If there is nowhere for the energy to go the inverter will lower the output from the panels. I think the main reason is because if they turn off the grid for maintenance, you cant start exporting and potentially kill the workers. There are also other complications like the inverter needing power before it can create power

just had ours installed and even today when its cloudy and raining we are producing enough to run the house (low usage). couple of things to be aware of - On a normal system, if the grid goes down you cant use you solar or battery(may not be a problem for you), for this you need a back up box with off grid capability. There will likely be an export limit set by the DNO so the excess may get wasted anyway. 180 watts isnt much, possibly run a fridge on it