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Comment by walrus01 | Hacker News Reader

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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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.

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.

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.

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.

Good question.

There are rotating restaurants in various towers and buildings.

It might be some thing as simple as a center section that doesn't rotate.

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