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Contents

Wind

Hydro-Scheme

Biomass

Solar

Wind

General Information on Wind Power

Wind energy stands out to be one of the most promising sources of electrical power. With the price of production from wind turbine falling dramatically over the last 30 year to achieve now a remarkable 4p/kWh, many countries in the world promote wind power technology and European countries are no exception to that rule. For example, the UK’s Non Fossil Fuel Obligation program will add 500 MW of wind power to the UK’s power grid by 2010.

Wind turbines capture the wind’s kinetic energy in a rotor consisting of 3 blades mechanically coupled with an electrical generator. The turbine is mounted on a tall tower to enhance the energy capture. Numerous wind turbines can be installed on one site to form a wind farm of the desired energy production. Most modern wind turbines use horizontal-axis up-wind design.

The power extracted by the wind is given by the formulae: P = 0.5 * Cp * r * A * V³

With Cp: Capacity Factor between 0.2 and 0.4

r: Air Density r=1.225kg/m³ at sea level, atmospheric pressure and 15°C

A: Rotor Swept Area in m² A=p*D²/4 with D the rotor diameter

V: wind Speed in m/s

Reasons for Large turbines

Economy of Scale:

Large machines deliver more electricity at lower cost since the cost of foundations, road building, electrical grid connection are basically the same and besides the number of components inside the turbine are independent of the size of the machine.

Larger Turbines are well suited for offshore:

The cost of foundation does not rise in proportion to the size of the machine, neither do the maintenance cost.

Efficiency:

Large turbines use existing wind more efficiently.

Reasons for Small Turbines

Local Grid Too Weak:

This is the case for remote parts of electrical grid with low population density and little electricity consumption.

Less Fluctuation in the Electric Output:

The fluctuation of the electricity output from a wind farm with smaller turbines are less likely to reach high values. As if the wind is not blowing on one turbine it is very likely to blow on a large proportion of the rest of the turbines.

Spread the risk of Momentary Failure:

E.g. if one turbine is struck by lightning.

Cost of Using Large Cranes:

In case of large machine, the road building has to be strong enough to support the weight of the cranes as well as the weight of the elements that make the turbine.

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Location

Situated at a height of around 300 m on an unobstructed terrain, the site is ideal for wind. Both the British Wind Energy Association (BWEA) and the Meteorological Office (MET Office) give us an annual average wind speed of about 8 m/s. We also understand that the Argyll and Bute Council has carried a survey to determine the areas of sensitive, preferred and intermediate preferences for the implementation of wind farms. The chosen site is actually in an area of preferred preferences.

Wind Speed Profile

The data available from the MET Office was a 10-minute average wind speed measured at 09:00 every morning and hence we felt it would be more appropriate and accurate to work with the monthly averages. This fact explains the stepwise form of the annual production of the turbine.

Selection of the Turbine

Because a cluster of three turbines is not considered to be wind farm according to the Argyll and Bute Council planning guidelines, we decided to limit the number of turbines on the site to three. And therefore after investigating a number of different wind turbines, we chose the Nordex 600 kW.

Below are the Nordex N43/600 kW manufacturer’s specifications:

Rotor Data:

Type	3 bladed, horizontal axis, upwind
Rotor Diameter	43m
Swept Area	1.452 m^2
Power Generation	Stall
RPM	27.2/18.1 rpm
Cut-in/cut-out Wind Speed	3-4/25 m/s
Rated Wind Speed	13.5 m/s
Calculated Lifetime	20 years

Power Curve:

Annual Production

The manufacturer predicts an annual production of approximately 1.8 GWh per annum for an annual average wind speed of 8 m/s.

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Hydro-Scheme

General Information on Small-Scale Hydro

Small hydropower, with its multiple advantages as a decentralized, low-cost and reliable form of energy, is in the forefront of many countries' programs to achieve energy self-efficiency. Small hydro allows for rural electrification, petroleum substitution, rural development of isolated communities and as well as creation of employment. Hydro is a well-established technology and there is vast potential for small-scale deployment worldwide.

