8/12/2019 Fact Sheet Batteries

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what are they?what are they?what are they?what are they?They are units containing combinations of metalsand chemicals, between which occur reversiblechemical reactions to store and provide electricalpower. We will focus on lead-acid batteries, whichform the heart of many off-grid, or hybridrenewable energy systems. Although otherchemical reactions can provide more electricity,

the lead-acid battery is the most successful,because of its affordability, availability, andbecause it is so robust. A basic lead-acid batterycomprises 3 elements - a collection of positiveplates, a collection of negative plates and a liquidor gel electrolyte. In a lead-acid battery, the activematerial of the plates is lead oxide, and theelectrolyte is dilute sulphuric acid. In a dischargesituation (when giving out energy), elements ofthe electrolyte react chemically with elements ofthe plates to release electrons. The flow ofelectrons through a conductor is electricity. Whenbeing charged, the reaction is reversed and thebattery absorbs electrons.Alessandro Volta (who gave his name to the volt)invented the first electric battery in 1800. Hisplates were of copper and zinc, and theelectrolyte was brine. The technology has beenconstantly improving since then, and now thereare many different kinds of battery, includingnickel-cadmium and lithium. But lead-acid are stillthe most popular, because of their bulkmanufacture and 2nd-hand availability. 

There are 3 kinds of lead-acid battery.gel: the electrolyte is in a gel form. They are usedmainly for emergency standby, and are no good ina cycling (charge/discharge) situation.glass mat: the electrolyte is held within a soakedglass mat between the plates. They are better

than gel batteries for cycling, butover time, anomalies will develop between the

individual cells as regards voltage and state ofcharge. They are used in situations where a liquidelectrolyte might spill.flooded battery: contains liquid electrolyte - thebest type for a renewable system. They need tobe topped up with distilled water from time to time.

what are the benefits?what are the benefits?what are the benefits?what are the benefits?The main benefit is for people who are off-grid. Ifyou're building a renewable electricity system,you're not looking to use electricity as it'sgenerated - the sun won't be shining all the time,

and the wind won't be blowing all the time(although if you've got micro-hydro, your stream isprobably going to be flowing all the time), andyou'll need more electricity at some times thanothers. So you'll need to store it. If you're not onthe grid, that means batteries. There is a strongenvironmental case for saying that if you can havea grid connection, then you should have one, anduse the grid like an enormous battery, as theinfrastructure is already there. Also, batteriescontain lots of noxious metals and chemicals - sothe fewer of them the better.A second benefit, however, is not environmental,it's about energy independence. Many peoplewant to be sure that they are in control of theirenergy supply all the time. They don't want to givemoney to giant electricity companies, or risk

24 x 600 amp-hour, 2-volt cells wired in series

testing the specific gravity of the electrolyte ina cell with a hydrometer

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