Төвийн эрчим хүчний системийг усны эрчим хүчээр хүчитгэх нь/Hydropower scheme to strengthen CES of Mongolia/

Hydropower scheme to strengthen CES of Mongolia

Энэхүү өгүүлэл нь Төвийн эрчим хүчний системийг Энерги хуримтлуулах усан станц (ЭХУС) байгуулсанаар хэрхэн тогтвортой найдвартай болгох талаарх шийдлийг дэвшүүлсэн төслийн санал юм. Хуулбарлахыг хориглоно. Иш татахыг зөвшөөрнө.

PROJECT TITLE

Hydropower scheme to strengthen Central Energy System of Mongolia [abbreviation is HPSCES]

OBJECTIVE OF PROJECT

Outcomes of this project will introduce solution with strategy of new hydropower scheme which would make stable electricity grid system to strengthen Central Energy System. Operation concept of proposed pumped storage power plant is to store excess electricity from CES produced by various power sources such as intermittent renewable source and to produce electricity to CES when it has peak load, therefor system will become more flexible than current condition. Moreover, proposed pumped storage facility will response of safety guarantee for CES.

Background

Introduction to Central energy system and problems

Mongolian energy system has split into three parts namely West Energy System (WES), Central Energy System (CES), and East Energy system (EES) as shown in figure 1. Government has been proved many acts such as “Energy Sector Development strategy” in 2002 and “Program on Integrated Energy System of Mongolia” in 2002 to unify those energy systems and to increase source of electricity especially in CES, which is 80 percent of all Mongolian Energy sector and consumption increasing dramatically. Many problems such as power shortage, unstable system, and inefficiency production are related to CES for last two decade and maybe in the further.

Figure 1. Colored are Central energy system and its subdivisions. Dashed lines are proposed to build by Program on Integrated Energy System of Mongolia, 2002.

Power sources of CES are becoming slightly alternative but mainly dependent with coal-fired thermal power plant (TPP or CHP – combined heat and power plant) which produces electricity and heat. Reason of Mongolia not directly going to have alternative energy source, say renewable energy, and to build new sources is aged coal power plants need to be replaced with new or so called base load power plants. Single type coal power plant source makes unstable and unsafe system (energy system security), since steam turbines can’t be manipulated by consumption. Besides, some drawbacks, which can be improved easily, appear from badly features of central energy system, listed in following.

• Difference between daily max and min consumption is around 240-330MW; energy system must be fully supplied by this amount of electricity.
• Electricity demand increased with 40-60MW by year mostly depends on the Mining and Industry.
• During off-peak time 200-250MWh exceeded electricity exported to Russia with cheap cost (46MNT[1])
• During peak time 255-350MWh electricity imported from Russia and China with high cost (145MNT)
• Under current condition, forecast of 2020, new source with 500-600NW is needed in only CES

To supply peak load around 900MW in the 18pm to 22pm, Coal power plant should work as maximum load to try to meet demand, after sharply decrease consumption (blue line in fig 2) by 330MW, loaded plant still working (purple line in fig 2) to produce electricity like during peak load as shown in figure 2 that shows daily load curves. This excess electricity exports to Russia with low cost around 46MNT[2] under condition to get back during peak load.  However, during the peak load (CES has two peak load morning and night) imported electricity is more expensive (145MNT) than exported before and max of additional imported electricity from Russia is around 180MW. It is obvious that importing cost is higher than export in the Central Energy System. This kind of unbalanced market mechanism and inefficiency management leads to “budget deficit” of system which is one of basic problem cannot extend to strengthen Energy system, itself.

Figure 2. This is daily load curve of CES. Consumption and CES operation curve is drawn based on mainly winter average daily load curves. Data source: http://www.ndc.energy.mn/

Furthermore, finance statement is unstable, losses are charged by Government, and this energy system is technically unsafe. This appraisal is arisen by slight analysis of daily load curves and aging of available sources.  Concerning of component of source type in CES, coal fired heat combined power plant is monopoly dominated 95 percent and rest of percent is renewable energy but not contain hydro sources.

Table 1. Power sources in Central Energy System and its aging

Power plant	Installed capacity, MW	Current statement, max MW	Age, type
Thermal Power Plant IV[3]	580	580	31
Thermal Power Plant III	186	136	46
Thermal Power Plant II	24	21.5	53
Darkhan Thermal PP	48	48	49
Erdenet Thermal PP	36	28.8	24
Salkhit Wind Farm	50	18	5
UkhaaKhudag TPP	18	18	4
Import from Russia	-	180	-

Confirmed potential production from power sources can supply barely base load amount of energy system and available range can be supplied from source is ranged between 600-810MW depends on TPP operation and wind farm in winter time. Generally harsh operation period is occurred in winter time since power plants must supply heat to regarded cities. Maximum amount of annual imported electricity is 330mln kWh in last year and peak was around 180MW which is increased at 6 percent from previous year and it will progressively keep in the long run. To view aspect of safety for CES, there is no power to accommodate any exceeded shortage outrange of importing agreement with Russia and no source for failure of system component, such as spinning reserve or other operation reserve. Therefore, some prevention and guarantees related to system stability and safety are certified by additional term of contract with Russia.

Government perspective to CES

Current sources such as coal fired plant and wind farm is devoted base load plants, which means that there must be safety reserve and peak loaded power plants urgently. Licensed and to be commissioned by 2020 renewable projects with capacity of 542.4MW (Sainbayar, 2015) are mainly focused on solar and wind resources in south region of CES, likewise two hydropower plants are proposed in northern part of system up to 400-542MW and one, namely Egiin HPP, is persistently supported by Governments of Mongolia.

