Case study- Wind Turbine

1. Introduction

Wind energy is a source of renewable power which comes from air current flowing across the earth's surface. Wind energy is clean, free and inexhaustible. 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 harnessed 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 size and the amount of power they would be able to generate.

Small scale wind turbines (turbines rated under 100kW) have over the years been used to power homes, small businesses and to meet the energy requirements of villages, cottages and telecommunication facilities in remotes locations without access to the grid around the world. These small scale wind turbines require cut – in speeds as low as 2.5m/s and rated speeds around 10m/s which are in most instances are readily available at most construction site locations.

2. Objectives

The objective of this study is to highlight the various findings by considering the upon use of small scale wind turbine as an option for renewable energy supply option at the construction site from project study conducted in the year 2005.

3. Methodology

A 15 kW wind turbine will be sufficient to meet a reasonable portion of the total demand across the construction site. These recommendation are done based on the below areas of analysis carried out at the Xscape site.

3.1 Wind Resource Assessment

Wind resource assessment is the first step towards estimating the current wind situation in the site. It is done by setting up an meteorological station at the site for measuring various data such as wind speed, wind direction, ambient temperature and air pressure at an hourly basis using a cup anemometer, wind vane, thermometer and barometer respectively. The data obtained are then extrapolated to three (15m, 30m and 80m) intended hub heights.

The above collected data is processed for the supply estimation. These estimated velocities are then used to quantify approximately how much more power could be harnessed at higher rotor heights on the Xscape site and further this is fed into a cost - benefit model for analysis on the technical and economical implications for increasing the tower height.

3.2 Site Energy Demand

The energy demands of equipment and appliances onsite were then grouped into those needed for lighting, heating and others using their power ratings in kilowatts and the number of hours they are used to estimate the total energy demand on a daily and annual basis.

Since a detailed study has been conducted on the demand side analysis part on the distribution of the various energy consumption patterns, the above data are used for calculating the capacity of the renewable for the Xscape project.

3.3 Siting

The turbine tower height is an important factor which is to be considered towards the selection of the type of the turbine. The reason behind the above fact is that there is a considerable change in the wind velocity profile at different heights. The much higher the turbine tower we get more constant and quite high wind speeds due to reduced obstruction to wind by other buildings, trees etc. The most common tower heights are 15, 30, 80 meter for small scale wind turbines. The cost of turbine tower plays a considerable role among the total cost of the turbine setup. According to the manufacturers sources it is found that the manufacturing cost per meter for the turbine tower comes to about £ 467 (1). The safety factors and risk involved in putting a high turbine tower has to be considered.

Wind turbine. Source: Proven

3.4 Turbine Selection: Turbine Options Appraisal

Information gathered from the two previous tasks were then used in addition to an outlined selection criteria (including power output, cost and Reliability) to select a turbine to supply power to meet the site’s lighting needs.

In selecting a turbine to supply the requisite power for the Xscape site, available small turbines were classified into groups based on their power ratings. All have capacities suitable for meeting the electricity demands on the Xscape site. One turbine was then short listed from each group based on the overall potential power and energy yield determined using the swept area intercepting the wind, rated speed, their robustness which was determined by the specific mass (weight to area ratio), cost and maintenance requirements specified by the manufacturers.

The various horizontal axis turbines of different make and size considered in this project are short listed as below:

• Renewable Device’s Swift (1.5 kW turbine)

• Bergey Wind power 1500-24 (1.5 kW turbines)

• Proven WT 6000 (6 kW turbine)

• Proven WT 15000 (15 kW turbine)

• Wind Turbine Industry’s WTI 26 -15 (15 kW turbines)

• Wind Turbine Industry’s WTI 29 -20 (20 kW turbines)

• West wind (20 kW turbine)

Vertical axis turbine (VAWT)

• Ropatec WRE.060 (6 kW turbine)

Hence upon analyzing various turbine model for a same wind pattern but for a different hub height it is found Proven WT 15000 was able to produce about 5626.2 kWh/month at hub height of 30m and about 7147.1 kWh/month for a hub height of 80m. As due to the non feasibility of using an 80m turbine tower due to the various safety aspects described above in the siting of the turbine tower it was considered that these factors ruled out further analysis.

Power and energy outputs for selected turbine at 15m. Source: PHd 2005 Universite of Strathclyde

Therefore, after calculating the annual output for various models it was found that the proven WT15000 seemed to be a more worthwhile investment.

After making an exclusive study on above turbines with respect to various aspect as described earlier we see that Proven WT 15000 was selected in this 15 kW rating category as it has reasonably higher generation capability due to greater swept area, being less expensive, and being known to be fairly robust requiring a low maintenance regime meant that upon comparing the turbines of the same size the Proven WT was a clear favourite.

3.5 Costing

Hence, based on the power output from each 15 kW turbine and depending upon the total demand on the construction site it is possible to calculate the number of turbines required for installation. One further factor which has to be considered is the type of storage medium to be used, such as a battery banks, or connecting the excess supply to the grid or using it for direct heating applications, the above choice entirely depends upon the site conditions. The first strategy which could be considered is by just using a single 15 kW turbine to meet the reasonable portion of the total loads during the morning hours and during the night the energy produced could be used for supplying energy for drying the clothes in the drying room. The second strategy is to install the required number of turbine to meet the total demand in the site. Upon considering the above two strategy it can be seen that the first option proves to be more advantageous in terms of feasibility in supply, having low risk involved due to less investment cost due to the reduction in the cost of battery bank for storage capacity.

