Is wind power a viable option for Sri Lanka?

by Dr. Janaka EKANAYAKE

Graph 1

The interest towards renewable energy is growing in all parts of the world. Out of the many renewable options wind power is considered as the most promising renewable energy option in many countries. Despite the economic downturn and financial crisis in many parts of the world, wind power is continuing to grow rapidly. As at the end of 2009, global wind generation stood at 158 GW.

In this article many aspects of wind power are discussed in detail. However, it is important to set the scene by discussing why there is a revival interest towards renewable energy, their economics and the place wind has in the renewable energy landscape.

Why renewable?

It is now being recognised that climate change is a real phenomena which is threatening the way of life for all plants and animals on our planet. Rising sea levels, temperature rises and extreme weather events are causing an irreversible loss of many species of plants and animals. Despite the outcome of the Copenhagen Summit, it is a responsibility of everybody to work towards a decarbonised society.

It is recognised that electrical energy is one of the main energy vectors which can bring an immediate impact to decarbonisation. To achieve this, renewable energy sources, energy efficient products and systems, and consumers should play a key role.

The graph shows the CO2 intensity values corresponding to electrical energy production in different countries. At present the CO2 intensity of Sri Lanka is comparatively low.

However, while other countries are working towards reducing CO2 emissions from their electricity sector, our situation with the addition of coal power plants is becoming quite the opposite. The only way to counteract this situation is to add more renewable.

(See Graph 1)

While climate change is considered as the main driver behind renewable energy generation, another key reason for promoting renewable is fuel security. Over the next few decades, the growth in global demand for energy will increase while the North Sea oil resource will deplete. This has led to re-think our approach to sourcing and using energy. At present oil prices are extremely volatile with an increasing trend.

It is expected that the oil prices will increase from its current value of nearly US$ 70 to about US$ 90 by 2030. The price of coal is standing at US$ 120 per ton and it is expected to drop and saturated at US$ 80 per ton after 2015. Renewable will play a role in reducing our dependency on imported oil thus leading to a sustainable and decarbonised electrical energy sector.

Are renewable cheap?

Even though the energy resources of renewables are free, their fixed costs are much higher than that of conventional generation plants. The following table compares the capital cost, fuel cost, non-fuel variable cost, fixed cost, build time and annual availability of different power generation technologies.

Plant		Capital	Fuel cost	Non-fuel	Fixed	Build	Annual
		 cost	(USc/kWh)	variable cost*	cost	time	availability
		(US$/kW)		(USc/kWh)	per 	year	(Years)	  
									%										
						

Combined	1000	3.0		3.0		25	3	83
cycle gas
turbines
(CCGT)	

Coal		2000	2.5		3.0		37	4	83

Open cycle	550	4.0		3.0		20	2	90
gas turbines
(OGCT)

Onshore wind	2000	0		0		60	1	20-30

Offshore wind	4250	0		0		100	2	20-30

Biomass		3800	5.8		1.7		95	2	80

Wave/Tidal	6500	0		0		150	2	30-35

* Excluding interest over capital
Source: http:/hmccc.s3.amazonaws.com/docs/FINAL%20Decarbonising%20the%20GB%20power%20sector_v1.pdf

When one looks at Table 1, a question that immediately comes to one’s mind is how renewable energy survives in a level playing field. For example, in the UK energy is traded in a market where both renewable and non-renewable energy sources bid for supplying electricity.

The renewable sources get a competitive price from the transaction in the market. However, their survival is guaranteed by a mechanism called renewable obligation (RO). A similar mechanism, know as feed-in-tariff, is in place in other European countries for renewable energy sources. The UK government has recently introduced feed-in-tariff for small-scale renewable.

The RO, was introduced by the UK government in 2002 to provide a framework of financial incentives to invest in renewable. The RO places an obligation on licensed electricity suppliers in the UK (large generating plants normally higher than 100 MW) to source an increasing proportion of electricity from renewable sources. Suppliers demonstrate their compliance with the RO through the production of Renewable Obligation Certificates (ROCs).

ROCs are certificates issued to a qualifying renewable electricity generator and provide evidence that the specified quantity of electricity has been supplied by a licensed supplier to a consumer from an eligible renewable source. Generators receive a ROC for each 1 MWh of renewable electricity they generate.

How wind generates power?

Wind turbines, essentially a rotating arrangement with two to three blades (three bladed turbines are now common), produce electricity by using the power of the wind to drive an electrical generator. Wind passes over the blades, generating lift and exerting a turning force.

The rotating blades turn a shaft inside the nacelle, which goes into a gearbox (gearless designs are also now available). The power output of the wind generator goes to a transformer, which converts the electricity from the generator at around 700 - 1,000 V, to the appropriate voltage for the power collection system, typically 33 kV.

As shown in the following figure, wind energy technology has evolved rapidly over the last three decades with increasing rotor diameters and the use of power electronics to allow operation at variable rotor speed. Initial wind turbines generated only a few hundreds of kWs and a generator essentially working at a fixed speed was employed. Today a single generator can generate up to 5 - 7.5 MW and variable speed generators are employed.

