Optimal Electricity Generation Expansion to Achieve Non-Conventional Renewable Energy Targets

Renewable Portfolio Standard (RPS) is rapidly emerging as a popular mechanism among policy makers to increase the penetration of renewable in the electricity markets, requiring the electricity supply industry to include a minimum threshold level of electricity generation from renewable energy sources. Sri Lankan energy policy has set a target of 10% of grid electricity by 2015 to come from mini-hydro, biomass including dendro power and wind energy, which have been identified as the three leading, sustainable, non-conventional forms of renewable energy promoted in Sri Lanka for electricity generation to feed into the national grid. The present installed capacity of grid-connected non-conventional renewable energy based electricity generation in Sri Lanka is around 100 MW and these plants are mainly connected to the primary distribution system. All these plants contribute to the nation's energy requirement generating only a small fraction of total generation amounting to approximately 2.5%. Further the long-term least-cost power generation expansion plan has given rise to the installation of oil-fired and coal-fired thermal plants to meet the increasing demand without giving adequate consideration to the non-conventional technologies as supply-side options. The study presented in this paper investigates the impact of the RPS of 10% on the least-cost power generation expansion plan considering aforementioned renewable technologies as supply-side options together with their technical potential and economic feasibility. The paper also examines the impact on emissions with this new renewable energy policy. It has been determined that this target can be achieved with an additional cost of US$ 93.18 million on the government by 2015. The results also show that mini-hydro is the only mature non-conventional technology. Wind power and dendro power require substantial government subsidies if they are to play a role in RPS.


Introduction
Renewable Portfolio Standard (RPS) requires the electricity sector to include a minimum amount of electricity from renewable energy sources.It is one of a number of policy instruments that can be used together to increase the production of electricity from renewable energy sources that are higher-cost, but have social, economic and environmental benefits.Support for renewable energy is currently needed since they are usually not yet financially competitive with conventional sources because of: subsidies to conventional sources, minimal pollution charges for conventional sources and newness of many nonconventional renewable technologies.Mechanisms normally used to support renewable electricity generation include direct financial support, such as capital grants and higher fixed tariffs, indirect support to accelerate the commercialization of renewable energy and pollution charges on conventional sources [9], [11].
However RPS, a new policy intervention is rapidly gaining popularity among policy makers.There are three major reasons for the growing popularity of the RPS [11].
• RPS maintains continuous incentives for renewable energy based producers to seek cost reductions and can be designed to ensure that these cost reductions are passed on to consumers.
• RPS can be directly linked to government policy targets since it ensures the attainment of a specific market share.
• The RPS minimizes the government involvement relative to other measures.
conditions during certain years, CEB r rt l the purchase of emergency power from tim t time.These power plants are operated on auto diesel [10].
ENGINEER Though there is no comprehensiv tud conducted to ascertain the total pot ntlul 111 these renewable technologies, CEB r how that 400 MW of total mini-hydro capacity n h • developed to feed the medium volt 11,; • distribution system [1].It has also b • in estimated that it is possible to have 10000 GWh of domestically sourced electricity annually from about 1200 MW of small (1 to 10 MW) wood-fuelled thermal power stations located throughout the country [3].According to th wind maps created by National Renewabl Energy Laboratory (NREL), 50000 MW of technical potential of wind power exists in Sri Lanka [3].But additional studies are required to accurately assess the economic potential of wind power, considering factors such as existing transmission grid and accessibility.
In terms of sector governance, the role of the government as the owner and the regulator of the sector are planned to be reorganized with the establishment of the Public Utilities commission of Sri Lanka (PUCSL) to regulate the sector.This new environment is likely to adopt methods of increasing non-conventional renewable energy technology penetration in the system such as Renewable Portfolio Standards (RPS).Thus the proposed power sector regulatory reforms will have a positive impact on renewable energy development.
Also there are privately owned Small Pow r Producers (SPPs) who are allowed to establi h power plants based on non-conventi n I Renewable Energy Technologies (RETs) up t maximum capacity of 10 MW.There i Standardized Power Purchase Agreem nt (SPPA) for such plants that is valid for 15 y , r period.The contribution of these n nconventional RETs in the context of total en r production is still at a relatively low value in rl Lanka.Renewable sources of energy that h v the technical potential for development in r Lanka for electricity generation are bi mt including dendro power, small-seal hy lru power, solar and wind.Present grid-conn lt d non-conventional capacity of the countr I around 100 MW. 161

