I’ve been lucky enough to spend the last 2 weeks in Greece with Kostas Latoufis at the National Technical University of Athens. Kostas is an electrical engineer and has been working on axial flux generators for many years now. Just like me, he’s part way through a PhD on the technology, but with a much more technical focus than myself. At the NTUA they have a wind tunnel that’s so big, you can’t even touch the ceiling when you’re inside it, a generator bench testing rig with a driving motor so powerful it barely even notices when you short circuit the generator under test and a PV-wind hybrid micro-grid on top of their office with state-of-the-art ‘hardware-in-the-loop’ capabilities to simulate a whole virtual village! What is more, Kostas has an army of Batchelors/Masters students working with him and has managed to make an incredible amount of progress in the field of axial flux generators for wind and hydro applications in the last few years.
Kostas and his research group have investigated and optimised permanent magnet configuration in Piggott generators, analysed the manufacturing process and modelled the entire system (see their recent publication here). They have also developed a bench testing procedure to enable characterisation of the performance of machines built anywhere in the world (see the full report here). What is more, they have also investigated simpler ways of achieving performance enhancement similar to Maximum Power Point Tracking (MPPT) through the use of inductors and more recently by choosing a thinner power cable than previously recommended, which loses more power in terms of voltage drop, but actually increases the overall energy yield delivered to the batteries, as it forces the blades to run faster and therefore more efficiently. They have done this through a combination of experimental measurements taken using test equipment and computer modelling techniques not available to Hugh or the majority of the other members of WindEmpowerment. This is a prime example of how researchers can use advanced techniques to optimise the performance of this troublesome technology, whilst still keeping the final product simple and therefore easy to manufacture and easy to repair.
Together with Kimon Silwal of KAPEG (Kathmandu Alternative Power and Energy Group) and Tom Wastling of EWB-Sheffield (Engineers Without Borders Sheffield), I was invited to accompany Kostas for two weeks at the NTUA, under the DERri Transnational Access project (www.der-ri.net), with the following goals:
- Comparing neodymium with ferrite as the magnetic material in an axial flux generator by bench testing. Neodymium magnets create a much more powerful field than ferrite, so much less magnetic material is required, making neodymium generators lighter and smaller. However, corrosion problems can be severe and the only source for the raw material is China, making prices extremely volatile and raising questions about the sustainability of the continued extraction of this rare earth metal.
- Comparing simple testing techniques that can be conducted In the field with only basic tools (multimeter, spanner, timer etc.) with those that we are doing in the laboratory.
The results of the tests are still being written up and will be published here and on WindEmpowerment in the next few months.