Revenue/ savings

The most significant source of revenue is the 'Feed in tariff' on all electricity generated. In addition we operate under a 'deemed usage' assumption that we use only 25% of what we generate.  This is not far off 20/70 but it becomes a relatively generous assumption when we decide to use part of the output to drive the heat pumps.  On the other hand it has been disappointing to still receive electricity bills!.. Even though we are a net exporter, to avoid any electricity bills we would have to avoid any importation by balancing our requirements within our output across 3 phases 24/7... not practicable.  So we have ended up with rather similar electricity bills and I have allocated half to the hydro and half to the heat pumps

Cost/ payback

We were fortunate that the installation of the required 3 phase electricity connection was relatively simple.  We were warned, however, that civil works can add significantly to the project cost and this was the case.  Other costs included installing the screw in a new dedicated channel and upgrading the river gates to handle storm flows.  The EA fish pass requirement added a further 35% to the base cost and pushed the payback beyond the target of 10 years.. although at 12.5 years (with no provision for inflation) it is close to our target.