Power Sector in Sri Lanka
Ceylon Electricity Board (CEB) is a statutory body with the responsibility of transmission and most of the generation and distribution of electric power.The total installed conventional capacity of the country is around 2240 MW; out of 1185 MW is based on large hydropower, which is the main indigenous source of primary commercial electrical energy.Further, 150 MW Upper Kotmale hydroelectric plant under construction, is expected to be completed in 2011.The system also consists of 500 MW of CEB owned thermal capacity, which are based on oil fired thermal generation with varying technologies such as oil steam, diesel engines, gas turbines and combined cycle plants [1].
A capacity of 534.5 MW thermal plants (mainly diesel based) is owned by Independent Power Producers (IPPs) under 'build, own, and operate' mode [1].Power so generated is sold to CEB.Also to meet the urgent requirements of the grid resulting from delays in implementing new generation projects and low hydro The main objective of this study is to determine the impact of this 10% RPS on the least-cost power generation expansion plan of Sri Lanka, considering these non-conventional resources based decentralized power generation options such as mini-hydropower for which there is a significant potential, wind generation and dendro thermal, which have gained increased interest in recent years as supply-side options.The study also determines the cost to the government when achieving this target and the associated greenhouse gas and other harmful emissions from the Sri Lankan pc,wer sector.These options are examined from the point of view of Traditional Resource Planning (TRP) where only the supply-side options are considered without any demand side management.
Though this policy has been earlier implemented in developed countries, such as USA, Australia and many European countries, developing countries like China, India, and Thailand are also interested in the same.Sri Lankan energy policy has also set a target of 10% of grid electricity by 2015 to come from mini-hydro, biomass including dendro power and wind energy [5].

Methodology
The Integrated Resource Planning (IRP) model and the related software developed by Asian Institute of Technology (AIT), Bangkok for longterm electricity generation expansion planning is used in this study.This model considers both supply-side and demand-side options.It is a mixed-integer linear programming based optimization model.The model determines the least-cost mix of supply-side and demand-side options for a given planning period.In the component of the study presented in this paper only the supply-side options are considered confining the model to Traditional Resource Planning (TRP).
The objective function is to minimize the total system cost, which is the sum of supply-side costs, which consists of capacity cost of candidate power plants, as well as costs of fuel, operation and maintenance of existing and candidate power plants.Further information about this planning model is given in [7], [8].
All technically feasible generation options are included in the objective function, which optimizes the total generation cost during a planning period of 20 years.Each year is divided into two seasons and the daily chronological load curve is divided into 19 blocks in order to capture variations in electrical power demand over different periods of a day.
The study tries to achieve a target of 10% of the grid electricity by 2015 using non-conventional renewable technologies.
Since these technologies are still immature in Sri Lanka, government intervention is justified in order to achieve this target within the set timescale.Therefore direct capital investment subsidies, which are the most straightforward incentive [4], are used to promote non-conventional renewable technologies due to the limitations of the planning model.Thus this study output would be to propose a plan with a minimum cost to the government.

Input data and Assumptions
The inputs to the long term generation expansion planning model used in this study are similar to those generally given to other planning models.

Electricity Demand
The demand for electricity in the country is forecasted annually by CEB using econometric analysis and is presented in LTGEP each year.Energy forecast is initially done for three consumer categories namely domestic, industrial and general purpose (including hotels) and other categories which include religious purpose and street lighting.The final energy generation forecast is done by adding total energy losses to the sum of sector wise energy forecasts.Peak demand forecast is done by assuming a load factor of 55.2% throughout the planning period.The base case demand forecast prepared by the CEB was used in this study [1].

Future Generation Options
The future generations options considered for planning purposes in the Sri Lankan power system are initially screened using specific generation costs of the individual options.
Based on this, eight options have been identified as candidate thermal options for expansion I ENGINEER planning studies.The important parameters of these options are given in [1].

Distributed Generation (DPG)
The DPG options considered in this study are limited to mini-hydro, wind and dendro power plants.The

Different Planning Scenarios
To examine the impact of 10% RPS in the pow r system, the study uses traditional resour planning (TRP) approach.As shown in tab! 5, the scenarios were selected to analyz th impact on the long term generation exp n. i 111 plan and the associated economic and mi I< n conditions.

