
A solar-powered home inspired by a sunflower - pm24601
https://www.bbc.com/reel/video/p06nstmg/the-stunning-solar-powered-home-inspired-by-a-sunflower
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olliej
Ok, architectural over design.

There's an outer shell for the house, that has a bunch of flat solar panels on
the roof. The entire shell is moved to change the pitch of the panels. Placing
the panels on gimbals (as is usual) would require less power, less time, be
easier to repair, and safer.

The entire building then rotates so that the floor to ceiling glass wall in
the front tracks the sun for warmth. That's at least partially needed because
of the giant outer shell being designed such that it blocks the other three
walls, so they can't let sun in to heat the room.

Then you lose realestate because the building is rectangular, but rotates. If
the building was circular, with glass right the way around, you'd have a more
effective use of space, and wouldn't require heavy mechanics and engineering
needed to support a moving building. (Of course you wouldn't get press for
making a round glass building with solar panels on the roof, as that's already
been done at quite a large scale :D )

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walrus01
I _really_ want to know how the non-mechanical engineer, non plumbers who
designed this thing intend to solve tricky problems like rotating municipal
water feed and sewer connections.

From a purely photovoltaic perspective, something that I think am qualified to
comment on... Moving/tilting/rotating photovoltaics haven't been economical
for a long time. As an example, the ground mount required to put six or nine
300W panels on a sun-tracking mount costs about $1900 in hardware and requires
a 4.50" or 6" pipe set into a concrete pier. Figure at least $2400 once built.
Nine 60-cell panels is a lot of wind load, it needs to be strong and robust,
and there's just no way to do that cheaply.

If you spend that $2400 on additional fixed-mount, fixed tilt PV panels part
of a big array, at $0.48/watt, you will produce _far_ more kWh in a month than
with an expensive mechanical tilting/swiveling apparatus.

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olliej
What is the actual power difference between facing and glancing?

e.g imagine a building with a flat horizontal roof covered in PV panels, vs
the roof being angled such that the tangent of the roof is directly to where
the sun is at noon at the height of summer (or maybe peak of winter? after all
less hours of sun could mean max peak exposure is more important then? I have
no idea).

It seems like angled to face the sun would make more power at times when the
sun is in the right place, but it seems like such an angled roof would lose
sunlight earlier/gain it later during the day, vs a horizontal one.

Clearly that intuition is incorrect as far as actual power output goes
(otherwise people wouldn't have angled solar panels :D), but I'm curious what
the difference in effective power output is.

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walrus01
It definitely does help to have a PV panel directly facing the sun. People
will try to install fixed-mount panels facing directly south at a tilt angle
approximately the same at their latitude (45N = 45 degree tilt, roughly). But
with the structures of most building roofs not matching this, it's often a
best effort scenario.

The +15-20% returns that you see from having a panel that perfectly tracks the
sun from sunrise to sunset are much more costly to build than to add another
string of twenty, 72-cell, 360W panels mounted in a more economical fixed
method.

If you are extremely space constrained and need the asbolute maximum Wh per
square meter of panel per day, then a tracker might be warranted. In which
case you should also be looking at super high efficiency mono panels composed
of 22.5%+ expensive monocrystalline cells.

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olliej
What if you had a flat roof (most multi unit building in sf for instance ).

In that case you’re not really constrained by existing roof geometry, so what
would be the best price/wh trade off?

I could imagine the dumbest thing would be a rotating fixed angle unit, which
doesn’t seem like it would (should?) cost that much compared to the total
installation cost anyway?

Mostly I’m curious as to what the crossover point between complexity of
tracking vs fixed angle looks like.

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walrus01
It would be possible to write a 100 page book on this topic. Best I can do
really is point you to the US DoE NREL (national renewable energy lab) website
which has a wealth of training materials and reference on photovoltaics.

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JoeAltmaier
Illustrates how private solar doesn't scale. With that roof you get 25KW. With
a tall building housing 20 families on the same footprint, you still get just
25KW. Just like the failure of 'rooftop gardens' which just work if you own
your own rooftop.

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skc
Incredible bit of engineering here.

But I can't see how this would be practical in real life.

