Renewable Energy Generation: Challenges and Practices

CHEN Guoping State Grid Corporation of China (SGCC) Sep 7, 2018 Contents

1. Developments of in SGCC

2. Challenges on Large-scale Wind and Integration

3. Work carried out and proposed by SGCC

2 Introduction of SGCC

SGCC is the world’s largest public utility company which serves over 1.1 billion people and covers 88 % of the Chinese territory.  By July 2018, the total generating capacity installed in SGCC’s service area had reached 1427 GW.  The maximum load in SGCC’s service area reached a historical high at 810 GW on July 25, 2018.

Generating capacity by energy source (July 2018) Load curve on July 25, 2018 GW 850 Nuclear 799GW, 56.9% 23GW, 1.6% (▲3.6%) 800 (▲10.1%)

750

Gas 700 Solar 60GW, 4.2% 142GW, 10.1% (▲7.7%) 650 (▲41.9%) Other thermal 600 Wind 42GW, 3.0% Hydro 137GW, 9.8% (▲10.5%) (▲11.5%) 225GW, 16.0% 550 (▲2.0%) 0:00 4:00 8:00 12:00 16:00 20:00 24:00 3 Promoting UHV Power Transmission

China’s coal, wind and solar energy resources concentrate in the Three-North areas, while hydro power resources are mainly located in the southwest. However, over 70% of electrical load resides in Central and East China. SGCC actively promotes the ultra-high voltage (UHV) power transmission to facilitate large-scale, long-distance allocation of energy resources. It has constructed 11 UHV DC projects with a total length of over 40,000 km, and the interregional transmission capability exceeds 96 GW. From Russia Northwest coal, North and wind & solar Northeast coal power base The ongoing Changji-Guquan and Northeast bases project is the world's state-of- the-art UHV DC project with North Northwest the highest voltage (±1100 kV), the largest capacity (12 GW) and the longest transmission distance (3324km). East Central Southwest Load HVDC center UHVDC Southwest hydro power base To South China 4 Renewable Power Generation

In 2011~2017, the average annual growth of hydro, wind and solar power generating capacity were 6%, 24% and 93%, respectively. By July 2018, SGCC has 504 GW of renewable power generation installed in its service area (225 GW hydro, 137 GW wind, 142 GW solar with 39 GW distributed PV).

Renewable power generation in SGCC Wind & solar power in provincial grids GW 224 225 240 216 208 黑龙江 210 199 185 蒙东 吉林 180 169 新疆 156 冀北 辽宁 142 蒙西 150 北京 129 137 冀南天津 117 115 宁夏 山西 120 103 青海 山东 甘肃 88 陕西 河南 90 70 江苏 67 西藏 安徽 上海 47 四川 重庆 湖北 60 35 36 0~20 浙江 24 湖南 江西 30 15 20~50 贵州 3 福建 2 云南 台 50~100 广西 广东 0 湾 2011 2012 2013 2014 2015 2016 2017 2018 100~200 Hydro/水电 Wind/风电 Solar/光伏 >200 Unit: GW 海南 5 Wind & Solar Energy Consumption

In 2011~2017, the average annual growth of wind and solar energy consumption were 26% and 134%, respectively. In 2018, wind and solar energy accounted for 8.4% of the total electricity generation in SGCC by August; the growth rate of wind and solar energy consumption (38.4%) was much higher than that of total electricity consumption.

Renewable energy generation in SGCC GWh 250 233 183 200 166 145 150 129 101 100 79 57 56 38 50 23 1 3 8 0 2011 2012 2013 2014 2015 2016 2017 Wind/风电 Solar/光伏

6 Contents

1. Developments of Renewable Energy in SGCC

2. Challenges on Large-scale Wind and Solar Power Integration

3. Work carried out and proposed by SGCC

7 Difficulties on Load Following

The volatility of wind power output results in difficulties on load following. In 2017, the total wind power output in SGCC varied from 63 to 7.9 GW, and the maximum intraday variation reached 32 GW. China heavily relies on coal power with limited regulation capability, while flexible power sources contributes a very small portion. The grid regulation capability further reduces during heating period.

Load and wind power in Northwest China, March 2018 85 35 80 30 In March 2018, the wind power 75 25 output in Northwest China grid 70 20 varied from 2 to 31 GW, and the 65 15 maximum intraday variation reached 60 10 17.72 GW. 55 5 Load 50 0 Wind (GW) 0:00 4:00 8:00 12:00 16:00 20:00 (GW)

8 Challenges from Power Electronics

Wind and solar power generation is integrated into the system via power electronic components, which lacks active/reactive power regulation abilities. As conventional generators are replaced by wind and solar power, the system presents weaker inertia, damping and robustness to grid disturbances. This is a large challenge to the security and stability of the system.

Grid in the past Present and future grid

Inertia from conventional Inertia from generators conventional generators Lost inertia Conventional<70% 100% conventional Wind & solar>30% The evolution of power system in China

9 Intolerance to Grid Disturbances

Wind and solar power generation lacks tolerance to grid disturbances such as high frequency and high/low voltage. It may be off the grid after a grid fault and worsen the situation.  In January 2014, the transient overvoltage (128%Un) caused by a Tianshan-Zhongzhou UHVDC fault resulted in the loss of 25 wind turbines by overvoltage protection in Qiaowan which is 400km away from Tianshan station.

