This is from the Solar Service Group website:
Solar Service Group are an independently owned, trusted Australian company that specialise in service, maintenance and repairs of PV Solar Systems nationally. With over 20 years’ industry experience and a genuine focus on our customer’s experience, as an independent Service Provider, we are a company you can trust.
They also retail and install battery systems.
The only info on battery trial in NSW I could find is this one....Collombatti Area Battery Storage Trial
Based on this and unless you reside in this trial area, I would tend to agree with @TheBBG that it is a 'clever marketing exercise' to make thise who read the letter think they are special and part of some sort of trial. It is bordering on deceptive advertising if it is.