Hacker News Reader

Comment by averros | Hacker News Reader

Well, producing solar panels and such also requires energy input, and these do have limited lifetime. What is the real full-cycle energy conversion ratio is?

Secondly... continuous distillation doesn't necessarily require lots of energy, since a lot of it could be recycled with counterflow heat exchangers and heat pumps instead of plain heaters (i.e. hot output and hot waste are used to heat up input to close to the proper fraction boiling temp, and the output and waste are only slightly warmer than the input mix). It still needs energy input to deal with losses and entropy reduction from mix to separate fractions, but this is also true about using any sort of membrane-based separation.

View on HN

* producing solar panels and such also requires energy input, and these do have limited lifetime. What is the real full-cycle energy conversion ratio is?

I wonder what this is, too, but a typical 300W panel with 20 year lifespan will generate something like 20MWh over its lifetime. You can't possibly use anywhere near that much energy to manufacture it.

My personal pet theory is that the energy consumption is more or less equivalent to the price. So as long as the solar panel is not economically viable, it does not provide an energy surplus.

20MWh is not much, it's $500-$3000 worth of energy, depending on taxes and stuff. Can you buy, install, connect, maintain, clean a 300W solar panel for 20 years for this price?

Edit: Also, 20MWh is quite high. That's 9h of perfect sun, each day, the whole 20 years.

If that were true, the cost of the energy consumed would be equivalent to GDP, and that is not the case.

That a good point. But a huge part of the GDP increase is an increase in efficiency, i.e., you can do more with less energy. A 2019 computer would cost a totally different price in 2009, and would be infeasible expensive in 1999.

But if you compare technologies within one year, the price tag gives you a very good idea how much energy was used for producing each one. Of course, there are scale effects at play, so an R&D cost (energy) might only occur once, but is then distributed within all units produced. This will very well be reflected in the price, once something enter mass market.

The same will happen with photovoltaic cells: They will continue to get cheaper (and more efficient) and at one point it will make economic sense to put them everywhere. And at this point it is clear that they are net energy producers, where currently it is still debatable, at least in more northern regions.

The price of energy in Australia is very expensive. 20MWh is worth approximately $6000-9000 AUD.

So a 3kW system @ about $8k purchase price should return about $50 - 80k gross.

You can lower your efficiency substantially and still offset a substantial expense.

Well-placed solar plants have capacity factors of about 20%, so 10MWh. That's worth about $1200 at the retail end of the grid (or $2600 if your local utility has gone bankrupt). At the production end, it costs anywhere from $100 for fully depreciated hydro[1] to $1400 for solar PPAs made by bankrupt utilities[2] to $600 for new solar when you assume an unrealistic cap factor and ignore Chinese subsidies[3] to $240 if you ignore a whole bunch of additional stuff.[4]

1 https://www.eia.gov/electricity/annual/html/epa_08_04.html

2 https://www.spglobal.com/marketintelligence/en/news-insights...

3 https://www.eia.gov/outlooks/archive/aeo18/pdf/electricity_g...

4 https://www.utilitydive.com/news/nv-energy-23-cent-solar-con...

Last time I checked retail prices were around 0.30 to 0.32 $ per Wp for large customers. So your high efficiency, last tech 300 Wp module would be around 100$ including shipping for large orders. Could go up to around 120 to 150 for smaller volumes. Of course, market prices may vary depending on demand and availability.

It's my impression that lifetime is mostly efficiency degradation from UV exposure. If that's true, then it seems that if you have fewer solar hours per day, the panel will just retain its efficiency longer until eventually you reach the same lifetime energy produced. (Until you get to ages where actual weathering of the enclosure etc destroys it, obviously.)

"My personal pet theory is that the energy consumption is more or less equivalent to the price."

This implies that energy is the only input to making PV, which is clearly wrong.

Or maybe you're saying that if we trace back costs into the economy, from the workers, to the grocery stores where they buy their food, to the farmers, etc. etc., it all eventually comes back to energy. In that case the energy return on investment is going to be 1:1 in steady state, which indicates that's not a useful metric either.

> Or maybe you're saying that if we trace back costs into the economy, from the workers, to the grocery stores where they buy their food, to the farmers, etc. etc., it all eventually comes back to energy.

Yes. Of course, this is greatly simplified and I'm not entirely sure where to put capital costs in my theory. But I think I'm not too far off. And of course I'm purely talking about energy, not whether it is environmentally friendly or not.

> In that case the energy return on investment is going to be 1:1 in steady state, which indicates that's not a useful metric either.

I'm not sure what you mean by this. If I pump up a barrel of oil from the ground, I end up with more energy than I started with. Otherwise I would not do this in this first place, because I could not make money.

It means that if you trace economic activity back to the point that it involves energy, ALL economic energy eventually traces back to energy. The EROEI becomes 1, by definition.

Of course this is ludicrous. If you double the energy efficiency of all activities, and cut the energy used in the economy by half, these long chains get longer, but they still end at the energy production, so that '1' doesn't change. What this kind of evaluation misses is the massive multiple counting going on: that displaced energy use is producing value all along the chains, and the longer the chains, the more value each unit of energy produces.

I read something about this a little while ago - if I recall the analysis correctly the energy payback was in the order of 1-2 years for the average (300W or so) panel. Not bad for a 20 year life, but we will need recycling advances in the meantime as we will have so many panels reaching end of life in the next decade.

Reply on news.ycombinator.com