Energy consumers will hear more about the idea of energy density. That is the amount of energy that is stored in a particular area per unit of volume. In other words, an exceptionally large space that contains little ability to make energy is low density. A small volume that can create a lot of energy is high density. Nuclear fuel, for instance, is high density. Lots in a little space.
“I look at density as ‘energy delivered,’” said South Carolinian Jim Little, principal, nuclear energy advisors, an industry consulting firm. “How much resources are used to generate electricity? For instance, the nuclear plant on Lake Norman (NC) has several hundred acres to make its power. Solar panels making the same power would have to cover all of Lake Norman – a lot more space. And, the output of the panels would have to improve since they only make power 8 to 10 hours a day. This doesn’t include the provision of required energy storage for hours when solar is not available. The best battery technology available today for that level of storage falls orders of magnitude short.”
Consumers may hear more about the idea of energy density soon – September 22 – as Elon Musk celebrates what Tesla is calling, Battery Day, which also is the day of Tesla’s annual meeting. The rumblings ahead of this event are about an improved battery. An improved battery can mean higher energy density.
Energy density is noted in watt-hours per kilogram. “For example, the energy density of a standard rechargeable battery ranges from 70 to 100 Wh/kg. This rises to 150 to 200 Wh/kg for a lithium-ion battery and up to 1,500 Wh/kg for some lithium or manganese batteries. This is far lower than the energy density of a liquid fuel, which is around 10,000 Wh/kg.” (Source)
There is this issue on density: Hydrocarbons – gasoline and diesel – have been efficient ways to power vehicles in the past from the standpoint of density and basic cost to consumers. (We know that there are varied ways to measure the ultimate societal costs of fuels, but we will stay basic on density for this overview.)
“The real issue of energy density relates to the capacity of energy storage, to me,” said Jim Little. “Look at batteries – capacity and weight. How much energy can it store and how much does it weigh? Think of how a car is designed to have enough energy so that a tank of gasoline has a range of about 350 miles. That is why a heavy Suburban has a big gas tank and a small car, a small tank to get the same distance from the energy.”
Better batteries can open the door wider for electric vehicles, and maybe even aircraft. Lower costs happen as breakthroughs happen. There are also reductions in overall emissions as the grid is increasingly fed by fewer carbon-emitting sources charging those batteries.
How does this relate to Tesla’s Battery Day?
“Energy density for lithium-ion cells in electric cars has been improving at a rate of roughly 7% a year. But that rule, which has held for consumer cells for decades might be thrown to the wayside if a remark from CEO Elon Musk holds true. He noted that cells with 400 Wh/kg, produced in volume, might be just 3-4 years away.” (Source)
That 7% boost would then be a 50% boost. Big news.
To show how fast the energy and battery industries are changing, take a look at a 2013 Energy Information Agency graph. Here’s is how EIA explains the chart, and it gets detailed:
“The chart compares energy densities (both per unit volume and per unit weight) for several transportation fuels that are available throughout the United States. … The typical fuel economy of an internal combustion engine in a light-duty vehicle is around 25 miles per gallon. On an equivalent basis, electric vehicles with fuel cells powered by hydrogen can double the fuel economy of a similarly sized gasoline vehicle, while battery-powered electric vehicles can achieve a quadrupling of fuel economy, but the costs of fuel cells, hydrogen storage, and batteries are prohibitively expensive to most consumers and the availability of refueling and charging facilities is extremely limited.”
That was 2013. Seven years is a long time in energy technology. One thing changing is energy density. Back in 2013, “In addition, the improvement in fuel economy of these vehicles does not compensate for the lower fuel densities of hydrogen and various battery types like lithium ion, lithium polymer, and nickel-metal hydride batteries that result in limited driving range relative to gasoline-powered vehicles.”
Battery Day may bring in a new look at energy density and performance for vehicle batteries.