Comment by philipkglass | Hacker News Reader

Comment by philipkglass | Hacker News Reader

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In some countries there's a high enough population density and/or little enough sunlight that land availability could prevent 100% solar electricity even if storage were magically solved; Germany, the UK, Belgium, the Netherlands, and Taiwan come to mind.

Land isn't going to be a constraint in most countries. Solar resources, while distributed unevenly, are significantly more evenly distributed than fossil or nuclear fuels, or even wind resources. See for example this map of insolation in the US: http://www.nrel.gov/gis/images/solar/national_photovoltaic_2...

In the continental US the very best solar resources are maybe ~7 kWh/m^2/day and there's hardly anything below 3.5. Or to put it in terms of cities, Seattle gets 58% as much annual insolation as sun-drenched Phoenix: http://www.i4at.org/lib2/solarrad.htm

So it took many historical performance:price doublings before unsubsidized solar electricity got within shouting distance of fossil electricity in even the sunniest places in the US, and then just one more to reach that threshold across most of the country.

The technical and economic performance of wind/PV has already improved enough, and has enough assured near-future improvements already in the pipeline, that I'd say it would be destined to "eat the world" for electricity if storage were a solved problem. But storage isn't a solved problem.

Most discoveries that get hyped as "battery breakthrough" by university press offices aren't really breakthroughs, but there's so much research that there's an abundance of riches even after you throw away the ~95% that looks bad on slightly closer examination. Common problems with battery "breakthroughs" that justify quick rejection: dependence on rare elements (lithium is reasonably abundant; I mean things like tellurium, germanium, rhenium...), low cycle life, effects demonstrated only at interfaces or in nanostructures without any obvious path to bulk scaling. Among the remaining ~5% that looks interesting, assuming the publications aren't fraudulent, I have little idea which ones will end up industrially significant. Chemistry is a lot easier to model than market success. There are also partial substitutions for electricity storage that could displace and/or complement it: supergrids, demand response, thermal buffering...

It's true that the amount of sunlight varies greatly per region. A lot of people imagine a future where northern Europe would get its energy from solar plants in Spain, or even the Sahara. That would require high capacity long-distance power grids of course, and I'm sure that's not trivial either, but I'm sure it's a solvable problem.

But if the price of solar panels keep plummeting like this, it seems sensible to first cover all roofs with them and see how far we can get.

What I am trying to understand is how is underground compressed air storage not the solution to the energy storage problem. LightSail is doing this, I don't see why others aren't too.

The tech is simple. Dig a hole in your backyard, put a large steel tank in it with an air compressor and a small turbine generator.

Putting the tank underground vastly improves the safety of the system and hides it. You can also derive heat from this process.

Some groups like LightSail think that compressed air storage is going to have the lowest lifetime costs. Others think that flow batteries will win. Others think that thermal storage will win. Others think that big banks of lithium ion batteries will win.

I don't know who's going to win. All of the above approaches are technically viable. The winners and losers are going to be shaped by things other than simple technical viability: business plan execution, manufacturing scalability, path dependency... I say that storage is not "solved" because there's no default good-enough solution proven yet. We have to wait for some years after plans leave PowerPoint and inhabit the real world to see what works well in practice.

Right now Lightsail is attempting to cross the startup death valley by first selling its pressure vessel technology before tackling the more demanding energy market. They recently announced a tractor trailer sized compressed natural gas module. The idea is to get their costs down to where they can be competitive in energy storage, its an open question on whether that is possible.

Btw, their vessels are carbon fiber, not steel. And deriving heat is a problem not a benefit. Every bit of heat that leaves the system is lost efficiency.

http://www.marketwired.com/press-release/lightsail-energy-la...

http://www.wsj.com/articles/energy-storage-startup-lightsail...

> Every bit of heat that leaves the system is lost efficiency.

Storing air underground absorbs heat, or at least results in less heat loss than storing it above ground.

Electrical engineering is far more advanced technologically than compressed gas thermodynamics and the gap continues to widen.

You can make a very efficient turbine jet that runs at one pressure and one power output at very high expense and ongoing maintenance of moving parts. But it won't run or only run as dismal efficiency at half pressure or quarter pressure.

Meanwhile you can very efficiently move electrical watts around in various formats, cheaply, and scalably, and no moving parts.

As an example of what I'm talking about, liquid fuel has insane amounts of energy stored in it and only recently can we make turbines efficient enough to keep spinning while having fuel poured into them, only at certain constrained power outputs. Meanwhile its very easy with modern technology to run an electric motor from 0.1% to 100% speed using electronic speed control VFDs. You might have trouble cooling it but you won't have trouble making it spin.

Why air? If you are using solar to compress the air...why not take it a step further. Use the underground storage you propose to store hydrogen. Solar energy drives electrolysis, leaving you with hydrogen and oxygen, both of which can be safely stored and have vastly greater energy potential(when burned) than the stored energy of air.

I love your idea of using solar to build a store of energy, but you could refine the idea a bit and really do something fun. Having a large quantity of oxygen(liquify it!) could be a boon to the backyard rocket engine enthusiasts :)

Without knowing too much about LightSail, the answer is likely due to cost. It is probably much cheaper to buy a bunch of lead-acid or li-ion batteries and put those in your backyard. It is not trivial to put huge steel tanks in the ground and keep air compressors and generators running smoothly over many years. This can change with time though.

> But storage isn't a solved problem.

Is there sufficient market pressure to drive demand for grid-scale storage? Batteries have been mostly driven by weight constraints (mobile tech, cars) and not by the need for large-scale stationary deployments.

I think that when renewables reach higher levels of grid penetration they will increase the demand for storage with different tradeoffs.

I think this lack of demand for storage has prevented innovation. Why bother with grid storage, when day and night prices aren't much different? Well now there are times with negative prices, so there is going to be incentive to get paid to store electricity and sell it later. This incentive should grow as renewable penetration grows. If we have deep solar penetration, then there is the big problem that demand is very high in the early evening and the PV suddenly ramps down production as the sun sets. You can cycle your storage every buying dirt cheap solar and selling to the peak price a few hours later.

Yes, there is a market for stationary energy storage for electrical grids. It's small so far, and pretty fragmented, though growing quickly from a small base. It's anyone's guess whether the stationary storage market will sustain distinct storage chemistries that aren't suitable for mobile applications (various kinds of flow batteries, sodium ion batteries, sodium-sulfur, liquid metal...) or whether lithium ion will end up everywhere due to its early lead and continuing cost/technical improvements. Even lithium ion ends up everywhere, there could still be chemistry differences between cells built for stationary grid backup and cars or phones, but they would be more subtle.

A weird thing is that northern countries such as Sweden, at or near the polar circle, are often considered dark and unsuitable for solar. But the thing is, during summer the sun shines 24/7 ... so there would be a lot of power during mid summer and no (solar) power during mid winter.

For most of the time in the summer, that light is coming in at an angle over the horizon that greatly attenuates the energy per square meter. There are maps of yearly solar irradiance that very clearly show this http://sustainabletechnologyforum.com/wp-content/uploads/201...

And then in the winter, it's very cold, so the energy cost of heating is very high.

Thanks

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