Investments in small scale hydro was rendered uneconomic in the 1950's by the availability of cheaper electricity through an expanding, province-wide grid; and by the availability of portable, flexible, low cost diesel generators. Diesel generators are still cheap to buy - but the rise in the cost of oil has made them expensive to operate. In most cases the national electrical grid, while extensive, do not include a number of small communities, resource-based businesses, farmers, and lodge owners.

Now things have changed – small-scale hydro has become economical attractive because it offers a stable, inflation-proof source of electricity, using proven technology. Small hydro installations have, historically, been cheap to run but expensive to build. That is changing now, with smaller, lighter, and higher speed turbine equipment, lower cost electronic speed and load control systems, and inexpensive plastic piping. Capital investments are still higher than investing in diesel equipment of comparable capacity; but the long life and low operating costs of small hydro make it an attractive investment for many applications.

Costs for small hydro installations vary considerably, because sites, conditions and sizes are all different. In establishing hydro installations the following factors, but not limited to, have to be taken into account:

(a) Estimate the power you need;

(b) Estimate the stream flow available;

(c) Measure or estimate the head available on the stream;

(d) Estimate the power and energy available from the stream;

Points necessary for Hydro Electric Power (HEP)Schemes:

• A high rainfall catchment area
• A river or water source with a suitable head of water
• A water intake placed within a weir or a dam
• A method of transporting this water to the turbine, through a pipe or channel
• A turbine, generator, and electrical grid connection
• The return of its water to the main flow

The exploitation of HEP schemes is dependent upon the topography, rainfall and the availability of funds, as a large capital outlay is initially needed. It is necessary to assess the visual intrusion upon the landscape and any changes to the local ecology that may be made. Very small schemes may use relatively cheap and very reliable electronic load control systems.

Types of turbines

Low, medium and high head are terms used to indicate the most suitable type of turbine for hydro projects. The various types of turbines are listed below:

- Low Head up to 10 m Use: Cross-flow, axial-flow or propeller turbine

- Medium Head 10 m to 200 m Use: Cross-flow, Francis, Pelton or Turgo turbine

- High Head 200 m to 1000 m Use: Pelton, Turgo-impulse or Francis turbine

Small Hydro System Components

Power House

The powerhouse stores and protects all the power-producing equipment and control devices. These devices can be operated and monitored either on site or remotely.

Feeder Canal

Water flows down the feeder canal from the intake to the forebay .The canal is usually made of earth or concrete, and is fitted with a grating to keep out solid objects carried by the stream.

Penstock

The penstock is a pipe connecting the forebay to the powerhouse. It pressurizes the water and must be capable of withstanding high pressures, and is therefore usually made of steel

Forebay

The forebay is a tank that holds water between the feeder canal and the penstock. It must be deep enough to ensure that penstock inlet is completely submerged so that air is excluded from the power equipment.

Tail Race

The tailrace is the flow of water out of the powerhouse back into the stream.

Reserve Flow

Hydroelectric plants are designed to use only part of the total water flow under normal operating conditions. The reserve flow is the portion of the flow not normally used

Intake

The intake is a buffer between the water supply and the hydroelectric plant. It is constructed of earth, masonry or concrete. Its shape is largely determined by the nature of the terrain.

Fish Ladder

The fish ladder allows migratory fish to move upstream to minimize the biological impact of the power plant.

Hydro Energy Production Equipment

Turbine

A hydraulic turbine is a rotating machine driven by water under pressure from a penstock or forebay. The energy in the flowing water is converted to mechanical energy by a revolving wheel fitted with blades buckets or vanes.

The flow is directed at the wheel by a nozzle or an injector allowing the flow to be adapted to the mechanical power required by the electrical equipment being driven.

Controls

Generators must conform to characteristics of the electrical equipment they are powering. Control systems act to modify the water flow to the turbine to maintain the desired characteristics, or to dissipate excess energy.

Set up Gearing

Electric generators are more efficient when they run at high speeds. If a turbine rotates at a low speed, "stem-up" gearing can be installed between the turbine and the power generator to increase the rotation speed.

Generator

Generators convert the mechanical energy produced by the turbine into electrical energy. Different types of generators are used depending on the characteristics of the electrical grid the hydroelectric systems are connected to.

