Hacker News Reader

Comment by nannePOPI | Hacker News Reader

Do solar panels produce more energy that the amount required to create and operate them? (including mining the materials)

View on HN

Yes: http://www.mdpi.com/1996-1073/9/8/622/htm

Energy pay-back time (EPBT) results for fixed-tilt ground mounted installations range from 0.5 years for CdTe PV at high-irradiation (2300 kWh/(m^2·yr)) to 2.8 years for sc-Si PV at low-irradiation (1000 kWh/(m^2·yr)), with corresponding quality-adjusted energy return on investment (EROIPE-eq) values ranging from over 60 to ~10.

If you want to see other publications on the same topic, try hitting Google Scholar with search terms "photovoltaic" "life cycle" "energy payback". For the most accurate results, restrict your search to recent years. Manufacturing processes are revised rapidly and studies from the turn of the millennium are now badly obsolete. (Though even in 1990 PV systems were net energy positive on average; the worry that PV system manufacturing consumes more energy than the lifetime output appears to be a holdover from the very early (1970s) days of terrestrial PV systems.)

I'm skeptical of your numbers. With such a quick payback time you'd expect to see solar power going up like crazy. (Like how wind was being installed quite fast for a while - although only in the best spots.)

Except you don't, you just see limited installations here and there.

If solar power has such a quick payback period why aren't more investment groups funding it?

Are the panels not available in sufficient quantity?

The main problem with solar is that it is not a full replacement for current power plants, since it does not produce power at all times. Until we have the capacity to store energy to use at night and on cloudy days, solar will be limited in potential.

I think his numbers didn't take into consideration the expensive backup power plant that you have to have ready even if you have adequate solar capacity.

Solar power is going up like crazy. The US just had its highest-ever quarterly solar installation rate, up 191% over Q3 2015: https://www.greentechmedia.com/articles/read/in-its-largest-...

Global installations for 2016 are also on track to set a new record, surpassing 2015 installations by 48%: https://cleantechnica.com/2016/11/30/global-solar-installati...

And despite these records, the manufacturing side of the industry is currently demand-constrained rather than supply-constrained.

When you say you there's just "limited installations here and there," are you estimating from whatever you personally see in your local area?

Energy payback time is a different concept than money payback time. Investors are interested in the latter, First one is a rudimentary requirement for long term feasibility without subsidies.

Also, global solar is going up like crazy. Global sustained growth rate of around 40% is crazy fast. If that keeps on for a bit more than ten years, 100% of current global electricity demand is covered by solar. Just for comparison, there exists no two subsequent full years of iPhone production where Apple would have managed to achieve 100% growth.

I have to echo the statement that PV is going up like crazy -- at least where I live. Admittedly I'm in one of the sunniest places in Japan (and at 34 degrees latitude to boot). They are clear cutting forest to put up installations everywhere. Virtually every single apartment building already has solar panels on top of them. Every house builder offers solar panels on new houses and while I've seen a couple of new houses without them, they are definitely the exception. Every electronics store sells solar panels and usually it is the thing that they are pushing hardest (weird to see huge solar panel displays next to the refigerators and TVs). I've done the math and with the price of electricity we pay here, it is a complete no brainer to get solar panels. If I lived in a house, I wouldn't even think twice.

Thats great to hear but Im not a fan of the idea of clear cutting forests in place of solar.

The term is EROI (energy returned on energy invested), for renewables its currently roughly equivalent to fossil fuels and getting higher as the technology improves. As oil and natural gas get more expensive and energy intensive to extract, their EROI is going down.

Going down from a fantastically high return to a slightly less fantastically high return.

Yes, but it's going to continue to go down. According to Wikipedia [1]

  EROI    Fuel
  ----    ----
  35.0	Oil imports 1990
  18.0	Oil imports 2005
  12.0	Oil imports 2007  
   6.8  Photovoltaic (wikipedia)
  14.4  Photovoltaic [2] (from recent analysis of post-2008 data)

The trend lines are clear and stark. The technologies for photovoltaic, wind turbines, and for fossil fuel extraction are all changing. It's certainly not the case that fossil fuels will disappear, but over the coming decades the sector will shrink dramatically due to market forces; investments will plummet.

And once you start looking at the slow and steady pace of improvement in storage technologies, it looks highly possible that around 2025-2030, only specialized energy applications ever make new investments in fossil fuel based technologies. And that's without accounting for the negative externalities that fossil fuel users (all of us) make everybody else subsidize. Existing infrastructure will continue as long as its economical, of course, but there's most definitely a huge turning point around the corner in energy technology.

