
New device can harvest indoor light to power electronics - tdrnd
https://arstechnica.com/science/2017/05/dye-sensitized-photovoltaic-cells-can-power-small-electronics-indoors/
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627467
How much efficiency improvement over calculator solar-cells are we talking
about? It's not like we couldn't power basic electronics (like solar powered
calculators) indoor before.

~~~
bArray
Apparently solar cells larger than a calculator one can give about 30mA, 5V at
peak power output [1]. We really need to know surface area and lumen to know
how good this thing performs.

[1] [https://www.amazon.com/53X30mm-Micro-Power-Solar-
Panels/dp/B...](https://www.amazon.com/53X30mm-Micro-Power-Solar-
Panels/dp/B01BFX65YK/)

~~~
wlesieutre
Units point of interest, the luminous flux per area is called "illuminance"
and measured in lux (lumens per square meter) or footcandles (lumens per
square foot)

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roesel
`footcandle` is a ridiculous name for a unit.

~~~
ouid
it's not even the right dimension.

~~~
wlesieutre
Originally comes from 1 fc being the illuminance on a surface 1 foot away from
a 1 candela light source.

A candela being roughly the intensity of light from a candle.

Intensity (candelas) breaking down to lumens per steradian. They're a measure
of how bright a light is in a particular direction, rather than its total
light output (which is lumens).

And steradians, for the unfamiliar, being a measure of "solid angle".
Steradians are to 3D angles as radians are to 2D angles. A 1 steradian solid
angle projects out to an area of 1 unit^2 on the surface of a unit sphere.

Fun stuff!

~~~
wlesieutre
Other fun fact, 1 fc = 10.7639 lux, because that's how many square feet make
up a square meter.

But in the lighting industry we just pretend 1 fc = 1 lux for most
conversions, because eh, close enough.

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syphilis2
I've been using Logitech's solar powered keyboard (uses traditional cells) for
years and I love the product. The biggest problem are:

1) doesn't charge well in low light

2) doesn't charge well from LED light

At first glance, the new approach looks to address one of those problems and
possibly both.

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veli_joza
Claimed 30 mW may not seem a lot, but most of electronic sensors (even
displays) are only used for short period of time. You continuously collect
charge over time, often in a supercapacitor, while most of device circuitry is
dormant. At some time the device wakes to take measurements, transmit data
over some wireless technology, schedule next wake-up and then goes back to
sleep.

Even if you need measurements every minute, 30 mW is plenty for these kinds of
devices to do their work.

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owenversteeg
TL;DR it's a special kind of solar panel that works better in low light
conditions. Super cheap solar panels are around 11% efficient, average cells
are around 18%, and these are around 29% efficient. So about a 50%-ish
improvement.

It is a fascinating breakthrough, but unfortunately even if it was 100%
efficient indoor solar cells would still be pretty useless. As a rule of thumb
indoor illuminance is 200-1000 lux, vs outdoor illuminance up to 120,000 lux.
A lux is slightly less than 1.5e-7 watts per centimeter. So for a 500 lux room
(which I'd call pretty well lit) with one of these devices the size of a
smartphone you'd be harvesting 1.5e-7w/cm2/lux _500 lux_ 7cm _14cm_ 0.29
efficiency = 0.00213 watts.

As cool as this breakthrough is, it's not going to get anywhere. Current
solar-powered household devices (pretty much just calculators) don't really
need 50% more power, and other household devices need many orders of magnitude
more power.

Even if it was 100% efficient, it'd still be gathering less than a hundredth
of a watt. That's not coming anywhere close to useful.

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nsxwolf
I love the idea of reclaiming some of the energy from our lighting. Perhaps
one day solar cell wall paints will be a thing.

~~~
morcheeba
If those solar cells are efficient, then they'll look you've painted the walls
black. Not only will the quality of the light become worse (harsher shadows
from less diffuse light), you'll probably install more light bulbs to
compensate.

~~~
lb1lf
The EU incidentally created a similar problem when banning most incandescent
bulbs.

Well, at least in some countries. Here in Norway, most buildings are heated by
electricity - so replacing incandescents with LED or fluorescent bulbs
effectively means that you spend less on lighting, more on heating and the sum
stays the same - except the new bulbs are costlier and (mostly) provide less
comfy light.

Sigh. Free lunches remain elusive.

~~~
monochromatic
Heat pumps are way more efficient than just resistive heating.

~~~
tigershark
I don't think they are more efficient in Norway harsh winters..

~~~
monochromatic
That's actually a reasonable point, and it may be true. There's got to some
temperature delta makes a heat pump a losing proposition, but I'm not sure how
big that threshold is.

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johnward
I accidentally replaced one of my heat pumps with an A/C only unit. So now I
have to run the emergency heat strip all winter. I haven't seen any real
increase in my power usage. The heat strip was running most of the time anyway
because of low temps.

