Have any challenges been experienced using the technology?

Oh yes - numerous (we could spend a few days talking on that) - and not all of them completely solved. Perhaps one can refer to these challenges in certain categories:

1. Algae cultivation - How to produce algae biomass at production rates that actually makes economic sense whilst keeping both capital and operating costs at reasonable levels;
2. Selecting an algae strain capable of giving the desired growth rates under South African conditions (high radiation levels and high temperatures); 
3. Harvesting the biomass - How to reduce the energy input costs during harvesting (which is well known to be one of the biggest challenges in micro-algae cultivation);
4. Finding a catalyst that would successfully liquefy micro-algae biomass in a water medium, that is at the same time active enough to give sufficient throughput rates at relative low energy input.

While there are many more improvements possible, we are confident that we are getting close to a "first generation" technology that could be demonstrated at semi- or even commercial scales.