Table 2. All Proposed and licensed on grid power sources for CES by Ministry of Energy

Licenses	Capacity, MW	Type	Licenses	Capacity	Type
Extension of existing TPP	70	Coal fired	Chandgana tal	600	Coal fired
Tsaidam nuur	600	Coal fired	Erdenetsogt	600	Coal fired
Buuruljuut	600	Coal fired	Tegshiin gobi	600	Coal fired
Shivee-ovoo	270	Coal fired	Baganuur	700	Coal fired
Cleantech	250-148(export)	Wind	Sainshand	52	Wind
AB solar wind	100	Wind (expired)	Cleanenergy Asia	50	Wind
Desert solar	30	Solar	Aydiner global	50.4	Wind (expired)
UB pumped storage	100	hydro	Egiin HPP	315	Hydro
		TOTAL:	4839.4MW

Above mentioned projects are not ongoing projects, many of them being proposed and studied for TOR stage. All licensed renewable energy capacity, supported to build including wind and solar, is 542.4MW and they have planned to deliver electricity to CES start around 2020.

National renewable energy program, NREP, is main action plan on CES until 2020 and approved with two implementation stage which are near term development goal 2005-2010 and midterm development goal 2011-2020. In this NREP, considered hydropower plants, they should be implemented in near term stage according to NREP, are left behind without studied in midterm term goal too. Abandon reason might be regards its initial high investment comparing with wind and solar system. But energy sources should be alternative and system should be safety and security, they must be protected by itself are important issue in CES development program. At least in order to improve operation of being proposed renewable energy sources, there is needed specified amount of energy storage facilities. UB pumped storage plant (commissioned by 2017, slacken now) can responsible for those operations but its capacity small than import peak. Regional water scarcity problem or capability of river does not effect on pumped storage hydro power potential.

Market survey of CES

The central energy system consists of five co-generators (thermal power plants as shown in table 1), the wind farm, one electricity transmission (CRETN) and 12 electricity distribution companies. Except three electricity distribution companies they are all state owned joint stock company. Energy regulatory Authority (ERA), established by 2001 Energy Law of Mongolia, introduced the Single Buyer Model (SBM) as a market model since Sep 2002 for CES. Singly buyer is Central Regional Electricity Transmission Network (CRETN) state owned company, purchases electricity from five sources with addition import and sell it to the 11 electricity distribution companies. In 2001, before the inception of the Single Buyer Model, the rate of sales revenue collection was only about 76.5%. This rate has increased every year and reached 101.8% in 2011 and collected additional MNT 4.3 billion more than planned (MNT 231.7 billion) in 2011 and accumulated debts of previous years were reduced accordingly (Mongolia, 2011). Being tested in 2005, the spot has been effective since 2006, therefore the National Dispatching Center was selected to act as a Spot market operator with suppliers five co-generators based on the real consumption and scheduled electricity rate difference. In 2011, about 3.9 million kWh of electricity or MNT 195.7 million was traded in the spot market. The amount of traded electricity reduced by 20.6% from 2010, which shows that generators’ imperfection had been reduced. TPP4 gained revenue of MNT 123.2 million from the spot market trade in 2011. However, other power plants had carried responsibility of paying amount MNT 123.2 million traded in 2011. Also ERA has started the auction market since Aug 2007, where an incremental electricity demand is auctioned among generation licensees for the best reduced tariff percentage. The National Dispatching Center operates the auction market and in 2013 only 0.2mln kWh power were sold on the market due to insufficient capacity reserve (Mongolia, 2013). Conclusion of this survey lies market is reforming and stable but connected new sources will be paid debts of aged co-generations except TPP4. According to approved Renewable energy law in 2007, following tariff range should be used for CES by Energy Regulatory Authority.

Table 3. Feed in tariff for renewable sources in energy system of Mongolia

Source type	Hydro				Wind	Solar
Capacity	Up to 0.5MW	From 0.5 to 2MW	From 2 to 5MW	Up to 5MW
On grid	0.045-0.06[4]	0.045-0.06	0.045-0.06	0.045-0.06	0.08-0.095	0.15-0.18
Off grid	0.08-0.10	0.05-0.06	0.045-0.05	0.045-0.06	0.10-0.15	0.2-0.3

Eventually on grid new power sources will work financially dependent with others due to single buyer model, which proposed to even incomes and expenses, to decrease accumulated debts. We need to concern large scale hydropower scheme with installed capacity can evaluated from further development consumption and excess electricity over 2030 and operating marked can be studied and assessed over current markets. Possibility and advantages of proposed facility can competently run on auction and spot market in CES.

Comparison of energy storage technologies

Currently, there are six categories energy storage technologies have been applied for power supply system. Pumped storage hydro power plant is widely used simple proven technology comparing with other five technologies. Principle of storage technology is to store energy of excess electricity in energy system during off-peak load and release energy back to energy system during peak load, all have same tasks. Also some largest facility such as pumped storage and thermal storage are response of operation reserve for emergency or unexpected failure in energy system.

Figure 3. Globally installed energy storage facilities are presented by categories since 2000 to 2015. Source: Global Energy Storage Database. In statistic of 2014, total grid connected PHS capacity was 138GW (International_Energy_Agency, 2015).

