Storage as the answer for wind and solar?

The wind doesn't blow all the time, the sun doesn't shine at night, and its local intensity can be reduced by clouds and weather. Often the argument is made buy those who push "green energy" that this isn't much of a problem because we can produce extra energy when possible and store it for when these sources produce little or no energy. But how well is that going to work, how much would it really cost. I'll do a few quick back of the envelope calculations, with data from a couple of quick searches. Not a perfect answer, but it should give a general idea of the magnitude of the problem.


For every $700 it pays for a compressed air system, the utility gets 1 kilowatt of electricity, supplied for more than 20 hours, enough to run one coffee maker all day [source: EAC, NSTAR]. Pumped hydroelectric costs more -- $2,250 per kilowatt.

For power that lasts minutes to hours, lithium-ion batteries cost $1,100 per kilowatt (or coffee maker), flywheels cost $1,250 per kilowatt, flow batteries cost $2,500 per kilowatt, and high-temperature batteries like sodium-sulfur cost $3,100 per kilowatt [source: EAC]. And storage in supercapacitors costs even more.

So lets say you need to store 100 GW/hours (5 gigawatts for 20 hours, more than 12 because some nights are longer and because you want to have extra in case you need it, after all your talking about solar providing virtually all the electricity in the country, so presumably some areas only have solar). Storage will probably go down in price lets assume its cost one half as much as the current price.. The compressed air system could then provide 1 kw for those twenty hours for $350. 5 GW would cost 5 million times as much or $1.75 bil just for the storage capacity.

At half the current price the cheapest storage would cost $350 for 1 kw for 20 hours, $350 per 20kwh is $17.5 per kw/hour.

"Actual electricity generation in 2007 was 4,157 Terawatt hours"

Lets try to scale that up to cover the electricity needs of the whole US (which I'm assuming, despite evidence to the contrary, does not grow over time)

4157 terrawatt hours, divided by 365 (2007 was not a leap year) Is 11,389 gigawatt hours. Cut that in half (I'll assume that we get no clouds or other interruptions during the daytime and only have to worry about nights), and you have 5700 gw/hour (rounded off since the reality won't be that precise, and giving more exact calculations would be false precision).

5700 GW/hours at $17.5 per kw/hour would be about a hundred trillion dollars.

But we typically use a bit less electricity at night so lets cut that in half. Now its about 50 trillion dollars.

Lets say technology improves in such a way that the costs goes down more than I thought, so cut the cost by a factor of 5 (meaning the total reduction is to 10% of the initial price), that brings the cost down to $10tril dollars, and that doesn't include maintenance, or spare capacity, or the cost for the solar plants, or the cost for additional distribution. Those would probably add trillions more. Lets say the total cost is $20tril. Assume we can reasonably apply $100bil a year to the effort (that seems high but I'm assuming we are making it a major priority), ok then it only takes 200 years to get it done.

Lets cut it in half again as a generous fudge factor. OK, it will take us a century.

And that doesn't include margin for increasing needs in the future.

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Is there a quiet way to retrieve the energy?

Every air tool I have seen is very noisy. Would the air power a slow speed piston engine?

The situation is worse/different/not as bad as Tim suggests

1. I believe Tim Fowler is attempting to estimate the added costs that an increased reliance on energy derived from wind and solar power would impose on the US. If so, then we might also want to consider transmission costs.

Traditionally our electrical grid has relied on large generating plants that we can build pretty much anywhere there is sufficient water to provide cooling. Typically we build these plants just outside urban areas. In contrast, we prefer to build wind turbines where the wind blows the best; these locations typically do not coincide with the locations of major metropolitan areas. Consequently we often need to build transmission lines to link the places where the wind power is harnessed to the places where electricity is needed.

2. But here Tim Fowler loses me:

Let’s try to scale that up to cover the electricity needs of the whole US (which I'm assuming, despite evidence to the contrary, does not grow over time).

Is Tim trying to calculate the cost of storing all the power needed to run the US under the assumption that we should prepare for the circumstance in which there is no sunshine or wind ANYWHERE in the US (and that no water is flowing over dams, no uranium is decaying in reactors, etc.)? That strikes me as an inappropriately stringent design criterion. After all, our current fossil-fuel powered system is not perfectly reliable either.

Doubtless the cost of completely eliminating our reliance of fossil fuels (and hydropower and nuclear power) would be large. But that analysis would seem to have little relevance to the debates about the merits of merely increasing somewhat our reliance on renewable sources of energy.

3. Finally, one proposal for using wind and solar and other intermittent sources of electricity is to find intermittent uses for electricity.

For example, I understand that many farmers rely heavily on nitrogen fertilizer. I also understand that the process for making nitrogen fertilizer is not complicated, but is energy intensive. Finally, I understand that we tend to build wind turbines in rural areas, far from transmission lines and urban demands, but near to farmers. Could we build small, automated fertilizer plants at the base of wind turbines that would begin operating whenever the wind blows?

Alternatively, could we build small, automated factories for extracting hydrogen from water, and help rural areas shift to a greater reliance on fuel cells?

If such proposals are viable, we might be able to reduce the need for fossil fuels to generate electricity for current purposes. We might avoid the need for storing electricity (at least, in the sense noted in this discussion). And we might avoid the need for new transmission lines.