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Assessment of hydro potential at Lochgilphead

Through a site visit undertaken to Lochgilphead and the use of a map (Landranger 55) three potential sites for deployment small scale hydro were identified:

1. Dippin Burn stream which flows through the village

2. River Add, which is about 6 km from the village and flowing westwards towards the ocean

3. The Crinan canal – a 10 km long canal joining the coast and Lochgilphead.

However, after further consultations and investigations the Dippin Burn and the Crinan canal were abandoned due to low flow rates and stringent water rights respectively.

Location

Rainfall data

The rainfall data was sourced from Websites of the Centre for Ecology and Hydrology and the Meteorological Office (U.K). Below are tabulated average annual rainfall statistics for the chosen site.

Month	River Add
	Average Annual Rainfall (mm)
Jan	169
Feb	106
March	139
April	81
May	83
June	92
July	114
August	132
September	181
October	194
November	175
December	167

Table 1. Showing the average annual rainfall for the site

Geology

Most of the Argyll and Bute area is formed of Dalrian rock. The township of Lochgilphead is built on a rock composed of alluvium and raised marine deposits.

Hydrology and Geography

Rainfall on the catchment area is important for the operational fie of a hydro scheme. The rain falling on the catchment area, the greater will be the river or burn flow, the greater the amount of power will be generated.

The catchment areas were estimated and with the knowledge of the monthly rainfall for the sites, as well as the evaporation and transpiration (E and T), which was estimated, to be 30%, the monthly run-offs were calculated. Most of the area is hilly and covered with forest.

Run –off and average annual flow of the River Add

The run-off of the Crinan canal was not determined because during the preliminary assessment it was found that canal is that is almost stagnant and the water usage (e.g. shipping). Hence, it was abandoned. The run-off and the annual flow of the Dippin Burn were determined in a similar way for the river and found to be low. Because of the low flows as shown in table 2, it was decided to abandon the burn.

With the help of the map, the catchment areas for the sites were estimated to be 10.9 km² and 71.2 km² for the stream and river respectively. From the rainfall and the catchment area, using the catchment boundary area method, the average monthly flow were estimated and consequently the turbine flow. To estimated the turbine flow, it was assumed that 10% of the run-off is residual. Evapo-transpiration losses were assumed to be 30%. To calculate the power output, turbine –generator efficiency was taken to be 80 %. The net head was estimated to be 10 m. The power output is calculated as follows: P = gQH (kW), where g = 9.81, Q is the turbine flow and H is the effective head.

Month	Stream Flow (m3/s)	Residual Flow (m3/s)	Turbine Flow (m3/s)	Turbine & Generator Power Output (kW)
Jan	0.51	0.051	0.459	36.02
Feb	0.32	0.032	0.288	22.60
March	0.42	0.042	0.378	29.67
April	0.24	0.024	0.216	16.95
May	0.25	0.025	0.225	17.66
June	0.27	0.027	0.243	19.07
July	0.34	0.034	0.306	24.01
August	0.4	0.04	0.36	28.25
September	0.51	0.051	0.459	36.02
October	0.58	0.058	0.522	40.97
November	0.53	0.053	0.477	37.43
December	0.51	0.051	0.459	36.02
Average Power (kW)				26.51
Average annual energy output (kWh)				232227.6

Table 2. Showing average annual stream flows and turbine flow for the Dippin Burn

Month	Stream Flow (m3/s)	Residual Flow (m3/s)	Turbine Flow (m3/s)	Average Power output (kW)
Jan	3.14	0.314	2.83	222
Feb	2.11	0.211	1.90	149
March	2.59	0.259	2.33	183
April	1.56	0.156	1.40	110
May	1.54	0.154	1.39	109
June	1.77	0.177	1.59	125
July	2.12	0.212	1.91	150
August	2.46	0.246	2.21	173
September	3.48	0.348	3.13	246
October	3.61	0.361	3.25	255
November	3.36	0.336	3.02	237
December	3.11	0.311	2.80	220
Average Power (kW)				182
Average Annual Energy output (kWh)				1 594 320

Table 3.Showing average annual stream flows and turbine flow: - River Add

Fig.1 Flow characteristics of the River Add

Fig.2 Power characteristics of the River Add

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Site selection and its characteristics parameters

The River Add was chosen because of its higher flow rates. However, it must be pointed out that to get much more accurate results flow measurement should be recorded for a longer period of ten years. The figures presented below are estimates.

