Aye, replication time.
Cost per month of DW for me is £4,617 / 9 monthly payments = £513
For April,
FIT1 - £289
FIT2 - £79
Ripple GF - £137
Total - £505
Actual bills - £47
Surplus - £458
Saving on 893 kWh (onsite solar actually used) even at cheapslot rate of 7.5p / kWh is £67 + surplus of £458 = £525.
DW pays for itself with enough left over for a decent bottle of red.