Is Storage the Solution?

In the energy discourse we hear often that once the challenge of grid scale energy storage is implemented, wind and solar energy will be able to fully replace fossil fuels for generating electricity.

Instead of just staying at this philosophical level, let's make our homework.

This exercise is an oversimplification to illustrate the challenges of relying on intermittent sources for all of our energy.

Let's take Germany as our working example.

According to the latest report by the IEA (International Energy Agency), Germany consumed 551 TWh during 2013*. To convert this amount into average power we perform the following calculation:

     551 TWh / 365 days / 24 hours = 0.63 TW = ~63 GW.

The actual energy consumed by this country fluctuates hour by hour and seasonally. Germany tends to consume more energy in winter than in summer. However, to simplify, we'll make our numbers with the average power consumed.

Let's consider a solar capacity factor (CF) of 12% for this country (a little generous).

Also (and again with the purpose of simplifying our homework) we'll consider that every day of the year is exactly the same and thus that the daily capacity factor is equal to the annual one.

Thus, the installed solar capacity we would need is (considering 90% efficiency in the battery / inverter system):

     63 GW / 0.15 CF / 0.90 efficiency = 583 GW 

     (Today Germany has ~36 GW of solar installed capacity).

At the very least, the batteries would need to store 12 hours of power and this translates into:

     63 GW x 12 = 756 GWh

According to the Guinness Book of World Records 2013 edition, the largest battery in the world** (pictured below) can store 36 MWh. Thus, we would need this many to store 756 GWh:

     # Batteries = (756 GWh x 1000) / 36 MWh = 21,000

According to the Energy Information Administration (EIA), by 2040 global solar electricity production will be 452 TWh. This would be 82% of the 551 TWh Germany consumed in 2013 (and would "leave" nothing for the rest of the world).***

To calculate the required investment we need to multiply the cost of the solar watt (including inverters and installation) by 583 billion (see installed capacity above). Additionally, the cost of the storage needs to be added. We are easily talking here of more than a trillion euros.

However, these "rosy" numbers won't pass muster in the real world. Why? Because in the real world we have sunlight variations between days and, even more important, seasonality. Germany, for example, tends to consume more energy during winter when there is less sunlight.

Thus the above amounts would have to increase significantly. In other words, in real life we would need considerably more than the 583 GW of installed solar capacity and at the same time the batteries would need to store not 12 hours of electricity, but full days or even weeks. The required investment would thus be much higher than in the simplified case we presented above.

Conclusion: storage for renewable energy is not a silver bullet and it is doubtful that a fully renewable economy (solar and wind) would ever make sense in financial or even environmental terms.

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

Thank you.

Notes:

1. Sure, the renewable energy doesn't have to be 100% solar. We could have a combination of solar and wind. This would obviously make the exercise much more complicated but would make more sense in the real world. However, solar and wind are not fully complementary. Solar (obviously) operates only during the day. Wind is more random. See graph below for the first months of 2012 where we can see that solar / wind do complement themselves somewhat. We can see that in January there was little solar production but was a very good month for wind. Then, July was a very low month for wind but had substantial solar production. However February (a full month) was low on both. More storage would be required for compensating those long lulls. Additionally, February was the month with the highest consumption in the first 7 months of 2012. (If somebody can share the full year statistics, they are welcomed). Let's bear in mind that the randomness of wind can only be somewhat compensated by solar during the day, so for half of the year (nights) wind is by itself.

2. Another concern is the variability of wind, here we can see annual variations (solar is more stable although its CF is considerably lower than wind's in Germany):

Both graphs are from the last reference below.



References:

* http://www.iea.org/statistics/relatedsurveys/monthlyelectricitysurvey/

** According to the Guinness Book of World Records, this battery is "larger than a soccer field."

*** http://www.eia.gov/forecasts/ieo/

German capacity factors for solar and wind:
http://cf01.erneuerbareenergien.schluetersche.de/files/smfiledata/1/1/2/2/4/7/WindPVProductivity1to712.pdf

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

Energy: Let's Do Our Homework

Energy is a complex subject in which many variables intervene and thus we do have to make our homework to choose wisely.

