Off-grid PV solutions, without storage

In rural areas and in developing countries the potential for off-grid photovoltaic applications is great. However, the initial costs can prove to be an impediment to more widespread usage. Researchers at the Fraunhofer Institute for Solar Energy Systems (ISE) have developed an energy management system which optimizes the use of electricity produced by a concentrated photovoltaic system therefore getting around the need for expensive batteries.

Working on a model project on a farm in Upper Egypt, a concentrated photovoltaic installation (CPV) was installed to power irrigation systems, which pump water from deep wells. The CPV installation also requires power to track the sun’s movement, optimizing the solar light yield.

The Fraunhofer energy management system monitors the amount of energy produced and then ensures that it is delivered to the devices that need it most. "By immediately using the largest share of the energy that is generated we can save on expensive storage media capacities," said Alexander Schies from the Fraunhofer ISE.

To illustrate, the submersible pump, which is 105 feet deep, can be powered to fill the reservoir when energy is available and the irrigation pump or desalination unit at other times. Only a relatively small battery is needed to ensure the CPV tracker and measuring system remains powered. “We need this reserve, in particular, to align the CPV modules in the morning to their morning position,“ explains Schies’ colleague Jakob Wachtel.

Technically all the components of the irrigation system have micro-controllers, to inform the energy management system at to their status. A Universal Energy Supply Protocol (UESP) was developed at the ISE to facilitate this communication and the communication of energy levels also.

The USEP is being integrated into the CANopen protocol, which is commonly used in automation technology. "All systems that work with these kinds of protocols can be expanded at any time with devices that ‘understand’ CANopen or UESP – completely independent of the manufacturer. This is practical if a defective component has to be replaced," said Schies. This allows for further system savings and simplifies maintenance.