Modernizing the Electric Grid And its Integration with the Transportation Sector

By Bill Brandon

Special to The Digest

Germany is a recognized leader in renewable electricity. Their Energiewende law set ambitious goals for renewables but may be stalling out because of infrastructure insufficiencies. Germany curtailed 1581 gigawatt-hours of green energy in 2014. PV penetration levels are unsustainable with curtailment increasing an average of 100% every year. This curtailment only represents a small percentage of renewable energy, but still costs about US$94 million for undelivered electricity. This does not include planned curtailments in wind power. Distribution operators are projected to spend US$11.8 Billion over the next 10 years for grid optimization and high voltage transmission lines. This figure does not include funds from the 2009 Power Grid Expansion Act, which is expected to be 40% finished at the end of 2016. The government reports that energy storage is not likely to be the primary resource for grid balancing with demand management playing the greatest role.

Obviously just harvesting intermittent renewable energy is not enough for greening our energy sources. What can we learn from Germany? I was honored a couple of weeks ago to be invited as an expert to a workshop on sustainable transportation sponsored by ASU and the New America Foundation. One topic of discussion was the integration of the transportation sector with the electrical sector. There were varied opinions on this, but a significant number did not believe that PEVs were the answer. While it might sound good, the devil is in the details. Some, like Mark Z. Jacobson, assert battery electric vehicles (BEV) are “the key transportation solution”. Although he is a respected researcher in climate and atmospheric modeling, he has often not shown much knowledge or foresight in his assumptions. I will address this issue shortly.

Greening the grid

Just deploying BEVs does not guarantee they will be clean. The Dutch effort to push BEVs resulted in an increased need for coal generation. While one can rationalize a solution to this, changing human behavior to accomplish it is another thing. The Internet of Things will not necessarily change human behavior to the good. In addition, BEVs do not dovetail well with existing infrastructure and manufacturing capacity. Other options exist for integrating transportation with the electric grid. Primary among these is the production of hydrogen, although other pathways are being sought. (See here. Note ‘Electro Fuels’).

The idea of using hydrogen to power fuel cell electric vehicles (FEV) has been around a long time, but starting up both a fuel side and a vehicle side simultaneously is a bit of a conundrum. Germany is experimenting with another approach by producing methane from waste CO2 and H2 produced from excess renewable power capacity. Storing electrons by producing H2, which is then attached to carbon, is a simple and elegant approach. It doesn’t need to be methane as it can be methanol or hydrocarbons. The simplicity of storing and transporting a liquid fuel cannot be ignored. It can also be more efficient. It doesn’t need to be compressed and stored in robust tanks. Liquid fuels are beautifully simple. So let’s look at efficiency.

Some people believe that BEVs will become a wide spread means of transportation; others think they will only have a limited use market. An understanding of the fundamentals of battery storage is necessary to understand the limitations of BEVs. When charging or discharging a battery, heat is created. The amount of heat depends on the rate of charging or discharging. Batteries for vehicles have a built-in cooling system. When charging or discharging at high rates this cooling system requires active cooling (like an air conditioner) that requires power to operate. This is why electron-to-electron energy storage is often not efficient.

If a BEV is charged at night with renewable electricity from a PV array, this inefficiency is increased, as energy must be first collected using something like an Elon Musk ‘power wall’. It is then discharged to charge the BEV battery before it is discharged for vehicle use. This method of charging small cars being driven only 35 – 50 miles per day may be acceptable but limits the use of the car. If vehicles are used more than this and especially for longer trips over 200 miles the charge cycle becomes an issue. Either trips must be interrupted for long charging times or battery charging efficiency really drops with fast charging.

Looking at the Hard Data

The following chart compares a Ford Focus BEV with a Ford Focus with an IC engine. It is a forward looking comparison using presently existing technologies not necessarily commercially deployed. It also assumes increased accessory draw required by more sensors and potential auto-drive technology. The BEV has a 23 KW battery or a theoretically expanded 70 KW battery similar to a Tesla. The I4, 1.6 liter engine is similar to the Ford Eco Boost turbocharged available today except optimized for a 100 RON fuel with a 1400 BTU/Gallon latent heat of evaporation (E30).

It is also assumed that it is a light hybrid where a battery is charged using waste heat similar to a system developed by Ricardo. Weight and range information is from Ford Motor Company. Weight penalties are from a Ricardo light weighting report from 2008. Battery charge/discharge information is hard to get from OEMs. I have relied on information obtained from a Tesla owners chat room and other basic scientific battery data. Electrical generation efficiencies are the best presently under development (combined cycle gas or Allum cycle gas generation). The fuel production and delivery is a standard figure that might be a bit high, depending on geography.

From the chart it is apparent that a modern IC engine with a modern high octane fuel can compete with a BEV on short trip efficiency and significantly out perform a BEV for longer trips. This analysis is based on total thermal efficiency only. GHG emissions are another, more complicated, matter. Generation from a 60% efficient gas generator is only a technical possibility now being demonstrated and other sources of traditional generation would result in a significantly larger carbon footprint. Electrical generation from a renewable source is a possibility, but sufficient development for a meaningful impact on transportation is a long way off and in the mean time applying those technologies to green the grid will be more efficient and more impactful. Low carbon fuels, on the other hand, already comprise over 10% of road transportation fuels and the technology is available to rapidly expand their market share. 

This analysis applies only to BEV vehicles. Fuel cell electric (FEV) vehicles are better, but the weight of a robust compressed hydrogen fuel tank and fuel cell will also carry a weight penalty. Energy necessary to compress hydrogen and present moderate efficiencies from fuel cells will also lower efficiencies. Assuming generation from a renewable electric source, total efficiencies might be about 31% – 38%.

Is hydrogen better?

A forward thinking review might suggest that hydrogen production could be a better interface with the electric grid. It could be a variable demand source taking excess capacity at varying times unconnected to drive convenience and leveling the grid balance. This would particularly apply to wind energy where production costs are already low and there is significant excess capacity potential.

Hydrogen production as a buffer method for the grid is a flexible platform that can be used in three ways:

1) It can be a second or third tier of grid resilience because it or produced liquid fuel can be used to produce electricity.

2) It can be used as hydrogen for transportation fuel cells.

3) It can be combined with waste CO2 to make liquid fuels.

This third use is often neglected or not known. Liquid fuels are advantaged because they are easy to store or transport with a low cost and energy efficient infrastructure. They may also prove to be a less costly way to modernize the grid, provide resilience and utilize intermittent renewable capacity.

A related discussion can be found here.