I have this friend. This friend has a good heart, but is a wee-bit lagging in the basic science department, which makes for interesting conversations. Recently, this friend posted this link in a discussion thread about alternative energy sources, as an example of "free energy" that refuted my statement the the conservation of energy = no free lunch, where energy is concerned.
The device described at the link is actually a really cool widget that coverts vibrational energy into electricity, via a weird class of compounds called piezoelectric materials that build up a charge as they undergo mechanical stress. Very cool. So they use this tiny device to scavenge energy from vibrating machines in factories to power microsensors that do various things that aren't really important here. The point is, my friend, and a lot of folks in the thread I was in, were talking about "free energy" and wondering why we didn't just build a billion of these things and make a power plant out of them.
This is, at least, better than the "zero point energy" thing I hear about pretty frequently in these circles (which is a topic for another post). Since I encounter basic misunderstanding about how energy flows through systems so regularly, I thought I'd put together a basic summary that would help someone figure out, without the need for advanced knowledge, why the idea that a piezoelectric generator yields free energy is bullshit. You can understand that immediately, without having to analyze it in a serious fashion, if you internalize two basic facts:
1.) Energy is not spontaneously created. It has to come from somewhere, and go somewhere.
2.) In the process of this moving about, some energy is always lost as waste heat. No mechanism for moving energy around is 100% efficient.
All I've done here is paraphrased the first two laws of thermodynamics (The Third law concerns the definition of absolute zero, and actually plays into why extracting zero-point energy is almost certainly impossible, but yeah, another post).
For the first point, consider that no human technology creates energy. They just turn various types of energy into our personal favorite, electricity. Generators convert kinetic energy into electricity via a spinning magnet. That kinetic energy in turn can come from a number of sources: steam pressure caused by heating water, as in the case of geothermal, coal, and nuclear power plants; the energy of falling water, as in the case of hydroelectric plants; moving air, as in the case of wind power, etc. Other materials generate electricity more directly, with no kinetic step in between: Photovoltaic cells convert sunlight directly into electricity using special materials, other materials can generate electicity using moving thermal energy (thermocouples, often used on space probes) or, as we just saw, from mechanical stress (piezoelectric materials).
In all of these cases, though, the energy comes from somewhere else, flows through the convertor of choice, becomes electricity, does our bidding, and dissipates as waste heat, never to return. That's the second law in action; eventually, the energy degrades into background heat, warming the universe imperceptibly and becoming impossible to use again. So energy is a unidirectional flow; we get useful work out of it as it meanders along, like a river, but eventually it reaches the sea and we can't do anything more with it. The energy river is long and has a lot of stops on the way, but ultimately we can trace it to only three sources:
1.) Geothermal heat. The residual heat from the gravitational compression that formed of the planet, plus quite a bit from the decay of natural radioactive isotopes. The Earth is not in thermal equilibrium with the space around it, and we can use that energy gradient to generate power.
2.) Radioactive isotopes. Ultimately these energy-dense elements got their energy from the immense energies released in the supernova that formed them, long before our solar system formed.
3.) The Sun. This is the biggie. A perpetual fusion explosion that bathes the planet in an incredible fucking wealth of high-energy photons. The sun is the source of solar energy via PV cells, but also drives wind power (wind is air moving around in response to temperature gradients caused by the sun) and hydroelectric (the water flowing into reservoirs gained its potential energy thanks to the sun's energy evaporating ocean water and driving it into the atmosphere). The Sun is also ultimately the source of fossil fuel energy, as fossil fuels are nothing except ancient plant and animal biomass that was created using solar energy harvested in photosynthesis. Fossil fuels are really just millions upon millions of years worth fo sunlight, stored up. John Michael Greer uses an excellent analogy for solar/fossil energy: if the energy striking our planet from the sun is like our income, our weekly paycheck, than fossil fuels represent an ENORMOUS savings account balance that the Earth racked up in the millions of years before we came along and strated drawing from the account.
So that's it. The energy harvested by that weird little vibrational gizmo is, ultimately, almost entirely solar energy (a portion of it may be from radioactive decay or geothermal, depending on whether the factory in question is hooked up to a nuke or geothermal plant). We can slap all the vibrational doodads on all the machines in the world, but the power we get from those doodads wills be less than the power that went into the machines themselves, and will ultimately be limited by the size of our three energy streams. 2nd law again. Everything we do, every power source we utilize, is ultimately just an attempt to harness one of these three energy flows. They are all there is, and they are finite.
That's right. THERE IS NO SUCH THING AS RENEWABLE ENERGY. Not in the long term. The Earth will eventually cool to the temperature of the space around it. The radioactive isotopes will eventually all decay into stable end-products. The Sun will eventually run out of fuel and explode. When we talk about "renewable" and "non-renewable" energy, what we're really talking about is the relative time in which we expect an energy source to be depleted. If the amount of time it takes the energy source to run out (reach equilibrium with its environment) is, say, longer than the amount of time we can reasonably expect our species to persist, we can go ahead and call it "renewable."
And this is where an undertanding of basic thermodynamics brings us to the coming energy crisis.
For our purposes, geothermal and solar are renewable, radioactive isotopes and fossil fuels ("banked" sunlight) are not. In the case of the latter two, we can expect to use all of the reserves available to us in well under the lifespan of the species. Oil either has or will soon peak in availability, coal may have another few decades, and fissile radioactive isotopes would likely tap out in less than a hundred years (and that's assuming we were willing to tolerate all of the side-effects that wide-spread utilization of nuclear power brings to the table). In other words, we got our hands on Mom's debit card a couple hundred years ago and have been spending like fiends ever since. So the energy crisis comes down to one question: using only the solar energy continuously reaching our planet (keep in mind that this means hydro and wind, as well, indirectly), and whatever we can extract from geothermal, can we maintain the level of energy use we currently enjoy?
Nope. Not a chance. We have to share the solar energy with the biosphere, which we directly depend on for food and indirectly depend on for little things like oxygen and climate mediation ("ecosystem services," Google it). What's left can only be harvested so efficiently, and ultimately there simply isn't enough solar energy striking the Earth to meet our current quotas when you consider that. When someone says, for instance, that there is enough solar energy hitting the Sahara to power the world, they are completely neglecting th inconceivable cost of covering an area that large with PV panels, the immense engineering challenges in maintaining such a cast array, the difficulties in moving electricity around from a single point (transmission wires lose a significant amount of energy due to resistance, and the maximum economical range for AC power distribution is perhaps 2,500 miles, and the fact that the best PV panels we have would only harvest about 29% of that energy anyway. And we've not even discussed the tremendous and unknown weather and ecological effects that dropping the albedo of the world's largest desert may have.
This is the essence of the energy crisis. We have but three energy flows available to us; they are all finite, and only two of them are really renewable for our purposes. And those two simply can't meet the absurd levels of consumption we enjoy in industrialized nations today. There is only one possibility: we will reduce our level of consumption. Whether we, as societies and individuals, reduce that consumption in a planned and sensible way, or suffer the pain and chaos of a systemic collapse, is ultimately up to us.