Currently, 1.3 billion people live without access to electricity. Most of them are inhabitants of rural regions in developing south, that don’t have connection to the electricity grid. 
Fortunately, clean energy technologies have been reaching these people more and more in the past years. Mostly, but not only, in Bangladesh, a renewable energy revolution is taking place: the emergence of small scale solar-home-systems that supply electricity for lighting, cellphones and household appliances - in Bangladesh alone, there are already over 5 million solar-home-systems installed! These system feature a small PV panel with a charging controller and a battery (The solar home systems are usually financed with a micro loan from a microfinance institution, because its owner sometimes earn as little as one dollar per day).

To cut costs in these systems, lead-acid batteries are usually installed. Unfortunately, lead-acid batteries have a limited number of charge-discharge-cycles, much less than, for example, modern LIFEPO batteries. Also, they age quickly if they are discharged below around 40% of their capacity. This leads to many of the batteries breaking within 2 years or less, rendering the solar home systems unusable.

Moreover, as developing countries don’t have proficient infrastructure to dispose or recycle the lead-acid batteries, each failing battery leads to waste of resources and significant environmental pollution.

>lead acid batties are vulnurable to cycling often

How to solve the problem?

-retrofitting hybrid charge controller!

Using LIFEPO based batteries would significantly increase the solar home system’s lifetime­, as LIFEPO batteries are less affected by cycling compared to lead-acid batteries. However, initial high investment costs for LIFEPO batteries are often not feasible for developing markets. To get the best of both, a hybrid charge controller which supports a small lithium-ion battery and a bigger lead-acid battery simultaneously, would be ideal.

> LIFEPO batteries are better but too expensive 



A normal charge controller is responsible for monitoring the battery’s voltage and for controlling the charge and discharge cycle. In comparison, a hybrid charge controller would be able to switch between the two battery types, considering environmental factors, such as load current, solar irradiance and state of charge of both batteries. This will result in the li-ion battery having a smaller capacity, therefore cutting its cost. An algorithm would then only use the lead acid battery if the load is too big for the lithium ion battery to handle. For smaller loads and thus more cycles, the lithium ion battery would be used.

> lead acid battery will be cycled less often



Thus, the new hybrid charge controller aims to prolong the lifespan of millions of already existing lead acid batteries inside solar home systems by reducing sulfuration.