How can wind and solar fulfill 80 percent of total energy in 25 years?


A common response to the climate roadmap by experts is “It’s just not possible.”

Their objections are general, not quantitative, so here is a physics 101 style explanation. That means that we take the simplest possible solution, and then add complications one by one.

  1. To replace FF we need to replace its energy with (clean energy + efficiency). We’ll add efficiency improvements later (when that costs less than new clean energy, of course). To start the analysis we’ll set efficiency to “unchanged”.
  2. Clean energy consists of a combination of wind, solar, nuclear, CCS, biofuels, and numerous others that are only locally interesting. As physics-101 students, well pick one, do the analysis, and later optimize with the panoply. We pick solar as a starting case because we can extrapolate its growth curves, doubling every 2 years for 10 years. Society appears to accept solar, and the costs are going in the right direction (down). Later in the exercise we’ll optimize–replace solar with others when and where they cost less than solar.
  3. Solar probably won’t make it in Alaska. In other words, almost anything else will be cheaper than solar in Alaska, maybe  they’ll use wind and biomass.
  4. Split the problem into two phases: 0-50% solar and 50-80% solar. After the 80% stage, in 25 years, we can assume that abundant new solutions are developed, and new problems as well. If tech innovation totally fails us, then solar stays at 80% and we use CCS, nuclear, wind, and biomass for the last 20%.
  5. 0-50% phase (15 years): Carbon fee goes from $0 to $1.30/gallon of gas.
    1. Very little storage needed. Off-grid locations will place a high value on storage, so the technology gets a running start. Compressed air (isothermal, 95% efficiency using foam or spray) storage is looking very strong in 2014. If storage technology totally fails, we can use NG peaker plants for the 3% of the year needed until they’re not needed–with little impact on total emissions.
    2. Cost: competitive with NG in much of the world. Low crude prices now will probably raise NG prices in the US because of reduced fracking.
    3. Area: In the US, the area required to replace all FF, if no wind or biofuel is added, is the same as we now use to grow corn for ethanol (40 million acres).
    4. Transportation: US mileage standards are doubling by 2025; it’s easy to imagine 25% BEVs, 30% hybrid vehicles, and electrification of 30% of trains in 15 years. The current grid of charging stations across the country spreads to most gas station locations. Airlines would be at 15% carbon-neutral jet fuel (bio or solar-manufactured).
    5. Heating: in 15 years it’s easy to imagine 30% of heating systems being converted to heat pumps, most with ground source.
  6. 50%-80% phase (10 years): Carbon fee goes from $1.30 to $2.20/gallon of gas.
    1. Storage capacity is gradually expanded from hours to days by expanding storage tanks and building more excess capacity.
    2. Cost: expected to reach pennies per watt
    3. Transportation: with charging and H2 stations common, increasingly heavy equipment becomes either electrical, H2, or methane-from-H2; By the end of 25 years, 80% of jet fuel is carbon neutral
    4. Heating: all new heating systems are heat pumps, most with ground source.
  7. Add wind energy where it is lower cost than solar: storage requirements decrease in most locations
    1. Wind generation costs decrease more slowly than solar, so the benefit of wind increases with distance from the equator because solar output decreases and variability increases as the sun goes lower.
  8. Add nuclear in countries with strong governments and lots of cash
    1. Modular nuclear reactors could become common by 2030, allowing easier replacement of the last 20% of FF
  9. Add efficiency improvements wherever they cost less than the lowest cost clean energy source.

We end up with an incremental solution which costs much less than we are spending on fossil fuels now, and which saves 13,000 lives per year in the US alone due to reduced pollution.


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