I was presenting yesterday at a conference in the magnificent St Gilles Church in Wrexham the largest parish Church in Wales. The conference was hosted by the Church in Wales and the theme of the day was sustainability with specific focus on the 1000 or so churches in Wales. I have been involved a few times with energy and churches. I find them difficult to deal with because you are sometimes looking to heat the whole building or parishioners to comfort levels for only 2 hours a week but you also need to maintain the relative humidity to look after the contents and stop the lime mortar from degrading. (my heart also sinks when i see UPVC on these buildings) . energy efficiency could yield quick wins such as more control, led lighting and so on.
There were some inspirational case studies such as the small church in Libanus near Brecon which is now an insulated box and is heated with an air source heat pump. The major lesson for me is not which technology for heating but what use and how to adapt the building. The successful case studies seem to have adapted their churches into a multi use community sites by bringing in more people, more use and making the energy decisions easier.
Today I was involved in a live radio debate on this subject and the presenter was being controversial and suggesting PV on everything. I it has really surprised me the willingness of people to adapt these buildings in quite dramatic ways. PV, Solar thermal, biomass and so on. But over their lives Churches go through quite dramatic adaptations as taste and use changes and so a PV system in the right place is just another layer in the buildings patina
when i got back i did some googling and there is quite a bit out there on the subject