Excellence By Design

Salvaging Prius Batteries

There are some wrecked Prius hybrids at the local salvage yard, and I can get their battery packs cheap. Can I put two or three of these together to power my pure-electric conversion?

John McElhattan • Fresno, California

Bundling these battery banks is not recommended, for a few reasons. The battery pack in the Prius (or any of the other hybrids) does not have the capacity for much range by itself. Even at low speeds in pure-electric mode, the Prius has only about 2 miles of range before the gas engine starts up to recharge the pack. So you would need a lot of packs to get any decent range.

Also, these batteries are not intended to be discharged very deeply. They were specifically designed to work with a gas engine frequently topping them off. In a pure electric vehicle, you need batteries that can tolerate being deeply discharged before getting recharged.

You would also need the battery management system that is part of the Prius's computer brain. While these battery packs are perfectly safe in the Prius, if they are installed or managed improperly, they can catch fire, which some tinkerers have already had the misfortune to experience.

Prius batteries work great in the original vehicle's system. There are other batteries that are better suited to a pure-electric conversion.

Mike Brown & Shari Prange • Home Power Transportation Editors

Horse Power

A local draft horseman has asked me whether a farmer, using what is at hand, could design and build a horse sweep capable of turning a generator and thereby producing electricity for his household and farm. Have you heard of such a thing?

Ted Smith • Quincy, Illinois

The short answer is: Yes—it is possible to produce electricity using draft animals. Realistically, however, it would probably only make sense if you already own a horse and are interested in combining a regular exercise regimen (for both the animal and the owner, as it turns out) with generating a modest amount of electricity.

The amount of power a horse can generate on a sustainable basis is—you guessed it—one horsepower (746 watts). For various reasons, both practical and humane, we probably don't want to use this system for more than one or two hours per day. At this rate, after taking into account losses in the entire system (mechanical and electrical), we might expect to generate 500 to 1,000 watt-hours (0.5 to 1 kWh) per day.

Now let's deal with the fine print—there are some energy costs to horse power. First of all, horses need to be fed. The best possible scenario is one in which the animal collects all of its food with no help from the owner. That's unlikely, so the energy it took to grow the food and feed the horse needs to be subtracted from the generated output. Next, horses produce a lot of manure—figure on 100 pounds per day as a good start. Unfortunately, while a horse might be able to eat on its own, it does a pretty poor job of cleaning up after itself. And the horse will be depositing its "exhaust products" in a very limited area when generating electricity (unlike the case when it is working in a field, for example). So the task of cleaning up falls squarely on the owner—along with harnessing and unharnessing the horse each day.

So this concept, while possible, will demand a significant amount of work from both the horse and the owner. When all is said and done, the owner may end up consuming and expending more energy (lights, water pumping, hauling of manure, etc.) than is supplied by the horse! An argument can be made either way, but personally, I say, "Neigh!"

Dominic Crea • Institute for Sustainable Energy & Education

"Even at low speeds in pure-electric mode, the Prius has only about 2 miles of range before the gas engine starts up to recharge the pack."

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