Intermitted sources such as solar and wind farm have to work with storage facilities to eliminate their disadvantage. Also many countries have been converting to green energy due to their limited coal and oil sources and renewable energy is becoming dominant sources. Therefore storage technology will develop together. All of storage technologies are under consideration and still developing.

Table 4. Comparison of main properties of energy storage technologies (Karl Zach, 2012) (Xing Luo, 2014)

Technology	Typical capacity	Power capital cost, USD/MW	Discharge time	Efficiency	Life time	Development stage	Application
Pumped storage hydro power (PSH)	5MW-2GW	500-4000	4-100h	65-85%	+50 yrs.	Mature	Primary/secondary/tertiary control, energy arbitrage
Compressed Air energy storage (CAES)	25MW-2.5GW	400-1550	2-24h	40-70%	15-40 yrs.	Mature/premature (AA-CAES[5])	Tertiary control, energy arbitrage
Batteries	1kW-50MW	300-4000	1min-3h	65-75%	2-10 yrs.	Premature	Uninterruptible power supply, primary/secondary control
Flywheels	5kW-20MW	250-350	4sec-15min	90-95%	20 yrs.	Mature	Primary control, power quality
Hydrogen fuel Cell storage system (HFCSS)	1kW-10GW	500-3000	0.01sec days	20-40%	5-10 yrs.	Prototype	RES-E[6] fluctuation reduction, tertiary reserve
Super magnetic Energy storage (SMES)	10kW-1MW	200-500	5sec-5min	95%	-30 yrs.	Premature	Uninterruptible power supply, power quality
Super capacitors	150kW	100-450	1sec-1min	85-95%	-10 yrs.	Premature	Uninterruptible power supply, power quality

Since 2000, there are commissioned 652 energy storage projects with total capacity of 45.77GW in world wide. Hence 82 projects with capacity of 42.96GW are pumped storage hydropower plant, 157 projects with 1.7GW are thermal energy storage, which is not included in comparison table and many different thermal storage technology can store energy from 0.1-100MW with capital cost 1000-15000USD/MW up to 20 years life time. For 2015, all up 21 pumped storage projects with capacity of 16.68GW are under construction in various countries such as China, Japan, Russia, India and France etc.

PLAN

Unsafety energy system with aged sources is receiving dramatically emerged consumption year by year. Aforementioned financial and technical problems and proposed renewable energy sources such as wind and solar in CES brings to purpose project of energy storage technology during expected hours, which can be pumped storage hydropower plant (PSHP) on grid. Proposed PSH plant not only store energy produced from other sources such as excess electricity, solar and wind, but also make more flexible manipulation to CES, which will be managed easily and production will meet quickly to consumption. Also to be flexible energy system, there must be peak load power plant or spinning reserve and consisted to renewable energy sources.

In the condition that will be occurred in 2020 case with total piloted projects (capacity of 542.4MW) being on grid, the problem might arise like as: how can improve effective of operation for those renewable sources, how to decrease curtailment of wind farm or how to store electricity from those renewable sources, how could be readiness of spinning reserve for main sources. Spinning reserve is additional premier supply source when failure of power generation or other shortage emergency case in energy system. At least one spinning reserve source should be designed with capacity of biggest generator in energy system. This project will be next generation after 2020.   

Capacity of purposed PSH

According to NPRE until 2020, capacity of being commissioned plants including extension of existing power plants is around 642.4MW. By approximate prediction, there need to be storage of 400MW in CES, even UB pumped storage hydro power plant is built (see table 2). And there is biggest generator of CES is 100MW, which can be added capacity of new pumped storage hydro power plant for response of spinning reserve. Hence capacity of new purposed pumped storage hydropower plant is calculated as around:

Where P_re is amount of storable renewable energy output including excess electricity of base load sources and P_spinning is capacity of energy system security source.

Figure 4. Conceptual operation plan for pumping and turbine mode of proposed Shurgait PSHP assumption on after 2020.

Off peak excess electricity arises from daily consumption curve, amount will continuously increase, is not included to this calculation. This means proposed facility will mainly use power produced from intermittent source such as solar and wind to balance and to maintain their efficiency in CES. Facility operation procedure is illustrated in figure 4.

Approximated technical design

Consumption of CES is centralized in main three cities, Erdenet, Darkhan and Ulaanbaatar. It implies that energy storage should be close costumers and placed in appropriate site for selling electricity or water sources. Therefore site of PSH is selected on the Shurgait river located 43km north of Ulaanbaatar city.

Figure 5. Location of Proposed Shurgait PSHP

Lower reservoir will created by concrete dam on the Shurgait river and upper reservoir will built on top of right side of Mountain hollow. This site is topologically suitable to create high head for hydropower. Assume the upper reservoir minimum level can be EL1580.0m while lower reservoir maximum level will be EL1400.0m. Difference between those levels gives minimum head for operation of PSHP as,

Assuming local friction loss and efficiency of facility is 85 percent, we can calculate discharge needed to produce electricity amount of 500MW with four unit that each with capacity of 125MW.

If supposing operation time is T=6 hours (on the current statement hours of day: 9, 10, night: 18, 19, 20, 21, see figure 2), available energy is

And total discharge volume with n=4 turbine pump unit will be

This amount of water is needed to achieve purpose of the project and should be contained upper and lower reservoir. Project side is chosen only on decision of online survey study. Therefore volumes of purposed reservoirs are roughly estimated in following chart. But it can give orientation to analysis of reservoirs.

Table 5. The Upper and lower reservoir volume calculation for Shurgait pumped storage hydropower.