Table 4 Summary of parameters of the River Add

Parameter	River Add
Head (m)	10
Minimum flow (m3/s)	1.40
Maximum flow (m3/s)	3.25
Minimum Power (kW)	109
Maximum Power (kW)	255
Overall efficiency (%)	0.8

Turbine selection

Because of low head and low flow, a cross-flow turbine would be the most appropriate choice. Based on the head and the minimum flow rate, a 100 kW turbine was chosen. This will provide an annual energy of 1 594 320kWh. Electric generators are more efficient when they run at high speeds. As the turbine would rotate at a low speed, a "stem-up" gearing could be installed between the turbine and the power generator to increase the rotation speed.

Costing of the system

The costing of the system was based on rates provided by the Small hydropower. The overall cost of the system was estimated to be £225 825.00.

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Biomass

Energy From Willow

Site selection

Moisture.

Willows grow best where there is at least 600 mm of rainfall, distributed evenly through the growing season, and moisture available within about one metre of the surface. Willow can grow on land that is too wet for other crops, but areas liable to winter flooding are unsuitable for mechanical harvesting.

Soil type.

Most agricultural soils with pH in the range 5.5 - 7.5 can be used for willow production. Conventional planting methods require 200 - 300 mm depth of cultivated soil. Dry limestone and chalk areas are not suitable. Heavy clays tend to be cold in spring and this results in slow establishment. Weed control can be a problem on organic soils, because very few suitable herbicides are available.

Temperature.

Willow can tolerate very low temperatures in winter, but frost in late spring, summer or early autumn will damage the top shoots. Valley bottoms are often frost pockets. Spring and autumn frosts limit the extent of willow plantations to the north more than does the length of the growing season.

Steep slopes.

Steep slopes can lead to problems with soil erosion. Harvesting machinery may have difficulty working on slopes greater than about 15%.

Overhead power cables

These must be considered, because willow could reach a height of 7 m before it is harvested.

Site Layout

Layout should be optimised to maximise the volume of willow planted per hectare. Typically 9000kg of dry willow can be obtained per hectare.

Harvesting techniques

Types of harvesting system
Harvest and chip in one operation	Most developed and cheapest system at present, but long term storage may involve costly drying to prevent mould growth
Harvest full length sticks, to be chipped later	Equipment needs further development, but storage likely to be easier
Gather sticks into bundles or bales during harvest

Willow harvesting is normally restricted to the winter months (November -February in northern Europe) in the period after leaf fall and before leaf set. An extended harvest period of late September to June is possible, but may lead to:

· higher moisture content at harvest;

· blockage of harvesters by leaf material;

· problems of contamination within the energy conversion equipment;

· reduction in long-term yield, as nutrients in leaves are not returned to the soil;

· reduced biodiversity.

Willow for energy production has generally been harvested on a three-year cycle. Harvesting on a 2-year, 4-year or 5-year cycle can be considered, depending on the rate of crop growth and the demand for fuel. Stem thickness influences the type and quality of fuel produced: shorter harvesting cycles will produce thinner stems, with a high proportion of bark.

Drying and storage

Freshly harvested willow contains over 50% moisture material. Willow sticks dry naturally during storage. Under typical European conditions the moisture content will eventually fall to 15 - 25% unless the material is re-wetted by rain. Heaps of sticks are sufficiently permeable to allow cooling by natural convection. Bundles or bales of willow sticks could probably be stored without major deterioration

Stacks of wet chips quickly heat up and start to decompose. Temperatures of 60° C can be reached within hours. Much of the energy value may be lost, and mould spores are a health hazard. This is a major issue for cut-and-chip harvesting systems. Storage characteristics of billets are intermediate between those of sticks and chips. Chips can be dried successfully, and then stored with little further loss of dry matter. Grain drying techniques have been adapted for willow chips, though the material is less dense than grain and does not flow so readily.

