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"Improving the long-term sustainability of off-grid renewable energy systems in developing countries."

A monitor for battery based renewable energy systems has long been on the to-do list for re-innovation. This page describes why such a monitor would be useful and introduces the design.


1.6 billion people do not have access to any electricity supply. Many more do not have access to a reliable electricity supply. Most of these people live within remote areas of developing countries.

Access to small amounts of electricity can radically change peoples lives. Electricity can be used to provide lighting, communications and refrigeration to improve healthcare, education and local economy.

To supply electricity to these communities diesel generators are typically used but this is not sustainable due to increasing fuel costs, accessibility to fuel, local and global environmental problems and noise and maintenance issues.

Renewable energy can be used as a more sustainable solution. The use of local and freely available sun, wind and water power buffers communities from increasing fuel costs and local and global environmental problems.

As the renewable energy source typically does not generate at the same time as energy is required (such as lighting in the evening) some form of energy storage is required. In the majority of these systems lead-acid batteries are used for energy storage.

Lead-acid batteries are electro-chemical devices which, from the outside, do not show any change with different state-of-charge. These batteries can be damaged by being over-charged and over-discharged, both of which can cause a reduction in the useful life-time of the battery. With no indication of the energy left in the battery, many people over-discharge the batteries, with associated reduction in battery life. When regularly over-discharged, battery life is reduced by around 3 to 6 times. Often the community cannot afford to replace the battery, due to its relatively high cost, and hence the whole renewable energy system does not function. This greatly affects the long-term sustainability of such systems.

Project aims

This project aims to provide a 'fuel gauge' for lead-acid batteries. This will monitor the state-of-charge of any battery and provide a user friendly reading of the energy left within the battery.

There are three levels of information:

The target price of the unit is $50. The project aims to be open-source for local manufacture.

Design information

Information about the design of this project can be found here.

Software information

Information and downloads relating to the software for this project can be found here.