Are small batteries the future for hybrid cars?

By Paul Lucas | 27 September 2011, 21:01 BST

28 September 2011

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Are small batteries the future for hybrid cars?

Small battery packs could offer more social benefits in the near term than large battery packs with longer electric range.

That’s the verdict of a new study by Carnegie Mellon University’s Jeremy Michalek, who determined that small battery packs could promote the adoption of hybrid electric vehicles and plug-in hybrid electric vehicles, ahead of plug-in hybrids and battery electric cars with larger battery packs.

According to Michalek, the study assesses how much externality damage reduction plug-in vehicles can offer in the US and at what cost. It gathered data on the quantity and location of emissions released from exhausts; the externality costs of damages caused by these emissions; and estimated other costs associated with oil consumption.

It then estimated lifecycle emissions damages for comparable new mid-size vehicles, including: a conventional vehicle; hybrid electric vehicle; plug-in hybrid electric vehicles with battery packs sized for storing enough range for 12miles and 37miles; and a battery electric car with a 149mile pack.

Under an optimistic scenario, the study suggested that plug-in vehicles with large battery packs could offer lower damage at lower lifetime costs – while under a pessimistic scenario, using low petrol prices, shorter battery life, and coal-powered charging; plug-in vehicles could produce more damages at a substantially higher cost.

As a consequence the report suggests that large battery packs offer the highest emissions and oil consumption reductions at the lowest cost but result in high costs and increased damages if not all the right factors fall into place. By contrast, hybrid electric vehicles and plug-in electric vehicles with small packs are robust and provide emission reductions at a lower cost with less infrastructure investment.

It points out that in the future, if there are sufficient decreases in battery costs and increases in petrol prices, the market may drive adoption of vehicles with larger battery packs. However, until then, a policy that focuses on small capacity hybrid electric vehicles and plug-ins may be more beneficial per dollar spent.