Intermittent Energy Storage

Your idea can be refined by understanding that a solar or wind powered fertilizer plant is a hydrogen plant that cracks water. The fertilizer (NH3) is a combination hydrogen with the abundant nitrogen in the air. NH3 is ammonia, which stores well, can be used directly in alkaline fuel cells, has many other industrial uses besides for fertilizer, transports well and is a commodity that is well understood and has handling facilities all over the world. It is a gas at ambient temperatures and pressures but easily liquifies at modest pressure making it compact compared to hydrogen, and is a reason why it is an effective refrigerant gas.

No I'm not assuming no sunshine

I am assuming 100% reliance on solar, because the calculations where part of a discussion I was in where someone submitted the idea that we could do exactly that (so "no water is flowing over dams, no uranium is decaying in reactors, etc." is irrelevant).

I gave the 2007 figure for total US electricity production. I divided it by 365 (it wasn't a leap year) to get the per day production. Then I cut it in half (the sun doesn't shine 24 hours a day) to get the storage needed. In reality you would need more storage than that. My calculations ignored future growth, ignored unsteadiness in demand (you need to be able to store enough to cover the highest demand night + a margin, not just the average night), ignored the fact that the sun does not shine at full intensity on your power station from sun up to sunset, ignored clouds and other weather effects, ignored extra capacity so some could be down for maitenence, etc.

Then I cut my figures in half again because on the average we use less power at night. (That was a very imprecise move, I don't know how much less we use at night).

Then I dropped the cost by four fifths, because of assumed future technological improvement.

Then I cut it in half again because of a fudge factor.

If you assuming 100% solar energy than I think I was being quite generous to the effort. Of course you could expand solar without going to 100% or anywhere close. I wasn't generally bashing solar, just saying it couldn't take over completely.

I don't think it can reasonably even mostly take over. Solar (at least if it isn't backed up by a lot of storage) isn't available often enough to be base load power, and it isn't something you can count on for peak load power. As a niche power source that doesn't really matter all that much. As a major player its a problem. Wind is even less reliable. At least most of the time we can count on solar in the desert during the day. We can never count on the wind, at least not over enough of an area for it to be a major power source for the country.

Say we built an interstate air pipeline

A 2 ft pipe would have about 3 sq ft internal area or about 15,000 cubic feet/mile. That's a lot of storage. Say 125PSI minimum to 150 PSI max, not much pressure but lots of energy. Solar and wind farms along the way would build stub lines and add their output. Old designs for compound steam engines could be the starting place for engines to extract the energy from the air pressure, say a 3 or 4 stage energy could extract most of the energy. Old steam engines ran under 150 PSI as I recall.

Interstate air piplines?

Sounds VERY pricey, and I have my doubts about the reliability of the operation.

Differential Pricing

I'm surprised no one has brought up using the market to decide what storage is cost effective and what isn't. I don't mean on a gross scale of choosing whether to power a region completely by coal or by wind, but on the scale of individual watt hours of power.

When I or my friends have used wind or solar, we adapt our usage to take advantage of when supply is cheapest. I lived off of water supplied by a windmill for years filling a 10,000 liter tank. When it was insufficient--mostly because we increased our water use by raising livestock--we either trucked in water at much greater expense or cut back our usage by selling livestock.

Similarly, many suburbanites in coastal Virginia get generators with about a week's worth of fuel to protect from power loss during hurricanes. They are looking at a cost comparison from the local coop of 13c/kWh during normal times or infinite cost (no availability) following a storm versus the capital and fuel costs of running their generator. Adding rooftop solar panels to the mix is simply another option (albeit one that will make them add enough intelligence to the system to automate switching and storage decisions). If the coop changed its pricing model from a fixed rate to a rate varying by time and delivery distance, all the better.

Having a mix of options available for supplying electricity--on site solar/wind/fuel generator, or off-site coal/hydro/nuclear--all at different prices at different times of day--means that each individual solves their unique cost/benefit/storage/delivery problems individually at much greater overall efficiency.

urban sprawl?

Half the people in the US live in an urban setting. I would love to put a 40 foot diameter turbine 0n my 50 foot wide backyard lot but the neighbors would object.

usable solar energy hours each day

"Cut that in half (I'll assume that we get no clouds or other interruptions during the daytime and only have to worry about nights)"

I'm assuming you're cutting it in half because of day/night? Even during the daytime -- there's only about 6 hours peak sunshine a day in areas with the best conditions. Most of the country ranges from between 3ish and 4ish hours.

So you'd have to double or triple your cost estimations all that much more. Yeah 100% solar power has some issues, and trying to store excess power as you mentioned above is ridiculous, but --

As for storing the power (with residential solar panel installation) -- net metering lets you pump power back into the grid. On one hand that isn't 100% solar power, on the other hand it is a 1:1 storage (because it prevents the fossil fuel plant from burning as much coal as it otherwise would need to if you didn't pump power back into the grid). When solar panels are at their peak output is when the most power is being consumed from the grid, so dumping the power back into the grid at that time is great.

You're making the point that alternative energy isn't feasible because if the grid is 100% alternative energy, you'd have to store it -- and having to store it is ridiculous, therefore alternative energy is ridiculous? Being realistic about it -- how inefficient would it be if you had to generate power from a coal plant, store it for 20 hours and then use it? That would be ridiculous too.

Alternative energy can compliment a power grid and offset peak hour usage and if you're not trying to factor in "storing" the power, the payoff is far less than 100 years and is getting less every year.

compressed air pipe line

I think a compressed air pipe line between cities could store energy. Any wind/solar project could pump in and towns could take out energy. The stupendus volume of the line would even out the working pressure to workable limits.