The expensive part is the battery
A solar home system studied by engineers at the University of Oxford is a 50 watt panel and a 12 volt battery, running lights, a phone charger, a fan and sometimes a television, all of it drawing under 8 watts. Ask most people which half costs more and they say the panel. It is the battery, at over 80% of the total, and it is usually the first part to fail.
Why it dies
The battery dies from corrosion. In most of these systems the battery sits nearly full for long stretches. Sitting at a high state of charge means sitting at a high voltage, which corrodes the plates inside. Corrosion turned out to be the dominant ageing mechanism in every use pattern except the heaviest.
That finding came out of real hardware rather than a laboratory. A separate study followed 1,027 lead acid batteries on solar systems across Africa south of the Sahara, each for 400 to 760 days, and collected 620 million readings of current, voltage and temperature. From that alone the researchers could flag a battery about to fail with 82% accuracy at the point of failure, and 73% accuracy 8 weeks ahead, with no extra equipment on the box.
What happens when it dies
The regulated market is roughly 30% of the total and mostly lithium. The rest is unregulated and mostly lead acid. The share varies widely by country, from 97% regulated in Rwanda to between 28% and 40% in Tanzania.
Show the numbers
| Regulated, lithium | 30 |
| Unregulated, lead acid | 70 |
About 30% of the off grid solar market is regulated and mostly runs on lithium. The other 70% is unregulated and mostly runs on lead. Lead acid is cheaper to buy and, in principle, easy to recycle, which is why it is still everywhere in low income countries. The trouble is where the recycling actually happens.
The 2 bars are the ends of 1 estimate, not 2 findings. The authors say the true figure is likely in the upper part of the range. This article does not pick a number for them.
Show the numbers
| Low estimate | 13 |
| High estimate | 47 |
The Center for Global Development estimates that off grid solar now accounts for somewhere between 13% and 47% of all used lead acid battery waste in Africa south of the Sahara, and thinks the true figure sits in the upper part of that range. Most of that recycling happens in backyards or in substandard plants, where up to half the recoverable lead escapes into the soil. About 4 in 10 children in the region already have blood lead above the level at which the World Health Organization says to intervene.
Safe recycling is expensive and that creates a strong incentive to do it unsafely.
Lee Crawford, senior research fellow at the Center for Global Development. Source 5.
What would actually fix it
The cheap half of the fix is the charging voltage. The Oxford engineers showed that changing how the charger holds the battery, so it spends less time sitting at high voltage, extends its life by 25% without the household noticing any difference in the power it gets. That is a software change to a device that already has a cellular connection.
The other half is safe recycling. It costs money that nobody currently pays, and the products tend to die after their warranty runs out, which is exactly when a take back scheme stops caring. Globally, off grid solar produced about 10,000 tonnes of electronic waste in 2020, against more than 50 million tonnes from everything else. It is a small share of the rubbish and possibly half the lead.
This is a silent threat. It's often invisible, but it affects health, cognitive development and economic productivity.
Lee Crawford, senior research fellow at the Center for Global Development. Source 5.