Houses can be designed to capture more of the sun's energy.
There are a few other ways gaining energy
from renewable sources that might be considered for small installations in a village such as Blewbury.
- The most traditional is the use of Wood Burning Stoves.
These now have more convenient options.
- Among the more modern solutions
the use of Solar Thermal Panels is the least expensive and most straight forward.
The output is hot water which can be stored for a reasonable time in an insulated water tank.
- An installation of Solar Cells is more expensive, but it generates electrical energy
which is typically of higher value than hot water. However the energy is generated when the sun shines and typically needs
to be stored for later use.
- Combined Heat and Power plants may not seem to be as ecologically
friendly as the direct use of solar energy,
however they generate electrical energy with less waste of energy than conventional power stations as the "waste" heat is also used.
They thus can save CO2 emissions. They have the potential to be a sensible investment and to be widely used.
However they are not yet an economic option for domestic installations.
- Heat Pumps may be viable in special cases.
Small Wind Turbines are appropriate in some locations, however their use in Blewbury is not likely to
be attractive because of low average wind speeds - the energy available depends on the cube of the wind speed -
screening by trees and planning restrictions. Any viable Wind Turbine would need to be high on the Downs.
The practical solutions to the storage of electrical energy not needed at the time of generation are to:
A wide variety of other ways of storing energy are not viable for any small installations.
Thus Wood Burning Stove and Solar Thermal Panel installations are likely to be the
best options for domestic renewable energy generation for existing houses in the village of Blewbury at present.
The Cost of Capital
In evaluating the economic results of an investment in Green Energy it is necessary to consider the cost of the capital used.
If an installation lasts 20 years and the money invested could have earned interest after tax of 3%,
an appropriate annual cost of the capital is about 6.7%. This figure is used in the assessments below.
However, a significant part of the reason for fitting such systems at present is likely to be the contribution they make
to reducing greenhouse gas emissions, as none is directly competitive with the use of mains gas and electricity.
Grant Assistance
The cost of an installation can be reduced by grants from the
Low Carbon Buildings Program.
These grants are only made if measures to reduce consumption, such as insulation and low energy light bulbs,
have already been taken. The grants depend on the actual technology being used in the installation, typically
with the most cost effective
technologies receiving the least support. In the past the sums allocated for such grants have been used up before new
resources are allocated, leading to a "stop go" effect on the market, which discourages suppliers.
However an extra £50 million was announced in the 2006 budget, which might keep the
subsidies in place for a reasonable time.
Further information can be found in the Energy Saving Trust web site.
The design of a house or extension makes a significant difference to its energy efficiency.
Good insulation is now required.
Designs can capture more of the sun's energy through appropriate south facing windows.
More complex schemes arrange that air carries heat from warmer areas, for example under tiles on
a south facing roof, to other parts of the building.
There are two main ways of using wood to heat a domestic property:
- Stand-alone stoves providing space heating for a room.
Generally they are 6-12 kW in output, and some models can be fitted with a back boiler to provide water heating.
- Boilers connected to central heating and hot water systems. These are generally larger than 15 kW.
Obviously it is necessary to buy fuel for these systems, and have room to store it. Wood requires more space for storage
than other fuels.
The fuel options for domestic use are logs, wood chips or wood pellets. It is important to avoid burning painted wood,
chipboard or other processed timber as these give off noxious gases.
Log fires are attractive but labour intensive. The work required can be minimised by using the fire
to heat a large quantity of water, which then supplies the heat required for the dwelling.
Wood Chips can be produced fairly easily from wood.
Their advantage over logs is that they can be fed automatically into the boiler.
Wood Pellets provide a consistent fuel, with a price per kilowatt similar to that of mains gas.
They can be used in automatic boilers which take fuel from a hopper, and only require the ash removed every few days, or in
some cases a few times a year. They provide more energy per unit weight than wood chips or logs,
partly because they have been dried to reduce the water content. The water content is typically 8% against the normal
for wood of over 22%.