Overvoltage caused by Tianshan-Zhongzhou UHVDC Comparison of tolerance levels of wind turbines and fault (PMU recordings) coal-fired generators

128%Un Wind Coal-fired

Overvoltage 1.1 p.u. 1.3 p.u.

Overfrequency 50.2Hz 51.5Hz

Primary frequency None 6% response

0.95 leading 0.95 leading ~0.95 lagging ~0.85 lagging

10 Grid Oscillation Problems

Multi-form sub/super-synchronous oscillations (SSOs) are likely to occur in a weak grid with high wind power penetration.  Since 2015, more than 100 SSOs have happened near Tianshan-Zhongzhou UHVDC converter stations and wind farms in Hami, Xinjiang.

牧场 照阳河 风电场 固定串补 500kV变电站 500kV线路 鹿原 长青 200kV变电站 200kV线路

至汗海 九龙泉 白龙山 博丰 沽源 华锦 乌登山 东山 中宝 察北站 莲花滩 至太平 国华佳鑫 永发 东湾 桦树岭 恒泰 宏达 麒麟山 金阳 秋林 义缘站 坝头 冰峰

韩家庄

Wind power oscillations in Guyuan, Hebei SSOs triggered by wind power in Hami, Xinjiang

11 Contents

1. Developments of Renewable Energy in SGCC

2. Challenges on Large-scale Wind and Solar Power Integration

3. Work carried out and proposed by SGCC

12 Analyzing Grid Characteristics

SGCC performs researches and innovations on basic theory, grid control and simulations, which improves the recognition of grid characteristics.  Construct the world’s largest hybrid analog/digital real-time power system simulation platform and the first 900-Tflops supercomputing platform designated for power system simulation.  Conduct hybrid electro-mechanical/electro-magnetic transient simulations to accommodate the trend of power-electronization of power systems.

Supercomputer center Verification of UHV DC simulation models

13 Enhancing and Utilizing Transmission

 Continuously strengthen the grid to improve long-distance power transmission capability.  Establish market mechanisms to reduce the number of online fossil-fuel power units and give full play to their regulation capabilities.  Closely monitor and effectively utilize the grid regulation capabilities and the available transmission capacity of tie-lines to consume renewable energy to the maximum extent.

Prospective interregional grid in 2030 Real-time grid balance monitoring 14 Improving Regulation Capability

 Support the upgrade of coal-fired generators to allow lower minimum load levels for wider ranges of power output adjustments.  Promote grid-scale and expedite the construction of pumped-hydro plants. Over 24 GW of pumped hydro is expected to be in service by 2020.  Establish power balancing mechanism with distributed energy storage and , and make room for renewable energy through markets of generation rights and ancillary services.

100% Load/Generation Load with 80% Wind + solar demand-side 60% management

40%

20% Load without demand- 0% China/中国 Denmark/丹麦 Germany/德国 side management Time

Minimum load level of coal-fired generators Power balance affected by demand-side management 15 Promoting Grid-friendly Wind & Solar Power

 Revise the compliance to include high/low voltage ride-through (LVRT/HVRT) requirements for wind turbines, and construct testbeds to support the upgrade of wind turbines for LVRT/HVRT capabilities.  Conduct researches on primary frequency response (PFR) capability of wind turbines and wind farms, and carry out experiments in Northwest China grid.  Promote virtual synchronous generator (VSG) control of wind turbines and PV units to enable grid-friendly capabilities including inertia, damping, PFR and reactive voltage regulation.

Frequency Pper

Hz kW 50.6 700 ua 650 ub 50.4 600 u 550 c 50.2 500 P、Q 450 50.0 功率计算 130%Un_500ms 400 49.8 350 300 49.6 250 VSG本体模型 Q 125%Un_1s 200 无功调节 49.4 150 R Qref 0 5 10 15 20 25 30 35 40 45 50 55 kq Eref Fref Pact Pref s 定子电流闭 - - uabc 120%Un_10s 1/Ls E 环及调制 0 Uac Hz MW + Uac_ref 50.10 20.5 sin Eabc AVR 115%Un_10s 50.05 20.0  19.5 sin( 2 / 3) 50.00 有功调节 ω 19.0 sin( 2 / 3) 49.95 P k ωref 110%Un_∞ 18.5 P f 49.90  0 prim 18.0 Pref 49.85  - 17.5 + Pm 1/s 1/Js Umppt 49.80 17.0 + - PI Pmppt 49.75 16.5 D 0 10 20 30 40 50 60 Udc s Revised requirements on LVRT/HVRT PFR test on wind turbines and VSG control of PV inverters of wind turbines wind farms 16 Conclusion and Outlook

By 2030, wind and solar power in SGCC is expected to make up 30% of generating capacity and 16% of electricity generation; the proportion will further rise to 50% and 30% by 2050. SGCC will dedicate to a next generation power system with better connectivity, intelligence, flexibility and safety, and actively promote the development of renewable power to support China’s transformation towards clean and low carbon economy.

Generating capacity 2015~2050 Electricity generation 2015~2050

80% 80% 4% 9% 11% 21% 16% 60% 60% 20% 30% 37% 34% 40% 52% 40% 60% 66% 64% 54% 54% 47% 20% 39% 20% 33% 29% 17% 0% 0% 2015 2020 2030 2035 2050 2015 2020 2030 2035 2050

Fossil fuel/火电 Wind + solar/新能源 Fossil fuel/火电 Wind + solar/新能源

17 Thank you for attention!

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