Supply at Xscape Site

Contents

1.       Introduction

2.       Objectives

3.       Methodology

4.       Analysis of the supply profile

5.       Connection to the grid

6.       Diesel generator

7.       Evaluation of efficiency solutions: CHP and Heat Pumps

7.1 Combined Heat and Power system

7.2 Heat Pumps

8.       Evaluation of renewable solutions

9.       A supply combination

10.   Conclusions

11.   References

12.   Other references

As it was described in the Methodology part of the Project Web Page, once the demand of the Xscape site is  reduced, the analysis of the supply side can be undertaken. This way a total energy efficiency analysis  for construction villages can be performed.

In this part of this project an evaluation of the supply side is conducted in order to improve the efficiency of the supply as well as reducing CO₂ emissions.

In addition, the use of efficient supply options such as Combined Heat and Power (CHP) systems and Heat Pumps as well as renewable supply technologies has been studied.

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The objectives of this study are to evaluate  alternative supply options for construction villages especially focusing on Laing O'Rourke's Xscape site.

 The alternatives have been studied by considering different aspects of construction villages and evaluating the advantages and disadvantages of the different supply options in terms of economic, social and environmental issues. In addition renewable supply technology that is most suitable for construction sites shall be identified and studied in more detail.

The study on Laing O'Rourke's Xscape site will be undertaken by considering the current supply options: diesel generator and connection to the grid; as well as the identified renewable solution.

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 For the evaluation of the supply side, the actual situation of the supply is analysed using the Xscape site as reference in this project. The following assumptions have been made for our analysis.

• The power output will be calculated by using the actual consumption records (metering data) and applying the identified demand reductions.

• The demand reduction is estimated according to the Demand Side study of this Project.

The topics studied have been:

• Actual kWh consumption

• Reduction by using Demand measures

• Future kWh consumption

• Evaluation of the actual supply: Diesel generator, connection to the grid.

• Evaluation of efficiency for : CHP and Heat Pumps system.

• Evaluation of Renewable options. RE selection.

• The efficiency results: combination of the supply systems.

The methodology to evaluate the supply side is shown in the above flow chart.

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The energy consumption profile for each construction site varies continuously and generally increases as a project progresses.  The usual practice of considering the annual energy demand is wholly inappropriate for the construction business as projects varies in both time and size.

In most construction sites Diesel generators acts as a major source for electricity supply, and thereby constitute to about 75 to 80 % of the fuel costs. For the remaining one third of the project electricity is used from the grid. It is important to note that the carbon emissions resulting from electricity generation by diesel generator are about twice those of mains electricity.

Electricity is used for space and water heating, lighting and electrical offices and catering equipment. A deep analysis of the energy use and the power installed can be followed at the demand side analysis of this web site.

The profile of the supply is as following.

      A)   In terms of used devices:

The electricity required is obtained from a diesel generator and directly from the grid through a grid connection.

      B)   In terms of costs:

Following the figures we have obtained from Laing O’Rourke, it can be  estimated that the average expenditure in energy (diesel and electricity) from a typical construction site could be about £126,000 per year. Note that depending on every company and every provider contract prices for fuel and electricity from the grid could be different.

Although data for electricity consumption were obtained for the Xscape site those values can not be shown on this web site for privacy reasons. Due to this the average value are assumed as the energy expenditure on the Xscape site.

            -          The diesel generator contributes to 88.16% of the total cost of energy supply.

            -          The electricity from the grid is about the 11.83% remained.

      C)   In terms of time:

Along the project duration the supply of a construction village is typically structured into the following periods.

            -          2/3 parts of the project:  supply by diesel generators.

            -          1/3 parts of the project: grid connection.

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On almost all the construction villages, there is a possibility to use temporary power supply from the grid. In order to connect to the grid some considerations must be followed:

-          The dates and other key programme dates

-          The location of existing supply lines

-          Local and seasonal environmental considerations

-          The evaluation of the existing supply companies

-          The evaluation of the different quotations, contracts and security of supply from every company.

-          The definition of the supply voltages required.