Upper reservoir
Elevation, m	Surface area, m2	Interval, m	Volume, m3	Accumulated volume, m3	Lateral	Drawdown or level variance for full operation stage in upper reservoir
1520	7246.852		0	0	0
1540	69357.2	20	766040.55	766040.55	0.895514
1560	245143.9	20	3145010.72	3911051.267	0.717076
1580	448700.4	20	6938442.83	10849494.1	0.453658
1600	685594.8	20	11342952.1	22192446.23	0.345531	Area	567147.6
	Total volume		22192446.2	22.2mln m3		h	12.68724
Lower reservoir on Shurgait river
Elevation, m	Surface area, m2	Interval, m	Volume, m3	Accumulated volume, m3	Lateral	Drawdown or level variance for full operation stage in lower reservoir
1349	136678.5		0	0	0
1360	243240.4	11	2089554.06	2089554.064	0.438093
1380	860929.1	20	11041694.5	13131248.6	0.717468
1400	1711799	20	25727279.4	38858528.02	0.497062	Area	1286364
	Total volume		38858528	38.8mln m3		h	5.593704

From the calculation, upper reservoir volume is 22.2mln m³ while lower reservoir volume is 38.3mln m³. Careful design is needed to determine volume of both reservoirs. During 6 hours operation time with turbine mode, upper reservoir level would be changed 12.6m, while lower reservoir level will be changed 5.59m. Hence hydropower operation heads are calculated in following table.

Table 6. Maximum and Normal/minimum operation head for Shurgait pumped storage hydropower.

Upper reservoir		Lower reservoir		Max head	Min head
Head	Value	Head	Value
Maximum operation level	1592.69	Maximum operation level	1400.00	198.28	180.00
Normal operation level	1580.00	Normal operation level	1394.41
Drawdown, m	12.68	Drawdown, m	5.59	Average head	189.14

Now it is possible to calculate average energy using average head.

Both reservoirs are created by dam and dam heights are around 40m and 51m at upper and lower reservoir, respectively. Dam heights are can be decreased by detailed design. Various materials can be used for dam construction such as earth and concrete on sound rocky basement. I hope geological condition and foundation of dam is good in selected site, since the site is mountainside of the Chingiltei mountain, which has metamorphic rock like granite and this kind of basement can be stable base for concrete dam (Urban_planning_institude_of_Ulaanbaatar, 2013). Upper reservoir should be protected seepage under reservoir and trough a dam. Most advanced technology in dam material is Rolled Compacted Concrete, RCC, which is low cost concrete with less cement consumption, use to fly ash and dry than conventional concrete.

Figure 6. General plan for proposed Shurgait pumped storage hydro power.

Figure 7. Longitudinal cross section through headrace (pressure tunnel) including pump/turbine house, upper and lower reservoir

Technical aspects

Water resource for Shurgait PSH

Liquidated organization, named Water Strategy Institute of Ministry of Nature and Environment was studied hydro power potential resources on river with annual mean discharge up to 1 cps throughout the northern and western part of Mongolia, and concerned around 3800 small and large rivers has the power of 6400MW, with possible energy output of 56200MWh. Very earlier study was carried out by cooperation between Hydro research and project implementation institute with Hungarian Water Resources Authorities and result and possible strategy was considered in Integrated water resource utilization and conservation scheme of Mongolia in 1976. Those general studies have not involved possibilities of pumped storage facilities. Thus, liable capacity of pumped storage should study and evaluate by region in Mongolian territory.

Proposed facility will build on upper stream of Shurgait river which has no hydrological observation station or accumulated data. But Shurgait river is not temporary river, that has minimum flow around 0.5m³/s which are noted during in situ observations in 2011. To argue water availability for proposed facility, let’s perform little analysis. Total required water volume to produce designed energy is V=7196040 m³. Time to refill this amount of water into reservoir would be

After the filled, river flow should be released to downstream in river stream, stored water will be recycled between two reservoirs to generate or store power. If assuming rainfall and floods in Shurgait river, time to collecting water will decrease. Whatever rainy or dry season, evaporation and filtration/percolation will be main problem for water resources. Such possible water losses should be added in effective reservoir volume range. Percolation losses would be less than evaporation and it will decrease progressively.

Current technology for PSH

There are several proven and widely researched technology to generate hydroelectricity namely conventional, run-of-river, and pumped storage including small to large facilities. Small and run-of-river technology will be harsh for Mongolian climate condition in winter time.

Figure 8. Power unit of hydropower plant with Kaplan turbine and Electricity generator. Source: Wikipedia

Main equipment to produce electricity is water turbine and generator and named “unit” in power technology since they installed. Flowing water is directed on to blade of turbine runner, creating a force on the blades. Since the runner is spinning, the force acts through a distance (force acting through a distance is the definition of work). In this way, energy is transferred from water flow to turbine and mechanical energy of spinning turbine switched to generator.  Water turbine are divided into two groups namely reaction and impulse turbines and they also split into four types called Pelton, Francis and two types Kaplan, respectively. They are used for aforesaid hydro power technology.

Reaction turbines are acted on by water, which changes pressure as it moves through the turbine and gives up its energy. Newton’s third law describes the transfer of energy for reaction turbines. Francis (stationary blades) and Kaplan turbines (movable blades) are reaction turbine. Impulse turbines change the velocity of water jet. The jet pushes on turbine’s curved blades which changes the direction of the flow. The resulting change in momentum causes a force on the turbine blades. Since turbine is spinning, the force acts through a distance and the diverted water flow is left with diminished energy. Pelton wheel is impulse turbine. Prior to hitting the turbine blades, water pressure is converted to kinetic energy by nozzle and focused on the turbine blades. This type of turbine is convention for small reservoir capacity with large potential energy (difference pressure of input and output of turbine).

