Comment by arcticbull | Hacker News Reader

Comment by arcticbull | Hacker News Reader

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> Solar panels don’t waste sunlight and have no input costs.

Not exactly, the point is that building and installing solar panels consumes resources and physical space. A solar plant with 100% efficient panels is 1/10th the size of today's solar plant, and as I mentioned, to generate comparable amounts of power to conventional sources requires huge amounts of landmass. Plus input materials. And it has to be replaced every 20 years.

> Rooftop solar turns 20% of something that would have been 100% wasted into high grade energy.

Not 20%, right, closer to 15%. Rooftop solar also kills about 10X as many people per generated TWh (0.44-0.83 people per TWh) as compared to nuclear power (0.04 people per TWh) - due to installation. [1]

I'm not advocating for coal of course, but it's wrong to say solar wastes nothing. There's input materials, plastics, silicon - all sorts of toxic chemicals - and generates tons and tons of e-waste that we don't really have a plan for right now. [2]

> Your numbers on solar panel degradation are also incorrect based on my experience in the industry. They do degrade but not at that at 2% per year for ten years.

As I mentioned, the degradation rate is highest in the first year, I said 2.5%, but then it drops off to about 0.5% in subsequent years. The data comes from an NREL analytical review. [3]

NOTE: I edited the number to more generously assume the 0.5%-1% degradation was not in percent efficiency but rather in percent capacity - which is 1/5th as much, to your point.

[1] https://www.nextbigfuture.com/2011/03/deaths-per-twh-by-ener...

[2] https://www.wired.com/story/solar-panels-are-starting-to-die...

[3] https://www.nrel.gov/docs/fy12osti/51664.pdf

Not sure why I am responding since you moved the goal posts from operating efficiency to lifecycle efficiency but even there you are wrong.

To your point re: land use, this is why I said rooftop solar. The roof is already there, the structure is already there, there is zero additional land use and very little opportunity cost for the space. Further, the land use for coal is much broader than the plant area because of mining, transit, and waste heat management. There was a recent post on HN comparing total land usage by prime mover.

Solar is only deadlier per unit than coal if you ignore substantial local health effects that aren’t priced in.[0]

Your implied rate of degradation to go from 20-10 is more than 7%. Even 15-10 is more than 2.5% and again that is an absurd number that contradicts observed performance. You misunderstand what degradation means in this context, to your point.

[0] https://surgery.duke.edu/news/despite-studies-health-effects...

I never said anything about coal, and I updated the degradation numbers per your suggestion, but the degradation numbers themselves come from NREL. I think you're confusing the derating due to temperature with degradation. They are additive.

Panel temps go up and down depending on time, date, location, and weather. On cool, sunny spring days you can see panels produce more than they are rated. You can’t simply apply a fixed worst-case derate for all time to all panels regardless of installation details.

Further, the derates are not additive, they are multiplicative. (A a 20% panel which has degraded in lab efficiency by 10% operating at 90% thermal efficiency is running at 16.2% efficient compared to 18% for a non-degraded panel).

Nothing you have said, however, addresses my first and principal point which is that operational efficiency has a different meaning for solar when compared to anything that has non-free inputs. Efficiency is outputs/inputs. One way to look at it is [energy out]/[energy hitting panel]. That is 20% for a solar plant, 45% for an nuclear analogue. Another, financial way is [value of output]/[cost of inputs]. This is infinity for solar setting aside fixed/financing costs and quite finite for nuclear using the same assumptions.

A device that's 15% efficient is inherently more wasteful than a device that's 100% efficient, right? Therefore we're wasting something. That thing isn't input fuel, it's the materials used to build the device, and manage its lifecycle. That doesn't mean it's free - it just means we're considering different inputs.

Total efficiency here is the sum of all inputs over outputs. For solar panels that's land use, that's glass, silicon, plastic, PCBs, etc - in addition to the sun.

Otherwise, in your model, a panel that's 100% efficient is inherently the same as one 15% efficient.

In your model, a battery is infinitely efficient - after all it has no inputs, only outputs! Once you get to that point your model needs to be adjusted.

A nuclear plant that is 100% efficient would be better than the current ~40% units but it is thermodynamically impossible. Thanks Carnot.

You are confusing operating/marginal efficiency with lifetime efficiency. Think about a power plant as a series of payments. You have one big up front payment to build the thing and a series of smaller payments to buy fuel and run it.

For solar, those smaller payments are zero. There is still the fixed upfront payment and that is why you would prefer 40% efficient panels to 20% efficient panels everything else being equal.

The marginal cost of rooftop solar is zero. Nothing is wasted. Really! No fuel is bought, the roof underneath is cooler and lasts longer, there are systemic benefits, etc. There is virtually no maintenance. No land is used (Solar land use is complicated but most places you can put solar wouldn’t support a nuclear plant). Light which would have bounced back into space or turned into infrared is instead made into usable, high grade energy. Land/build area that would otherwise do nothing is made useful. It is literally close to economic and physical magic. It is true that panels break, inverters die, upgrading is compelling, etc. However, most components are silicon, glass, copper, and aluminum. These are some of the most recyclable materials on earth. There are plenty of analyses of lifecycle energy and material costs and it is generally pretty favorable (1-2 year operating recovery time). The panels are warrantied in many cases for 25 years so idk where your 20 year then scrap lifespan comes from. Inverters tend to be the weaker link.

Finally batteries have marginal round trip efficiency because what you put in doesn’t come back out 1-1 so I am not sure I follow your point.

> The marginal cost of rooftop solar is zero. Nothing is wasted. Really!

No, it isn't. There's literally materials consumed to build the solar panels, and a 0.4-0.8 deaths per TWh generated. To your own point a 1-2 year recovery period on panels that last 20 is 5-10% loss in energy off the mark. We don't really have a recycling plan, but we better get one, because solar generates a ton of waste materials. To power the entire United States, we'd need 20,000 square miles of solar panel - the entire landmass of West Virginia. Replaced every 20 years, we'd need almost 100,000 square miles of solar panel in my lifetime. That's the entire surface area of Colorado.

But that's ok because I'm not arguing against rooftop solar lol. I never was. That doesn't change the fact they're not particularly efficient, and there's a lot of room to improve. I was arguing in favor of nuclear, which, with seawater extraction, can be completely renewable.

MARGINAL. I will try one more time because a stranger is wrong on the internet. It is the difference between how much a car costs and how many miles per gallon it gets. Once you have paid for the car, the only thing that matters with respect to fuel efficiency is MPG. The MPG of solar is infinity because there are no gallons to buy/use once you have bought the car. You are confusing purchase price with MPG for some reason. There is no additional material used once the panels are installed and nothing wasted. For a car, 65% or more of every gallon you buy is wasted.

There isn’t a lot of demand for panel recycling because most panels have been installed in the last 10-15 years are not end of life. When there is demand there will be recyclers, you don’t need to centrally plan it.

There actually is NOT a lot of room to improve with monocrystalline silicon and other single band panels. The theoretical max efficiency on them is 40% so they are currently more than 50% of their max, room but not a lot. The technical efficiency (how much of the energy hitting the panel is turned in to electricity) is subsumed by the economics. For ROOFTOP, small systems can offset residential load 100%. I am not sure what is inefficient about that on any definition.

> to generate comparable amounts of power to conventional sources requires huge amounts of landmass.

It would take about 0.01% of the US land area to generate all the electricity we need. Meanwhile we use 30% (over 1000x) to grow food. And if we prioritize solar on rooftops and deserts, we really are not using any useful land.

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