High temperature rotary driers are an option for large-scale operations, but not generally economic for individual farms. Most continuous grain driers can only work with flowable materials, though the conveyor type may be adaptable for willow chips. Volatile components can create atmospheric pollution in the form of "blue haze" where wood fuel is dried at temperatures above 100° C. Low rate aeration can be used to minimise moulding and dry matter loss from a stack of wet chips, built over a simple perforated duct fitted with a small fan. Airtight storage can greatly reduce dry matter losses, but commercial scale methods have not yet been developed.

Density of willow fuel is low, therefore large volumes have to be stored. Many farms have suitable areas available, but storing large quantities at a power station may be impractical. Chipping after harvest

Freshly harvested willow can be chipped using less energy than sticks that have dried during storage.

If sticks are chipped in a separate operation, a large static machine at the power plant will probably be more economical than either small individual chippers on farms or a larger mobile chipper moved from site to site.

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Cost Information

Assumptions

The willow costs are linked to the overall plant-sizing sheet through the PRIMA software. The assumptions for the costings are given below. The cost information was provided by the Scottish Agricultural College, a document that is referenced in the overall financial assumptions sheet.

· Growing costs are 33% of total costs

· Harvesting costs are 33% of total costs

· Transportation and Drying Costs are 33% of total costs

· 9000 kg harvested per hectare on a 3 yearly cycle

· Establishment costs can be capitalized

	£ Per Ha
Cost of Cuttings	1,500
Ground Preparation	300
Fencing	400
Weed Control	150
Management	230
Total - Year 1	2,580
Total - Year 2	380
Total - Year 3	380
Capital Cost	3,340
Operating Cost (pa)	6,680
Fuel Consumption - SRC (kg/kWh)	0.235
Fuel Cost - SRC - (£/kg)	0.104
		Availability	Electrical Output (kWh)
Size of CHP Unit 1 (MW)	2.3	0.95	2,871,090
Size of CHP Unit 2 (MW)	2.2	0.58	1,676,664
Energy From MSW (kWh)	1,560,000
Energy from forestry Residue (kWh)	466,000
Total Electrical Output (kWh)	2,521,754
Weight of Willow Required (kg)	592,612
Size of Willow Plantation (ha)	66
Capital Cost of Willow (£)	219,925
Operating Cost of Willow (£)	439,850

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CHP and District Heating – Technology Review

Introduction

The development of Community heating schemes offers significant opportunity for supplying affordable warmth to residents, for delivering energy efficiency to a wide range of clients and for reducing greenhouse gas emissions. It is an extremely flexible energy supply system because virtually any fuel can be used and production from a wide variety of plants can be utilised in the same network. This is important in maximises security of supply given future fuel scenarios.

Description of CHP

Current methods of producing electricity from thermal source (fossil or ‘renewable’) are largely based around gas turbine, steam turbine or combined cycle gas turbine. In the latter case some of the heat used during production of the high pressure gas is collected and used to raise steam to drive a steam turbine. The efficiencies of these systems have a theoretical maximum of around 60% and currently run at no better than 55%.

Much of the electricity produced from these largely in-efficient methods is used in buildings for space heating – approximately 30% in the UK. Space heating represents an extremely low grade of power requirement. From a domestic perspective, temperatures of 15-18 degrees in living rooms and 18-21 degrees in bedroom represent typical comfort levels. Using electricity as the energy source to deliver these temperatures represents an extremely inefficient use of a precise energy source.

CHP units reclaim almost all of the heat used in producing the electricity to heat water to 90-120 degrees. This hot water can then be used in domestic heating schemes to generate space-heating requirements for domestic, commercial and industrial use. As a result CHP units typically run at 85% efficiency and therefore represent a far more responsible use of energy than their alternatives. This is illustrated in Figure 1.

Figure 1: Comparison between separate heat and power production and CHP

The operating costs of a CHP plant are very low dependant on fuel source, however the capital costs are very high and are related to matching peak demands. It is important therefore that the emphasis of any demand side reduction techniques employed should be to reduce peak demands rather than reducing overall heat consumption. Typically, the heat output from the CHP plant could be used to meet 50% of the peak load.

