In GNC #532, Todd mentioned that the price of solar was going to fall by 30%.  In this, case, he was talking about photovoltaic cells, i.e. ones that generate electricity from sunlight, but there are a whole host of green energy technologies.  So what gives the best return on your green investment?

The Self Build show was on in Belfast in the summer.  It’s an exhibition much like any other with stands and booths but this one caters for people who want to plan, build or extend their home.  The exhibitors are really diverse from brick manufacturers to bespoke furniture makers but this year it was the green technologies that were most prevalent.
 
I’d visited the show a couple of years ago and then there might have been a handful at most of stands doing eco-friendly stuff.  Wind turbines, heat recovery and roof tiles made from recycled car tyres was about it.  This year there was a whole hall of stands with ground source heat pumps, solar panels, woodchip-fired boilers, wind
turbines, super insulation, triple-glazed windows – the works.
 
What I wanted to pass on was a presentation given by a local housing association who had been proactive in trying out different energy sources and properly measuring the energy benefit gained.  Given that it was only a ten minute presentation, he didn’t go into detailed facts and figures but the findings were still of interest.  Remember this relates to about 55 degrees North and there may be regional variations.
 
Here are the technologies that were investigated and a summary of the findings.
 
i) Ground source heat pumps – these work well where underfloor heating or air heating is used to heat the house, as the temperature only needs to be raised to 25-30C.  Savings are greatly reduced if trying to raise temperature to 60C for hot water or for radiator-based
central heating.  Consequently, it’s difficult to retro-fit this technology to an existing house, but it’s ideal for new builds.
 
ii) Air source heat pumps – as for the ground source heat pumps but pumps tend to be less reliable and noisier.  This may not be so much of an issue in the US or hot countries, where air conditioning units are more prevalent.
 
iii) Wind turbines – the small wind turbines used in domestic situations are often not high enough off the ground and suffer badly from turbulence.  The cost / benefit of these devices was often marginal, but it does depend a great deal on location.  The presenter
thought that vertical axis turbines might overcome some of the issues but hadn’t been able to do a study.  If the turbine does generate surplus electricity, this can be sold back to the grid.
 
iv) Photovoltaic cells – currently too expensive and provide too little energy in northerly latitudes to be worthwhile.
 
v) Solar panels (evacuated tube) – after the ground source heat pump, probably the best next thing to consider.  Usually only used to heat hot water as heating effect varies during the year, but overall good cost-benefit, even in northerly climates.  Evacuated tubes are more efficient than similar flat plat models and are easier to fix if damaged.  Can be retrofitted to existing properties.
 
vi) Solar panels (flat plate) – as for evacuated tube but less efficient.
 
vii) Woodchip fired boilers – instead of burning oil or natural gas, the fuel is woodchip pellets.  The main benefit of these boilers is the low cost of the fuel which is typically a quarter that of oil or gas for a similar heat output.  The biggest downside is the storage space need for the storing the woodchip pellets.  If you have the space, can be fitted into existing homes.
 
While this is not an exhaustive analysis, it should provide enough information for you to start your own in-depth analysis.  I’m installing into an existing property and previously, I’d been considering the wind turbines.  However, I think that the evacuated tube solar panels are now the best choice and will be looking into those instead.

Do also bear in mind the environmental conditions that you currently live in – this study was for the northerly part of the UK so pick your tech accordingly and do your homework.