Special reaction type turbine often preferred pump-turbine, usually Francis turbine, is designed for pumped storage hydropower plant. They can reserve flow and operate as a pump to fill upper reservoir during off-peak hours, and then revert to turbine mode for power generation during peak demand. It is important that pumped storage is not energy source but can be small amount of producer in energy system, which has been proven on various researches. Historically, in future there are several type of pumped storage technology will be used (Giovanna Cavazzini, 2014). Type of pumped storage is characterized by set of hydraulic and electrical machines such as turbine/pump or generator/motor as follow.

• Binary set: one pump-turbine (Francis) and one electrical machine (motor/generator) including single or multistage
• Ternary set: one turbine (mainly Pelton), one pump and one electrical machine (motor/generator)
• Quaternary set: turbine and pump drives generator and motor, respectively.

Advanced technology on PSH

There are not special advanced technology in convention hydropower and used water turbines, but some of afford has been done for Pumped storage technology. In the advanced pumped storage technology, researchers have been study on following three categories:

• Effective site and method surveying which include underground reservoir and coupled with compressed air storage etc. – not related this project.
• Adjustable speed pump-turbine including advanced runner like splitter runner
• Ternary unit, which employ a separate turbine and pump on a single shaft with the generator/motor.

Figure 9. Ternary Unit with a Vertical arrangement and motor-generator above the turbine and pump. Source: http://ceeesa.es.anl.gov/

Ternary unit is most advanced technology innovated recently by Argonne National Laboratory. The main difference between ternary unit and standard pump/turbine (binary set) unit is that the ternary unit can simultaneously operate both the pump and turbine mode. Three components – turbine, pump and generator – can have two vertical configurations. Figure 10 shows vertical arrangement of generator located above the turbine and pump (Koritarov, 2013). Another configuration is generator can be located between pump and turbine, turbine is above the generator. This configuration is successfully applied Kopswork II PSH in Austria and they use to Pelton turbine with 6 nozzles. Turbine output is 180MW, while pump input is 155MW (Hirtenlehner, 2006). This means that using this ternary unit they have able to produce more than 25MW power from absorbed electricity from energy system.

Like above, every project has its own unique properties and contains some innovation of technology. For example Kannagawa pumped storage hydropower plant in Japan introduced splitter runner for turbine/pump and full faced boring TBM machine which can excavate steep angle of 48 degrees.

Figure 10. Splitter Runner for Pump/turbine unit installed in Kannagawa PSH plants.

Splitter runner is multi-blade pump/turbine runner that was jointly developed by TEPCO and Toshiba Corporation. With the introduction of this runner, ten blades shown in Figure 11, Kannagawa Hydropower plant increased its power generation and pumping operation efficiency by about 4 percent. There are also implemented and tested double and multi stage pump/turbine for high head which would increase efficiency for both of turbine and pump mode. This project will include innovation to improve efficiency or to decrease cost like above mentioned advances.

Prospective to pump turbines of Shurgait PSH

Except in terms of hydraulics and electrical machine, there are number of notable things such as controls, distributions and automations and they are carried out cooperation between cross disciplinary companies. We will discuss about possible innovation or design criteria for “unit” related to proposed facility based one technological advance. Generally reversible machine unit consist of a motor-generator (M/G) and a reversible pump turbine (P/T) that works either pump or turbine depending on the direction of rotation. For motor-generator to exploit its capacity to have variable speed for pump and turbine, possible solution is tied with synchronous and asynchronous whose difference is a rotor. Both solutions have its merit and demerit related their start up times, energized current (direct or alternative current), and ancillary equipment (frequency convertor) (Beyer, 2007). If we use asynchronous motor-generators in proposed facility, we have possibility to earn following advantages, including:

• More flexible in unit operation
• Higher efficiency over a wide range of operations at partial load conditions
• A wide range of controllable and optimized power consumption in pump operation
• Additional and faster features for grid control, such as fast power outlet regulation
• Better use of the reservoir because higher water level variations can be allowed
• Better contribution to grid stability because of the high moment of inertia of rotating masses
• Regulate power both mode pump and turbine mode.

To have successfully variable/adjustable speed for pump or turbine, we need to use asynchronous motor-generator. But it would be costly than synchronous one. In case of low head and speed, it would be gain efficiency turbine and pump mode using synchronous motor-generator for variable speed, but not sufficient to offset the substantial cost of power electronics convertor (Gish, et al., 1981). Hence appropriate model should be carried out to determine optimization of operation in both cases in order to have right solutions on it.

One of important thing should be embedded in this project is able to work simultaneously in pumping and generating mode. In fig 4, we can see that during the pumping water to upper reservoir facility need to produce electricity to energy system. But most case of operation except of ternary facility, modes are transposed like one by one for whole facility whatever it has many units. It can be possible in our project since facility have four units, two units can work pumping mode while remaining two can work turbine mode. In this case main problem will be headrace for each unit (it will be costly) and electricity regulation problems. 

Final abstract idea is that coupling with variable speed technology into ternary unit can be innovation in this project. To become technically feasible this idea, many researches and modeling should be done as well as possible experiments. Ternary unit has numerous advantages such as hydraulic circuit for load frequency control. Also if we set ternary unit in facility, pump and turbine mode can be work on single unit to use single headrace. Using this so called “hydraulic short-circuit operation”, facility can goes on balancing of CES during its unrequired time.