Results
The data discussed in section 4 was fed to the TRP model used in the study.During the calculation of emissions in each of the scenarios analyzed in the paper, the emission factors agreed upon by the Intergovernmental Panel on Climate Change (IPCC) were used for the different generation technologies [1].
Table 6a shows the plant sequence under the base case scenario where the system is planned according to the traditional approach without any additional constraints.Table 6b shows the ENGINEER plant sequence when non-conventional renewable generation options are considered for generation expansion planning with their actual costs as given in tables 2 and 3.The costs and C0 2 emissions of each scenario are given in table 7. Since the projected future plant additions are all thermal based, the C0 2 emissions will undoubtedly increase though still it is at a relatively low value in Sri Lanka.When DPG options are considered for system expansion, the total generation cost reduces by almost 5% following overall C0 2 emission reduction of 8.14%.
The total generation cost including th the government under 10% RPS increases slightly than that under scenari reduction in overall C0 2 emissions under th 1.  scenario is about 2.77% at an average abatem nt cost of US$ 30.25 per ton of COi-Thus th increase in generation cost to achieve thi reduction is almost 1 %.
of each plant.It has been determined that thi target is achievable with an additional cost of US$ 93.18 million on the government by 2015.
Non-conventional renewable options were not considered as supply-side options during scenarios 4 and 5 in order to determine the CDM impact of UKHP plant.Further the CEB also does not consider these as supply-side options for system expansion.It was mentioned earlier that a 150 MW steam oil plant is selected for the UKHP plant in the same year resulting 3.4% increase in generation cost followed by a 24.7% increase in C0 2 emissions compared to the base case scenario (scenario 1).This will give a CDM impact of UKHP plant as US$ 19 million assuming a US$ 10 per ton of C0 2 emission reduction.
The main intention of the study presented in this paper was to examine the impact on the leastcost long-term power generation expansion plan of the new non-conventional renewable energy 165 300 MW and 150 MW plants in 2009 and 2011 are the Kerawalapitiya combined cycle plant and Upper Kothmale large hydropower plant which were considered as committed plants for the long-term generation expansion planning.

Analysis
It can be seen that the Sri Lankan power system needs a rapid expansion over the coming years.Further it will be a thermal based system since the least-cost generation expansion plans under all scenarios have given rise to the installation of oil-fired and coal-fired thermal plants to meet the increasing demand.
When these DPG options are-considered for system expansion, total non-conventional renewable electricity generation by 2015 is only 6.08% of total generation.Thus government intervention is essential in order to achieve its target of 10% of grid electricity in 2015 to come from mini-hydro, dendro and wind energy.Direct capital investment subsidies were therefore used as the method of promoting these DPG options considering the limitations of the planning model.These capital subsidies were included as negative costs_ to the model.Further these capital subsidies can be converted into the equivalent operating cost given the plant factors In addition to the existing grid-connected Distributed Power Generation (DPG) options of mini-hydro, dendro and wind as given in section 4.4, these three options were also offered as candidate plants to be implemented on a realistically achievable time-scale.The total centralized generation capacity reduces to 7150 MW with a plant combination of 5400 MW of coal steam and 1020 MW of gas turbines when these DPG options are considered as supplyside options.Thus 285 MW of gas turbines requirement is replaced by 280 MW of total new non-conventional capacity comprising 170 MW mini-hydro, 100 MW dendro thermal and 10 MW wind plant.
It can also be seen that the generation system consists of a total capacity of 7155 MW without any non-conventional generation options.This comprises 5400 MW of coal steam and 1305 MW of oil-fired gas turbines.Further when the UKHP is not considered as a committed plant, the least-cost generation plan leads to the installation of 150 MW steam-oil plant in 2011.policy of the government; i.e. 10% of grid electricity by 2015 from mini-hydro, dendro power and wind energy.
From the analysis it can be concluded that mini- hydro, dendro power and wind energy, which are the three leading renewable based distributed power generation (DPG) options in Sri Lanka need adequate consideration as supply-side options for system expansion.
Introducing aforementioned DPG technologies as supply-side options for generation planning results in overall emission reductions in Sri Lanka followed by a marginal reduction in total generation cost though these DPG options are high capital intensive plants.
Further it can also be concluded that the government target of 10% of grid electricity from DPG options by 2015 is achievable within the set time-scale.Further only the COM benefit of the UKHP plant cannot bear the additional cost on the government in order to achieve this RPS target.Mini-hydro can be considered as the only non-conventional renewable technology which does not require additional support while wind and dendro require substantial government intervention if they are to play a role in this new target.

Table 1 :
All the data used in this study are based on actual 2005 data and were obtained from Long Term Generation Expansion Plan (LTGEP) 2006-2020 report published by Generation Planning Branch of CEB [1].4.1 Existing and Committed Plants The list of existing and committed plants consists of all generation options considered in the list of future options, excluding coal steam and dendro thermal.All plants for which funding has been already arranged and those that are at various stages of development are used as committed plants in this study.The important parameters of the existing and committed hydropower plants are given in table 1 and those of thermal plants were quoted from Table 2.6 and Table 2.7 in LTGEP in page 2-10 [1].Data on Existing and Committed Hydro Plants

Table 2 :
Data on Candidate Nondispatchable Plants

Table 3 :
Candidate Dendro Plant Data 163 Also the data of the fuel types used are given in

Table 4 :
Fuel Costs Used in the Study

Table 6a :
Selection of Plants under Base Case

Table 6c :
Selection of Plants under 10% RPS by 2015