is right, and if I understand it right……

Wendy was also replying:

Hey Aniela
Some notes on solar power – whilst it is raining raining raining :-/
–> all depends on the efficiency of the solar panels
The better the model, the higher the amps!
You should check out the panels Pauline van Dongen used
-> Also, direct sunlight is the way to go – solar panels do not like clouds..
Alas, the current models of solar panels will never produce mega high values
In Spain for example, they use the heat of  the sun to create steam (yes!) -> that makes turbines turn that churn out electricity –> so no photovoltaic activity there..