Benefits

This project will contain number of benefits related to economic and social and also may influence negative result to environmental. Negative result can be specific amount of area will be submerged by reservoir, which cannot be used other purpose anymore. Here we will explain some important explicit benefits which can be seen directly from output of this project.

Economic benefits

New facility will offer employment to various fields of workers and engineers during all stage from starting of the project. After commissioned, there still will be position for engineers and workers. We will later discuss about capacity of work force during the project detailed research and designing stage. Next processing stages are unclear, we can’t specify proper status about employment for it and they are determined sequentially in previous stage of implementation.

Basic idea of this project is emerge from figure 2, to use excess electricity for pumping water to upper reservoir and to response peak load using electricity production of turbine mode. Excess electricity and demand are not equal means there needs extra source to pumping water to upper reservoir to prepare expected peak time in current condition of CES. On the other hand if the peak is 180MW according to figure 2, proposed facility requires this amount of electricity which can be used to pump up water to upper reservoir. In this case, other intermittent source can be used to pumping like following conceptual.

Figure 11. Conceptual operation plan for current situation of CES that maximum peak load of 180MW is imported from Russia.

Day time, 8am to 18pm, proposed power plant will buy electricity from intermittent renewable sources with cost of storing agreement, let’s assume current market cost of 0.04USD/kWh which is equal to 78MNT rather than current exporting rate to Russia, and purchased electricity will spend to pump up water from lower reservoir to upper reservoir. During peak time or power shortage time, pumping mode will switch to turbine mode to generate electricity with cost equally to solar or wind selling price, say 0.08USD/kWh see table 3. Considering efficiency, it is possible that totally E_buy=600MWh electricity would be stored and produced in proposed facility under current condition. Let’s calculate one day revenue of this facility using total selling and buying electricity.

Condition without proposed facility and with same peak load (condition fig 2), the CES lost 30000USD every day in export and import electricity. Hence, if purposed facility is private, the intermittent sources lost 6000USD every day but they can find more nonmonetary profit with storage facility i.e. for wind farm, they are balanced and for solar, they would be able to use full capacity of them on every sunny day.

Now we can estimate how much revenue will receive when facility works with full capacity, E_av= 1150.68MWh/year,

If consider selling cost is 0.1USD per kWh, revenue would be 69.04mln USD. Those calculation and cost stands on Feed in tariff for in Mongolian Renewable energy law, see table 3. We need to check out and evaluate electricity price based on facility investment cost.

Table 7. Conceptual cost estimates and bill of quantities of proposed Shurgait PSHP

Items	Size	Quantity	Rate	Amount cost	Description
Upper dam	40m/932m	236106m3	140	33054840	Volume is approximated. Reference cost is used[7]
Lower dam	51m/470m	151810m3	140	21253400	Volume is approximated. Reference cost is used
Instrumentation		1	2744000	2744000	Construction equipment for RCC dam building
Access roads	15km	1	262000	262000	Global reference cost compared with Mongolian reference cost
Tunnel	Ф8.78m/1431m	86596m3	0.29	25112.84	Based on cost analysis result of (Nathaniel Efron, 2012). Cost shows single tunnel but couple tunnel can be built.
Surge shaft	25m	1	9419800	9419800	Reference cost is used
Steel tunnel line	Ф8.78m/200m	1	9014492	9014492	Inflation added research of (Waal, 2000)
Underground power house	20/120/45	1	64537979	64537979	Reference cost is used
Generators	125MW	4	2954307	11817228	Same as turbine
Turbine/pumps	125MW	4	2954307	11817228	Cost evaluation formula for Francis turbine
Transformers	220kV	1	36648262	36648262	Reference cost is used
Transmission line	220kV*10km	4	264807	1059228	Based on research work of (Yli-Hannuksela, 2011)
Total, USD			201653570
Allowance for other[8] (10%)				40330713.97	Approximated
Project management (10%)				20165356.98
Total contingency (20%)				40330713.97
Total estimated cost USD				302480354.8	Cinv

From this conceptual cost estimates, capital cost of proposed facility would be 604.96USD/kW, if the estimate is proper. Total cost of UB pumped storage project in listed table 2 is 285mln USD, which gives capital cost of 2850USD/kW. Capital cost of our proposed facility is grounded nearest in lower range of global cost, which implies this project is economically feasible, while UB pumped storage project is stood in middle of global cost, see global cost range from table 4. Our conceptual cost estimate may be seen abstract and missed some important activity cost related construction and implementation. One of great example existing facility with same capacity and near in cost, La Ta Khong Pumped storage hydropower in Thailand, is built in 1994 with total cost of 18242mln JPY, which gives today’s capital cost of 517USD/kW concerning inflation between 1994 and 2014. This is one of verification that conceptual cost estimates is proper. Very similar project is Alqueva pumped storage power plant (130MWx4=520MW) in Portugal, which has been commissioned within two stages. Overall cost including both stages (2004, 2013) is 1.7billion USD, which gives us 3269USD/kW of capital cost investment. Comparing to Alquenve PSH, our proposed capital cost is quite small but dams specifications or civil works are also small than Alquenve PSH dams.

One of other important term of economy is payback period, which can be found for proposed facility like:

Here we use annual revenue instead of net annual revenue because of undefinable cost of operation. According to this analysis, payback period of 6.57 year is acceptable and again we can conclude that proposed project is economically feasible and cost of selling electricity can be decrease. 