Choice of System Temperatures

The selection of the temperature parameters of the system has major implications for the overall economy of the CHP system. The fundamental design parameters to be considered are:

· Flow and return temperatures supplied to the buildings at design conditions and at part load.

· Flow temperature at design conditions produced at the CHP heat generating plant

· Flow temperature at design load conditions at furthest customer

· Temperature control by consumers

· Minimum acceptable flow temperature at minimum flow condition

It is important that maximum use of the hot water temperature is made i.e. that the return temperature be low. This is important for overall economics of the system affecting transmission capacity utilisation, pumping costs and CHP power production.

An acceptable maximum flow temperature entering a dwelling is 90°C. Internal heating systems in the UK are designed for 82/71°C (flow and return). This is to minimise the size of radiators. The resulting mean temperature of 76°C is a major constraint on CHP system design. Converting a system to 90/60°C is feasible providing the re-balancing of the secondary side systems can be achieved. Basically it means that the radiators have to be bigger. However, if the building fabric is also upgraded then a mean temperature of 65 (80/50)°C could be delivered – this would require a reduction in heat losses from the building of 25%.

The supply temperature should not be reduced below the level required to provide an adequate source of hot water from storage facility and also ensure that stored water can be maintained above 60°C for legionella control. This effectively sets a lower limit of flow temperature at 70°C.

Selecting low temperatures for distribution will improve the efficiency of electricity production and reduce mains losses. However, if as a result the temperature drop through the system is reduced then the volume of water required is greater and mains and pumping costs are increased.

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Common Design Temperature Levels

1. Medium temperature is up to 120°C and 16bar for large CHP systems with high static pressure usually with indirect consumer connection.

The cost of community heating network for large scale CHP tends to dominate the overall optimisation. Ensuring that the differential between peak design flow and return temperatures is as large as practible reduces both capital and running costs. A figure of 50°C is attainable.

It is common practice in large citywide CHP systems to use a peak design temperature of 120°C but to vary the supply temperature according to the ambient conditions using as low a supply temperature as possible to meet customer requirements.

2. Low temperature and low-pressure systems are favoured where the connections are predominantly individual houses. Direct connection of each dwelling to the network will be the lowest cost option but the flow temperature will then be constrained to 90°C and the pressure to 6 bars (if plastic pipe is used).

With existing UK specified radiator building fabric design the temperature would be 90/60°C. If improvements to building fabric could be made then 80/50°C or lower could be used.

If steam turbine CHP plant is applying the scheme then reducing the differential between flow temperature and outside air temperature will be economic.

Optimisation of Flow Pressure

Variable flow with variable speed pumping is the most economic CHP distribution.

With plastic pipes the maximum pressure, which can be used, is 6 bars.

Older radiators have been tested to 4.4 bars only. Modern radiators have been tested to between 6 and 10 bar. 6 bars is acceptable for small schemes where there is not a ferocious requirement to pump the water up either big hills or tall buildings or if long transmission lines are not proposed.

Summary

The most cost effective heat distribution method for large-scale CHP systems is medium hot water designed for a large temperature drop.

The underground pre-insulated steel pipes will be designed for 16 bars and 120°C according to EN253.

Large building will be connected indirectly to the CHP network.

For housing, a heat exchanger substation supplying a number of houses in a terrace will be more economic.

Lochgilphead CHP Technology

Steam turbines were considered for this project for the following reasons:

They can take any type of fuel. Gas turbines require the gaseous products of the combustion to be relatively pure. This would be the case if the project were only using willow as a fuel source. However, it is more economical to use waste material as part of the fuel source.

Highly reliable – 99%

Variable heat:power ratio dependant on the pressure of steam exiting the turbine. As the CHP plant is being sized to meet a particular demand, this means that the ratio can be altered to provide some degree of seasonal adjustment. The ratio of usable heat to power in a steam turbine CHP set is unilikely to be less than 3:1 and may be 10:1 or more

Back Pressure Steam Turbine

Simple backpressure sets, using hot water as the primary heat distribution medium, can expand to low pressures and temperatures to give a good balance between power and heat output.

