Here’s an old high school physics puzzle, let’s see if you can get the right answer:
You have perfectly insulated room (i.e., no heat can escape). Inside the room is a refrigerator, plugged in and running – but the refrigerator door is left wide open.
As the refrigerator runs, does the room:
A – get colder
B – get warmer
C – stay the same temperature
Think about it for a minute ... (and yes, I first heard this from my high school science teacher back in the late 70’s)
The answer is ... (drum roll please!) ...
“B” – the room will get warmer. In fact, the room will get hot. So hot that the refrigerator will likely catch fire and the insulation will melt off the walls.
Why? Because a refrigerator doesn’t “create” a cool environment, it just transfers heat from the inside chamber to the outside environment. And since it’s not 100% efficient, it actually creates substantial heat while doing this. (Don’t worry, I didn’t get it right the first time either).
Another way to look at it – you have energy going INTO the room (in the form of electricity) but because the room is perfectly insulated, no energy (in the form of heat) can ever escape FROM the room.
I was thinking about this puzzle the other day while reading a report on global warming, and I thought of a follow up question: lets say that instead of having the refrigerator plugged into an outlet, you have a big bank of car batteries in the room – which are strong enough to power the refrigerator for some reasonable amount of time. Now, the energy is already IN the room from the beginning. Hmmm.
As long as the fridge is not connected to the batteries, the temperature in the room will stay the same, of course. But as soon as you connect the batteries and the refrigerator starts running, heat will be generated. Batteries that store electricity are said to have “potential” energy; the energy isn’t actually consumed until a circuit is made.
Coal and oil in the ground have a similar “potential” energy; the energy isn’t consumed until the fuel is burned. And there isn’t any way to extract the energy from coal except to burn it, which turns it directly into heat. This heat can then be used to boil water into steam, which can then be used to drive a turbine generator and convert the energy into electricity. It’s a very inefficient process.
In fact, coal powered electrical plants run at a little over 30% efficiency – meaning that for every 100 watts of power that is generated, about 200 watts worth of heat is dissipated into the environment. But then you also need to consider that there’s additional energy consumed in mining the coal and transporting it to the power plant. (And yes I know what you are probably thinking: with coal fired plants, the environmental damage is primarily from the greenhouse gasses that are released. But the excess heat produced is a huge problem as well)
If you define “efficiency” as a ratio of power produced versus excess heat produced, nuclear power generators are well over 80% efficient. I do believe that nuclear power plants are very safe – and with modern designs, the risk of radiation leakage is very very low. But we have not yet solved the waste disposal issue. This is a HUGE drawback to nuclear energy.
Most “alternative” energy sources – primarily wind and solar – do not emit any excess heat into the environment. This doesn’t mean that they are 100% efficient, as they don’t turn all of the potential solar and wind energy into electricity, I’m just saying they don’t produce any excess heat.
When I lived in Washington DC last year, a lobbyist friend of mine got me interested in Space Based Solar Power, SBSP for short. She has a graduate degree in “Space Policy” (I had never heard of such a thing ...) and she is a big proponent of SBSP.
With normal solar power, you capture the energy from the sun’s rays. But as sunlight transverses through the atmosphere, about 40% of the total energy is lost – more if it’s a cloudy day. And you only get direct sunlight for an average of 8 hours a day throughout the year. Even with very large solar arrays, the total power you can generate is limited.
If you put the solar panels in space, on the other hand, there is no atmosphere to attenuate the sunlight. From a conceptual level, the idea is simple: you build a HUGE array of solar panels (about 1KM in diameter) in geostationary orbit, and use wireless power transfer to beam the energy down to a huge receiving antenna (called a ‘rectenna’) on the ground. You get pure sunlight at all wavelengths, 24 hours a day, 365 days a year (except for just a few hours during the night on the spring and fall equinox, this is the only time the array would be behind the earth’s shadow).
I had the exact same initial response as everyone ALWAYS has – is this “wireless power transfer” safe? What happens if a bird or a plane flies through the beam?
Wireless Power Transfer has been around for over a hundred years. After quite a bit of investigation into how this technology is proposed to be used for SBSP, I am convinced it is safe, very efficient, and I am quite impressed with the whole concept. The microwave beam would be at a non-ionizing frequency, so there is minimal environmental impact, and the beam is quite diffuse at about 23 milliwatt per sq. centimeter at the center; this is a safe exposure level, you can walk right through it (or a bird can fly through it) with no ill effects (it’s less than the power you get exposed to while holding a cell phone against your ear). But since it IS so diffuse, it requires a very large rectenna (up to 10kM in diameter) to capture all the energy. However, the rectenna can be made of very lightweight transparent mesh, which can be erected over farmland or forests – so it’s not a total waste of land area.
It’s all very efficient and very environmentally friendly. And most importantly, it’s the ONLY “alternative” energy source that has the potential to produce power on a large enough scale that can possibly reduce our reliance on coal and oil. A one kilometer SBSP array and a ten kilometer diameter rectenna could produce between five and ten GIGAWATTS of electricity. That’s huge.
So why don’t we have SBSP operational today? There’s one issue, and it’s a biggie: launch costs.
With current technologies, it would take almost 150 rocket launches to haul the components required for a one kilometer array of solar panels into space. The cost of this is mind-numbingly astronomical. We need to reduce the cost of sending a rocket into space by a factor of 1000 to make it competitive with constructing a coal-fired plant. Of course, the overhead of a government organization like NASA makes rocket launches more expensive than they need to be – private contractors can do it much more cheaply. But not cheap enough ... yet. Maybe over the next ten to twenty years, the cost will come down enough to bring this within a reasonable range.
If you built the system today, it would take over 50 years of power generation just to pay for the launch costs. But ... that was the estimated payback period when they built Grand Coulee Dam in Washington State. Grand Coulee Dam, which was completed in 1942, produces whopping 6.8 Gigawatts of electricity today! This was an enormously expensive project for it’s time. It had a lot of critics who said that it was just too DAM expensive (pun intended) – but here we are, 70 years later, and it’s still THE LARGEST single producer of electricity in the USA!
Unfortunately, we don’t need one SBSP array (or Grand Coulee sized dams) to help with our energy problems; we need dozens. In the meantime, we’re building new coal fired plants at a dizzying rate – expelling hundreds of gigawatts of excess heat, and thousands of tons of greenhouse gasses, into our atmosphere.
So think about the original puzzle posed above. Earth is the room and our coal fired plants is the refrigerator, and it’s starting to get hot in here. Let’s figure out a way to turn off the fridge and shut the door. And don’t forget to turn off the light on your way out as well.