DR MATT TREWHELLA
Consultant from Independent Energy
Dr Matt Trewhella from Independent Energy talked about different types of renewable energy we can use to heat and generate electricity for our homes. Listen to his talk:
- Tony and Julie's introduction (3mb)
- Types of energy we use (5mb)
- Summary of each type (6mb)
- Ways of delivering heat (2mb)
- Heat pumps - ground, air or water source (17mb)
- Biomass - wood burners, chips and pellets (16mb)
- Passive solar heating - design your house right (7mb)
- Solar thermal (10.6mb)
- Wind turbines (18mb)
- Solar PV - photo voltaic cells (10.5mb)
Options for renewable energy in your home are listed below, or see the heating cost summary.
Electricity Generation
Electricity generated from renewable energy can be used to power the lighting and appliances in your home. Most houses use 3,000 - 5,000 kWh (units) per year. Properties that are not attached to the national grid can use batteries to store the generated electricity to use when needed. If the property is currently connected to the national grid then you can dispense with the battery storage. The controls will automatically feed your home, feed into the grid or draw from the grid depending on how much electricity you are generating and how much the panels are producing. You are then only billed (or paid!) for the total electricity you have taken from (or given to!) the grid each quarter. You also get credited with Renewable Obligation Certificates for renewable energy generation. These can be sold to energy companies trying to meet their targets whether you export the energy or use it on site - currently around 3.4p per unit.
Photovoltaic (PV) panels
These panels produce DC electricity directly from light. The electricity can be converted into standard 240V AC electricity to feed into your home. They are normally rated according to their peak power output. The panels can be fitted onto a roof or on frames in the garden. Allow 8m2 for every 1kW peak power installed. You can expect to generate around 1000 kWh (units) of electricity per year for every 1kW installed. Costs are £5,000 - £8,000 per kW installed.
Wind Turbine
Wind turbines generate electricity using wind power to turn blades attached to a turbine. They are rated according to their peak power output. Typical domestic or light commercial turbines are in the region of 2.5 - 25 kW and can generate 3,000 - 100,000 kWh of electricity per year. They have blades from 3.5 - 11m are normally mounted on freestanding towers of 6 - 18m high and should be sited 50 - 300m from your property. Costs are £15,000 - £70,000.
Microhydro
For properties that have access to a strong stream, it is possible to generate electricity with a small hydro-electric generator. The power you generate is related to the flow rate and the height drop of the stream. You sometimes need to remove a portion of the energy in a duct upstream and then drop it sharply back into the stream through the generator.
Combined Heat and Power
These are engines that generate electricity. The heat that most engines produce as a by-product is fed into your heating system. Although these are not strictly renewable energy, they still give CO2 savings by cutting out transmission losses of up to 50%.
Heat Energy
These technologies produce heat that you can use to heat your home, swimming pool or hot water. A typical house will require around 10,000 - 20,000 kWh per year to heat and around 3,000 - 5,000 for hot water.
Solar Thermal Panels
These convert light directly into heat. In most properties, this is best used for domestic hot water as a large fraction of this is required during the best solar months of April - September. Costs are £3,000 - £5,000 and you should expect to produce 50-70% of your hot water from solar.
Heat Pump
These work on the same principles of compression and expansion as found in your fridge/freezer. Cold fluid (down to -20°C) is passed through a loop outside where it absorbs heat from the not-so-cold (e.g. 8°C) ground (or air or lake). This is then compressed inside your house which causes it to heat up to boiler temperatures (40-60°C). You then use this heat in your heating or hot water circuit which cools it (to 20-40°C). The fluid is then allowed to re-expand outdoors to absorb more heat. Heat pumps use electricity to pump the fluid around but typically generate 3-4 times more heat than the electricity used by the pump. This efficiency produces good Carbon Dioxide and financial savings compared to mains gas and excellent compared to oil, electricity or propane.
Biomass Boilers
The most common of these burn logs, wood chips or pellets. Of these, logs are the simplest and most reliable supply and pellets are the easiest to automate. The Carbon Dioxide savings are massive as the wood releases the same amount of CO2 when it is burnt as it took in when the plant was growing. In a well managed woodland/forest this is infinitely renewable, sustainable and does not significantly contribute to global warming.
Biomass boilers are often combined with a large (1500 Litre) water tank to store the energy. This means that the boilers do not have to be filled and lit so often.
Figures accurate at 1st March 2008.