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Comment by wmil | Hacker News Reader

I'm curious what HN thinks of that last line in the article, about solar.

"More likely, cheap photovoltaic and energy-storage technology will mean that much of humanity’s energy comes from a different fusion reactor—one 150m kilometres away, called the sun."

5 billion years of evolution haven't given us solar powered animals that can run around. It seems like there are some significant hard limits on solar technology.

Energy storage technology actually makes nuclear much more practical... the big problem it faces is that it generates very consistent power, but power demand fluctuates by time of day.

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> 5 billion years of evolution haven't given us solar powered animals that can run around. It seems like there are some significant hard limits on solar technology.

What do you think animals run on? Gasoline? Plants are like batteries, storing solar energy. Animals, including humans, charge up by consuming these plants. And for those who don't eat plants, they eat charge up by eating the animals who charge up on the plants.

There are some organisms that get energy off of chemical gradients deep underground.

Again, we can call oil 'solar powered' by that means. Of course 'solar powered' should mean 'directly powered by sunlight captured by the creature itself'. No animal can do this, because the light X capture efficiency is far too low.

Solar power for electricity more closely resembles animals getting energy from plants which get energy from the sun, rather than animals which directly get energy from the sun. Aside from calculators and a couple other items, we don't put solar panels on our machines to power them, we connect solar panels to the electrical grid and connect machines to the grid too.

Fossil oil qualifies too, but the fact it's all ancient stored solar energy rather than solar energy captured now makes it vastly different. Oil produced by capturing solar power now should qualify as "solar power" just as much as photovoltaics.

Oil is considered a non-renewable resource. Plants however are renewable, so they are fundamentally different.

You can consider the solar->plant->animal cycle to effectively be similar to using solar panels. Using solar panels directly would be inefficient without batteries anyways, so the solar->plant->animal cycle is directly analogous to how we would use solar panels.

Quick google search is about 100 wH per square foot of surface area. I'm just estimating about 8 square feet of surface area (one sided) for a human. Assuming 12 hours a day at that rate you get about 9.6 KwH or ~8000 kcal. With perfect efficiency and a storage system inside the body (which we do have, but not for light energy) that's probably doable.

Obviously our tissue is much well less adapted to so many hours of sunlight compared to plants. Also even plants only absorb a relatively small part of the light spectrum (none of the green light). Also even plants required compounds from the earth and the air to actually harvest the energy to store so it's a pretty complicated process to do in an actively moving human.

It appears you are assuming 100% efficiency for conversion of solar energy. The maximum efficiency possible for solar cells is the carnot efficiency at 86%.

Yea, this was kind of giving an upper bound. Actually that's not very impressive given that people CAN burn more than 8000 calories in a single day.

Oil is solar powered. If it didn't take so long to form we wouldn't be having the discussion at all.

I don't see why you would expect animals to evolve a way to "capture sunlight" (though some do: http://umich.uloop.com/news/view.php/77109/4-incredible-phot...) when it's far more efficient from the standpoint of the animal to eat plant matter.

> 5 billion years of evolution haven't given us solar powered animals that can run around.

Pretty much every animal that can run around is solar powered, consuming as fuel an energy storage medium for which the input energy is gathered by (mostly stationary) solar collectors. (Or consuming other animals, which are themselves fuel synthesized from such fuel or other animals, etc.)

> It seems like there are some significant hard limits on solar technology.

What hasn't been produced by evolution isn't strong evidence of hard limits of any technology, so even if the premise was true, that still wouldn't justify this conclusion.

Come on; all of the world is 'solar powered' by that stretch. Oil came from algae which grew from sunlight.

The point is valid: the density of solar exposure at the surface of earth, times the capture/conversion rate to chemical energy, is too low to support animal life. As demonstrated by billions of years of evolution.

Oil involves collecting solar power for billions of years, then using that collected energy over tens or hundreds of years.

Animals eating plants, on the other hand, involves collecting solar power for weeks or months, then using that collected energy over weeks or months. Animals eating other animals might involve collecting solar power for years, or a decade or two at most, but no more.

Global solar flux is clearly sufficient to sustain all animal life on the planet because that's exactly what it does, while it's clearly insufficient to sustain current oil usage because we're using it orders of magnitude faster than it was produced.

That makes no sense. Animals don't consume oil; they consume plant matter (directly or indirectly) which derived its energy from sunlight fairly recently (days to months). The total amount of energy in and out balances, over evolutionarily short timescales.

Where do you think animals are getting their energy from, if not from the sun?

Highly concentrated sources of calories (originally sun energy) that they burn at a far greater rate than they could possibly collect themselves.

> Come on; all of the world is 'solar powered' by that stretch.

Much, but not all.

> Oil came from algae which grew from sunlight.

