Net space heating
demand = gross space heating demand – free heat – solar gain
In the summer months,
free heat and solar gain combined provide sufficient space heating that there
is no need for additional (net) space heating. In fact, as can be seen in the calculations
in June and July net space heating demand figures are negative meaning that the
household is ‘overheated’, i.e. the temperature inside the dwelling is more
than comfortably necessary, cooling/air conditioning may be required. Hardly
any net space heating is required in August.
Total annual gross
space heating demand
Total annual free heat
and solar gain contribution
Total annual net
space heating demand , slightly less than half the annual gross
space heating demand
Cells are connected
in series, therefore total PV voltage is:
Total power provided
Total PV power
divided by 8 should then be 1500mW.
Total energy required
by battery for 72 hours
Power dedicated to
charge the battery = PV power available – link power demand
Energy required to
Number of hours taken
to fully recharge battery
It is important that
the energy input required to operate the biomass energy system is lower than
the actual energy benefitted from the system otherwise there would be no net
energy output. This is the relationship (the energy required to operate biomass
energy system and the energy output from the system) that is described by
energy payback ratio.
The payback ratio will be different for different forms
of derived energy e.g. heat or using the heat to generate electrical energy. The
energy used to create and run the coppice may be in the form of producing
fertilizer to grow the wood, and that required in the various activities to run
the coppice system such as planting the trees in the first place, then
harvesting and transporting the wood.
This ratio has to be defined over a certain time period,
for example a number of years. This is because the energy input does not
immediately lead to energy being derived (output).
Total energy content
Total energy output
Total energy required
to facilitate process
Energy payback ratio
Total energy output
Energy payback ratio
countries, such as the USA, Canada, EU countries and Japan a large portion of
the available hydro power has already been exploited. Hydropower plants found
in these countries were built 30-40 years. These can be refurbished and
extended to increase their generation capacity. This is the most cost-effective
way of increasing hydro power generation in these countries. Also, there are
proportionately fewer unexploited potential sites for large dam based power
plants. The developed countries have good integrated grid systems. They
experience large disparities in power demand at different times of the day.
Pumped storage system which can be brought on line easily and quickly at high
peak demand may play an important part in augmenting the power grid.
The majority of the
45000 large dams mainly in developing countries do not incorporate hydro
generation. This is a major potential for future hydro electricity generation.
These countries also do not have a fully developed electricity infrastructure.
Building hydroelectric generation plants at these sites is particularly
attractive. They do not require the huge financial costs of creating
dams, with their attendant environmental, human and economic costs. Also,
the process is fast compared to that using a newly created dam.
such as China, have desperate requirement for more electricity generation, this
has resulted in more coal-fired power plants to be constructed as they take
short time to build. Building plant on existing dams may take longer than coal
fired plants but would still be competitive in terms of time taken
against systems built on new dams.
Barrage systems are normally located in estuaries and
they benefit from the vertical rise and fall of tides. When sea level rises due
to the gravitational interaction between the Earth and the Moon water is
captured in an enclosure called barrage. After sea level has dropped (ebb or
low tide) there will be a water level difference across the barrage and the sea
giving large potential energy, which is then converted to kinetic energy by the
flow of barrage water through pre-constructed passages with built-in turbines.
The turbines then drive generators to produce electricity.
Barrage systems exploit energy from the vertical movement
of the tides, whereas tidal stream systems benefit from the horizontal
movement. The velocity of the tidal ebbs and flows is fairly low but when these
tidal movements are narrowed to channels or other topographical confines the
movement speed increases significantly. Tidal turbines (most common being HAWT
type) installed in these passages generate electricity at an enhanced rate due
to the higher speed of currents.
Tidal stream systems are less costly than tidal barrage
systems as well as less ecologically damaging. Other advantage could be stream
systems can operate on both ebb and flood tides, thus having higher capacity
factor. Also, more units can be attached and installed to the existing system
gradually increasing power output at low price. Smaller visual impact is also
Maximum potential energy E per tide cycle:
Number of cycles
Adjusted annual electrical output
Adjusted 150MW capacity
Annual energy output of 37.5MW, which is
It cannot be assumed that this 150MW plant is driven 24
hours a day because of the nature of the tide ebb and flood cycle, therefore
the generator will run only a few hours a day. The annual available potential power is not spread
evenly throughout the year but is squeezed into cycles of few hours every day.