-          The earthing requirements and proximity to communications equipment

-          The siting and protection of metering, switchgear, distribution boards etc

-          The correct rating of fuses and switchgear for safety and plant protection

-          The arrangements for controlling, operating and maintaining the system

-          The provision of lockable switches and means of isolation

-          The commissioning and handover arrangements 

-          Future modifications or extensions to the temporary supply system

Using some information obtained from experienced civil engineers as well as referring to the Site Layout part of this web site, it can be said that grid connection is not made until roughly two thirds of the project is because of the need to keep the electrical supply options flexible. Temporary facilities are often moved around on site and diesel generators are ideal for shunting around with the facilities. Although ideally they should not be moved as this costs money and is inefficient, it usually happens because of external uncontrolled conditions and/or sometimes poorly planning. Furthermore, the connection into the grid is delayed in order to reduce the risk of accidents by damaging the electricity connections during the buildings activities.

It is estimated that it takes between two to four weeks to get a high capacity connection to the national grid. The electricity from the grid is purchased at 7-8 p/kWh.

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 As it has been shown in previous chapters of this report, power for the Xscape site at the time of this study was provided mainly by a diesel generator. The diesel generator supplied 66% of the electricity over the whole project duration which incurred 80% of the total electricity costs.

On the Xscape, a 200kVA generator is used to provide electricity for lighting, space and water heating, office and catering equipment in the site accommodation. A 27kVA generator is used to supply electricity primarily for temporary lighting with some subcontractors using this generator for their power tools. 

Diesel generators are the preferred supply systems on sites mainly due to flexibility reasons as well as the ease of obtaining the fuel supply. Nevertheless, some problems are detected regarding diesel generators.

•        Fuel cost and dependency on prices

Every company has a different contract for their oil price but an average of 20p/litre is considered as a good approximation of a fixed oil price. Thus, at 35% maximum generator efficiency, the price of the diesel is estimated at 5.76 p/kWh.

However the price of fuel varies in huge ranges and can be said to increase significantly in the near future.

•         Efficiency

The efficiency of the generator is an important aspect to be considered. The efficiency shows the relationship between the energy use and the total power output from the generator.

On of the main problem is that diesel generators are mostly operated only on part of their load. Following the curve shown in the following figure, the efficiency of a diesel generator is strongly related to the load. Thus, with decreasing generator load the efficiency is reducing accordingly. On the Xscape site the load of the generator is fixed at the 35.5% what means an efficiency of the 30%.

•        CO₂

The lower the efficiency of the diesel generator the higher is the amount of CO₂ emitted by the generator. Hence, at a load of 35.5% the CO₂ emissions from the generator are 0.72 kg/ kWh, which means almost a 70% of increase with respect to the standard of 0.43kg/kWh CO₂ applying to the national grid. 

Thus, electricity produced by the generator is not more expensive than the electricity purchased from the grid, the associated CO₂ emissions are extensively higher. This shows that an alternative must be developed to reduce the CO₂ emissions by improving the generator efficiency or by reducing the generator use.

Typical Diesel Generator

                              Efficiency Vs Load for a Diesel Generator.

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A few energy efficient supply solutions have been studied which are:

-          Combined Heat and Power (CHP).

-          Heat Pumps.

A typical small scale cogeneration system

Dimplex Brine-to-Water Heat Pumps: heating and cooling with a single system

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A CHP plant generates both usable heat and power (usually electricity) from a single process. The term CHP is synonymous with 'cogeneration' and 'total energy'. The basic elements of a CHP plant comprises one or more prime movers usually driving the electrical generators, but whereas the heat generated from the process is utilised via suitable heat recovery equipment for a variety of purposes including: industrial processes, community heating and space heating. Hence CHP can provide a secure and highly efficient method of generating electricity and heat at the point of use.

Nowadays many types of cogeneration system could be found in the market. For construction sites, especially for the Xscape site, the most appropriate system is small-scale CHP with an operating capacity of less than 1MW.

Cogeneration system will supply:

-          hot air for heating,

-          hot water,

-          electricity for the general use.

In the following some issues about cogeneration systems will be discussed.

A)  WHY IS IT USEFUL?

•        Efficiency:

The basic idea of the performance of a cogeneration system is that small-scale CHP units will use a standard diesel engine converted for operation with diesel or gas as fuel. The engine drives an electrical generator which produces electricity. Heat is recovered from the engine exhaust system, water jacket and oil cooler via suitable heat exchangers. This heat can be used to heat air directly or to heat water via a heat exchanger. The total efficiency of the cogeneration system is about 70-90 %, with the conversion of fuel energy into about 30% electricity and 55 % heat.

