A tariff is a tax that is charged for certain imports or exports of energy. There are different types of tariffs such as the 'time of use' tariff when you pay more during peak demand periods, like in the late afternoon and early evening.
When you have a solar system, the feed-in tariff is the figure you want to see higher because you are paid credits for exporting power back to the grid.
By adjusting your behaviour of electricity use, you will pay less, however, installing solar panels is the ultimate way to slash or even eliminate your electricity bill.