Sunday, December 6, 2015

Last words on rechargeable batteries

My last two posts may have left the impression in some that I am anti rechargeables, which I am NOT.

But it is important to know when and where things belong, and what is the best use and misuse of resources.

If you need to dig out a hole for a mailbox post, you use a shovel. When you need to dig out a basement for a new house, you use a backhoe.

The same is true of batteries.

Rechargeables are great for flashlights you use every day, they'll save you and the planet a fortune in disposable batteries. Same with cell phones, laptops, etc., these are heavily used, every day items. Rechargeables are ideal and the clear choice when they compete against disposable batteries. And yes, disposable batteries can power these everyday items, but it would be foolish to.

Take my flashlight example. Used 8hrs a day, 5 days a week by a security guard working nights, disposables would cost anywhere between $5 and $20 a week, where rechargeables would cost $30 for the next 3 years (including charging costs). An obvious savings.

But, if you only use the flashlight for emergencies, disposables are again ideal and rechargeables lose, and they lose for the following reasons. 1. The life of a rechargeable, used or not, is rarely over 6 years (think of it as rust, but on the inside), so even if it held a charge for that long (it won't) it's still a bad use of a very expensive battery. 2. Disposables keep their 'charge' much longer, and are generally more powerful. That's why we still use them in clocks, watches, smoke detectors and the likes.

Basic rule, rechargeables are perfect for replacing disposable batteries in items that are used every day.

So, you would think that this would extend to cars, except nobody ever would make cars that used disposable batteries.

Again, the boring math comes into play.

Rechargeables have a max life cycle of a thousand or so recharges. That effectively puts a 'replacement battery tax' on the electricity it stores of somewhere around 50%. This means for every dollar you spend charging a battery, it wears out 50 cents worth of the battery. That's trivial for an iPad or iPhone, but hundreds a year for a Prius and thousands a year for a Tesla... on top of the price for electricity itself. Even if the batteries lasted forever and cost nothing, electric cars generally don't break even unless gas prices are over $2.50/g.

Again, there are solutions to this math problem.

First, cheaper electricity would take a lot of the sting out of replacing batteries. People would happily pay $500 a year in batteries if it only cost them $100 in electricity, when in today's world it is more like $1,000. It's possible, but unlikely to happen any time soon.

The costs of rechargeables could drop by 90%, nobody would bat an eye at shelling out $50 a year and paying $1,000 in electricity for charging the car.

Third, my choice and achievable today. Compressed air. It can store a similar power to weight ratios as rechargeables, but it doesn't wear out. It is entirely possible, with today's tech, to build compressed air cars with 100 mile range that refill in 10 minutes, cost less than gasoline cars, and would have useful life spans of 20-40 years.

Now, one stumbling block is it loses/wastes a lot of stored power with a cryogenic effect (compressed air, when it decompresses, is cold, sometimes cold enough to form dry ice). This waste can be harnessed to nearly double the range/efficiency of compressed air by adding a stirling, but even without it, it is margineably competitive with rechargeables today and should not be overlooked, especially because it uses none of the exotic materials rechargeables do.

Compressed air would not work well with cellphones, laptops, drills, but like a lot of things, it has a scale where it does make sense.

And the department of energy, unfortunately, knows these thing but, sadly, is a place where math and good ideas go to get buried under political pet projects and connected corporate handouts.

No comments:

Post a Comment