The total lifetime cost was determined by estimating the annual loan repayments, overall operation and maintenance expenses, property tax and insurance for the design lifetime and expenses for reserving equipment parts and others in store for unexpected breakdown. This total lifetime cost was then used to estimate the cost per kWh of electricity generated from the turbines. The economic viability of a small wind power system depends to a large extent on the generating costs and the associated market value of wind energy Capital cost, financial cost, operating and maintenance costs, turbine availability, energy efficiency, life time of turbine and site wind regime constitute the total generating costs. On the other hand, environmental benefits which comprise emissions reduction (CO₂ savings) and reduced fossil fuel use, together with fuel savings and capital savings make up the associated market value of wind energy.

3.5.1 Capital Costs

These are the total cost involved including the material cost, foundation cost, and installation cost for the turbine. Generally, wind turbine installed costs are normalized to cost per unit of rotor area or cost per rated kW.

The price of Proven WT 15 kW turbines comes up depending upon the type of connection associated with it.

	Wind Turbine System with	Basic Cost (£)
1.	Grid Connected	39,000
2.	Battery Charging	46,500

Source: Proven Energy

The reason behind the price difference between two connections, are due to the extra cost associated with putting up batteries for storing the produced energy. Further the connection to the grid normally takes place at <16 amps/phase.

3.5.2 Financing Costs

As most wind power projects are capital intensive. Usually most developers make a down payment and finance the rest of the project with a loan obtained from the financial institution, in most cases a bank loan. Then in long term interest has to be paid for the money borrowed from the bank.

3.5.3 Operation and Maintenance Costs

As the turbine contains more moving parts, hence it requires a considerable maintenance to be done, for an efficient running. It is considered that the during the early years the maintenance cost are between 1.5% and 3% of the turbine cost but increase with time as the turbines get older.

3.5.4 Payback

The detailed analysis done regarding the payback shows that with good wind resource at the installed site, the payback for a 15kW wind turbine will normally be about 10 years. Further with the usage of additional storage facilities like battery would increase an additional payback period of 13 years.

3.6 Battery charging system

A battery charging system provides us with a continuous uninterrupted power supply for our applications via an inverter which makes the power from the turbine usable. According to manufactures recommendation 48V DC battery storage can be used for storing the generated electricity. This is then converted into AC by means of an inverter before we are capable of using it for our utilities. The number of batteries required for a particular installation depends upon how long we need to have electricity supply when there is no wind. Normally the battery storage is planned for storing electricity for about say one or two weeks. Hence the cost of each battery varies depending upon its storage capacity.

A general idea about the cost of batteries and inverters are given below in the table as

The cost of 48V Varta Lead Acid Battery (Tubular Plate, Flooded cell) depends on the storage capacity in Ampere hours

No	Ampere hours(Ah)	Cost (£)
1.	470	2962
2.	785	4631
3.	1250	7178

The selection of a medium capacity storage battery of 48V, 785Ah could be considered based on the continuous demand required from the construction site.

Similarly the below is the price list for the inverters for a typical SMA Windy boy inverter model of the following capacity

No	Rating (kW)	Cost (£)
1.	2.5	1338
2.	3	1453
3.	6	2527

3.7 Funding

The UK government providers funding through various means towards the implementation of various renewable energy sources through various scheme means such as

1. Low carbon building programme.

2. Green energy trust Scottish power.

3. Green energy fund.

4. Leader plus programme.

4. Emissions Reduction

The supply results from this project will tell us about the expected amount of carbon dioxide savings depending upon the portion of electricity generated from the turbine to the use of diesel generator or grid connected electricity supply. The installation of the above wind turbine will reduce the connected load on the generator and the grid thereby we are able to save a considerable amount of Carbon Dioxide emissions.

5. Results

Hence upon analyzing various turbine model for a same wind pattern but for a different hub height it is found Proven WT 15000 was able to produce about 5626.2 kWh/month at hub height of 30m(these values vary highly depending upon the prevailing wind condition and hence the manufacturers recommendation for annual energy production has to be considered)

Device

Size

Investment

( ₤ )

Payback

( years )

Cost

( p/kWh )

CO₂emissions

( kg/kWh )

Wind turbine+ Battery + Inverter

15 kW

48 V DC

46,500

8.8

Wind turbine+ grid connected

15 kW

39,000

7.3

* Wind turbine has no Carbon Dioxide emissions but savings.

6. Conclusions

It is reasonable to conclude that from the analysis shown above considering exclusively small scale wind turbines, we see that the 15kW Proven turbine is the optimum selection, after considering various factors for its selection process. Hence a single turbine is capable of meeting the current lighting demand with an excess supply which can be used for direct heating or storage purposes. A single 15kW proves to be more economical to meet the lighting demand or we need to install 3 turbines which considerably increases the investment cost and raise the risk involved in it. The normal payback estimated is between 10-15 years.

This initiative will give more long term result proving the corporate social responsibility of the firm for the investors and the sustainability effort taken towards the CO₂ reduction and from the environmental point of view.

7. References

1. Small Scale Wind Turbines: Alternative Power Supply Option for Construction Sites, --By Kenneth Edem Agbeko

2. http://www.windustry.com/basics/03-knowwind.htm

3. http://www.wind.appstate.edu/photogallery/swindgallery.php