It's a blog.
In: Uncategorized25 Mar 2012
Every now and then I start reading something on Wikipedia, and end up getting pulled into a long series of digressions wholly removed from what I set out to read about. But it’s invariably fascinating.
Take, for instance, solar power. I’ve read before that solar panels are really quite inefficient. At its peak, the energy from the sun reaching Earth is about 1kW per square meter, but solar panels tend to convert only about 10-15% of that into power — 100 to 150 Watts per square meter. That seems almost impractical. And then there’s the high capital cost upfront; Wikipedia suggests it takes about a decade before you’re recouped your costs. So I had, perhaps naively, assumed that solar power just wasn’t workable.
But it turns out that the sun actually provides massively more power than we need. This diagram on Wikipedia shows the hypothetical placement of large solar farms across the world in such a way that would meet all of the world’s power demands, taking into account average cloud cover, and assuming only 8% efficiency. (Recall from above that it’s actually a little bit better than that.) Granted, there are all sorts of practical problems with this plan (for example: the people who currently live under the black dots, or how to export electricity from Algeria to the United States in an efficient manner), but it’s kind of intriguing to know that it’s actually possible.
Of course, the output of solar panels doesn’t align with our usage of power. (For example: sometimes people want to use electricity when it’s dark outside.) There are various means of storing energy, and it turns out that batteries really don’t scale to massive needs very well. An overwhelming majority of “bulk energy storage” is in the form of pumped-storage hydroelectricity — when you have a surplus of power, use it to pump water up a hill. When you have a shortage of electricity, let gravity run the water down the hill and run a hydroelectric generator. The world’s largest installation of such a system is the Bath County Pumped Storage System, which, when releasing energy, is capable of an astonishing 13.5 million gallons per minute water flow, and which has a capacity of just over 3,000 Megawatts. The efficiency of such a system is unclear to me, but it operates at a net loss.
Of course, no energy-storage system is going to operate at a net gain. The goal is to store power when you have a surplus of power being generated, and release it when you have a deficit. But of course you want to be as efficient as you can in doing this, and there are a few methods beyond pumping water up and down a hill.
One method that intrigues me is that of using flywheels – spin up a large rotor inside a vacuum-sealed enclosure. The latest designs suspend the rotor on magnets, further increasing efficiency. The net efficiency is apparently close to 90%. (Another interesting aspect of flywheels is that they’re capable of building up a massive charge over time and then discharing it near-instantaneously, leading to their use in niche fields where you need a sudden surge of current that would wreak havoc on the power grid — such as testing a million-Amp circuit breaker.)
But more interesting still is the idea of using superconducting magnets. Superconductivity itself fascinates me — as you approach an absolute zero temperature, you reach a point of superconductivity where resistance becomes exactly zero. It’s possible to accomplish with liquid nitrogen. While superconductivity has all sorts of interesting applications, one is that you can apply a charge to a superconductor and have it persist without discharge indefinitely. Seemingly the only inefficiency is in the AC/DC conversion, plus the overhead of keeping the superconductor in a cryogenic state, but it sounds like net efficiency is around 95%. (Though they apparently don’t scale up very well right now.) As an aside, although it sounds like superconductivity is a sort of bleeding-edge science, the concept was discovered in 1911, making it more than 100 years old.
And even though the sun can apparently meet our energy needs many times over and we can store the surplus energy from sunny days with very high efficiency, there’s always another source of power: garbage. Using plasma to vaporize garbage appears viable. And while conventional incineration is a tremendous source of dangerous emissions, vaporizing it with plasma atomizes it, and anything remaining is turned into a glass-like pulp. (This technique has apparently seen prior applications in cleaning up nuclear waste, leaving behind an inert glass-like substance.) And while vaporizing garbage with plasma consumes a tremendous amount of energy, it also releases a tremendous amount of energy, with the potential to be a net producer of energy.