Too early to say as regards electricity but the the thermal panel provides all hot water for 9 months of the year and may be 25% for 3 months
Disastrous experience with rain water harvester for 2 reasons. 1. Dreadful after sales service from Rainwater Harvesting Ltd of Peterborough. 2. I used the house builders to fit it and they had no experience in fitting them and completely ruined it. It now lies under my garden unused. An expensive white elephant. I suggest you always use both local suppliers and builders with experience in fitting them as they are much more complicated than it first appears.