Technical Feasibility

That something is somehow technically feasible, doesn't mean it makes economic or even environmental sense.

Let's consider the following question:


1. Is it feasible for a country to transition to 100% renewable* electricity? (Assuming there are no financial or material constraints).

The answer is almost certainly yes.**

However, that is not the important question. The important question is:

a. What would be the purpose of generating all the electricity of a country with renewables?

If the answer is: to reduce CO2 emissions, then I think we first need to make our homework.

Off the bat, neither solar PV nor wind are zero carbon emitters (once their lifecycle is considered). Sure, no technology, not even hydro, is zero emissions but according to the IPCC**** utility scale solar PV has a median value of 48 grams of CO2 equivalent per kWh. Low, but not extremely low. Wind clocks in at 11 grams. Much better.

However, the numbers above do not include either the back up plant (usually fossil fuel powered) that is needed most of the time to support the relatively low capacity factors of renewable energy, nor the lifecycle emissions of the massive storage that would be required to somewhat wean renewables from fossil fuel plants.

So say, if on an annual basis wind supplies power 25% of the time and a natural gas power plant the rest of the time, the weighted emissions would be:

          25% x 11 grams/kWh + 75% x 490 grams/kWh = 370 grams/kWh

Yes, it is lower than a natural gas power plant by itself, (reduction of 120 grams/kWh) but are these modest CO2 reductions worth the double investment?

And, more important, is there a better way to invest our limited financial (and material) resources to achieve more bang for the buck?

As an exercise, the replacement of a coal plant with a natural gas plant would result in the following reduction:

          820 grams/kWh (coal) - 490 grams/kWh (natural gas) = 330 grams/kWh

The reduction in emission is almost three times larger and probably with a smaller investment that would last longer. (How long before wind turbines have to be replaced?).

Now, if we replace the coal plant with a nuclear one the numbers look this way:

          820 grams/kWh (coal) - 12 grams/kWh (nuclear) = 808 grams /kWh.

The reduction in emissions is almost seven times larger than with renewables.

Conclusion: technical feasibility by itself does not justify investments in renewable energy. More important is to consider the financial and environmental factors.

Feel free to add to the conversation in Twitter: @luisbaram


* By renewables we mean solar and wind in this article. Hydro is also a renewable but it is in a league by itself and we actually already have countries generating 100% of its electricity with it. Among them we have Paraguay and Albania.

** Sure, the manufacture of the wind turbines and solar panels would require massive inputs of fossil fuels, but for simplification we won't consider them at this moment.

***http://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emissions_of_energy_sources

Renewable Energy Reduces Emissions

Is renewable energy (solar and wind) the best way to reduce carbon emissions?

At first sight, this question seems almost absurd and we are tempted to say: of course it is the best way!

But, is it? Before jumping to hasty conclusions let's do our homework.

This exercise is going to be a simplification, the purpose is mainly to show us that things in real life are not as simple as in the lab.

So, let's consider a country that supplies 100% of its electricity with coal plants.

According to this table (see link at the bottom of this page), these are the emissions per kWh generated with the different energy sources: **

Thus, if this country generates 100% of its energy with coal, their emissions per kWh would be ~1001 grams.

Now, let's say we install wind turbines (enough to supply 100% of the power when the turbines are producing at full capacity):

Let's say wind capacity factor at this country is 25% (in other words, turbines actually produce 25% of their plate rating on average). It is important to underline that this is not constant power: at some moments the turbines are producing at 100%, at other they produce nothing and at any other moment their output can be anywhere in between these extremes.

So, (simplifying) wind will produce 25% of the energy on an annual basis and the coal plants will produce the rest (75%).

Then we calculate the emissions that are really just a weighted average:

Annual average emissions per kWh = (25% x 12 g/kWh) + (75% x 1001 g/kWh) = 754 g/kWh.

We can see that the emissions of the system did drop, but they are still too high.

What better options do we have?

1. If we replace the coal plants with natural gas plants (which have much higher capacity factors and can be staggered since they are not wind / sun dependent) then the emissions would be:

          469 g/kWh

2. If we replace the coal plants with nuclear plants then the emissions would be:

          16 g/kWh

As we may see from the calculations above, Renewable energy investments are not the best way to reduce emissions.

Arguably, the fastest way to reduce emissions is to replace coal plants with natural gas plants, however, if the higher investment can be made (and the longer lead times are acceptable), nuclear is truly the low carbon energy solution.

Conclusion: Yes, Renewable energy reduces carbon emissions in most systems, however natural gas, nuclear and of course hydro, are better options.

Thank you.



Notes:
a. In the developed world little new electrical capacity is needed and thus Renewable energy almost directly replaces some other energy source, however in the developing world substantial additional electrical capacity is required and thus a double investment would be required: the Renewable one, plus the reliable one.
b. Sure, Renewables (wind and sun) could be combined to somewhat compensate the fluctuations of the other one. Still, at any particular moment of the year we may have no sun and no wind. At another moment we may have both which could even force us to divert (or disconnect) capacity.
c. To simplify, here we are not considering the possibility of "dumping" energy into another country or using massive storage systems.

**
http://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emissions_of_energy_sources

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.

Clean Energy

Clean Energy is really a misnomer.  There is no such thing as "clean energy".  All energy sources emit pollutants during their life-cycles.

All we can say is that there are cleaner energy sources.  In other words, some sources are cleaner than others.

Since CO2 is the main green-house gas we are now concerned about, following is a comparison of carbon emissions when different energy sources are used for generating electricity.

"A literature review of numerous energy sources CO2 emissions by the IPCC in 2011 found that that the CO2 emission value, that fell within the 50th percentile of all total life cycle emissions studies conducted, was as follows." (From Wikipedia):

Now, depending on what lobby calculates the above numbers they tend to vary somewhat, but the point is that NO energy source is clean.  Sure, there is no doubt that coal is the dirtiest one but on the other hand it is significant that, at least in this particular study, solar (which is considered by many the ultimate green energy) is dirtier than nuclear energy.

Why is this?  

Answer: although solar panels produce no carbon emissions during operation, the emissions produced during their manufacture have to be "amortized" in the energy produced by the panels during their useful life.  And these emissions are not negligible.  The silicon has to be mined, purified, fused, doped, cut, soldered, transported, installed, etc.  Plus the aluminum and glass components of the panels also go through an energy intensive manufacturing process.

And by the way, oil is located somewhere between coal and natural gas.

So, even though ALL energy sources emit carbon dioxide when you factor in their complete life cycle,  it is obvious that fossil fuels are the dirtiest.  All the rest we could label as "low carbon" energy sources.  

What humanity needs to do to prevent a climate catastrophe is to move from "high carbon" to "low carbon" energy sources.

Today the USA is significantly reducing it's carbon emissions by switching part of their coal electric utilities to natural gas.  This is probably the simplest and fastest way to reduce carbon emissions but is obviously only an intermediate step in the solution.

Long term we have to move aggressively to "low carbon" sources.