Renewable Energy & Resources

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This section deals with renewable energy systems and water capture for houses. These are usually comparatively small systems, so for the larger stuff please see the same topic under Office, Commercial & Industrial. If you are interested in commercial scale projects (such as wind farms), serious techy stuff, ethics etc., then the same topic under The Bigger Picture / Renewable Energy is probably your best option. Or the Forum, of course.

I’ll start off this section with an overview of the subject and tales of experience. The different types of systems (such as solar or turbines) are discussed at depth in sub-articles, links to which can be found at the end of this article.

There are two major forms of renewable energy systems: those that produce heat and those that produce electricity. These are:

Heating and hot water

• Solar Thermal - water is passed through thin pipes so that the sunlight heats it up. Quite good efficiency, even on overcast days, with water able to get quite hot. Needs to be used in conjunction with other water heaters, such as gas boilers or the other renewable systems.
• Biomass - wood or other organic matter is burnt to produce heat (basically it’s a fire). The options are log-burning stoves to heat a room, log-burning stoves with back-boiler to heat a room and water, and automatic pellet boilers for water heating (including central heating).
• Ground or air source heat pump - works like a fridge, but in reverse. The heat from the ground is sort of sucked out and pumped into the house. The same can be done in the air (called ‘air source heat pumps’, surprisingly), which is not as efficient but is cheaper and easier to install. The ground (or air) does not have to be particularly warm for this to work, so anywhere in the UK is fine, but very cold and damp weather will cause problems for air source.

Electricity

• Solar voltaic - the energy from sunlight is converted into electricity, which is then gathered together and fed into the ring main. It is not very efficient yet, with around 10% of the energy in the sunlight being converted to useable electricity. The latest panels are achieving efficiencies of close to 20%.
• Wind turbines - think of small windmills powering dynamos and you have pretty much got the right idea. Turbines are excellent when there is enough wind to make it worthwhile.
• Micro hydro – using water power to create electricity. This is a bit like wind turbines, but flowing water is used to turn the blades rather than wind.

There are also some micro CHP (Combined Heat & Power) units being developed, which are more or less standard generators which also make use of the heat produced when generating electricity. These are having a few problems at the moment, but there is some exciting research underway that could lead to them working well. The existing technology works very well at larger scales, just not for individual houses.

Solar voltaic systems are now becoming financially sound, especially as electricity companies are offering much higher purchaser prices for excess electricity from solar panels. They are still relatively expensive to buy and payback times can run to a decade or two, but this is a lot better than it was.

Biomass is great for the right application, but is unlikely to be a good primary heating source for most people. If you want a wood-burning stove, then getting one with a back boiler is a good idea as it can go a long way to running the central heating and hot water throughout the winter months, when most needed. You are not going to want a fire in summer, so will need to revert to other methods of heating water. Pellet boilers will work all year and most do not produce much heat to the room they are placed in – they are just like normal boilers, but run on wood pellets. Being highly automated, the main problem with these is fuel storage space.

Wind Turbines need lots of wind. The fairly small units can provide almost all the electricity needed to run a three bed home in the right spot, but if you live in a town or amongst trees you can more or less forget it. As a rule of thumb, a turbine is only worth considering if you have a clear, uninterrupted view for several miles in the direction of the prevailing wind. If this is you, then a turbine may well be an excellent option environmentally and financially.

Ground and air source heat pumps are very good at heating water to around 40^oC, but lose efficiency rapidly above that temperature. This means they are excellent at powering underfloor heating systems, but not appropriate for powering radiators (which need to be much hotter to give adequate heating). They can heat water for washing as well, but to keep the efficiency high the water will only just get hot enough for baths and showers. I have a friend who powers his whole house from a small turbine and a ground source heat pump, with no mains electricity or traditional boiler as backup (although he does have a wood stove for cooking). He very rarely needs to borrow a generator to charge up his batteries, but he does live in an unusually windy spot.

Solar thermal systems may be the best option for the largest number of households in the UK, depending on how much hot water they use (please see Solar article). They can easily be fitted on existing buildings, are generally very efficient and can easily be incorporated into the existing plumbing. The two main limitations are loft conversions and combi boilers. Both these can be made to work with solar water heating, but it can often be impracticable.

For more about each system, visit the individual pages below:

• Solar voltaic & thermal
• Wind turbines
• Ground source heat pump (plus air source heat pumps)
• Biomass
• Micro hydro
• Micro Combined Heat & Power
• Water capture

When comparing different systems, it is worth knowing roughly what energy is required to make a standard hot water and heating system work. So, a standard hot water tank needs around 10,000 BTUs to work well and each radiator needs an additional 4,000 BTUs. 1kW roughly equals 3,000 BTUs, so the hot water tank will need around 3.3kW input and each radiator an extra 1.3kW.

The average household in the UK uses between 3,000kWh and 6,000kWh per year (2 bed flat to 4 bed house). More or less.

Cambridgeshire have a good interactive map with explanations about various renewable energy options. It's aimed at community-scale projects and is fairly brief, but is well put together and definitely worth a peek.

Grants of up to £2,500 are available for householders to install renewable energy systems, with the process starting at the Department of Energy & Climate Change (will probably change its name next week). This will change from 1 April 2010 (great choice of date) to the Feed-in Tariff system, whereby householders get paid for every kWh of electricity generated by microrenewables, plus 3p more per kWh for any excess they export to the grid. The actual cash you can get for the different sizes of various systems is listed on the DECC website and reproduced here:

What to do

If you are building a house or extension, try to put in underfloor heating and consider a ground source heat pump.

If you use lots of hot water and have a roof facing south-ish, or a flat roof, or a south-facing wall, fit solar panels to heat your water. If you don't use lots of hot water, look into fitting solar voltaic panels and combine with a heat pump.

If you live in a windy spot, fit a small turbine to generate electricity. Consider combining with a heat pump.

If you like a real fire, or the Aga/Raeburn concept, a biomass heating system is a great idea.

A great combination for many homes would be a wood-burning stove with back boiler and a solar thermal panel. The solar will provide hot water during the summer and the wood-burner will fire up in the winter to ensure enough hot water and heat throughout the cold, dark months. 

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