
Glass Sphere Betaray Concentrates Solar and Lunar Energy - urumcsi
http://understandsolar.com/glass-sphere/
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NickM
Like many "advances" in solar energy, nobody is going to care about the
efficiency gains if they are overshadowed by cost increases.

The article tries to make it sound like a miracle technology that concentrates
light "up to 10,000x", but that doesn't mean you get 10,000x more energy out
of it, it just means that you can use a much smaller panel since the light is
concentrated on a smaller spot by a comparatively large, bulky piece of
hardware.

Panels are already pretty cheap, so it's not clear if the cost of a giant
glass sphere, plus heavy-duty steel frame, plus tracking hardware will beat
just blanketing your roof with stationary panels. It looks cool, sure, and
maybe it's a bit more efficient at converting sunlight to electrical energy,
but the real figure that's going to matter is the $/kW ratio.

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todd8
A water filled glass sphere? Really? A single typical (300 to 400 watt) solar
panel has a surface area of around 2 square meters. A glass sphere with the
same cross sectional area is 0.8 meters in radius and would weight over 2130
kg or around 4700 pounds.

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dghughes
Second last paragraph.

>"Rather than glass lenses, the consumer models will rely on water-filled
acrylic polymer lenses and will also be able to handle thermal energy
generation in addition to solar energy generation."

~~~
alexhawdon
I don't think the weight of the glass is the main problem here. (Though
obviously plastic will be lighter and easier to transport.)

Where do you mount this contraption? Solar PV is light enough for any roof -
otherwise wasted space. You probably have to mount this on the ground unless
you want to spend a ton of money reinforcing everything.

~~~
dghughes
Here is eastern Canada pitched rooves are capable of withstanding about a
metre of snow. Wet snow supposedly has a mass of close to a tonne per cubic
metre, a cube of pure water is one tonne at 4C. I can't imagine these devices
would weigh more than a tonne (1,000 kg) per square metre.

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adrianN
[https://en.wikipedia.org/wiki/Concentrator_photovoltaics](https://en.wikipedia.org/wiki/Concentrator_photovoltaics)

has been a thing for a while and seem to be more expensive than normal PV
panels.

If this design really focuses the sun "10000 times", then it'll need
complicated cooling to avoid killing the solar cell. I wonder how that is
supposed to work.

~~~
dougk16
I believe the heat will be used to drive a Stirling engine. Most concentrated
solar power rigs use steam engines of some kind.

[https://en.wikipedia.org/wiki/Concentrated_solar_power](https://en.wikipedia.org/wiki/Concentrated_solar_power)

~~~
splawn
In that case.... there goes their moonlight claim.

[https://what-if.xkcd.com/145/](https://what-if.xkcd.com/145/)

~~~
FiatLuxDave
I'm a huge Randall Munroe fan, and so I was hugely disappointed when he posted
that "What if", because it is 100% wrong.

Moonlight is pretty much partially reflected sunlight. The moon is acting more
like a dirty mirror than like a blackbody emitter. This is easily apparent
through two simple facts:

1) If the moon was emitting light due to its temperature rather than
reflecting light from a higher temperature object, we couldn't see it all.
Objects at 120 C don't really emit light in the visible range.

2) The color temperature of moonlight is around ~4000K, about 1000 K lower
than sunlight. It's not like we haven't measured this stuff.

So, yes, you could start a fire with moonlight. I leave this as an exercise
for the Mythbusters-inspired reader.

[1]
[https://en.wikipedia.org/wiki/Color_temperature](https://en.wikipedia.org/wiki/Color_temperature)

[2] [http://physics.stackexchange.com/questions/244922/why-
does-m...](http://physics.stackexchange.com/questions/244922/why-does-
moonlight-have-a-lower-color-temperature)

~~~
splawn
Im not following your reasoning. Which I admit has more to do with my lack of
knowledge than anything else, so don't read that as "I think you are wrong". I
did find other places with the question asked... some have similar answers to
the what-if... others came to a different conclusion as you did. Either way
even if it is on some boundary of what is possible, it seems weird for this
company to mention it as a feature considering it would be many many times
less effective than using it with sunlight and even then only on a few nights
out of the month if that..

