Friday, May 01, 2009

Batteries and Oil to Solar

Talk on twitter last night got on to the topic 'oil to solar'. I think the topic needs a post about batteries just to make things more informed and complex.

The are 3 battery types I wish to expend on. What I call electrochemical, potential energy and thermal.


These are what we normally think of as batteries. It covers many chemical reaction the produce electrical current. They are all example of Galvanic cells. The two most common are the Lead-acid battery used in cars and the ubiquitous Alkaline battery of screaming children on Christmas day fame. Some are rechargeable, some aren't.

In some application, like electric cars, where size and weight is an issue there a many exotic reactions under consideration. Being exotic, cost and rarity become an issue for wide spread application becomes.

At the other end of the scale is the Nickel-iron battery. An old, bulky and relatively benign chemistry that uses cheaper common materials.

Potential Energy

This type of battery system is not common, but where the situation is right, it can be very large store of energy. It involves two bodies of water at different heights (the bigger the difference, the better). Water is pumped from the low storage to the high storage when excess power of available. When power is needed the water is allowed to return to the lower storage, generating hydroelectric power in the process.


These are systems where energy is store at heat. The simplest example is a well design fireplace. A single evenings fire can stores enough heat is the mass of the fire place to keep a well insulated rooms temperate elevated for 48 hours.

I divide these systems into Low temperature differential (LTD) and High temperature differential (HTD). LTD is where the store's temperature is less than 100C above ambient and HTD is where it's greater than 100C above.

A example of a LTD system is a Solar pond. An idea battery for providing heat to industrial processes like desalination. Electricity can also be generated using LTD heat engines.

A example of a HTD system is a Molten salt thermal system (not to be confused with Molten salt electrochemical batteries). There are many salts and these many temperature ranges to play with here. Right up to like 1600C, which start to made designs trickier/more expense, since common materials like iron & steel also melt at these higher temperatures.

Hope this gives people an idea of the range and have exotic battery systems can get.