Storage 101

So the other thing about electricity is: you can’t store it.  We don’t have superconductors, we don’t have fields of batteries.  The best that anyone has come up with is to pump water uphill at night and run it downhill through turbines during the day.  Alternatively, you can use night electricity for chores like pumping water up a water tower.  Then you have nice steady water pressure all day, thanks to gravity, without needing to power an electric pump during the day.

Today’s dams come in two flavors: run-of-the-river (which simply generates electricity depending on the speed and volume of the river) and “pumped storage” reservoir systems (lakes in mountains).  Pumped storage is the transmission operator’s favorite form of electrical generation, and wind/solar are their least favorite.

That’s because demand varies in 5- or 10-minute blocks as power is auctioned throughout the day, and reversible turbines attached to a reservoir can, in 3 minutes, switch from pumping water uphill to generating electricity.  At the height of a summer day, power sells for 30c per kWh, but at night it can be 2c or 3c per kWh.  The “seller” is the power plant, the “buyer” is your utility, and the consumer is you.  The consumer pays a steady rate of 6.5c or so, but that’s because utilities have not yet rolled out “smart metering” to match their costs with consumer prices.  People shift their phone usage depending on the time of day, and once the utilities upgrade to smart metering, people will shift their energy usage too.  A lot of industrial customers already pay at smart metering prices, so they run automated tasks (like ice-making) during the night.

Reservoir hydro comes online in 3 minutes, and gas takes 30-60 minutes, and coal takes 24-48 hours.  We really don’t have any control at all over wind and sun.  Denmark has shown that despite this inherent weakness, 20% of Denmark’s power comes from wind, and the lights stay on.  To get beyond 20%:

1. Different kinds of renewables need to hedge each other.  When the wind isn’t blowing, the sun is more likely to be shining.

2. If we had a super transmission grid, it would matter less that any particular point is intermittent.

3. Storage.  Any reversible pump/generator can store energy, so in theory electricity from wind could be hooked up to a reservoir system.  People are also investigating compressed air storage, where a pump forces air in and then generates in a controlled release.  There are weird things like flywheels, which are super-low-friction spinny-things that you start spinning, and when you want the energy back, you make them stop spinning.  There are people who want to hook renewables up to hydrogen fuel cell production facilities.  There are people who want to use all of the country’s plugged-in electric cars as a gigantic virtual battery in a net metering scheme.

New storage systems are pretty much essential to switching to a majority-renewable energy industry.  Aside from that, storage on its own would be fabulous because the 30c/kWh times are when power plants say “OK, fire up that 30-year-old coal generator, we need every watt we can muster.”  Better storage and better transmission would let us retire a lot of hulking dirty plants.


6 responses to “Storage 101

  1. Anything on Storing Lightning Energy?
    I loved this post. Made me feel, you know, educated. Unless one’s already working with hydro, I bet we can come up with potential-energy storers that require less flooding. Build a tower, use excess generated energy to raise a massive weight. Let that weight come down again to recover the energy. Same principle.

    • Re: Anything on Storing Lightning Energy?
      1. Lightning has a lot of energy content, but it all comes in a mighty flash. Trying to catch that would burn the hell out of the equipment, though I do believe people are working on it. Generally, energy is best harnessed when it’s steady. For example, windmills are carefully designed to shed power in storms, or else they will (a) blow over or (b) overload the grid with a massive surge. Remember the Northeast blackout of 2004? That was because one power plant had a big surge and all the others shut down defensively until the surge wore itself out through line loss.
      2. The flywheel thing is an attempt to store potential energy in the form of a heavy object. There are ways and ways, each with their own inefficiencies. A true superconductor is one of the holy grails.

  2. Yeah, I’d say that storage is in general a big problem for our current technology level. There was a sci fi story written something like 30 years ago where a guy invents “capacitite” and accidentally knocks over most of the world’s infrastrucure and political systems. It has a happy ending, though.
    Hey, livingbyfiction, question. Do you have an opinion one way or the other on nuclear? You know what they say – “green is keen, but fission is bitchin”.
    They really do say that. I swear.

  3. also. we have superconductors, we just don’t have superconductors that are practical for power transmission, which i assume is what you meant. note also that superconductors have current density limitations, so that in addition to being a fragile and expensive pipe, they also have finite carrying capacity

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