[1] https://en.wikipedia.org/wiki/Energy_returned_on_energy_inve...

[2] https://www.researchgate.net/publication/311170056_Solar-PV_...

I believe those EROI numbers also don't include converting the energy into the useful output that you need and so are a a pointless apple-to-oranges comparison

PV output is electricity already, to get electricity from coal you'd need to throw away 2/3rds of the energy as heat, about half for gas, reducing their EROI by that factor in a correct comparison. So if it's electricity you want then PV is already winning over fossil fuels I think.

Similarly, for powering cars with gasoline they're not as efficient in converting that energy "well-to-wheel" as EVs, as the losses in battery storage and electric motors are much smaller, giving you a "miles driven return on energy input" measure about 3x higher for a PV charged car vs ICE.

You can avoid the generation loss on natural gas by piping to the home and burning it directly for heat in areas that need heat, getting close to 100% efficiency with modern central heating systems, but then in those same situations you can use an electric heat pump and get 3-500% efficiency, since you're only moving the heat around, not generating it.

Don't heat pumps only work in temperate climates though? The low in Denver tomorrow is going to be 7 below...

At very low temperatures an air source heat pump does not have an advantage over simple resistance heating. But -7 F is not too cold for leading edge ASHP technology (or rather, this was about the leading edge 5 years ago): http://www.franklinenergy.com/wp-content/uploads/2014/10/Air...

"Independent research has verified the ability of air source heat pumps to maintain energy efficiency well above other electric heating systems, with coefficients of performance (COP) of between 2 to 3, in temperatures as low as -15⁰ F. Multiple manufacturers have developed ASHPs designed for cold climate operation, incorporating features such as two-stage compressors and advanced defrost capabilities.

Where data is available to evaluate the energy savings impacts of [Western Minnesota] customers moving from less efficient electric heating systems, the energy savings associated with the heating demand served by the hybrid ASHP systems is found to be in the range from 10% to more than 40%, with median savings of around 22%."

It looks like the Western Minnesota region where they ran this trial has colder winters than Denver, so Denver-area results would be even better. The best air source heat pumps should be able to save energy over resistance heating for the vast majority of American households. They will also save energy over direct combustion of natural gas in a household furnace if the natural gas is instead burned in a combined cycle electrical plant. They will not reduce energy consumption or emissions vs. a home natural gas furnace if your winter-time grid electricity mix has a substantial coal component.

for climates with colder winters, you can get high efficiency with ground heat pumps instead. It costs more to install since you have to drill a borehole, but the efficiency doesn't drop with colder weather.

Yep. Many forms of petroleum are also very convenient for energy storage. So even an EROI less than 1 they would still have utility.

1 L of diesel has about 39 MJ of energy. That's about 10 kWH (a Tesla Powerwall) in the size of a Nalgene bottle.

Most definitely, chemical energy storage is fantastically dense.

I think that as intermittent renewable energy sources get cheaper and cheaper, in addition to time-shifting of arbitrage from batteries, energy storage in chemical bonds may make sense. Methods to create synthetic fuels from electricity are in their very early days, and all of them are terribly inefficient; most go through hydrogen and that step alone results in a huge loss of energy.

So for applications where energy density is needed, e.g. jets, the fuel costs will just be that X% higher than being able to use straight electricity + battery.

I can definitely imagine a world where creating synthetic fuels from excess grid energy is cheaper than fossil fuel extraction, but it involves tons of research and development in those synthetic fuel methods, and many decades of improving renewable technologies at their current rate.

From what I understand, for electric generation storage, at present the technology with the best promise seems to be flow batteries.

In doing a quick google search on this question, it seems to be "YES". Payback is in the 4 year range where the service life of the panel is in the 20-plus year range.

Was also discussed (more in terms of carbon footprint) in The Economist this week:

http://www.economist.com/news/science-and-technology/2171130...

Don't forget the costs to dispose of them once they are not producing energy (or enough energy), typically after 15 to 20 years, and the overcosts for replacements due to "natural" events, like hailstorms.

There could actually be an interesting secondary market for solar cell recycling. My understanding is that the primary degredation is due to the contacts, which could likely be reapplied or annealed in order to reach their original efficiency.

No one ever really likes to provide these numbers. Hopefully they are a net gain, but I'm a bit skeptical

Reply on news.ycombinator.com