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Comment by roenxi | Hacker News Reader

The uncertainties here are demonstrated by the fact that the article is quoting 25.2% efficiencies. Solar panel efficiency wouldn't matter as much as the ratio of energy/m2/$ ratio.

Nobody cares if a solar panel is 2% efficient if it costs 100 times less to fabricate and install. Just build more of them. Still, it is good news to see this sort of energy research bearing fruit.

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When we kitted our boat with solar panels the cheapest part of the entire system were the panels, ~$1/W. Half of the budget went into mounting and the fabrication of the mounting hardware and 1/3, or the remainder, went to wiring and controllers. This nearly lines up with domestic solar. 1/3 to panles, 1/3 to frames and mounting, and 1/3 towards electrical.

Panels at 2% efficiency would be wildly uneconomical at practical any price.

> Panels at 2% efficiency would be wildly uneconomical at practical any price.

I guarantee that is wrong, if the price got low enough it would be economical. Wikipedia suggests to me [0] plants operate at 3-6%, and plants are extremely economical. Even starving African children can afford access to plants. If solar panels were as cheap and easy to produce/distribute as plants but could be plugged in to a grid then 2% efficiency would be wildly economical - it would be the greatest energy revolution in human history.

[0] https://en.wikipedia.org/wiki/Photosynthetic_efficiency

Lots to unpack here - is there a more straightforward way to word your argument here? To put GP's post in terms of yours, the planters and water cost much more than the plant, so even if "starving kids in Africa can afford access to plants", it doesn't mean greenhouses are free

It isn't an analogy. Plants are literal solar systems. The only reasons they can't be plugged into the grid is they deal with energy chemically instead of electrically.

It doesn't require that much imagination to say that solar cells might one day be work in an extremely similar fashion to plants. Not likely, but not an outrageous thought.

Nature has produced a cheaper, more ubiquitous and more self-replicating solar system using efficiencies in the 5% range with a theoretical cap of 11%. That suggests we don't need 25% efficiency to accomplish amazing things. It isn't a critical metric.

I'm fine with your equation of plants with solar power. But it's not cheaper; look at the price of biofuels. Aren't they in fact more expensive than fossil fuels and solar panels?

The energy that a plant captures doesn't go in to biofuels; it goes into growing the plant. Pushing roots through rock, extracting minerals from the earth or whatever it is plants do. Pushing water from the soil up trunks or through stems.

The biofuel is burning what amounts to the plant's surplus energy that it wasn't using for anything, and recovering some of the energy that went growing the mass of the plant. It isn't comparable.

The point here is plants are covered with tiny green solar panels that are grossly inefficient compared to what humans produce. However, they are beyond cheap to produce (in fact they grow themselves) and suggest that we are not even close to pushing the limits on what we can do with solar energy design wise.

Efficiency of the solar panels really isn't all that important compared to making something with the flexibility and weight of a leaf. Comparing efficiency between solar panels is a waste of time outside the research community; all that matters is total cost to install vs. watts produced.

I think most biofuel is currently more expensive because it is diverting high input monoculture crops that are typically grown for feed like say corn ethanol or soybean oil. I believe ethanol from sugar cane in Brazil was cheap but only because the humans laboring to harvest it and process it were paid very little. But yeah the current choice of using industrially farmed high input crops to source biofuel does make it expensive. I think ultimately heavily refined energy dense fuel does require lots of time or energy input to produce.

Ok, good points. But I am thinking some of that could be saved if perovskites, or silicon plus perovskites became more efficient than silocon alone.

> Nobody cares if a solar panel is 2% efficient if it costs 100 times less to fabricate and install

I use a modern portable solar panel that's in the realm of ~25% efficiency when camping, and I certainly wish it were smaller for the same output. I'd be willing to pay more for that.

There's obviously segments that care more about efficiency than cost, not all solar applications have unlimited space.

At 2% efficient and 0 cost they would probably be more expensive than current when looking at total installed cost for commercial/residential, maybe even utility.

You can see even at utility scale the panel prices are generally less than 50%.[1] I think 2018 increase was tariff related. Been out of the industry ~5 years so don't follow stuff that closely. Many of the other costs are basically a multiple of # of panels which would be 10x at 2% efficiency.

[1]https://www.nrel.gov/docs/fy19osti/72399.pdf

I did say fabricate and install you'll notice. If they came up with something really light and cheap to produce installation costs would plummet. Compare the cost of installing windows to installing solar panels - windows don't even have a rate of return but everyone has windows. It is a no-brainer to install windows. Solar panels are not a no brainer decision (yet, hopefully).

And that was the point - weight and difficulty of transporting the final system is a very important variable. Probably more important than efficiency when orders of magnitude are concerned. From a 25% base efficiency can double and double then it stops improving. Weights and installation costs due to the panel technology can halve and halve and halve and so on - and each halving reduces the cost of transporting the panels. There are more gains to be made there. It would be worth trading efficiency away to make big gains there.

Solar cells have been getting quite cheap. At some point covering materials and installation cost start to have an effect - and those are smaller with better efficiency.

I think what's happening is bare processed silicon wafers are cheap enough that that other costs of a panel are starting to dominate. That pushes you towards using high efficiency cells in order to reduce number of panels needed.

I think Perovskites are interesting because they are cheap and can get you 25% efficiency in a single layer cell.

It matters for mobile applications where space and weight are limited.

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