EDIT: After giving TFA another look, I see that they do mention using PV and
not just steam engines... so I guess you could use moonlight sometimes to
charge a PV, then switch it to the steam engine during the day or something.

~~~
FiatLuxDave
Another way that you could look at it, is as LeifCarrotson said below, that
the moon is like a mirror. If RM's idea that the sun's light reflected from
the moon could not start a fire was true, what makes the situation different
if you are reflecting the sun's light from a cold mirror? Can the light from
the mirror not cause a higher temperature than the temperature of the mirror?
We know that mirrors (and even lenses made of ice) can be used to create
temperatures at their focus high enough to melt them. So, what is it about the
moon that is different from a mirror, besides a lower reflectivity?

I suspect that RM just got a little lost in the weeds on this one. I remember
making a similar mistake in undergrad when I was thinking about a problem with
two light sources with an optical filter in between. The key insight I needed
to make was that the filter was a physical object with its own temperature.

Thinking about things like this is how you develop what physicists call
"physical intuition".

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mark-r
Light concentrating lenses and mirrors have been a thing for a very long time.
This article doesn't go into any detail about what makes the globe so special,
other than it looks kind of cool.

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sp332
Why does it need to track the sun if it's a sphere? Why wouldn't current solar
panels work for heat generation?

~~~
dougk16
The focal point for light going through a sphere is right at the surface of
the sphere on the opposite side of the light source. So the focal point will
rotate around the outer surface of the sphere as the sun moves throughout the
day (and it also changes slightly each day in a perpendicular direction to the
sun's daily movement). Assuming this is using some kind of steam engine, the
water tank that gets heated by the focused light needs to follow this focal
point.

That's for efficient electrical generation, which I assume is the point of
this thing. As far as pure heat, you're right. You could just have a big
curved metal water tank wrapped around the bottom half of the sphere and you
might get pretty good water heating capabilities without a complicated
tracking system.

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etrautmann
Beautiful art, but it's inconceivable that this would be cost effective per
unit area if it's only increasing panel efficiency by 35%

That's roughly 500Kg of water, in a glass sphere, and the whole thing would
have to cost a couple hundred dollars to beat standard PV, an it STILL needs
an active tracking system.

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virgil_disgr4ce
Bummer Questions: \- How much does it cost? \- Does it require special
expertise to install? I'd hope/assume the sphere can be filled with water on-
site \- How often will it need to be inspected/repaired? Will that require a
specialist? \- How often will it need to be cleaned?

This wouldn't seem to make much sense for individual installations (unless
you're wealthy and want something to show off on your roof), but I wonder if
the economics would work out in medium-sized arrays, to fill the gap between
small residential/commercial installations and huge solar collector
operations. Still though, is a 35% efficiency increase enough to justify this
particular design? Is it that much better than other concentration methods?

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abakker
This is obnoxious, but why do they report the percentage improvement, but not
the actual yield?

If it is 35% improvement, it would be nice to know what it was an improvement
on. One of the linked sources suggests that current maximums on PV efficiency
are around 24% of total sun energy converted to electricity out of a maximum
of 33.7%. so, if that is the case then does this get us from 24% to 32%, or
very close to the maximum solar electricity extraction per area?

Please double check my math or correct me where I'm wrong, but putting
everything in marginal terms is very confusing.

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IanCal
What would be the comparison between this and a fresnel lens?

This feels enormously wasteful in construction, a huge sphere doesn't feel
like the most obvious lens shape. Am I missing something?

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Retric
Trying to solve the wrong problem, PV solar has gotten fairly cheap and works
on overcast days so this is going to cost more and be less useful.

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ris
Looks like a recipe for fire if one goes a bit awry.

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ElijahLynn
I wonder if SolarCity will pivot and get rid of the panels or do both?

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ElijahLynn
This looks amazing, and seems like a big win for renewable energy tech!

