My garden is at its best in May, so I thought I’d post a recent photo of the pond. The pond was built at the end of 2007 and mostly planted in 2008. It’s home to tadpoles, dragonflies, snails and water beetles.
The house was built in 1976 and has gas central heating. The main modifications we’ve made have been to make the house warmer and more energy-efficient – they have included fitting a condensing boiler, solar thermal panel, cavity wall and roof insulation (2007), double glazing (2008), a back porch and an energy-efficient fridge (2009), and solar PV panels (2010).
Has this made a difference?
We have utility bills back to Sept 2006 for gas and electricity consumption, and since 2009 have been taking weekly readings of gas, electricity, solar thermal and solar PV panel activity.
From the annual readings, we used 42% less gas and 44% less electricity in Sept 2011-Sept 2012 compared to Sept 2006-Sept 2007 (the last full year before we made major changes).
[A note on the measurement of solar hours pumped: when the ethylene glycol in the solar panel gets hot enough, it is pumped around the system and heats the water in the cylinder. The time that the pump runs is recorded. The panel does not heat our central heating, just the hot water (Jonathan has just patiently explained to me again exactly why that is the case).]
The changes that affected gas consumption all took place in 2007 and probably the condensing boiler and insulation made more difference than the solar thermal panel, as it was only properly working by April 2008, and so did not contribute so much in that year.
It’s more difficult to attribute reasons for changes in electricity consumption, as we made modifications to the house or appliances in most years. Replacing two old fridges with one (large) energy efficient one made an immediate and significant saving. Since 2010 the only change has been to install solar panels. Comparing Sept 2011-Sept 2012 to Sept 2009-Sept 2010, we see a 23% fall in electricity consumption.
Since we (our son, in fact) has been collecting weekly readings since 2009, we can look at this in a much more fine-grained manner.
The solar thermal panel has made us nearly self-sufficient in hot water in the summer. In 2007 we used 360 m3 of gas between April and September, now we use about 80 m3.
The solar PV panels also appear to have an effect, reducing the electricity that we draw from the grid each summer. We are clearly not using our generated electricity very efficiently (otherwise our summer consumption would be much lower). That could be improved by using appliances more during the day and less during the evening in summer (something we try to do, but have not made huge efforts in that direction). Or of course if we could store the electricity somehow.
Was it worth it?
I’m not even going to attempt a cost/benefit analysis! The improved insulation and draught-proofing (not to mention the pond) have made our home much more pleasant to live in, and the condensing boiler is far more efficient than the old one. I’m less persuaded by the solar panels, which contribute most during daytime in the summer when we are using least energy. But the panels are working at least as well as we hoped they would, the FITs, of course, reduce our electricity bill, and the whole process has made us rather more aware of how we use energy in our home.