We've only had them running for a few days, so it's hard to tell. You can download the data from our other panels or see it on https://pvoutput.org/list.jsp?sid=25687. This time last year, our 4kWp system generated about 22kWh in Oxford. Yesterday in London, we generated about 16kWh on our 5kWp system. That's a snapshot, and doesn't take into account weather. After a month we should be able to get a more realistic comparison. So, there's probably a small hit in terms of energy generation. But the average house uses 10kWh per day, so we're completely offsetting our use. Total cost was around £7k - but we have a townhouse which required extra scaffolding, a larger installation crew, nd we deliberately chose fairly high spec panels and inverter. The fixed costs of installation time and effort haven't changed much.