Batteries for Load Balancing and Locomotion

I read through the middle third of Schallenberg’s "Energy in a Bottle" today, which focused primarily on the use of lead-acid batteries as electrochemical transformer devices and short term storage for load balancing in the early days of the electrical distribution industry. As the AC vs DC debate raged around the end of the 19th century, it was found that large scale AC distribution systems could easily incorporate existing DC systems by using the AC to run a motor/generator set. Efficiencies above 90% were possible, which wasn’t too far off the AC transformers of the day. It reminded me of a suggestion I made back in the early 90’s to an engineer who had charge of a large PV pilot installation on a school roof, on the order of 100 kW if I recall. The project was rusting away because the inverters had failed early on, and the money (grant) wasn’t their to replace them new solid state inverters. I suggested adapting a surplus motor/generator set, but he rejected the idea out of hand thinking it inefficient and I suspect, not sufficiently elegant for a PV installation.

Schallenberg wrote on the subject of using batteries for anything other than energy storage, "Despite their illusory simplicity, storage batteries are inherently expensive devices, both in capital and maintenance costs. Electromechanical or electromagnetic devices are almost always cheaper and better than electrochemical ones, if both can be used for the same function." It’s also interesting to note that lead-acid battery capital costs don’t seem to move at all, with whatever minor price reductions we may see coming from more efficient retailing rather than manufacturing. Power tool prices have dropped like a rock in my lifetime, by well over 50% on average, while battery prices have remained fixed.

The early generation and distribution engineers soon discovered that sizing systems with an inconsistent load led to tremendous inefficiencies (i.e., costs). R.E.B. Compton coined the term "load factor" which was defined by the average demand over the peak demand, and found to his dismay that the load factor on any given day for some installations was as low as 5%! Batteries were used as a temporary solution to this problem is some places for a few decades, but improvements in loading (round the clock demand) combined with other electromechanical fixes made them an expensive option.

At the dawn of the automobile, the most promising application for storage batteries seemed to be trolley cars. Although these systems had been tried with miserable results for decades, the rapid growth of cities and the inability of horse draw trolleys to keep up with demand helped the idea current. In the end, electric trolleys were a big winner, but the power source was overhead wires or conduits. Schallenberg wrote, "Therefore, the chief reason that the battery car turned out to be almost as expensive to run as the horsecar is the battery suffered from the same technological limitation as the horse… The cars needed to go faster and carry more passengers as the cities expanded. The horses could not do this without shortening their lives to an unprofitable extent."

The main failure mechanism of these batteries was the peak demand put on them during acceleration. Drawing too much current from a battery, any battery, will adversely effect it’s life. Trolley requirements did bring about the development of the deep discharge battery, essentially a heavy duty version of the lead acid battery that could be exhausted without great harm, though at a cost of a heavier battery and greater size. These same problems remain with lead-acid battery systems if used to build an electric car today, though I wonder if some of the peak demand couldn’t be addressed with lightweight super capacitors.