Tuesday, April 08, 2014

Emissions and Renewable Energy

Does Renewable Energy (sun and wind) reduce emissions?

The short answer is: in theory it does reduce emissions.

But what about in practice?

Here things look quite differently. Let us show why with an example.

This is obviously going to be an over simplification, but please bear with us.

Let's consider an isolated country that decides to go all out for renewable energy, in this case wind turbines.

Let's make our estimates below with a wind annual capacity factor of 30%.

So, this country will get 30% of its energy from wind turbines and the rest, say, from natural gas powered plants.

The emissions of the turbines are ~ 12 grams per kWh.

The emissions of natural gas plants are ~ 469 grams per kWh.

Thus, the emissions of the whole system would be:

     (0.30 x 12) + (0.7 x 469) = 332 grams per kWh.

If we replace natural gas by coal (with 1001 grams per kWh) then the numbers look less attractive: 704 grams per kWh for the system.

The same exercise with solar photo-voltaic would result in larger emissions since the capacity factor of solar is even lower than that of wind.

Sure, it could be argued that renewable energy could be "stored" but for the most part those systems have not been deployed and would require important investments and additional emissions during their manufacture.

Conclusion: in real life we have to consider the emissions of systems, not of individual components and when the system is considered, the ability of renewable energy to reduce emissions is limited.

This is one of the reasons why German emissions per kWh remain stubbornly high in spite of all the renewable capacity they have installed.

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