This article was previously published in Marine Renewable Energy.
It was probably only to be expected in a market as young and fickle as energy storage. We spend our time espousing the benefits of battery storage then a study comes to light that puts those benefits in doubt.
Earlier this year, Stanford University researchers Charles Barnhart and Sally Benson decided to find out what storage technologies are the most energy efficient, or to put it simply: how much energy do you need to put in, in order to get it back?
Their Global Climate and Energy Project, called On the importance of reducing the energetic and material demands of electrical energy storage, was published in the Royal Society of Chemistry’s Journal of Energy & Environmental Science. The researchers made a comparison of pumped hydroelectric storage, compressed air energy storage, and lead-acid, lithium-ion, sodium-sulphur, vanadium-redox and zinc-bromine batteries.
The criteria in each case was looking at how much energy it would take to produce the technology, compared with the amount of energy it could store during a 30-year lifespan. The greater the ratio of energy stored to energy expended, the better the option the technology would be, over the longer term. The report found that pumped hydro gave by far the best return in terms of energy stored to energy expended, with a ratio of 210.
The best lithium-ion batteries, by comparison, only managed a score of 10, while the worst batteries, lead-acid, only score two. The reason for such small ratios is the relatively small number of recharge cycles. Lithium-ion batteries can handle at most around 6,000 cycles and lead-acid batteries only 700, compared to more than 25,000 cycles for a pumped hydro project. Fair enough, so far. But what does this all mean?
John Petersen, a partner in the law firm of Fefer Petersen & Co, which focuses on services for manufacturers, innovators and investors in the energy storage and renewable energy sectors, took the analysis a step further.
In a blog for the investor website Seeking Alpha, he combined data from the Stanford report with material from a 2010 Argonne National Laboratory report titled A Review of Battery Life-Cycle Analysis: State of Knowledge and Critical Needs. What emerged is confirmation that for many battery technologies you have to put almost as much energy into creating the technology as it will be able to give back over its entire lifetime.
“The implications are staggering, but they’ve been completely ignored by clean energy advocates, policy-makers and investors alike,” Petersen said. “Everybody focuses on what batteries can do, but nobody pays attention to the embodied energy costs.”
He continued: “In the last century people used small amounts of battery capacity for high value applications, so nobody really cared if the manufacturing process used 2 kWhe of energy to make a cellphone battery….
“In this century … advocates discuss kWh-scale batteries for electric cars and MWh-scale batteries for renewables integration without considering the massive front-loaded primary energy investment that battery manufacturing requires.”
His conclusion, summarised in the title of the article, was: “Batteries are too valuable to waste on solar power integration and electric cars.”
Does this mean there needs to be a rethink around the use of battery storage for renewable energy integration? It depends. First of all, it is unclear from the published material whether the energy costs of battery manufacture are immutable or are likely to drop significantly owing to improved manufacturing processes and economies of scale.
Second, while it is true (as Petersen points out) that most battery manufacturing currently relies on processes that use energy from diesel, coal, gas and other non-renewable sources, this will not necessarily be the case forever.
Mining companies, for example, are at the forefront in the adoption of renewable power sources such as solar and wind, since their operations are frequently far from grid lines, in places where non-renewable energy costs are high. If battery manufacturing can derive its initial energy inputs from renewable sources, does it matter whether batteries consume almost as much energy as they can deliver?
Third, there is still a question mark over the extent to which renewable power production will lean on energy storage in general, and batteries in particular. Right now many large industrial concerns are rushing to commercialise grid-scale battery arrays but the actual level of deployment is still low, with projects to date mostly using storage on a tactical basis.
Alongside these, many utilities are building out smart grids that will help more renewable energy be used at the time it is generated, rather than it having to be stored. Batteries may become important, but that does not necessarily mean they will be widespread.
With all that, though, it is also clear that right now it probably makes more sense for renewable energy to stick as far as possible to tried-and-tested forms of storage, such as pumped hydro, to be assured of the best return. No big deal: pumped hydro still pretty much represents the status quo in energy storage.
Where perhaps the Stanford research could justifiably cause more consternation is in the electric car market, since that has very significant growth ambitions. As we have discussed previously, car batteries might end up forming part of the energy storage solution for marine renewables.
Whether this study and the economics underlying it carry enough weight to change the way the auto industry is heading, and perhaps favour alternative power sources such as hydrogen, very much remains to be seen.