Useful chart comparing bang for the buck of various battery technologies

The other day, some other curious people and I ran numbers comparing the per-kWh price of the Tesla Powerwall & Powerpacks (the utility-scale battery options described on the bottom of this page) with top competitors on the market. Admittedly, that was too simplistic a comparison. The kWh rating provided for all of these products is simply the maximum amount of electricity they can store at one point in time. So, in the case of the Powerwall, 7 kWh means that the battery can hold up to 7 kWh of electricity at one time, similar to how a 5-gallon jug of water can hold up to 5 gallons of water.

You have to multiply that capacity rating by # of cycles (# of times the battery will be filled up and then emptied), depth of discharge (whether the battery can be fully emptied during each cycle or needs to be only 80% emptied, 70% emptied, etc), and efficiency (how much electricity is actually transmitted, not lost, in each cycle), and then divide by price to determine a per-kWh price for all of the kilowatt-hours your system is expected to produce… before degrading to 80% of its rated capacity, that is (at which point it’s actually still useful, but that’s apparently the global standard for “end of product life”).

As you can see, there are a number of assumptions you have to make to perform these calculations, and even if all of your assumptions are correct, it’s not like the products are completely dead at the end of the studied time period. This also leaves out operational costs (which we’ll assume to be $0 in the calculations below).

Anyhow, this is the best method I’ve found for comparing Tesla’s Powerwall and Powerpacks to top products on the market. More importantly, on the residential side, the numbers should help a consumer to evaluate the cost-effectiveness of getting a Powerwall (should you get commercial access to one) — that’s the main aim in the next section of this article. Note that I’ve actually left out “competing” lithium-ion and lead-acid batteries in the residential section. Basically, even at a glance, it’s clear that they don’t compete with the Powerwall, so I didn’t bother finding all of the specs and doing the calculations. If you want to do so for any particular battery, I’m happy to add the info in, but I’ll need links or company spec sheets indicating cycle life, expected DoD, efficiency, and price in order to do so.

With a ridiculous amount of help from three wonderful CleanTechnica readers, below are the assumptions and results, split into a “residential” section and a “utility-scale” section.
Residential Battery Storage — Tesla Powerwall x 4 vs Aquion Energy x 2 vs Iron Edison x 1

Subheading have you confused? I ran the numbers for 4 Powerwall purchase scenarios, 2 Aquion Energy products, and 1 Iron Edison product. Since the intro above was too long already, I’ll jump into the table first and list some of the takeaways and the assumptions underneath it:
http://cleantechnica.com/2015/05/09/tesla-powerwall-powerblocks-per-kwh-lifetime-prices-vs-aquion-energy-eos-energy-imergy/

The End Of The Lithium-Ion Era?

Lithium-ion technology is still the gold standard for energy storage as demonstrated by the popularity of the new Powerwall battery, Tesla Energy’s much-publicized foray into Li-ion energy storage for homes and businesses. However, some new technologies are sneaking up behind. In the latest development, lithium-sulfur batteries could benefit from a new “designer carbon” engineered by a team of researchers at Stanford University.


Li-S energy storage has important advantages over Li-ion in terms of cost, energy density, and toxicity, but until recently, some major drawbacks have stymied the development of Li-S batteries.

One solution crossed our radar back in 2013, when researchers at Oak Ridge National Laboratory developed a sulfur-enriched cathode (our sister site Gas2.org also took note).

In other developments, the University of Arizona has also been developing a method for converting waste sulfur to a lightweight plastic that could be used in EV batteries. Last December, researchers at Cambridge University came up with a graphene-based solution, and earlier this year, Drexel University announced that it has been leveraging its experience with MAX phase ceramics to push the Li-S envelope.

The new Stanford findings add more fuel to the energy storage findings. The team tested its new designer carbon material under real-world conditions in lithium-sulfur batteries and supercapacitors (supercapacitors are energy storage devices that charge and discharge rapidly).

For supercapacitors, the results were “dramatic,” with a threefold increase in conductivity compared to electrodes made with conventional activated carbon. Power delivery and stability also improved.

