Renewables aren’t perfect solutions

As I stated previously, no energy solution answer perfectly to all our needs. Renewables are no exception as they also suffer from two main issues : low energy density and intermittance.

According to the French magazine Science & Vie, this poses a serious problem which compromises the dream of a future where we would get all our energy from renewables.

Albeit those weak points, everything should be done to enable these low carbon dioxide energies to have a much bigger share in the world energy mix.

The magazine provides data which is exemplified. To provide the electricity needed by Paris – 3.65 GW – it takes more or less space according to the energy solution :

• Nuclear is the best solution as it needs only 0.2 km²
• Then comes solar photovoltaïc with 91.2 km²
• Hydro and wind energy requires respectively 365 and 454 km²
• Biomass is the least energy dense solution with a staggering 3,000 km².

Other problem posed by renewables, they suffer from important intermittence. Here is the data :

• Nuclear produces electricity 85 percent of the time or 312 days per year
• Biomass this times have a good score of 75 percent or 275 days ;
• Then comes hydro power with 38 percent or 139 days ;
• Wind and solar lag behind with 25 and 12 percent respectively (92 and 44 days).

Concerning the energy density, you might infer that with energy efficiency it might be more profitable. Here are a few calculations I did on my own :

If we increased our energy efficiency by 50 percent and that the efficiency of solar panels doubled (estimation for the third generation of solar panels), we would still need 22.5 km² to provide electricity to Paris.

That’s not huge, but it would still be more than a hundred times more than the space currently needed by a nuclear plant.

According to the International Energy Agency quoted by the magazine, we have to solve a most complex equation : decreasing our greenhouse gases emissions by 2050 while providing a lot more energy.

Now let us have a loot at the world energy mix.

Currently, natural gas accounts for 21 percent, coal, 25 percent and oil a staggering 35 percent of 430,000 Peta Joules.

Wind and solar energy provide only 0.1 percent of the global energy mix nowadays and renewables less than 13 percent. Out of these 13 percent biomass and hydro have the lion’s share with 10 and 2 percent respectively.

Now let us have a look at the energy scenarios in 2030.

• The specialists of the IEA outlined a green scenario with energy efficiency enable us to reach “only ” 640,000 Peta Joules. Oil would account for 32 percent, natural gas 22percent and coal for 22 percent. Nuclear would account for 7 percent, biomass 11, hydro 2 and the other renewables a mere 3 percent.

• The people from Greenpeace propose a qute similar scenario, with 400,000 Peta Joules. Oil would account for 28 percent, natural gas 28 percent, coal 11 percent, biomass 19 percent, hydro 11 and the other renewables… three little percent.

To me, if oil and gas prices keep on increasing sharply as they have been doing for the past five years, I seriously doubt that they will keep on providing us half of our needs. We need cheap and clean energy sources, fast !

So, to infer this article, renewable energies sources have to be developed in an important and global way.

Source : Science et Vie, March 2008, issue 1086.

Edited on October 20th, 2008 to improve readability.