Earth Notes: Composting vs Domestic Solar Power (2007)Updated 2023-10-01.
Which makes for a greener life? Composting your kitchen waste or domestic solar power? Both are in the spirit of "think global, act local."
Composting your kitchen and garden waste saves landfill space. It also reduces methane production and global warming.
Adding your shredded sensitive documents protects you from ID theft, and helps the composting! I am tickled by the idea of worms mincing my words. Bad guys can't piece together what the worms have chewed!
Composting at home is mainly aerobic (has plenty of air). So it produces mainly CO2. (And a little compost.)
Dumping your waste in the bin for the council to collect results in much or all of it ending up in scarce landfill. There it produces methane by anaerobic (airless, oxygen-free) breakdown. As much as 97% then escapes into the atmosphere. Also, toxic compounds can leach into the surrounding area.
CO2 is a greenhouse gas (GHG), but methane is far more potent (more than 20x) at retaining heat in the atmosphere.
With a rat-proofed garden compost bin even cooked food can be composted. Without a garden an outdoor or indoor wormery can be used to compost uncooked food. Well-managed composting does not smell nor present a hygiene problem. And it's cheap or free.
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.)
What can really save you some money, and maybe the planet, is to eliminate waste by improving thermal insulation and saving electricity. Go vampire hunting with a gadget such as the PM230 kWh meter, or the 2000MU-UK meter from Maplin, or a "Kill-a-Watt". Did you know that your microwave oven may use more energy in its lifetime running the clock 24x7 than you ever use to heat food? Turn stuff off at the wall when you're not using it!
(You can also run clothes/dish washing and other big deferrable loads late at night. At that time less CO2 is produced to generate the same amount of electricity. This can save you maybe 10% to 33% CO2 emissions. I set up one of my Web servers to reduce power, and our dishwasher not to run, until grid intensity is below average. This is usually between 10:30pm and 7am.)
It's typically 5 to 10 times cheaper to conserve 1kWh/day than to generate it in the UK.
In our case we're saving 1kWh/day by buying a replacement A+ fridge/freezer. (Slightly bigger because we needed more freezer space.) It cost us ~£550.
We're saving maybe another 0.5--1kWh/day by replacing our washer/dryer. The new one has A-rated wash efficiency. It can also wash in cold water with suitable detergent. (Cost: ~£470).
Putting in solar power to generate an average of 2kWh/day over the course of a year cost ~£7000. (Allowing for a good discount but poor roof direction.) Thus it is about 6x cheaper in our case to conserve each 1kWh per day.
(Here's some of our done/to-do list. A lot of the tasks are improving insulation to reduce waste.)
2023: Solar Is Much Cheaper Now!
It is worth noting that solar PV has dropped in price hugely, so the sums are very different.