More to the point, the results showed a promising pathway to improving Li-S battery performance, as the designer carbon was able to trap lithium polysulfides, an undesirable byproduct from the interaction of lithium and sulfur.

The new material’s relatively low cost and easy fabrication method are added pluses. You can get all the details from the published study in ACS Central Science under the title “Ultrahigh Surface Area Three-Dimensional Porous Graphitic Carbon from Conjugated Polymeric Molecular Framework.”

You might not see much in the way of competition for Li-ion market share yet, but stay tuned.

Why Natural Is Not Better, Energy Storage Edition

The new designer carbon material could have a variety of applications, but the Stanford University team has zeroed in on the energy storage potential, particularly in respect to lithium-sulfur (Li-S) batteries.

The new material is actually a synthetic form of bio-based activated carbon. For those of you new to the topic, activated carbon is a common material that shows up in water filters and deodorizers, among many other things — but not energy storage devices, at least not yet.

Inexpensive forms of activated carbon are typically made from coconut shells, which involves a lot of high-temperature processing and chemical finishing. The result is a material rich in nanoscale pores, which gives it a high surface area ideal for storing electrical charges.

However, this “natural” form of activated carbon falls flat in terms of transporting a charge, partly because there is little connectivity between the pores. Here’s lead researcher Zhenan Bao describing the problem:

With activated carbon, there’s no way to control pore connectivity. Also, lots of impurities from the coconut shells and other raw starting materials get carried into the carbon. As a refrigerator deodorant, conventional activated carbon is fine, but it doesn’t provide high enough performance for electronic devices and energy-storage applications.

As a workaround, the Stanford team created its own synthetic sheets of carbon from a hydrogel polymer (hydrogel is fancyspeak for a class of super-absorbing “smart” materials). To activate the material, they added potassium hydroxide, which also increased its surface area.

The result is a carbon material with characteristics that can be controlled in two ways: by using different polymers and organic linkers, and by changing the temperature of the fabrication process.

Here are a couple of snippets from the new study:

For example, raising the processing temperature from 750 degrees Fahrenheit (400 degrees Celsius) to 1,650 F (900 C) resulted in a 10-fold increase in pore volume.

Subsequent processing produced carbon material with a record-high surface area of 4,073 square meters per gram – the equivalent of three American football fields packed into an ounce of carbon. The maximum surface area achieved with conventional activated carbon is about 3,000 square meters per gram.
The End Of The Lithium-Ion Era

Li-S energy storage has important advantages over Li-ion in terms of cost, energy density, and toxicity, but until recently, some major drawbacks have stymied the development of Li-S batteries.

One solution crossed our radar back in 2013, when researchers at Oak Ridge National Laboratory developed a sulfur-enriched cathode (our sister site Gas2.org also took note).

In other developments, the University of Arizona has also been developing a method for converting waste sulfur to a lightweight plastic that could be used in EV batteries. Last December, researchers at Cambridge University came up with a graphene-based solution, and earlier this year, Drexel University announced that it has been leveraging its experience with MAX phase ceramics to push the Li-S envelope.

The new Stanford findings add more fuel to the energy storage findings. The team tested its new designer carbon material under real-world conditions in lithium-sulfur batteries and supercapacitors (supercapacitors are energy storage devices that charge and discharge rapidly).

For supercapacitors, the results were “dramatic,” with a threefold increase in conductivity compared to electrodes made with conventional activated carbon. Power delivery and stability also improved.

More to the point, the results showed a promising pathway to improving Li-S battery performance, as the designer carbon was able to trap lithium polysulfides, an undesirable byproduct from the interaction of lithium and sulfur.

The new material’s relatively low cost and easy fabrication method are added pluses. You can get all the details from the published study in ACS Central Science under the title “Ultrahigh Surface Area Three-Dimensional Porous Graphitic Carbon from Conjugated Polymeric Molecular Framework.”

You might not see much in the way of competition for Li-ion market share yet, but stay tuned.

http://cleantechnica.com/2015/05/31/new-designer-energy-storage-breakthrough-packs-3-football-fields-1-ounce-carbon/