As wood is now a fairly rare choice for heating, it is important to arrange for a supply of fuel before committing
to this kind of fuel. If you are using wood because of its green credentials it should come from
a sustainable source rather than, for example, virgin forest. It is also desirable to ensure that the wood
does not have to be transported too far.
Unfortunately while wood pellets are common in Scandinavia and the USA, they are much rarer in the UK.
Welsh Biofuels is a well established supplier but rather far away.
The main customers of local suppliers TV Bio Energy Ltd and
Biojoule Ltd are power stations, industrial units and schools.
Logpile provides a list of suppliers in
Britain. However some of these will import their supplies.
Wood for burning is competitive in cost with other fuels such as oil and gas for the same heat output, however
the stoves and boilers are about twice the price. Home Sources
provide a list of stove suppliers. Grants are sometimes available for installing wood boilers.
The National Energy Foundation provides a good
introduction to this subject. "Wood is a renewable energy source because
the carbon dioxide emitted when the wood is burned has been taken out of the atmosphere by the growing plant.
Even allowing for emissions of fossil carbon dioxide in planting, harvesting, processing and transporting the fuel,
replacing fossil fuel with wood fuel will typically reduce net CO2 emissions by over 90%."
Wood Stoves is a good way of avoiding the use of fossil fuels, provided you can store the fuel
and manage the extra work involved. The installation is more expensive, but once installed the ongoing costs
are likely to be similar to those of fossil fuel alternatives. However as this is an unusual choice of fuel, it is important to
establish a reliable and renewable source for the fuel chosen. Ideally this should be local so that the energy used
in transport is minimised.
These are panels facing the sun which heat water. The most common use is for domestic hot water.
When the panels are hot enough water is pumped through them and then through a coil in a hot water tank.
Installations are designed to avoid any need to heat water by other means during the summer.
In Oxfordshire the solar energy falling on a square metre of roof, facing south and angled at 30 degrees,
is about 1100 kWh per year. A typical dwelling uses about 3000 kWh a year on water heating.
Four square metres of solar panels, without any screening from trees or other obstacles,
would receive about 4400 kWh of solar energy. It is difficult to capture more than 40 to 50% of this usefully because
of losses on collection, heat loss from the storage tank, and the fact that in summer some of the heat will be
produced when it is not needed.
If placed on the roof of a house with a north south ridge line, a larger area of solar thermal panels is needed for
the same effect.
If the water would otherwise have been heated by electricity at 8 pence per unit a saving of 1750 kWh would be worth £140.
If the alternative heating was by mains gas, the saving might be around £60.
There are two main varieties of Solar Thermal Panel being installed on houses at present. An Evacuated Tubes panel
is the most efficient, however the alternative Flat Plate panel is less expensive, and
a larger area of Flat Plates may be the preferable solution.
The National Energy Foundation web site quotes cost of
£2000-£5000 for a commercially installed system. The cost depends on ease of access to the collection site,
on whether a new hot water tank is required, and on the controls fitted. The same site quotes £500-£1500 for
a DIY system but other sites quote up to £3000 for the components required.
The break even cost of an installation
saving £60 a year would be £895 and one saving £140 a year would be £2100. At present (2006) a grant of
£400 is available to households for a system installed by a recognised installer.
Where the site and type of a building makes them practical, Solar Thermal Panels provide an effective way of
saving CO2 in the supply of domestic hot water.
While they are unlikely to be justified purely as a financial investment, the environmental benefits are
make them an attractive option.
Solar Panels do not normally need planning permission, however planning permission is needed for installations on
listed buildings and within a conservation area.
Advice should be sought from the
Vale of White Horse Planning Department for such installations.
Relevant data on solar panels in practice is provided in a
Department of Trade and Industry Report.
Solar heating is also used for warming swimming pools. This requires less costly Solar Thermal Panels
as the output temperature required is lower.
Solar Cells are also known as Photo Voltaic(PV) Systems. They convert incident energy from the sun into electricity.
The output of each cell is a low voltage direct current,
but the output of an installation will typically be converted into 240 volt alternating current to supplement the
electricity mains. They may also feed electricity into the mains through an export meter.