(See Graph 2)

Evolution of wind turbine dimensions

Onshore turbine installations are frequently in upland terrain to exploit the higher wind speeds. However, wind farm permitting and sighting onshore can be difficult as high wind-speed sites are often of high visual amenity value and environmentally sensitive.

Offshore developments, particularly of larger wind farms, generally take place several kilometres away from land to reduce environmental impact. For example, the proposed Dogger Bank wind farm in the UK, which is about 125; 180 km away from the sea shore, will add 9 GW to the UK grid.

There are significant differences between wind power and conventional synchronous central generation:

Wind turbines employ different, often converter-based, generating systems compared with those used in conventional power plants.

The prime mover of wind turbines, i.e. the wind, is not controllable and fluctuates.

Even though the capacity of a wind farm is comparable to a conventional power plant, it consists of a number of small size wind turbines.

Due to these differences, wind generation interacts differently with the network and wind generation may introduce connection (as they are usually remotely located) and operational (as their output has a large variability and day-ahead uncertainty) challenges.

Traditionally, uncertainties in the power system (mainly due to the unpredicted nature of loads) are handled by initially selecting power plants to meet the expected load during each hour (called unit commitment) and then maintaining a set of generators (called reserve) whose power output can be controlled to maintain the second-by-second balance of the load.

When wind power is in the equation, the unit commitment becomes more difficult (mainly due to uncertainties in predicting wind) and reserve requirements become more critical (due to the variable nature of wind farm power output).

Possible solutions

Integrating a large amount of wind power into our power system should be done carefully. There are two issues associated with the wind integration: connection problems-what is the best way to connect a wind farm? and operational problems-how we should operate the system under a large penetration of wind?

Connection issue

The connection problem is invariably on the shoulders of CEB. Their main concern is how to integrate an intermittent power source to the grid while maintaining the security and the quality of supply. It is obvious that one will have a natural fear about this new technology which is very different from the existing technologies. Therefore careful studies are required before facilitating wind connections. Some may include:

(a) Extend the existing wind resource studies to understand the best locations for wind power plants. The variability of wind will smooth out to some extent if there is a geographical spread of wind power plants.

The spatial variations of wind from turbine to turbine in a wind power plant, and to a greater degree from wind power plant to wind power plant always help to smooth out the variability of wind.

(b) It is important to integrate the planning options for transmission networks and wind connections to minimise any security and reliability issues. For example, an HVDC interconnection is already planned between India and Sri Lanka.

As wind power connection through HVDC offers many advantages over AC connections for the system operator, it is important to plan this link with provisions for offshore wind power connections.

Multi-terminal HVDC is now under consideration for many wind farms and country-to-country connections in Northern Europe. A similar approach would bring more benefits than planning a point-to-point connection between India and Sri Lanka.

(c) The only way the country can attract more wind farm developers is by opening doors to large wind farms (in excess of 100s of MWs; which are more economical than smaller ones) which are connected to the transmission grid. However before opening up doors, it is important to develop a wind farm connection code which considers all the possible issues arising from wind farm connections.

Operational issues

By 2020, if the targets are met, the UK power system will end up with nearly 31% of renewable on their system. Out of which a large proportion will come from wind (expected to be as high as 32 GW).

How are they going to operate the power system with a large proportion of wind and a large proportion of inflexible power plants (where power output cannot be changed to absorb short-term variations of wind and loads) such as nuclear? Have the power system engineers in the UK neglected the prediction and variability issues of the wind?

In terms of wind predictions and selecting plants, the UK transmission system operator is in a better situation than us. In the UK, there is a market and a power plant to produce electricity for a period of one hour which is selected one to half an hour before the real time. The wind prediction algorithms during this time horizon are very accurate and the uncertainties are much less. However, preliminary studies show that the reserve requirement with 32 GW of wind will increase by three fold (current 3 GW to 9 GW).

Of course this will increase the cost of operation of the power system and many research initiatives are in place to see how this reserve margin could be reduced. The situation in Sri Lanka is in favour of wind power as hydro power plants could be ramped up and down much higher rate than thermal units.

Renewable Energy World International Magazine (September/October 2009 - Volume 12 Issue 5) reported a study which compares the possibility of using conventional power plants (conventional hydro, pumped storage, conventional thermal, and simple cycle or combined cycle gas-fired turbines) to offset for variability in wind. By considering start-up and shutdown capacity, regulation velocity, and technical minimum load, the report suggests that hydro plants have several advantages over other plants.

In conclusion, wind power is a favourable choice to produce electrical energy in Sri Lanka. However proper planning is essential before siting, connecting and operating them.

Dr. Janaka Ekanayake is attached to the Cardiff University, UK. Prior to that he was a Professor at the Department of Electrical and Electronic Engineering, University of Peradeniya.