Both is the answer to that Jerry. The inverter converts DC electric from the panels to AC electric for use within the home or export to the grid. What the inverter does is monitor the grid and output a slightly higher voltage, so like water at a higher level it flows first. If you are using electric within your home, then it will use electric from the panels first (and if necessary pull electric from the grid to top up demand). Hence it reduces the amount of electric you buy from the grid. When you are not using the electric it flows back into the grid for other people to use (they don't get a bill reduction though). In the UK, and I'm sure it's the same in Holland, you get paid for what goes back to the grid, and a subsidy from the government ( feed in tariff) for every unit you generate.
