Hydrogen Powered Cars

This post is about the Toyota Mirai, a hydrogen powered car that is now entering production.

First, let us state that yes, we should all support technological innovation. And yes, when a new technology is introduced into the market, significant improvements tend to be made in a relatively short time.

However, after saying the above, let us make some pertinent questions.

One important sale point for a hydrogen car is that it produces no emissions (the car itself during operation), but since free hydrogen is not available on Earth, it first has to be produced. Thus, we come to the first question.

1. How is hydrogen currently produced? 
     Currently most hydrogen is produced from natural gas at an efficiency of ~80%*. Off the bat, this
     means two things: a) 20% of natural gas' energy is lost in the conversion and b) significant
     amounts of CO2 are produced during the conversion itself. Thus, these emissions need to be
     considered part of the system emissions of the hydrogen car.

2. What is the efficiency of the fuel cell (the device with which the Mirai converts the hydrogen 
     into useful electricity)?
     Without cogeneration, the efficiency of a fuel cell is in the range of 40 to 60%.**
     As a reference, rechargeable batteries have efficiencies above 90%. Consequently, just combining
     the production of hydrogen with electricity generation in the fuel cell, the combined efficiency
     drops to ~50%.

Thus it could be stated that the Mirai is competing with EVs (electric vehicles) on the one hand and with NGV (natural gas vehicles) on the other.

Today, the EV is clearly more efficient and lower cost than the Mirai. In other words, the EV would produce less emissions in most scenarios.

The NGV is much less expensive (and less efficient) than the Mirai. However, it remains to be seen if the considerably higher cost justifies moving to a Mirai rather than just buying a conventional electric vehicle.

Conclussion: Innovation should be supported but the hard questions need to be made.
   
Feel free to add to the conversation at Twitter: @luisbaram



*http://en.wikipedia.org/wiki/Hydrogen_production

** http://en.wikipedia.org/wiki/Fuel_cell

***http://batteryuniversity.com/learn/article/comparing_the_battery_with_other_power_sources

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

Is Hydrogen a Viable Alternative?

Feelings, feelings and more feelings are what we see in many energy discussions. If we are talking about religion or maybe even about politics, it is OK to mix as much feelings as we want, but not when we are talking about energy. In this subject we should stay cozy to the facts, the laws of physics and yes, economics. 

Can renewable energy provide 100% of our energy? Yes but at a prohibitive cost. Consequently renewables are not really a total solution (yes, they have their place in our energy mix but their penetration is and will continue to be quite modest in a global scale).

For example, some renewable enthusiasts mention that excess electricity produced by the sun can be converted into hydrogen and then burned when we need the power. 

Technically this is 100% feasible, but economically... 

1. A say, one megawatt solar installation in a nice and sunny place produces on an annual basis only close to 200 kW average power (five times less than the "plate" rating).

2. The efficiency of electrolysis (to produce the hydrogen) is around 70%.

3. The efficiency of the hydrogen turbine (to move the generator) is probably less than 50%.

4. The efficiency of the generator should be in the order of 90%.

So, just the last three steps above result in a combined efficiency of 31.5%. In other words, 68.5% of the energy produced by the solar panels is lost in this hydrogen conversion process! And you still have to add the capital expenditures of the electrolysis plant, turbines, generators, storage tanks, etc. It makes absolutely no sense. 

Besides we wouldn't have to beat so much around the bush, there is something called rechargeable batteries with much better conversion efficiencies than the above. We could use them to store the excess electricity, but again it requires considerable investment that will impact the cost of the electricity produced: the batteries themselves, the inverters, warehouses, replacement of the batteries every so often, etc., etc. And sure, it is not particularly "green" to produce and then dispose of so many batteries. Even then if the sky were cloudy for several days the batteries would be completely depleted and conventional energy will have to come to the rescue. In other words, solar (or wind) cannot really replace conventional power plants.

Let's face it, the reason renewables require subsidies to survive is because they are more expensive than conventional energy and, specially, that they fully depend on the conventional electrical grid. 

So, let's not talk about wishes, let's talk about facts: when Japan shut down its nuclear plants after the tsunami almost 100% of the replacement energy came from fossil fuels. That's right: not solar, not wind but fossil fuels. They imported more coal, more natural gas and more oil. Their emissions went up and their balance of trade suffered. These are the FACTS. Not the wishes.

Now Germany is embarking in a very expensive renewable experiment and the only reason Germany will not go exactly the way of Japan (that is in substituting all nuclear with fossil fuels) is that France and other neighboring countries will gladly sell them nuclear electricity. Sure, German carbon emissions will go up (because they will increase their coal and natural gas use in generating electricity) but not as much as could be expected if France were not there to help.

As we all know the country at the center of the nuclear hurricane, Japan, is already re-starting its nuclear plants. It is time for all of us to also stop running away scared from nuclear power.