In the energy discourse we still see oversimplifications in which energy is divided into "dirty" and "clean." Discussions at that shallow level are not useful for establishing energy policy or even for educating the world on the difficult decisions we have to make.

With this article we want to motivate a quest for deeper understanding and the application of more reason and less feelings in this all important subject.

Let us first start by stating that there is no such thing as clean energy. When considering their full life-cycle, even the cleanest sources (hydro, wind and nuclear) have greenhouse gas (GHG) emissions and create other types of wastes that impact the environment. So, here are some of the things we should be asking ourselves:

1. What are the carbon emissions per kWh of the specific energy source (including all processes from cradle to grave)?
2. Is the energy reliable?
3. If it is not reliable, how are we going to compensate for its unreliability (other reliable energy will cover the lulls or would storage be used)?
4. If other forms of energy cover the lulls, then these emissions need to be considered in the emissions of the "system."
5. If storage will be used, we also need to consider the GHG emitted in the cradle to grave processes of the storage technology and add it to the emissions of the "system." Also, how many hours / days / weeks of energy do we plan to store? How much storage area would be required for the banks of batteries or other storage technologies? What is the leasing cost of this space?
6. Emissions are obviously not the only variable we need to be concerned about, resources utilization and costs have to also be high in the list.
7. What are the capacity factors of the different technologies in the specific place where we are planning to locate them?
8. Is it advisable to combine several types of renewable energy to somewhat compensate for the peaks and valleys in electricity generation? If so, say, how much solar capacity and how much wind capacity should be installed?
9. Should we go "all out" for a particular technology or only as much as makes financial / environmental sense?
10. Could climate change seriously modify our design assumptions in the short / medium term (e.g. less / more wind in a particular place on Earth)?
11. How much intermittency can the current grid absorb? Are additional investments required in the grid so it will be able to handle high penetrations of intermittent energy?
12. What type of investments would achieve the most bang for the buck (in other words, the best reduction in emissions)?

The above questions are just to get the conversation started.

The next step would be to model the complete system and calculate (among many other things) these two all important parameters:

1. Cost per kWh of the generated electricity.
2. Emissions per kWh of the system.

If either of the above is too high, we may need to go back to the drawing board until an acceptable system is designed.

Again, the purpose of this article is to make people realize that energy is a very complex subject and it is better to leave it to the engineers to design energy systems. Many times well intentioned but naive persons want to lead the energy discourse and this can take us to the wrong results: high cost / high emission systems.

Thank you.

Types of People in the AGW Discourse

The Anthropogenic Global Warming discourse is supposed to be happening between the Deniers and the Believers but this is an oversimplification that does not fit well into the actual reality, so we are presenting below a more useful classification.



1. The Deniers: they don't believe AGW is happening and no evidence will make them change their mind.

2. The Believers: they believe AGW is happening but they have their feet on the ground.

3. The Naivers: they believe Renewable Energy (RE) will replace fossil fuels (FF) and save the day.

4. The Black Swanners: they believe in AGW but at the same time understand that humans will not voluntarily reduce their standards of living. Thus humanity will NOT reduce their FF consumption for many decades to come. The way out? A serious black swan event that will solve the emissions problem "through the back door." Examples:
     a. A gigantic volcanic eruption in Indonesia.
     b. An ebola like virus that drastically decimates human population.
     c. What have you.

5. Gamblers: they do believe AGW is happening but decide to wait and see. There might even be some unintended positive consequences of climate change. If nothing else, their investments in Greenland may become more valuable.

6. Opportunistic: the ones that make loads of money by selling the RE to the Naivers (above).

7. Liars / Lobbyists: what they believe in their heart is irrelevant. They follow the money and fully support their sponsors no matter how much they have to bend themselves backward to seem reasonable.

Framing people is never good, but it is certainly better to frame them in SEVEN camps rather than limit them to only two.

We hope the above classification adds something positive to the energy discourse.