An typical engine fuelled by gasoline for a size of 0.2 MWe will have an efficiency of about 35 – 45% and a typical overall efficiency of about 65 to 90%.

Hence, this kind of reciprocating engine may be suitable because:

-          power, or processes are cyclical and not continuous.

-          medium or low temperature hot water is required.

According to the previous analysis the need of heat is about 81% of the total supply in terms of electricity demand with a need for heat maintained along the day. Thus, cogeneration system could best provide for this requirement.

•       Environmental:

From the environmental point of view, a cogeneration system would provide some benefits in terms of the emissions of CO₂. Thus, the actual situation of the use of the diesel generator will provide about the 70% of CO₂ produced by using mains electricity, showing an unsustainable situation that will be penalty in a near future.

Carbon emissions with diesel fuel in a CHP system. Educogen Guide. March 2001.

•       Cost:

The hot water produced by cogeneration will cost about a third of the cost of direct electric water heating. The electricity generated will be part of the heating process and therefore, it can be assumed that the cost will be less than that of the actual situation. The current share of electricity produced from cogeneration in the EU is about 10%.  The EU target is to reach 18% by 2010, and some grants are available for companies desiring to implement those measures.

Generally, at current fuel prices and electricity tariffs, and allowing for installation and life-cycle maintenance costs, payback periods of three to five years can be achieved on many cogeneration installations.

B)   WHY  IS IT NOT USEFUL?

•       Ratio of power demand:

A possible configuration would be using the heat and electricity produced along the day, and storing the electricity produced along the night. However as the ratio of energy use along the day and the night is very high (about 90% of the energy is used for the day) this system is not suitable for the Xscape site. It will result in a low energy efficiency of the CHP system.

•       The installation:

The installation of a CHP system is very complex and it will cost money in the initial phases and also during the maintenance cycle. In addition, considering that actually the construction villages are moving around several times during the life cycle of the project along the site, the idea of this sophisticated installation do not fit in the real needs of the supply sites.

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A heat pump is a device that uses waste heat to produce valuable heat on a higher temperature level than that of the waste heat. The basic idea of all heat pump concepts is that waste heat is absorbed by a medium, which releases the heat at a higher temperature after a physical or chemical transformation.

The heat pump is an air conditioner that reverses the process of removing heat from the inside of the house in summer to absorbing the heat from outside air and moving it inside in winter. It is effective down to temperatures around 30 degrees Fahrenheit.

A) WHY IS IT USEFUL?

Advantages

·       Are energy-efficient,

·       Are environmentally sound heating solution of the future

·       Uses freely available and inexhaustible energy from the ground or air

·       Can be used for both heating and cooling the space or water

·       They can provide effective space heating, cooling and humidity control

·       Easy to integrate into buildings

·       Has huge potential for CO₂ savings

·       An estimated saving of about 20-30 % can be achieved than a conventional heating system

Classification of Heat Pumps

• Ground Source Heat Pumps

• Air to Water Heat Pumps

• Sanitary Water Heat Pumps

1. Ground Source Heat Pumps

The brine-to-water heat pumps draw up to 80 % of the required heating energy from the ground. The solar energy stored in the ground is available free of charge and in unlimited abundance. To be able to extract geothermal energy from the ground and use it for heating purposes on a continuous basis, ground collectors in the form of flexible PE pipes are buried in the garden at a depth of around 1.2 m. A mixture of water and antifreeze, the so-called brine, is circulated in the pipe loops. Where not enough area for laying the pipes is available or if cooling is to be provided in addition, ground coils are installed in vertical direction.

Ground source heat pumps are for indoor installation, for example in a garage or basement and use the earth as a heat source, via vertical or horizontal collectors. There is a range of capacities as well as reversible models able to provide heating and cooling.

2. Air to Water \heat Pumps
Air to water heat pumps use the free environmental energy of the ambient air and are able to provide efficient heating at air temperatures as low as even -20°C. Air to water heat pumps are suitable for either indoor or outdoor installation, and provide significant installation cost benefits over ground source systems

3. Sanitary Water Heat Pump

The sanitary water heat pump provides energy efficient central water heating for the home, using a specially designed air to water heat pump fitted to an un vented water cylinder. 70% of the energy needed to heat the water is extracted from the ambient air.

An evaluation of those aspects can be seen in the table below.

