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Comment by InclinedPlane | Hacker News Reader

Solve the storage problem first, then everything else follows. Otherwise this is a recipe for disaster.

The problem with building out solar or especially wind power generation is that it's unreliable, it doesn't produce power when you want it. This means that you need to supplement power generation with low latency backup systems. Unfortunately, those systems tend to be gasoline-powered generators. Building those and operating them is expensive and also not so beneficial from a total CO2 emissions perspective. More so when you compare the whole system to simply replacing the windmill and the generator with a natural gas generator, which is more reliable, cheaper, and produces less total net CO2.

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Why not handle the daytime excess problem first, and keep shutting down more coal plants as the storage gets better? Summer requires more energy than winter (good for solar), and daytime requires more power than nightime. (Again, good for solar.) Spread the solar plants around enough, modernize the grid to work nationally/internationally (US, EU) and take advantage of what we can do now.

Besides, as we bring more cars off of fossil fuels, we will need the electricity on the grid anyway.

In most of the world winter uses more energy than summer.

That's not really true for electricity though. In the US we use more electricity in the summer for ac than than heating in the winter. Partly this is based on where people live, but also because people in the north use fuel oil etc in the winter for heating and people in the south have little need for winter heating and less need for AC. There is some regional spikes in demand though unusual cold snaps in southern regions, but as the overall grid has lower demands they just import power from other regions.

As to why AC uses so much power, a lot of it relates to dehumidifying air which takes a lot more power than you might expect.

PS: In most areas you can substitute solar hot water heaters for the vast majority of home heating needs so long term it's not really a problem.

I said in most of the world. The US uses more energy on AC than the rest of the world combined. It is true that gas heating is common elsewhere, but so is electric heating. Fuel oil globally is no longer that important an energy source.

Isn't the energy storage problem what lightsail is trying to address? http://lightsailenergy.com

Wow, claimed 90% thermodynamic efficiency!

Having read through their workflow diagram, I'm really unclear why they can achieve 90% efficiency. Isn't that basically just a Carnot engine? If not, why not? If it is, how can they possibly achieve 90% efficiency when the best Carnot-like engine I've seen is around 35%?

There is a way to feed the energy you make using renewable sources into the grid so you can use them when they are around. Since you're still connected to the grid, conventional energy sources or better yet, renewable energy being generated elsewhere, can take over when the renewables aren't available.

Which is what I said.

The problem is still severe. In a country the size of the US it is still possible for there to be days of very little wind across the whole country. And, of course, once the Sun goes down on the West coast there won't be any power coming from solar for many hours. Which means that in a worst case scenario you need to rely on nuclear, coal, or hydrocarbon based power generation. And it means that you can't avoid having to build out conventional power generation capacity to match peak loads (which can occur when solar and wind power production is effectively zero).

Germany gets 25% of their power from renewable energe.

http://en.wikipedia.org/wiki/Renewable_energy_in_Germany

It's possible

You completely ignored my points, some additional facts (Germany is becoming an electrical power importer, relying on France's nuclear plants, is relying more and more on coal, and may end up increasing its CO2 emissions. Meanwhile, the US has actually decreased its CO2 emissions mostly by relying more heavily on natural gas and should hit 1990 levels soon, despite population growth.):

http://www.bloomberg.com/news/2011-05-30/germany-becomes-net...

http://www.bloomberg.com/news/2012-08-19/merkel-s-green-shif...

http://www.spiegel.de/international/germany/new-coal-fired-p...

Yes, but that doesn't contradict InclinedPlane's point in the least.

It's easy to generate a lot of renewable energy when you've got the old power plants ready to cover any shortfalls in generation capacity. Just because you can acheive 25% under those conditions by prioritizing renewables does not imply that you can push renewables up to 90%+.

The wind can stop blowing for quite some time, even on a country wide scale. You either have to store the energy, import it from other countries or have backup power stations to cover the shortfall.

The (free) book Without Hot Air is a fantastic read for more information. It's written by a no nonsense physicist that dives pretty deep into possible plans for a future energy grid, including all the messy details.

And the details are messy. Any renewable energy plan that doesn't sound like a momentus undertaking is cheating by 1) Only talking about electricity, not total energy 2) Discounting embodied energy of imports 3) Keeping a country sized fossil fuel infrastructure around to fill in the gaps 4) Importing energy

Sometimes all four.

Why is storing energy at hydroelectric dams not sufficient? It's been done for ages.. (ie. pumping water back up the dam when there is an energy surplus, and using the dam when there is a deficit)

Because it's not enough and it's not everywhere. Hydroelectric power is pretty good, but it's only about 7% of the US's total electrical power production. There are parts of the country where there aren't hydropower stations, and you also can't use hydropower storage to generate 100% of the US's base power load.

Seems to me that storage cost and renewables reliability are specifically the concerns their study was all about.

The study just handwaves storage, in reality it will be an enormous problem to tackle. If it were so easy it would be done already, due to the ability to play the "buy low, sell high" game on the spot power market.

I'd definitely like to see how they got their cost figures for storage. The numbers I've seen have been quite a bit higher.

It'd be nice if the actual study were online somewhere without a paywall.

http://www.ceoe.udel.edu/windpower/resources/BudischakEtAl-2...

And I haven't read it yet, but I guess storage costs rise very sharply for every additional 9 you want in your reliability. 90% could mean a month without power each year. To get from there to 99% or a week one very two years by improving storage capacity, you would likely need capacity for at least three weeks of full load.

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