Sure, oil is indirect solar power. The problem with oil is that's rapid consumption of a stockpile accumulated over a much longer time, which produces sustainability and carbon-balance problems.

> The point is valid: the density of solar exposure at the surface of earth, times the capture/conversion rate to chemical energy, is too low to support animal life. As demonstrated by billions of years of evolution.

Er, no, it does support animal life. IF it was too low to support animal life, than animal life could only exist by the equivalent of burning oil; e.g., it could only evolve with an accumulated stockpile of stored energy which it is burning down. That's not the case, so the negation of your conclusion is, in fact, proven by nature.

(And even evolution hadn't produced a mechanism that did that -- in which case we wouldn't be having this discussion -- that wouldn't prove it was impossible. Otherwise, all the technologies that we have developed for which there are no biological analogs produced by evolution would be impossible, which is clearly not the case.)

You're misinterpreting. The amount of light that hits the animal is not enough, it takes a much larger area covered with plants.

Nuclear power isn't solar power even by that definition.

It ultimately comes from a star, but not Sol.

"Running" is a very difficult trick. Only a small subset of the Animalia, which is itself a small subset of the Eukaryotes, which is only a small subset of life, has managed to do it.

"Photosynthesis" is another difficult trick. It's believed that (with the exception of the amoeboid Paulinella chromatophora), all chloroplasts in eukaryotes derive from a single endosymbiotic event that took place over a billion years ago, though after the last common ancestor to animals and plants.

What you want requires both tricks to have occurred in the evolutionary history of a single animal.

As evolution doesn't go towards a global optimization, but only acts on what's available, the lack of directly solar powered animals does not place a low intrinsic limit on solar technology. An alternate evolutionary history, perhaps where something like Paulinella chromatophora acquired a chloroplast 1 billion years ago instead of 60 million years ago, may have resulted in the world you envision.

While you do have a point that animal life is not solar powered, only by proxy, using vegetables as fuel, so would our machines not be solar powered, only by proxy, using a vast network of solar arrays as energy. Thus, as, let's say, a gazelle needs, let's say, 1ha of grassland to live, so would a car need 1ha of solar panles to move.

On the other hand, I agree, I see fusion as the future and I think it is necessary if we want to meet the future demand for energy.

I'd also love for us to become a space faring civilization, and for that, we need to be able to make our own little sun. We'd then be able to build our own self-contained solar system.

After all, if you look further enough down the chain, all energy we're using is solar. Yet, if you look even further down the chain, all energy is fusion.

> 5 billion years of evolution haven't given us solar powered animals that can run around

Actually, that's exactly what evolution has given us. Nearly every living thing on the planet gets it's energy from the sun. Taking that a step further, nearly every bit of energy extracted from fossil fuels comes from stored solar energy.

Energy storage is most likely the wrong way to solve the problem. We need a much more efficient transport system to where all solar arrays are interconnect similar to how we connected continents with cables.

Just as someone is getting sunlight someone is getting wind. So connect them all along the same distribution pipes. How much loss per mile is there now in a sealed cable? What is the possibility for reducing that?

There are a few interesting energy storage startup (ambri and others) talking about storage costs of 1/4-1 cents per kwh. If that's the price , that could be a good solution.

The problem with solar powered animals is likely in storage, not with power generation.

The Oriental Hornet has been found to harness solar rays, but it largely active during the brightest hours of the day.

http://news.bbc.co.uk/earth/hi/earth_news/newsid_9254000/925...

Surface area is a problem as well. Humans require something like 100W of energy when sedentary and more when active. At 10% conversion efficiency and with the sun providing useful energy 33% of the time, you'd need at least 3 square meters of collector area.

Which of course is why we outsource our collector area to plants. That solves the storage problem too. Animals are solar powered, just indirectly.

Not to mention that there's only so much land on Earth on which we can put solar panels. Sure, we might only need a few percent of the Earth's surface (!) now, but capitalism requires the credible possibility of boundless growth. Ground-based solar and wind cannot provide that, and I think fusion is capitalism's last great hope.

Plants suck at solar conversion. Plants are typically 3-6% efficient at converting solar energy, while commercially available solar cells are 14-19% efficient. We even have solar cells in the lab that are 44.4% efficient.

It's also given us "an entertainment complex in the middle of a sewage system." (Tyson)

Many(imo most) evolutionary solutions are clearly local maxima. Try s/solar powered/wheeled in your comment. I encourage you to learn more about evolution.

Are you familiar with any fusion or fission powered animals?

There are radiation powered archae aren't there?

> 5 billion years of evolution haven't given us solar powered animals that can run around

Right outside my window is my solar-powered lawn.

(also: https://en.wikipedia.org/wiki/Elysia_chlorotica)

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