 Selection of Heat Pumps

• Quiet Operation

• Consistent Temperatures

• Balanced Humidity

• Energy Efficiency

• Environmental Responsibility

• Indoor Air Quality

• Reliable Performance

• Value

B) WHY IS IT NOT USEFUL?

The main difficulties which deter the use of Heat Pumps in the Xscape site are found to be that it:

• Requires high drilling, installation and underground piping cost in case of geothermal or ground source heat pumps
• Horizontal installation space has to be checked for any hindrance
• Requires external power source to run the compressor
• Requires periodic maintenance for efficient operations

·    Heat Pumps requires complex installation where it cost money in the start and also during the maintenance process. But, the main issue is that it does not allow the flexibility of movement during the life cycle of the project in the site. Thus, the use of Heat Pumps is not a good solution in addressing the heating and energy supply needs for construction villages.

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The following renewable energy technologies have been considered:

• Photo-voltaic Technology.

• Solar Collector.                                                 

• Wind Turbine.                                                   

• Fuel Cell.                                              

• Biomass. 

Photovoltaic system in a home and home business.

Solar Collector

Wind Turbine

Fuel Cell

A) A RENEWABLE TECHNOLOGIES DESCRIPTION

The above mentioned renewable technologies are discussed in detailed.

1.- Photo-voltaic (PV)

Photo-voltaic technology is a renewable technology which converts the suns energy into electrical energy. The principal behind PV technology is the ability of the photons contained within the suns rays to cause electrons to be moved to a higher energy level or orbit so that they are free and are capable of conduction. The energy required for an electron to jump to the next energy level is commonly known as the band gap energy denoted generally by Eg. Materials have their own Eg value and silicon which is the material used in most PV applications has a band gap energy of 1.12eV. PV’s are made from semi-conducting material which has been doped with a different atom or impurity.

The three main types of materials used in PV modules are: 

• Monocrystalline or single crystalline silicon

• Polycrystalline or multi crystalline solution

• Thin film

2.- Solar Collector         

A solar collector is basically a flat box and is composed of three main parts, a transparent cover, tubes which carry a coolant and an insulated back plate. The solar collector works on the green house effect principle; solar radiation incident upon the transparent surface of the solar collector is transmitted through though this surface. The inside of the solar collector is usually evacuated, the energy contained within the solar collect is basically trapped and thus heats the coolant contained within the tubes. The tubes are usually made from copper, and the back plate is painted black to help absorb solar radiation. The solar collector is usually insulated to avoid heat losses.

The main components on an active solar water heating system are: 

• Solar collector to capture the suns energy and to transfer is to the coolant medium

• A circulation system that moves the fluid between the solar collector and the storage tank

• Storage tank

• Back up heating system

• Control system to regulate the system operation

Classification of Solar water heating System are:

• Open loop system

• Closed loop system

3.- Wind turbine

Wind energy is a source of renewable power which comes from air current flowing across the earth's surface.  It can be harnessed for producing electricity using a wind turbine. Wind turbines extract the energy from the wind by transferring the momentum of the air passing through the wind turbine rotor, into the rotor blades.  The rotor blades are aerofoil, and used for concentrating the energy in the air flow, into a single rotating shaft. The power in the shaft can then be used by coupling it with an alternator for power electricity generation.  Wind turbine could be classified into small-scale wind turbine and large-scale wind turbine depending on their sizes and the amount of power they would be able to generate. 

4.- Fuel Cells

A fuel cell is a device which combines oxygen and hydrogen electrochemically to produce electricity and water. Hydrogen is normally produced by reforming natural gas with oxygen and water to produce hydrogen, carbon dioxide and carbon monoxide. Water is then added and the carbon monoxide is converted to carbon dioxide and hydrogen. The carbon dioxide is then removed and the hydrogen is changed by a catalytic reaction onto its component form which is hydrogen ion (protons) and electrons. The electrons then flow through a circuit as an electric current thus providing the power to operate appliances such as a light bulb.  The protons pass through the polymer electrolyte membrane. The protons and electrons then combine with the oxygen to form the final product which is ordinary water.

5.- Biomass

Biomass is a collective term which applies to organic matter (fuel) which can be converted to energy. Biomass is utilized for the production of electricity on construction sites from the construction waste generated and using the strategy for the mitigation of CO₂. The electricity or power that is produced from biomass fuel is theoretically carbon cycle neutral. The biomass utilization process can be through direct combustion of biomass using  wood fuels in boilers or gasification and other chemical processes.

