Batteries
When you decide that you are going to use battery storage it is important to decide where your battery storage area will be, while modern batteries are reasonably robust the do need some basic amenities in their accommodation. The area must be out of the weather, not too hot or cold (ie below freezing) and have good ventilation. Charging batteries results in hydrogen gas being produced which is highly flammable and too much of a build up that come in contact with a source of ignition (which can be as little as a lightswitch being turned on and you have a most disconcerting bang! You will also need to be able to get to them easily, that will make it more likely they will get maintained (see later).
One of the (few) advantages of being the wrong side of fifty and not the right side of twenty is that I still have books on alternative energy that came out in the ‘70s and are out of print now. I still have my copy of Wind and Wind spinners by Michael Hackleman and it was this book that advocated the use of 6 volt batteries in series to obtain 12 volts and I have used that system ever since. My first batteries were obtained in 1983 and they were a pair of 138 amphour reconditioned second hand truck batteries and they served me well for 4 years, but they were not deep cycle (Note - deep cycle batteries are specifically designed to survive deep discharge and recharge cycles, but having said that repeated deep discharge will reduce their life). Some time after I commissioned the first set, I put in a second set, the same batteries form the same reconditioner, but they never would hold a charge and when connected in parallel only served to drain the originals. They were certified as OK by the reconditioner, but I was never able to make them work. I suppose this illustrates the first law of battery banks – thou shalt always buy all thy batteries at the same time and install them together.
In 1987 I was offered 8 x 90 amphour deep cycle batteries ex telecom, standby batteries out of a telephone exchange from a friend of mine. They could have been in the exchange for ten years, and my friend had them under his house for five years, by the time I recycled them 13 years later they wouldn’t carry a charge in a bucket but I got pretty good use out of them. In 2000 I inherited some money about the same time that the batteries shuffed off their mortal coils and used some of it to buy 4 x 6 volt 220 amphour deep cycle batteries. They are American – (US2200 made by US Batteries) - generally I prefer to buy Australian but they were by far the best price per amphour that I could get. This gave me 440 amphours of storage, but I got greedy and put on another bank of 4 of the same batteries. Initially I broke the above rule and wired them into one large bank, but the performance was down so I had split them and manually change over the charging lines to keep both banks charged. There are regulators these days that will automatically switch between banks as one becomes charged, they are expensive but I got one (the Morningstar SunSaver Duo 12 volt) but it only lasted a couple of months before refusing to transmit any charge at all to either battery bank. I have a replacement (under warranty) at the moment waiting to be installed and we’ll see how long it lasts.
About 2 years ago just as I had started three months of unpaid “long service” leave several batteries in the original bank had cells collapse, rendering them useless. This necessitated buying in another bank after only 6 years. This was m own fault as I had discharged the batteries to a ridiculously low level (9 volts) and let the electrolyte reach critically low levels before topping up. The result was poor battery life. Thus the second law of batteries is – look after them and they’ll look after you. Check the electrolyte levels at least monthly and give them a wipe over to clean off dust, and don’t discharge them below 12 volts if you can help it. Deep discharge means 12 volts not the 6 to 9 volts I originally thought it did!
Battery Types
Ideally the batteries that you choose for your system should be :-
A. Readily available
B. Low in cost
C. Able to store large amounts of power (amp hours)
D. Easily maintained and
E. Able to be repeatedly cycled (ie charged then discharged) deeply
without harm .
Keeping these criteria in mind lets look at the batteries currently available for storing 12vDC power -
1) Car Batteries - New car batteries are expensive and not well suited to home power storage as they do not take kindly to being deeply discharged . If you are just beginning to experiment with 12v power however second hand and/or reconditioned batteries are cheap and available . Their ability to store power is only average though and they can be subject to unexpected collapse of one of the cells , this is fatal for the battery and it requires replacement .
Working within these problems there is still a place for car batteries in your system when you are starting out . This is especially the case if your system is to be a backup only for mains failure and is not to be your primary power source . This way deep cycling of the batteries is kept to a minimum and their useful life extended . Car batteries are designed for a heavy discharge of a short duration , as when supplying the power to start a car .They are also designed to be kept topped up by the car alternator and when left in a slightly discharged condition can suffer from "sulphation". This is the formation of a film of Lead Sulphate over the plates which interferes with charging and discharging of the battery . It can be avoided by continuously supplying a trickle charge or adding a teaspoon of tetra sodium E.D.T.A ( available from lab. suppliers ) to each cell .
2) Truck or Forklift Batteries (reconditioned) - These are less readily available and more expensive than reconditioned car batteries but they are better adapted for home power system as they are designed to deliver a sustained power output . They hold more power kilogram for kilogram than do car batteries and they stand up to deep cycling better . They have about the same maintenance requirements as car batteries .
3) Deep Cycle Batteries - These are purpose designed and built for home power storage . They are expensive but they are becoming more and more readily available as the interest in alternative energy sources booms . Deep cycle batteries are available alternative energy retailers (see above ) which can be found in most capital cities . They can store large amounts of energy and withstand many deep discharges although their life will be increased by not discharging below 50% of the batteries' capacity . They require the usual battery maintenance .If you have the money deep cycle batteries are the best option .
Battery Maintenance
All lead/acid batteries have a number of points in common as far as maintenance is concerned .
1. Check your batteries regularly for water level and when topping up is required always use distilled water. The water in the battery is either disassociated (into hydrogen and oxygen)or evaporated off but any salts dissolved in the water remain and accumulate over time . This accumulation of salts can reduce the working life of your batteries so prevent it by only using distilled water to replace any losses.
2. Home storage batteries do not get the agitation and vibration that car batteries do , this means they will last longer but it also allows stratification of the sulphuric acid to occur . Sulphuric acid is heavier than water so under the action of gravity and in the absence of agitation it will tend to sink to the bottom of the battery . This means that the
electrolyte solution is no longer homogenous which prevents the battery working to its full potential . This situation can be remedied by periodically fast charging the batteries to the point where "gassing" occurs which is the evolution of hydrogen at the negative plate . The resultant bubbling remixes the sulphuric acid and water without the danger of stirring
up any sediment that jostling the battery would cause. Hydrogen is highly flammable so ensure that there are no sources of ignition where this procedure is being carried out . Even the spark generated when turning a light switch on or off may cause hydrogen to ignite if the circumstances are right .
3. Always make sure that the battery surfaces and terminals are free of dust ,grit , chemicals and corrosion. Dust ,grit and garbage on the surface of the battery can be knocked into the electrolyte solution during checking and this will reduce the batteries life . It can also form an electrically conductive path between the terminals , especially in wet or humid weather , allowing power to be bled off and lost . Corrosion on the terminals will interfere with the transfer of electricity from the batteries to the point of use so clean them regularly and protect them with a thin coating of vaseline.
4. If the water level in the batteries keeps dropping it can mean that your batteries are subject to excessive gassing due to overcharging .This means that your generation capacity is exceeding your storage capacity and the system needs a regulator .
5.Ensure that the plates inside the battery are always covered with solution but do not overfill.
Battery Hints
1.Don't use normal car-type batteries and deep cycle batteries in the same system as they are incompatible .
2.A voltmeter in the system will tell you at a glance the state of charge of your batteries . Another and perhaps more accurate way is to use a battery hydrometer to test the degree of charge in each cell of each battery . It is more time consuming but if done regularly will keep you up to date on the state of your batteries .
