The offset ratio is at 1-to-1. Which effectively means, 1 credit = up to 0.51 cents per kilowatt hour(kWh) for domestic tariff. Of course, it is dependent on voltage supply(e.g. low/medium/high voltage supply).
Another way to word the offset is by; if i lived in a house with a new solar PV system installed and it generated and excess of 1 unit of energy during January. In February’s electricity bill, i will get charged less 1 unit of energy (due to the 1 unit of excess energy i generated in January).
So hypothetically, if my wife and i have a day job and are at the office working. Our solar PV system would be generating a lot of excess electricity the whole day due to no one utilizing electricity at home – say 50 units of excess energy. All 50 units of excess energy/credits will be minus’ed off in next month’s bill.