The vast majority of battery banks for solar in India (est. 80+%) are thrown away with between 1-3 years of potential life unrecovered due to poorly designed charging systems.
This is primarily due to the fact that most system providers do not monitor how much energy is supplied to the battery and when. We are seeing solar systems trickle-charging batteries on sunny afternoons when the battery is so heavily discharged that it is starving for lack of a bulk charge. This is so common that is seems to be the rule rather than the exception.
Just so I have this straight. Batteries are being thrown away due to the charging systems not working properly. How would one monitor the amount of charge that is going to the battery--the controllers should have a cut off at the high end and low end of battery's charge. Could you explain more about why the batteries are not charging when they are discharged?
Most batteries in use in India are Lead-Acid batteries. While they are not so trendy these days, particularly for portable products, they still have the lowest cost and the only fully developed ecosystem (in India at least!) for recycling used batteries. Their charging profile is well understood and information is available as Hans mentioned below. Deep discharge should be avoided, but usually happens because of poorly matched PV output with the battery (a basic description on PV design issues here).
Monitoring is easier to build into a controller for a larger system, such as a centralized village microgrid, but can be determined through an accurate measurement of state of charge (SoC). There are many factors which can distort a typical terminal Voltage measurement of SoC, including temperature (common in developing countries!) These distortions can confuse the charge controller into thinking that the battery is more charged than it really is and in worst case, cut off charging prematurely. If that happens, the end user won't know and will use the same amount of power at night, pushing the net state of charge lower every day!
In any case, batteries which are deeply discharged need to be brought back to full charge periodically or else the internal chemistry will develop 'memory' by losing the ability to charge and discharge to and from 100%. To the end user, this seems like a dead battery, which actually starved from not being sufficiently charged often enough. Good controller design solves all of these problems.
Thanks Vincent for raising this issue. Batteries are critical, especially for BOP solar products. Even Boeing 787 Dreamliner was down for quite long because of them. This is in fact another good reason for LA, GOOGLA and other stakeholders to make sure batteries quality takes no second place.
In fact there is no point in having s/panels and LED lasting > 20 years, while batteries fail in a year or so (some even well before), with replacements hard to find too. Based on my local experience even with LA certified products, I believe D.Light's products, especially on batteries, should help establish a minimum serious example to follow. This may be valid both on quality, durability and local 2 years guarantee. In my opinion, batteries "effective" life less than 5 solid years, should not be taken seriously to solve the problems of BOP families. Regards.
The knowledge for battery layout and treatment is known and documented on tons of paper as well as terrabyte of information in the web - free for everybody.
However, as long a a system mainly has to be cheap, nobody cares for the basic rules.
I remember so many discussions with amateur-experts, seriously exited about the loe prices of lead batteries, the chance to deliver payable energy to villagers. Unfortunately, some of them are so exited, that they disregard the thechnical basics. They squeeze lead batteries to a depth of discharge of 70% (sometimes even more), they charge full power when the batteries are already in a critical temperature range and if the batteries are "death" after 2 years, the customers are left allone.
One of the first things I had to learn from my teachers, was "You can not bear cheat the physics - so do not try"