Lower backpressures can be used in the summer when CH flow temperatures can be reduced. This gives higher efficiency electricity production.

Schematic of a Backpressure Steam CHP Unit

Optimisation of Steam Turbine

The quantity of electricity produced by the steam turbine depends upon the temperature at which steam is exhausted from the turbine. The lower the exhaust steam temperature the more efficient the turbine. High-efficiency turbines exhaust at near vacuum conditions that is obviously of no use if you subsequently want to use the water in a DHS. In order to distribute and use reject heat effectively

The water/steam temperature has to be exhausted at 75/120°C. Consequently to maximise electricity production the flow and return temperatures should be kept as low as possible.

A small temperature drop will result in higher cost of pipe network

Fuel Types considered in the Project

Fuel Type	Energy Derived MJ/kg)	Contribution	Problems
Willow	17.02	55%	Capital Intensive No return in first 3 years Competition for land use Visual impact
MSW	10.06	33%	Handling Storage
Forestry Residue	18.9	17%	Current logging methods Handling Storage

Agricultural waste was not considered, as the data was not available at time of press. Safe to say that the system could accept dried slurry from dairy cow farming practices. There are 600 dairy cows in Argyll so there is potential for the amount of Willow required to be reduced even further.

Current logging practice uses the residue as brash mats for removing the ‘useful’ timber. This would render the residue useless. The forestry industry would have to adopt Scandinavian logging practice where the residue is treated with the same care as the ‘useful’ timber. Studies have shown no ill effects of removal of the timber that would normally rot back to the soil. The presence of the stump provides enough organic retrieval for the soil conditions not to be impaired.

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Lochgilphead District Heating Scheme

The length of network was estimated at 7km assuming the CHP units were located within the boundaries of the village.

The costs are based on the following assumptions:

The pipe size was 150mm diameter, pre-insulated steel pipes designed for 16 bars and 120°C according to EN253.

The cost depends on the size, rock, services encountered, and difficulty with traffic, number of valves bends etc.

In a road, £300 per metre of pipe was allowed. This is for both pipes.

House connection costs were taken to be £2,500 per household based on the average achieved in Shetland

Total cost of the system is therefore taken to be (7000m x £300)+(904 Households x £2,500). This comes to £4.36m.

Solar

General Information

In a conventional hot water system, the water is usually heated by a boiler, burner or electric immersion heater. A solar hot water system uses solar energy to heat water, with auxiliary heating provided by a conventional system. Solar energy is captured and transferred to the water in a collector, and stored in an insulated hot water cylinder until is required.

Solar water system for a home

A high-pressure hot water pump attached to a hot water storage tank supplies hot water quickly and at high volume. This makes the system appropriate for showers. The system automatically switches between the solar hot water supply and the boiler to provide an economic, low energy consumption hot water supply. There is no need for the customer to make complex adjustments.

1. Solar heat collector

2. Hot water storage tank (heat exchanger, internal high pressure pump)

3. Hot water supply (boiler)

4. Remote control with water temperature display, used to set the temperature at which the system switches from the solar water supply to the boiler.

Lochgilphead Solar Collector Information

Resource

Demand

· Total Annual energy water heating demand = 2,143 GWh

· Mean Daily Demand

· 1 person (336 houses) = 5.12 kWh

· 2 persons (250 houses) = 6.145 kWh

· 4 persons (364 houses) = 7.168 kWh

Supply

· Designed to supply 100% of the energy for the best month

· The auxiliary resource is electricity.

· Annual system efficiency 40%

· Annual energy from Solar Heater = 1282.3 MWh

· Annual energy from electricity = 859.9 MWh

· To supply the above solar demand it would be necessary 2690 m2 of solar heat collectors.

Economics

Mean Price of m2 is £350

Total price of the installation 2690*350= £941500

Annual generation 1282300 kWh *0.08=£102584

Simple pay-back = 941500/102584=9.18 years

CONCLUSIONS

The installation of solar collectors for water heating is expensive and is only efficient during the summer when the needs of hot water are less. All this with the scarce solar resource due to the latitude and the weather makes the solar collector use not a good decision.

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