If, assuming, the generator is driven only 5 hours a day, is the required power capacity of the
generator to fully exploit available energy. This figure is more than twice as
much of the installed capacity of the plant, i.e. 150MW with 25% capacity
Three main types of large scale hydropower systems are
used in different sites in the world. Each one is suitable for a different type
of geographical location. The most common uses a storage dam. A large storage
reservoir is created by building a dam across a river. Water is released
through channels to drop a certain height and drive turbines which in turn
drive electrical generators. The potential energy of the stored water is
converted to kinetic energy and finally to electrical energy. Building dams
alters the geography of the area and has major environmental and social
A second type requires a river whose water is diverted
through a channel to drive a turbine and then an electrical generator. Such
systems disturb the environment the least as no dams or reservoirs need to be
A third type is the pumped storage system. The
principle is the same as the dam. It incorporates a low-level reservoir and a
high-level reservoir. During off-peak time when power demand is low, water from
the lower reservoir is pumped to the higher storage by the use of energy from
an external source. At high demand this potential energy is released to the
lower reservoir and generates electricity the same way the conventional dam
In 2009 the useable hydroelectric power of the world
called the technical potential was estimated to be per annum Ramage J. 2012a. Existing plants
were generating only , or about
20% of the total technical potential. More recent studies show the available
global hydro potential is approximately World
Energy Council 2012. This paper argues that more of the unused resources
should be developed. To do this the benefits and disadvantages of hydro power
There are a number of environmental and social
benefits and penalties to the development of large-scale hydro systems. By not
using fossil fuels there is no carbon dioxide emission into the atmosphere or
emission of particulates and other harmful compounds such as sulphur and nitrogen
dioxide which contribute to acid rain. Some methane, a greenhouse gas is
released from hydro plants due to the anaerobic digestion of vegetable matter
deposited into the reservoir by the river feeding it. However, a coal power
plant would produce 40 times more greenhouse gases expressed in CO2
equivalent to generate the same amount of electrical energy Ramage J. 2012a, Condliffe J, 2016. The amount of
methane released may not be significant.
For hydroelectric plants, there is no danger of the
leakage of radioactive emission into the atmosphere or cost of treating and
storing spent radioactive fuel as is the case with nuclear power stations. The
sun drives the water cycle making hydropower a renewable energy source. A
number of recreational opportunities that benefit the community come with the
large water reservoirs, such as fishing, water sports, and a visual improvement
to the landscape.
Large dam based hydropower may allow irrigation
schemes and flood control to be implemented, allowing short and long term
economic advantages to the community. Hydropower offers strategic political and
economic advantages because it is harnessed locally. Therefore, there is no
need to import any fuel sources. This reduces the reliance of nations on others
who control the supply and price of fuels especially fossil fuels. This is
particularly true for nations in Africa and Asia whose proportion of unused
technical potential, at present, is greater than that of developed nations.
However, there are social and environmental costs.
Existing hydro power schemes such as the Aswan dam on the Nile Biggs D, 2001
lead to the displacement of millions of people when their abodes were flooded
to accommodate the reservoir dam. The local ecosystems are damaged and land is
eroded. Sediment which is normally found in rivers is held back by the dam.
This deprives the downriver areas and often fertile soil as in the case of the
Nile through Lower Egypt. The downstream river tends to erode its channel due
to an absence of the sediment, thus lowering the riverbed and endangering
vegetation and wildlife.
For new schemes the initial costs dominate as there
are no fuel costs and the cost of maintenance of equipment is low in comparison
with the initial cost. Therefore, the cost of servicing the capital loans used
as the initial expenditure dominates the cost over the operating life of the
plant. This may incur a high risk if interest rates become too high Ramage J.
The diversion of a river or a mountain stream may
affect the environment in a disadvantageous way. For instance, water wells can
dry up, vegetation may die and the scheme may lead to the necessity of
artificial irrigation where none was required before. In addition, the scheme
may pose a danger to the habitat of wildlife.
Pumped storage systems are very important to developed
countries where there is already significant capacity from other sources such
as nuclear and fossil fuel. Hydro plants are easy to turn off and bring into
service in a national grid system. The non-hydro power plants can be run at a
steady rate. There is significant disparity in demand at different times,
pumped storage systems can make up the shortfall. At periods of low demand the
extra energy can be used to pump up water to upper reservoirs and at high
demands the hydropower system can generate energy and feed it into the system.
They can be used to back up other sources in case of failure or during periods
of outage due to maintenance. Pumped storage can be used to back up renewable
energy sources, which by their nature are intermittent such as wind and solar
For nations with less accessible capacity, it may be
attractive to install hydro plant at existing lakes or dams constructed for
other purposes. Existing hydro plants may also be upgraded and refurbished.