B) COMPARATIVE EVALUATION ASPECTS

In order to conduct a comparative evaluation of those technologies for the Xscape site, some technical, economic and environmental aspects from previous projects have been used. Those aspects have been evaluated under the perspective of the Xscape site and the renewable alternatives.

C) THE EVALUATION

The evaluations of the renewable technologies were conducted based on the applicability to the Xscape project site and are displayed in the following table.

D) THE CHOSEN SOLUTION

From the comparative analysis conducted, the WIND TURBINE option has be considered as the best solution to improve the actual supply by implementing a renewable technology. A detail analysis was conducted in the case study which can be found in the Supply side section of the Project Web Site. 

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Considering the previous analysis and extrapolating those results to the Xscape site with a duration of 1 year and a half, the following results have been obtained:

Note:

a- The wind turbine will reduce the total CO₂ emissions. The figure obtained is 75 ton of CO₂ per kWh, according to the calculations.

b- The cost depends on every site, company, contracts, consumption, distances and others variable aspects. However, the figure will be almost negligible compared with the other investments.

A ) Diesel

By ensuring that the generator operate at its maximum efficiency, an improvement of 5% efficiency could be obtained which would generate an energy savings of about £1,120 per year with the additional benefit of reducing the CO₂ emissions. According to calculations, a 100 kVA generator will be sufficient to cater for the peak load.

B) Wind turbine + Battery + Inverter with diesel generator

Generator capacity = 100 kVA

Diesel Electricity Supply = 200,000 kWh/year x 44%

                                     = 88,000 kWh/year

Wind Electricity Supply = 36,562.8 kWh/year

Hours = 3120 hours/year (12hours/day * 5days/week * 52weeks/year)

CEF = 0.71 kgCO2/kWh

Load Factor (LF) = (Diesel Electricity – Wind Electricity) / (Capacity * Hours)

LF = (88,000-36,562) / (100*3120) = 0.16

E = 100 * 0.71 * 0.16* 3120 = 35,443 kg CO₂/year (for the diesel generator)

C) Wind turbine and Grid connected electricity supply:

Generator capacity = 100 kVA

Diesel Electricity Supply = 200,000 kWh/year x 22.8%

                                    = 45,600 kWh/year

Wind Electricity Supply = 36,562.8 kWh/year

Hours = 3120 hours/year (12hours/day * 5days/week * 52weeks/year)

CEF = 0.43 kgCO2/kWh

Load Factor (LF) = (Grid Electricity – Wind Electricity) / (Capacity * Hours) 

LF = (45,600-36,562) / (100*3120) = 0.03

E = 100 * 0.43 * 0.03* 3120 = 3,847 kg CO₂/year (for grid connected system)

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At present, construction works on site very often are not planned in advance causing construction villages to be moved on site more than necessary. This fact makes the efficiency of the project poor and also affects the supply system. Due to this and other reasons, the diesel generator is the preferred solution on site.

In this study, the use of diesel generators and also the connection into the grid have been evaluated. In addition, the integration of suitable renewable energy technologies were also being looked at. As no renewable energy systems can supply the total electricity demand for the Xscape site, it has been considered together with the integration with a diesel generator.

In conclusions, a combination of the diesel generator, a wind turbine with a battery system and connection to the grid have been recommended and presented in the result of the case study. This combination will give the best value in terms of efficiency and costs savings.

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• Energy Systems and Sustainability: Power for a Sustainable Future. Oxford: The Open University 2004. Godfrey Boyle, Bob Everett and Janet Ramage.
• Renewable energy: Power for a Sustainable Future. Oxford: The Open University 2004. Godfrey Boyle, Bob Everett and Janet Ramage.
• EDUCOGEN (European Education on Cogeneration) Contract No. XVII/4.1031/P/99-159. March 2001        
• EDUCOGEN (European Education on Cogeneration) The European Educational Tool on Cogeneration. Second Edition, December 2001

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http://europa.eu.int/comm/energy_transport/atlas/htmlu/hptorint.html

www.greenenergy.org.uk

www.est.org.uk/housingbuildings/localauthorities/theguide/scotland/

www.portakabin.co.uk

www.chpa.co.uk
www.geocapture.co.uk
www.greenenergy.org.uk
www.inreb.org

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