How to be paid for this electricity is discussed below.
Solar Cells are provided in panels which ideally should
be mounted at about a 30 degree angle facing south, with no shading by trees or other buildings.
Photovoltaic cells are less efficient in extracting solar energy than Thermal Panels. The current silicon based
cells have a theoretical maximum efficiency of about 28%, partly because they only extract energy from part of the sun's
spectrum. Practical efficiencies at present are about 15% - so for a
given energy capture the area covered needs to be about six times that of Thermal Panels collecting the
same amount of useful energy. Meanwhile the cost per unit area is greater.
As a result the payback on domestic Solar Cell installations is lower than for Solar Panel systems.
However the energy generated is electrical, which is more valuable than heat, and
the installation does not need a pump and special plumbing and so is likely to need less maintenance.
A typical domestic Solar Cell installation will be rated to generate a maximum of 1 kilowatt of energy.
This requires about 10 square metres of solar cells. On an open south facing
location on Oxfordshire this may collect about 750 kWh a year. At 8 pence a kWh this is worth £60.
Currently the PhotoVoltaic Association states
that a typical grid connected installation costs about 6 or 7 pence per watt, so a 1 kilowatt installation
may cost £6,000 to £7,000. At this price the payback time at current fuel prices is 100 years.
As the life of the system may only be 30 years, the decision to make an installation will not be based simple economics.
The amount that can be earned in a grid connected system exporting small amounts of electricity depends very much on
government subsidy, so the installation is most effective if the energy is to be used locally.
As maximum power requirements do not normally arise at the time
of maximum solar energy, local storage of energy might be considered. This is discussed below.
These systems are subsidised, but even so they are not economic for individual houses.
A system generating a maximum of 1.5 Kilowatt
might cost £6,000 after allowing for receiving a grant, this might be assumed to cost about
£400 per year. Since the system can generate full power for only a few hours each day,
the energy generated in a year might be around 1000 kilowatt/hours, worth currently
about £80.
Solar Cells use considerable energy to make, so in the UK they need to be run for 5 years before they have generated
the energy used in their construction. However thereafter they are benefiting the environment.
It is difficult to see any justification for a domestic Solar Cell installation in Blewbury.
The cost is too high, and the energy generated cannot be used effectively.
Domestic Combined Heat and Power(CHP) installations use a conventional fuel - normally mains gas -
to generate electricity and also to supply hot water. While the efficiency of electrical generation does not approach
that of a large power station, the fact that
the heat is also used means that overall the domestic installation would use the fossil fuel more effectively.
The design aim of a domestic CHP unit is to replace a conventional gas boiler, and to require no special
installation skills. The electricity generated reduces the demand from the mains, and may feed electricity back into the mains when
local demand is lower. This requires a new electricity meter which records exported electricity separately.
Currently leading contenders for CHP systems are PowerGen, Baxi and Honda.
- Powergen has contracted a small New Zealand company to supply 80,000 WisperGen units over
the next 5 years, and offer to buy any surplus power. The WhisperGen can generate 8 kW of heat
and about 1.3 kW of electricity. Obviously a suitable house for the WisperGen will be one where the maximum heat loss
is around 8 kW. This might apply to a new 5 bedroom house, or an old - less well insulated - 3 bedroom one.
Such a house might use 18,000 kWh of heat a year, and so the WisperGen would generate about 3,000 kWh of electricity.
Powergen will buy any electricity generated and not needed locally currently at a price of 3p a unit. If 2,000 kWh
of that generated is used domestically and mains electricity costs 8p a unit this will save £160, and
if the remaining 1,000 kWh is exported this will earn £30.
The WisperGen costs about £3000. The efficiency is not quoted but from the benefits claimed appears to be about 80%.
If so, the WhisperGen would appear to have an advantage over a more efficient condensing boiler giving 90% efficiency both on
fuel cost - a saving of around £60 per year - and on greenhouse gas emissions though the saving here is only about 4%.
This is probably the only feasible CHP solution for a typical house at present.