Both these approaches will deliver an increase in hydroelectricity at a cost
estimated to be a third to a half respectively when compared with completely
new schemes. The environmental consequences will be minimized Ramage D.
The alternatives to hydropower to meet increasing
demand are fossil fuel, nuclear or other renewable sources. Fossil fuel based
generation is mature and well established but has severe and almost prohibitive
environmental costs. Nuclear fuel based generation is costly and there are
environmental and security issues in case of accidents or sabotage. Renewable
energy sources are still immature. The environmental costs are not as great but
the capacity and costs of installation and maintenance may still be too high.
Overall it is considered that hydroelectricity with its flexibility may be
desirable in conjunction with other renewable sources.
Biggs D. 2000 ‘This Dam Project’, Philosophy of
Structures, Mc. Gill University Online. Available at
Condliffe J, 2016 ‘Hydroelectric
Power Isn’t as Green as We Thought’, MIT Technical Review Online. Available
Ramage J. 2012a,
‘Hydroelectricity’ in Boyle G (Ed.) ‘Renewable Energy Power for a Sustainable
Future’ 3rd. edn., Oxford, Oxford University Press, pp.185-240.
Ramage J. 2012b,
‘Hydroelectricity’ in Boyle G (Ed.) ‘Renewable Energy Power for a Sustainable
Future’ 3rd. edn., Oxford, Oxford University Press, pp. 230
World Energy Council (2016),
‘World Energy Resources, Hydropower’ Online. Available at https://www.worldenergy.org/wp-content/uploads/2017/03/WEResources_Hydropower_2016.pdf
Lower Slaughter, Gloucestershire. GL54
coordinates: 51°54?4.87?N, 1°45?47.8?W
Decimal coordinates: 51.901354, -1.763279
Ordnance Survey: SP1638422561
Heating (HDD) and Cooling (CDD) degree days
for nearest weather Station – Brize Norton (1.58W, 51.76N)
Five Year average (2013-2017). Base temperature 15.5oC.
Table 1. Degree days for Lower Slaughter
Average solar insolation at this
location is 3360Wh/m2/day, annually 1226400Wh/m2.
Table 2. Annual solar insolation for Lower Slaughter
Figure 1. Annual solar insolation graph for Lower Slaughter
Micro hydroelectricity, solar thermal energy
and solar photovoltaic are considered. A micro-scale hydro power plant is
plausible as River Eye flows through the village. A disused water mill is
located in the village. The kinetic energy of the river would drive the plant. Solar
thermal energy is the second technology. Two hotels and some holiday cottages
accommodate visitors mostly in summer, hot water demand increases during this
period. Solar photovoltaic energy would be the third option to reduce
electricity demand from the grid.
Renewables First online https://www.renewablesfirst.co.uk/hydropower
B. 2012, ‘Solar thermal energy’ in Boyle G (Ed.) ‘Renewable Energy Power for a
Sustainable Future’ 3rd edition. Oxford University Press, pp. 21-74.
Hydro facility manufacturers quote 25 years
lifetimes, with regular maintenance up to 50 years. Lifetimes for solar heating
systems are quoted at 10 years and with maintenance around 20 years. PV systems
life times are quoted as more than 20 years.
Eye energy availability is based on the following assumptions:
Velocity of river
Volume of water available
Weight of water
Kinetic energy extracted per second
Taking into account 90% capacity factor a
hydro plant with power capacity of approximately may
fully exploit available kinetic energy.
Rooftop PV systems are considered in the
scale of .
Evacuated tube solar collectors may be
considered for thermal energy generation to provide hot water for the hotels as
is done in some hotels in London.
Installation costs for solar water heating
are quoted as £3000 for a 2-bedroom home and £6000 for a 6-bedroom property.
Scaling this to a 20-bedroom hotel would be around £20000. The photovoltaic
electricity generation systems would be considered for residential and
commercial properties. A typical 3.5kW grid-connected PV roof costs
Figure 2 shows
the capital cost of hydro plants in £ per kW. A 20kW system costs approximately
£7000 for every kW, therefore the estimated construction cost would be £140000.
Hydropower system build cost
Capital cost of hydro plant chart
Project title: Renewable energy for Lower Slaughter
Three renewable energy sources will be investigated,
starting with a hydro power plant at a disused water mill. The village
population is augmented by visitors during summer. A solar thermal source will
be evaluated to meet the consequential increased hot water demand. A photovoltaic
plant will be investigated to further reduce the carbon footprint. The
available and total annual energy demand, the expected lifetime of the power
plants and capital, operating and maintenance costs will be estimated to prepare
a technically viable and cost-effective plan.