On the other hands, feasible capital cost make possibility to use above concerned buying and selling price within Feed in tariff for in Mongolian Renewable energy law, table 3. Consequently, to be paid money for importing is circulating in own (Mongolian market) market and economic deficit of state owned company will decrease gradually and those changes let to offer cheap electricity tariff to costumers.

Other benefits

This proposed project will bring us numerous positive benefits after its completion. Here some non-monetary like technical benefits are listed.

·         Firstly, Central energy system would become flexible due to operation of storage facility and general operation process will be suitable for implementing market in CES such as spot and auction market, they are required more flexible, stable energy grid.

•          Proposed storage facility will response operation reserve for emergency or any failure related electricity distribution and all existing CHP steam turbines will have been guaranteed by Shurgait hydropower. Consequently, CES will become security and safety. Everyday electricity restriction by region in summer time will be decreased tangible (main costumer complaint is restriction now).
•         Existing and coming to be commission energy sources, especially for renewable energy source, will be operated properly and fully by their capacity in on grid. Nowadays, main problem of existing wind farm, Salkhit with capacity of 50MW, is curtailment of power production because of balancing. Pumped storage is good balancer for wind farm, for solar too. Even without storage, if there is no demand, solar facility cannot work properly sunny day.
•          It will be possible and open to create new renewable sources in CES, particularly wind farm nearest proposed facility where wind is rich, to transit gradually coal to renewable sources. In this case we need more storage facility. Launched project, UB pumped storage hydropower, is not enough for increasing demand in 5 years later in CES from now. Decision makers or experts should always think about next generation of current plan.
•          This project will provide much experience to regarded facility or educate engineers to experts for this field. This also can be one of good prototype or model for building next pumped storage hydropower in western energy system where many suitable sites are existed.
•          Most important thing is that proposed storage facility will provide independent energy system to neighbor country and furthermore it is also offer easy implementation of Unified smart grid which is essential strategy of Ministry of Energy referred in Program on Integrated Energy System of Mongolia 2007.
•          It also will reduce CO₂ emission for generating power. CO₂ emissions per kWh from produced electricity are around 1091.44 ton in annual. 

Conclusion

Based on current condition and forecast of the Central Energy system of Mongolia, new pumped storage hydro power plant named Shurgait PSH is proposed to build on Shurgait river in northern side of Ulaanbaatar city to stabilize and maintain operation of energy system. Purpose of this facility is to equalize power balance for between costumer and sources, to response to operational reserve (spinning) for any failure which can encounter in energy sources. This project will serve its function after 2020 and many reasonable technical benefits will be offered to CES such as flexible and security energy grid. Generally it will be used to store electricity from intermittent sources like wind and solar which are depended from more nature.

Shurgait PSH plant has two reservoirs and one underground cavern had four units with installed capacity of 500MW. Each unit has capacity of 125MW and planned to be built couple headrace (head tunnel) connected to upper reservoir whereas each unit has four tailraces to lower reservoir. Two reservoirs will be created by new RCC dams, one in cross the river while another one is top of the mountain side. Variable speed technology and ternary set technology have been considered for hydro power units to meet and exploit current development on pumped storage technology. Initial and crucial technological aspects are discussed and evaluated in Technical aspect section.

For energy system, which is base loaded and also slightly alternated by intermittent sources, pumped storage hydropower plant will offer many advantage in terms of economy and society. It is notable reason to propose this project that to be independent, certified to costumer, technically stable, security and flexible energy system must have energy storage and reserve facility. This proposed facility will responsible both function to energy system during more long time than its payback period. Some economic and social observable benefits are discussed in the Benefit section. From the calculation, Conceptual capital investment/cost and economic terms of proposed facility is reasonable to evaluate that project is economically feasible. To comparing capital cost of commissioned facility which has same capacity, total cost is possible that conceptual cost estimation is closer to correct. In literature, European weighted cost of pumped storage plant through ongoing projects is estimated as cost of 980-1150USD/kW (Steffen, 2012) and cheapest capital cost of 275USD/kW (Beyer, 2007) is experienced in Avce PSH in Slovenia. Proposed facility has capital cost of 604.96USD/kW and it may be decreased by detailed design.

Project will be challenged for Mongolian, because of no experience to pumped storage. But in future development, it is true for them that they will face pumped storage hydropower plant in several sites in Mongolia. No reason to avoid it, because of resource of the nature is limited.

REFERENCES

Beyer Thomas Goldisthal Pumped-Storage Plant: More than Power Production [Online] // Hydro review worldwide. - Hydro world, 03 01, 2007. - 1. - http://www.hydroworld.com/articles/print/volume-15/issue-1/articles/goldisthal-pumped-storage-plant-more-than-power-production.html.

Burentsagaan Boldbaatar Assessment of Future Hydropower plant investment in Mongolia [Thesis]. - Seoul : Seoul National University, 2013. - Vol. master thesis.

Giovanna Cavazzini Juan Ignacio Perez-Diaz Technological development for pumped hydro energy storage [Report]. - Madrid : European Energy Research Alliance, 2014.

Gish W.B. [et al.] An Adjustable Speed Synchronous Machine for Hydroelectric Power Applications [Journal]. - [s.l.] : IEEE, 1981. - 5 : Vols. PAS-100.

Hirtenlehner Klaus Real efficiency of Pelton Turbine in Back Pressure Operation [Journal]. - Steyr-Gleink : [s.n.], 2006.