- Baxi have a larger unit generating 5.3 KW electrical and 10.4 KW of heat. It is too large for domestic use and costs
around £15,000.
- The Honda Micro CHP generates 1 kW of electricity and 3 kW of heat. The efficiency claimed is 85%.
15,000 of these units have been installed in Japan.
The amount of heat is small for most UK houses, and so a top up heating unit
would be required. CHP units work best when they run for long periods, so this combination of a CHP installation
sized to match normal heating requirements with a more rarely used conventional boiler could be sensible. The installed cost is said to be about
£5,600, which means that it would not be an economic choice.
- BG (British Gas) has invested considerable sums in developing their MicroGen system,
to be available in a range of sizes. This development was halted early in 2007.
A major advantage of such systems could be that they can continue to power essential services such as freezers and
a few lights if there
is a power cut. This requires specific design, as such systems must be designed not to
generate electricity if the mains fails.
PowerGen say their system may cost £600 more than a conventional boiler of the same size.
The electricity from CHP
does not come from a renewable resource and so does not qualify for Renewable Obligation Certificates (ROCs).
So for the export of electricity to be economically sensible it is necessary to find a supplier prepared to buy
the exported electricity. The suppliers considering doing this at present include PowerGen and BG (British Gas).
However they link the agreement to buy the power to the use of their selected CHP system, which may not suit the requirement.
The most appropriate comparison for a CHP system would be
with the alternative of a modern condensing boiler. With a typical
condensing boiler about 88% of the energy in the incoming gas is converted to the energy in the heated water. If the
CHP system does not reach a similar efficiency the benefit of generating some of the output as
electricity does not compensate for the poorer performance.
CHP installations can be sensible for factories, large offices or whole estates.
CHP for domestic installations is less attractive, partly because the technology for domestic use is still in an early stage
of development, and partly because the electrical energy generated may not be required.
As explained elsewhere it is difficult to be paid for this electricity.
Domestic CHP is potentially a very significant development. If such units were available in a suitable range of sizes,
at reasonable prices, with efficiencies similar to that of Condensing Boilers, and with an easy means of being paid for
the spare electricity generated, they could become the normal installation for central heating.
The industry is represented by the Combined Heat and Power Association.
Ground Source Heat Pumps act as refrigerators in reverse, cooling the external ground while heating the house.
Some installations can also be used to cool the house during the summer, though this uses some of the energy that might have
been saved during the winter and, possibly for this reason, such heat pumps do not attract grants.
The heat sink outside the house requires a network of pipes covering about 10 metres per kilowatt required.
This can be achieved either by burying horizontally at perhaps 1.5 to 2 metres below the surface, or
if space is not available by using a vertical bore hole.
The advantage is that, particularly if only a modest temperature is required, the amount of heat supplied can be 3 or 4 times
greater than the electrical energy used to run the system.
A typical 8 kW system costs
£6,400-£9,600 plus the price of the
heat distribution system. This can vary with property and location.
The efficient delivery of warmth rather than hot water makes them most
appropriate for heating swimming pools and for under floor heating.
They are most suitable for new construction in locations without access to mains gas.
Heat pumps are more efficient generating warm water rather than hot water so can be considered for supplying under-floor heating.
Where gas is available for heating, a heat pump relying on
mains electricity is unlikely to be a good choice either economically or for saving greenhouse gases.
The energy gains made by the heat pump are largely cancelled by the losses in generating and transmitting
the electricity in the first place.
Heat Pumps are not likely to be a sensible option for existing houses with access to mains gas.
Their best role is in supplying warm water, typically for under floor heating, to new developments where gas is not available.
Wind Turbines extract energy from the wind and are normally designed to generate electricity.
However similar devices are used for pumping water, and for the direct generation of hot water.
With small devices a fairly high wind speed is
required in electricity generation applications. They are thus most suitable for remote fairly windy locations free of trees.
Small wind turbines to generate electricity for household use might generate between 1 and 3 kilowatts at maximum.
They cost from £3,000 to £10,000 and require regular maintenance.
