I should point out at the outset that I’m very much in favor of using alternative energy sources (particularly solar thermal, wind, and geothermal).  This diary isn’t an argument against alternative energy.  It is however an argument against having unreasonable expectations for what alternative energy sources can deliver in the short time span in which we’ll need to transition to them (roughly 2 decades).

I’m going to survey the challenges for alternative energy David Fridley’s excellent article considers in turn.

First, Fridley points out that there are two broad classes of alternatives:

“Alternative energy” generally falls into two categories:

  • Substitutes for existing petroleum liquids (ethanol, biodiesel, biobutanol, dimethyl ether, coal-to-liquids, tar sands, oil shale), both from biomass and fossil feedstocks.
  • Alternatives for the generation of electric power, including power-storage technologies (wind, solar photovoltaics, solar thermal, tidal, biomass, fuel cells, batteries).

The pitfalls alternatives face are as follows:

1. Scalability and Timing.

For the promise of an alternative energy source to be achieved, it must be supplied in the time frame needed, in the volume needed, and at a reasonable cost.

Fridley goes on to observe how many alternative energy projects currently hailed as great options are only producing on a small scale – not nearly at the scale of production required.  Timing is important as well – many of these production facilities, while they’re scaling up fast, will still take decades to reach the production capacity that we’d need today if we’re to make a transition in time.

2. Commercialization.

Closely related to the issue of scalability and timing is commercialization, or the question of how far away a proposed alternative energy source stands from being fully commercialized.

Many projects we hear about – especially in the excitable tech press – are often still research projects.  Commercializing energy technology typically takes many years if not decades, and building up production capacity to useful levels takes many years more.

3. Substitutability.

Ideally, an alternative energy form would integrate directly into the current energy system as a “drop-in” substitute for an existing form without requiring fur- ther infrastructure changes. This is rarely the case, and the lack of substitutability is particularly pronounced in the case of the electrification of transportation, such as with electric vehicles.

Almost none of the alternatives typically discussed provides a dense liquid fuel substitute for oil that can be used in transportation or agriculture.  The net-energy-positive alternative that does – algae-based biofuel – is extremely far from commercial viability and requires even more land area per unit energy than corn-based ethanol.

4. Material Input Requirements.

Unlike what is generally assumed, the input to an alter- native energy process is not money per se: It is resources and energy, and the type and volume of the resources and energy needed may in turn limit the scalability and affect the cost and feasibility of an alternative.

Given the scarcity of rare earths and other minerals that go into manufacturing of solar PV, wind turbines, etc. Fridley points out that if we were to scale up production even at the rate currently projected today (not even the rate that we actually would need to make a transition to alternatives), we’d be well beyond the supply of these minerals.  Also, fossil fuels are currently providing an invisible energy subsidy to alternative energy production, and that subsidy will steadily go away as oil depletes.

5. Intermittency.

Modern societies expect that electrons will flow when a switch is flipped, that gas will flow when a knob is turned, and that liquids will flow when the pump handle is squeezed. This system of continuous supply is possible because of our exploitation of large stores of fossil fuels, which are the result of millions of years of intermittent sunlight concentrated into a continuously extractable source of energy.

What happens when the sun isn’t shining, the wind isn’t blowing, or there’s a drought that cripples hydroelectric production?

These aren’t insurmountable challenges, but they require a large investment in energy storage, which itself is expensive.  (One of the reasons I particularly like solar thermal is that it’s the easiest to use for low-tech molten salt storage.)

6. Energy Density.

The consequence of low energy density is that larger amounts of material or resources are needed to provide the same amount of energy as a denser material or fuel. Many alternative energies and storage technologies are characterized by low energy densities, and their deployment will result in higher levels of resource consumption.

Here’s a graph showing energy densities of various energy options:

Nothing comes close to liquid fuels.

7. Water.

Water ranks with energy as a potential source of con- flict among peoples and nations, but a number of alternative energy sources, primarily biomass-based energy, are large water consumers critically dependent on a dependable water supply.

Fridley considers the water needs of various biofuels and finds that they’re far far above what we need for current liquid fuels production per gallon of fuel output.  Given that aquifer depletion is bad enough now that it’s detectable from space, using biofuels would quickly run into water challenges.

8. The Law of Receding Horizons.

An often-cited metric of the viability of alternatives is the expected break-even cost of the alternative with oil, or the price that crude oil would have to be to make the alternative cost competitive. Underlying this calculation, however, is an assumption that the input costs to alternative energy production would remain static as oil prices rise, thereby providing the economic incentive to development.

In other words, as peak oil exacerbates boom-bust economic cycles and overall puts an end to economic growth, it will be difficult to steadily continue building alternatives despite economic fluctuations.  At oil price troughs it will be hard to justify building alternatives due to price, and at peaks the input costs of fossil fuels will make alternatives more expensive than they otherwise would have been.  Efforts to mitigate this, such as feed-in tariffs are worth implementing, but it is difficult for governments to always keep their promises on these guarantees.

9. Energy Return on Investment.

The complexity of our economy and society is a func- tion of the amount of net energy we have available. “Net energy” is, simply, the amount of energy remaining after we consume energy to produce energy. Consuming energy to produce energy is unavoidable, but only that which is not consumed to produce energy is available to sustain our industrial, transport, residential, commercial, agricultural, and military activities. The ratio of the amount of energy we put into energy production and the amount of energy we produce is called “energy return on investment” (EROI).

By all indications our biofuel options are well below the needed EROI to make them worthwhile, while alternatives for electricity generation have decent EROI.

In summary, when considering any possible transition program to alternatives, we need to consider all of the above pitfalls and examine how to avoid them.  To my knowledge, none of the various proposed transitions to alternatives address them all.