International Energy Agency Energy Technology Perspectives 2015 [Report]. - Paris : International Energy Agency, 2015.

Karl Zach Hans Auer et al Facilitating energy storage to allow penetration of intermittent renewable energy [Report]. - Munich : Intelligent Energy Europe, 2012.

Koritarov Vladimir Modeling Ternary Pumped Storage Units [Report]. - Oak Ridge : Argonne National Laboratory, 2013.

Mongolia Energy Regulation Commision Annual report 2011 [Report]. - Ulaanbaatar : Energy Regulation Autority, 2011.

Mongolia Energy Regulatory Commition of Annual report 2013 [Report]. - Ulaanbaatar : Energy Regulatory Commition of Mongolia, 2013.

Nathaniel Efron Megan Read Analysing International Tunnel Costs [Report]. - Worcester : AECOM, 2012.

Sainbayar Otgonbayar Renewable Energy Regulation Policy [Conference] // ASEM: Mongolia-Country of Renewable Energy. - Ulaanbaatar : [s.n.], 2015. - pp. 6-7.

Steffen Bjarne Prospects for pumped hydro storage in Germany [Journal]. - Essen : Elsevier, 2012. - 2012 : Vol. 45.

Urban planning institude of Ulaanbaatar Environmental research and current statement of Ulaanbaatar city for General development planning of UB to 2020 [Report]. - Ulaanbaatar : Ministry of Construction and Urban development, 2013.

Waal Roland Dee Steel fible reinforced tunnel segments [Book]. - Delft : Delft, 2000. - Vol. 1.

Xing Luo Jihong Wang et al Overview of current development in electrical energy storage technologies and appliaction in power system operation [Journal]. - [s.l.] : Elsevier, 2014. - Applied science : Vol. 137.

Yli-Hannuksela Juho The transmission line cost [Report]. - Vaasa : Technology and communication, 2011.

Reviewer’s comment and advices

I am very appreciate to Prof. Mikami Yoshiki, Prof. Aruna Rohra Suda for their worth advice and guidance and also to students of Interdisciplinary Joint project seminar for their discussion.

Following comments and corrections from reviewers are included in final version of project proposal. Clarification of reviewer’s are responded with blue italic form after their paragraph respectively.

Prof. Aruna Rohra Suda [email of Jul 29]

Here are my comments regarding your project report:

• Overall, the report is much more detailed and clear now. You have included many calculations and verifications, which is good.
• Two clarifications:

a.       In Fig 8 (fig 11) you have shown buying of electricity, even during midnight hours (1-6am). I understand that this is buying from the power generating plants. Are you expecting plants to be generating electricity during that time? No, I not expect that proposed plant to be work in midnight (off-peak time) time. Regarding to question, at that time existing base load power plants will be produce excess electricity independently with demand, whereas proposed plant will use to store this generated electricity. Fig 11 represents conceptual operation of proposed plant to current condition of CES (between periods of 2015-2020, this condition which had excess electricity in night will be dominant in CES).  Does that part of buying affect your calculations of daily cost? Yes, it affects to daily revenue of proposed plants. But considered costs or prices of selling and buying electricity between sources and storages should be detailed by agreements in its implementing stage. I think those cost are suitable and addable cost in current or future condition.

b.      In the Technical aspects section, the calculation for filling the reservoir, is related to this project, it is good. But regarding turbines and pumps, you have describes the general principles, but have not described what this project will use. If you have not decided yet, you can make some comment about how (on what factors) will it be decided. I slightly discussed about turbine pump for proposed facility in Prospective to pump turbines of Shurgait PSH section. Technically it is cumbersome for me to sort out what factor is critical for turbine pump.

•      I have not verified your calculations, please make sure that they are correct. There are many projects of commissioned and ongoing now and their capital costs are evaluated to determine range of tentative investment (500-4000USD/kW) for pumped storage. Proposed project has capital cost of 604.96USD/kW which is verified by range of tentative cost and cost of some other similar projects such as La Ta Lhong (517USD/kW) and Alqueva I&II (3269USD/kW).
•      Structurally, I think you can put the Technical Aspects section as Appendix or bring it before the Section on Benefits. Secondly, you should have a Conclusion section after Benefits, which summarizes the Plan and the Benefits. One large paragraph to one page, should be good. Thirdly, you need a References section. In various places, you have mentioned your references, but it is better to put them in one section and include ones, which you currently don’t have, but which are relevant, especially, ones which have similar calculations about other installed HP Storages.

That is all.

Overall, it has turned out to be a good Project Plan, I think.

2015 © Зохиогч УБ инженер Б.Аюурзана.
pdf хуулбараар татах

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[1] MNT is Mongolian currency tugrik. 1USD=1974MNT, 1JPY=16.04MNT on July 1, 2015

[2] Exporting rate to Russia 46MNT/kW = 0.02USD/kW and importing rate from Russia 145MNT/kW=0.07USD/kW.

[3] TPP IV is the main work horse in central energy system. Table data source: Energy Regulation Committee of Mongolia.

[4] Prices are given USD per kWh. Source: http://en.energy.gov.mn/laws/show/id/2

[5] (Advance-) Adiabatic Compressed Air Energy Storage

[6] Renewable Energy Source for Electricity Generation

[7] In the most estimated cost has been used reference cost introduced by consulting service company, called Hewitt Estimating. http://www.infrastructurecost.com/

[8] Other includes some wages, intake, tailrace structures, transportation and construction equipment cost.