Average wind speeds in central England are lower than in the rest of the United Kingdom,
and Blewbury is in a location sheltered by trees, and by the downs in the south.
The lower wind speed is particularly important as the energy available increases as the cube of the wind speed.
Thus the energy available from a wind installation is likely to be a third of that provided by the same installation
in open country in other parts of the UK, and an eighth of that available on a hill or ridge.
Wind turbines work best in a steady breeze. Where small turbines are to be mounted on roofs, the turbulence
generated by the roof may significantly reduce the power available. The need for occasional access to the turbine
for servicing should be considered. In some cases the turbine will generate an unacceptable flicker
with the sun in some directions. There can also be problems with noise and vibration.
It is unlikely that a wind turbine would be a sensible investment in a Blewbury village garden.
Temporary Storage of Energy
If the energy for hot water is to be obtained by a daily collection of solar energy, the storage tank must be able to
hold enough water for all normal uses between say 5 p.m. and 10 a.m.
The normal water usage in the Thames Valley is about 168 litres a person a day - a bath may use about 80 litres of water,
a 3 minute shower might use 50 litres. Washing up by hand can use 25 litres.
About a third of usage is of hot water - say 220 litres a day for a four person household.
Typically hot water tanks hold 150-300 litres.
Solar Thermal systems will normally be sized so that they can meet the normal requirements for hot water over
the course of a day for six to eight months each the year.
The cylinder to store this heat should be able to hold all the hot water to be used over the next 24 hours, as most of the
usage is between 5 p.m. and 10 a.m.
A hot water tank of diameter 50 cm and height 120 cm holds about 235 litres of water.
To heat this volume of water to 60 degrees Celsius from a cold water supply at 10 degrees takes about 13.5 kWh.
To generate this in a normal summer day Solar Panels occupying at least 4 sq. metres are desirable. Doubling
the area of panels would have no benefit on many days.
If the tank is insulated by 75 mm of foam, with a U value of 0.1, a further 1.5 kWh of energy may be lost by convection each day.
This would cool the tank by about 4 degrees overnight. Thicker insulation would be an advantage.
To avoid scalding hot water temperatures, any local heating should normally be stopped once the water in the tank reaches a
maximum temperature e.g. 65 degrees Celsius. However if the system has been designed appropriately it is possible to heat
the water in the tank to a higher temperature, say 80 or 90 degrees Celsius. This needs better insulation to minimise heat loss,
precautions to ensure that noone can touch the tank surface, and a thermostatic mixer valve to reduce the temperature of
the hot water feed by adding cold water. Advantages of this high temperature storage is that more energy can be stored in
a tank of a given size, and that the hot water supplied is at a more constant temperature.
It is very desirable that the supply of hot water should use the locally generated heat when it is available. This should
be as automatic as possible, as many users will not remember to switch off conventional water heaters when solar energy is available.
If conventional heating were to ensure that the hot water tank is already hot at the start of the day, the extra heating from
solar panels is largely wasted. An ideal system would use water from the solar heated tank as long as it is over some
acceptable temperature, say 45 degrees, and otherwise gets hot water heated directly from
a combi boiler without any storage. If a single tank is to have two kinds of heating, for example one coil from solar panels
and one from a boiler, heating from the boiler might be controlled to run only in the evening, and to have a
set point perhaps 5 degrees below the maximum for solar heating.
A system can be designed to try to store enough hot water to support two days' usage. This allows continuing use of solar
energy for hot water if a sunny day is followed by a cloudy one. This would be a more expensive system with a larger
solar panel and a larger hot water tank.
Storing solar energy as hot water is a practical option for the hot water usage of a dwelling.
A separate larger hot water tank could be used to store Economy 7 electricity to drive a flexible central heating system, but a
gas boiler without storage is usually a better solution. It might be thought that Economy 7 electricity generated
less CO2 than the direct use of gas, because of the greater proportion of nuclear and renewable energy in the
electricity used at night.
However the overnight consumption of electricity in England currently far exceeds the available nuclear and renewable generation
capacity so any additional load would be supplied by from fossil fuel power stations.
