Thursday, May 3, 2012

On solar power


While I was living in my house last year, I had a small solar panel charging an old car battery through a cheap charge controller. It was a very basic photovoltaic system that was used to power an audio amplifier and to charge my phone . The panel was only 15 watts but it seemed to do the job. Part of my vision of the house is to have it be off the grid, even if I can plug in easily. I have always planned to have a couple hundred watts of power coming from a set of solar panels and a small wind turbine to help supplement the charging on cloudy windy days. A dream would be to be located near a stream and get some power from a micro hydro turbine.

Whatever the source is, storage of electricity is always an issue. The most common storage device for off grid power installations is a bank of lead acid batteries- similar to what is in your car. Car batteries are easy to find for free, but unfortunately they are designed to provide a huge amount of current for a sort period of time to start your car. They do not take well to being discharged over 20% of there capacity more than a few times. The proper type of lead acid battery is deep cycle. These are used in some marine applications, golfcarts and some battery backup applications. These batteries are expensive, heavy and still cant be discharged fully without harming them. I thought I might just have to bite the bullet and do it when the time came... Until a friend living off the grid in vermont told me about another option. NiCd train signal light batteries.

These are the same type as the small sealed rechargeable batteries in drills and old phones, but they are bigger and unsealed. They have a lifespan of up to 30 years, can take a huge amount of abuse, can be fully discharged and really don't care if they are overcharged. Sounds perfect right? Unfortunately they are usually prohibitively expensive. They are really only used in backup applications for aviation and train systems where the durability and lifespan is worth the investment.


As my friend suggested, I walked into the local train yard and started asking around. They often replace these on a fixed schedule so that they know that there is always a good battery in a critical application. Sure enough, they had several pallets of them and the engineer was happy to sell them to me for pennies. Now I am the proud owner of 36 1.2 volt Edison (as in the company that Thomas Edison started!) NiCad cells with a 240 amp-hour capacity. In layman's terms, they are huge!  When I got home I checked the voltage and every cell seemed to be holding a charge. I will have to do some reconditioning and more testing on them, but it seems that my battery worries are over! For those of you interested, I will be posting everything I do to them and the test results.

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