Earth Notes: Composting vs Solar Power (2007)

Domestic Solar Power/Heat

My family has been able to trim its consumption of energy, mainly mains gas and electricity, by conservation and also by generating some renewably.

Millions of local domestic power generation facilities might also help increase electricity supply robustness against peak load, storm or even sabotage. This is in much the same way that the distributed nature of the Internet helps it survive individual failures. However, it remains possible that I might be expensively failing to save the planet and my money...

Domestic solar heating and electricity generation will not save money but can reduce overall CO₂ emissions.

A domestic solar power system will likely not pay for itself in the UK.

In September 2005 a group of well-respected UK academics reported that the payback period for an investment in a solar PV system in the UK was 47 years. The equipment life might be 25+ years, so the chance of financial payback is low. Government grants improve the position, and there are reasons other than purely financial for installing solar PV (photovoltaics aka solar cells/panels). However, high capital and financing costs and sunlight of perhaps 2.5 hours per day may simply mean that pure financial payback never arrives for a small domestic installation. On the other hand, if your aim is to reduce your total carbon/energy footprint, then PV may save its manufacturing footprint in the first few years of a 25-year life.

Solar water heating looks a lot more attractive than PV in terms of financial payback. Maybe much less than 10 years, and it is very likely that the equipment will last at least that long. And you should be able to recover/save the manufacturing 'carbon' input with no great difficulty within a year or so. But of course you don't get much hot water when you most want it, ie in winter. It should be possible to integrate it with an existing system to get some gain year-round.

The study Can PV or Solar Thermal be cost effective ways of reducing CO₂ emissions for residential buildings? (2006) reports that the carbon payback for [a] solar thermal system is 2 years, [and a] BIPV system has a carbon payback of 6 years. Simple economic payback times for both systems are more than 50 years. Calculations considering the [then] current UK energy price increase (10%/yr), reduce the economic payback time for the PV roof to under 30 years. The costs to reduce overall carbon dioxide emissions using a BIPV roof are £196/tonne CO₂, solar thermal individual systems at £65/tonne CO₂ and community solar thermal at £38/tonne CO₂. The current spot market price for CO₂ is £15/tonne CO₂ (20). Capital costs for PV systems in particular must be significantly reduced for them to be a cost-effective way to reduce CO₂.

Hybrid solar PV/thermal (PV/T) systems may make more sense. The is because the unused (heat) energy that reduces the performance of PV can be usefully soaked up by the thermal system instead.

In other words, you are very unlikely to save significant money with domestic solar energy in the UK. But you are more likely to help reduce CO₂ emissions.

(In spite of this apparent doom and gloom, I'm running a small off-grid solar PV power pilot project, based on low-voltage lighting, I'm making my office zero-carbon with grid-tie PV. Indeed I'm making the house a net generator not consumer of grid electricity as of 2009. I'm also looking to see what it would take to get really LZC (Low/Zero-Carbon) at home.)