The CO2 produced by these for each kWh of useful heating far exceeds that from the direct use of gas..
The use of hot water to store energy from other
sources such as wind turbines fails to attract because the other energy sources are not viable.
Electrical energy can be stored in rechargeable batteries, and can be regenerated later. It can be converted
to match and supplement the mains supply. Special batteries are available designed for the storage of
solar or wind generated energy
but their general characteristics are similar to those of a conventional car battery, which can hold about 0.5 kWh.
Batteries will only return a proportion of the energy used to charge them.
The proportion depends on the charging and discharging rates
and the depth of discharge, but it is difficult to achieve more than 80% efficiency. Batteries will only last a limited number
of charge and discharge cycles. For the fairly deep discharge cycles likely in this kind of application
this might be around 400 cycles. If so the cost of the battery must be spread over the storage of 200 kWh. This is likely to
be too high to be viable. For example a new Trojan deep cycle battery L16H intended for this purpose holds about 3 kWH and the
makers state it can supply
1004 kWh during its life. This costs about £220, making the battery cost per kWh 22 pence.
In addition the disposal of failed batteries is a significant environmental problem.
For greatest efficiency and life batteries should be charged and discharged fairly slowly, e.g. over a period of 10 hours.
Heavy short term loads such as electric showers and clothes dryers should be met from the public supply. This can
be achieved by limiting the maximum energy output from the batteries.
It is not sensible for a battery to feed electricity into the public mains supply at times of low demand,
so a sensor of the metered electricity input is required.
A practical installation might use 20 batteries able to hold say 8 kWh of electrical energy. These would be able
to accept the full output of a 1 kWh generator such as a solar cell panel or wind turbine.
On an average day such a generator might provide a total of 8 kWh,
and the system might then be able to replace about half the 12 kWh electrical energy used by a typical household.
It may be possible to connect the system to the mains through a normal 13 amp plug.
Any system able to feed the public mains must switch off if the mains is not present. This is to protect engineers working
on the public lines. Thus such systems do not normally provide backup power for mains failure.
Battery storage may also be used to accept energy from the mains on a low overnight tariff and return it during the day.
This is used in Japan, where there is a large difference between the two tariffs. It is less viable in the UK where the tariff
reduction is about 50%, and part of the benefit of this is lost during the storage process.
This process of smoothing demand has some environmental benefits
as the power stations providing the base load at night are typically more efficient, or use nuclear fuel.
Battery storage does not seem likely to be an effective or economic method of storing energy domestically.
Exporting surplus energy to the mains should be the best way of using surplus electrical energy effectively. The only
extra equipment needed is a meter to record the electricity exported.
Currently the restrictions and costs of exporting more than 16 amps into each phase of the mains are too expensive
for individual household installations. The fair price for energy exported to the grid is less than that for energy being received.
However there are also losses
if the electricity is stored locally, for example in batteries.
Unit-e is a company organising green energy supplies and payment for such energy
when generated locally. Some major suppliers such as Southern Electric are now prepared to pay for locally generated electricity.
The price is about 4p a unit.
If the source is renewable, e.g. Wind or Solar cells but not Combined Heat and Power, an additional financial return
can also be achieved
by gaining Renewable Obligation Certificates (ROCs). These can be provided for the multiples of 500 kWh generated either
each month or in a year. The total generated in the period is rounded down. Thus there is no payment for 499 kWh.
The commercial value of a ROC arises as utilities are fined if they do not meet their renewable target. As an alternative
they can buy ROCs. The value of an ROC is thus limited by the fine on utilities if they do not meet their renewables target.
This is typically between 3 and 4 pence a unit. Thus one ROC is worth about £15.
A single phase 3 kW unit would generate a maximum of 13 amps. If it operated at 30% of full rating over a month
it would generate about 648 kWh. If it was from a renewable source, the income might be 7.5p per unit or
£48 per month.
