One payment is for your solarZero service. The second is for your grid power from Ecotricity. Your monthly payment for solarZero has been set up as a direct debit and will stay the same amount, except for any changes to GST, for the full term of the 20-year agreement. Your invoice from Ecotricity is variable and includes your grid power at wholesale spot prices, plus network fees and the EA Levy passed on at cost. It may also include a credit for any surplus solar power sold back to the grid.