On a 3 phase system it would be possible to supply up to 10 kW. If the local system generated at an average of
30% of this full rating, it might generate 2400 kWh a month, and in this time could earn perhaps £180.
If a system can feed the mains, it must shut down if the mains supply fails, to ensure that it does not electrocute
engineers working on the lines. Thus such systems are not suitable for standby power.
When an alternative energy system is installed and reported, there will typically be a long time before the electricity supplier
gets round to installing a two way meter. During this time, when electricity is being exported the normal meter typically runs
bachwards. This effectively earns the householder the retail rate.
Just relying on Reuseable Obligation Certificates
The simplest method of being paid for renewable energy is probably that arranged by
Good Energy . The company pays 4.5p for every kWh generated, whether it is used in
the household or exported. This is a simple and convenient arrangement particularly if most of the electrical energy
is being used locally.
Systems are available for storing energy in a variety of other ways. However none is competitive in small installations
with those already discussed.
Energy can be stored as hydrogen by electrolysing water. With a suitable system the hydrogen could be created
at high pressure, avoiding the need to compress it to minimise the volume needed to store it.
If atmospheric pressure storage was used,
an ability to store about 5 cubic metres of hydrogen would be needed to deliver 10 kWh. The hydrogen could be
converted back into electricity when required using a Fuel Cell. This is the most promising of the alternative
solutions, but the technology is not yet mature enough for use as a practical storage medium.
Energy can be stored by raising water to a high reservoir, and allowing the energy to be released
through a turbine when is needed. This is used very effectively in large scale "pumped storage" power stations,
but the concept does not scale down well. If a domestic installation pumped water between two reservoirs each 1 metre cube,
with a vertical separation of 10 metres, the maximum energy stored would be 0.03 kWh worth perhaps 0.2 pence.
A more dramatic installation might imagine a reservoir on Churn Hill of say 10 x 10 x 10 metres,
capable of holding 1000 tonnes of water, connected to a similar reservoir 50 metres lower down.
This installation would be able to store a potential energy 5,000 times greater than the domestic option or 150 kWh.
Such a system might act as the backup storage for a wind turbine or solar cell installation rated at 15 kW,
and the combination might meet most of the electrical needs of 10 houses. However it would be very expensive
to build and maintain. A system that fed the excess energy back to the mains would be much less expensive
and more efficient.
Another way of storing energy is in the rotation of a flywheel. Existing flywheel technology can store
energy for a year or more. See for example the Active Power company.
Compared with batteries, the materials used are more benign, the power extracted is closer
to the power stored, and the system does not deteriorate after a limited number of cycles. However a flywheel installation
with the same energy storage as a normal car battery is expensive and weighs a quarter of a tonne.
Utilities can store energy as compressed air in airtight underground caverns.
When required the air expands through a turbine to create electricity. The decisive problem with
much smaller systems is the limited power that can be generated. A container holding a cubic metre of air at 100 atmospheres
would only have a potential energy of about 0.1 kWh, worth about 1 penny.
Supercapacitors can store a modest amount of electrical energy very efficiently in enhanced versions of
standard electronic components. They can provide very large bursts of power.
Their ideal application is as a means of providing bursts of energy for road vehicles when overtaking or climbing
hills, thus allowing the main engine to be sized for the normal load, making it more efficient.
However they are not appropriate for storing the energy needed in domestic installations.
Storage of energy in Superconducting Magnetic fields is practicable for power utilities, aiming to
improve the stability of supplies with rapidly varying loads. However introducing very large magnetic fields and
cryogenic temperatures into a domestic installation would be as unwelcome as it is impractical.
The TV Energy page on renewable energy sources provides more
information on the technologies.
The Office of Gas and Electricity Markets (OFGEM) the industry regulator.
Wind & Sun design, supply and install wind and solar systems to customers' requirements.
Proven Energy are a supplier of wind and photovoltaic components and systems.
Blewbury Energy Initiative
All rights reserved
|
If you have any comments on these pages,
or wish to communicate with the Blewbury Energy Initiative,
please contact the webmaster.
The committee meets monthly,
so please allow time for a response.
|
