EU-IPA12/CS02 Development of the Renewable Energy Sector Consulting Services for Development of the Renewable Energy Sector Technical risks and solutions from periodic, large surpluses or deficits of available renewable generation 12 May 2017

Energy Transition shift from conventional generation to more renewable generation the amount of renewable energy sources (RES) has increased to a significant level in many countries of the world. in some grid areas the installed capacity of RES exceeds the customers load. (large surpluses and deficits of RES infeed in) the power system and also high ramps between the different system conditions several challenges for the responsible system operator in the transmission grid and also in the distribution grid. Definition of solution (technical, market based, or regulatory) Identification of the risks

Potential Risk for a fast & massive RES growthing 10 potential risks Potential Risk for a fast & massive RES growthing Flexibility is needed as the residual load can change very quickly. Reserve capacity for short term balancing is needed as the forecast of the residual load can be wrong. System adequacy has to be maintained as RES generation can be low for a long period of time. Voltage profile has to be kept within the operational limits even under the influence of changing power flows. System security has to be kept in maintenance situations as system condition may change very quickly. Congestion of the transmission system occurs due to large power flows. Observability and controllability of a large number of RES units is needed. Small RES units have to behave system friendly due to their large numbers. A lack of short-circuit power for system stability and protection purposes may occur. Due to a lack of system inertia larger frequency deviations can occur.

Potential Risk for a fast & massive RES growthing Flexibility is need : variability of residual load under strong development of renewable energy sources (RES), and with the challenges introduced for dispatchable generation.. Photovoltaic power generation is very seasonal. Average monthly load factors range between 5 % in December and almost 20 % in summer. On average, photovoltaic output is three times higher in summer than in winter. Photovoltaic output is also characterised by significant daily periodicity; its generation profile resembles a bell curve with a peak in the middle of the day

Potential Risk for a fast & massive RES growthing Reserve capacity for short term balancing is needed : In a stable and secure power system the power generated must be balanced correctly to meet the demand. The base load is supplied by power plants that take a long period of time to achieve an optimum operating mode (nuclear, coal and gas). The peak load is covered by flexible plants that can vary their output within minutes or even seconds, such as gas turbines and pumped-storage hydropower. As the share of renewable sources increase in the energy mix, a power system will need more power plants that are capable of providing rapid response to system fluctuations. 3 potential risk System adequacy has to be maintained: Weather conditions, such as wind speeds and sunlight, have a direct impact on the output of wind and photovoltaic power plants, so their generation is variable and difficult to predict with accuracy. Because of the fact that wind and solar power are variable and not dispatchable, 1 GW of wind or solar capacity does not have the same value as 1 GW of dispatchable capacity for security of supply

Potential Risk for a fast & massive RES growthing Voltage profile has to be kept: In a power system, the net apparent load at one bus bar can be defined by the difference between the load and the non-controllable generation connected at that bus bar (like generation from renewable energy sources). The net apparent load must then be supplied by the external power system. In the transmission grid to keep voltages in acceptable bounds reactive power is normally delivered by the synchronous generators of the conventional power plants. Additionally, reactive power compensation devices were installed. Transmission Apparent load Distribution Grid

Potential Risk for a fast & massive RES growthing System secur ity has to be kept in maintenance situations Maintenance represents all the operations needed to be made in order to ensure a normal functioning and development of the system. The maintenance for the classic power plants becomes very difficult due to the rapid variation of RES generation that in some times is difficult to handle. Both TSO and DSO. 6 Potential risk Congestion of the transmission system The energy from renewable sources reduces the energy from the rest of the generation fleet, which changes the commitment and dispatch of the rest of the fleet and significantly changes the utilization of the transmission system.

Potential Risk for a fast & massive RES growthing Observability and controllability of a large number of RES Units Countries around the world had a significant growth of new distributed production units, mainly from renewable energy sources, in the last two decades. Another important issue with RES is the fact that its production takes priority towards conventional production. This new reality completely changes the system paradigm, interactions, established procedures and specific requirements in order to comply with all players’ issues. 8 Potential risk Small RES units have to behave system friendly Increased renewable generation penetration on distribution lines can lead to a number of issues due to their variable nature, particularly issues with voltage levels causing issues with droop, flicker, secondary network protection, distribution switching automation schemes, distribution feeder re-closers, capacitor banks and harmonics.

Potential Risk for a fast & massive RES growthing Lack of shor t-circuit power It is a commonly used indicator for static in sense of necessary voltage level and synchronizing torque during faults. A lack of short circuit power can lead to system stability issues, e.g. voltage collapse. 10 Potential risk Lack of system inertia The loss of rotational inertia and its increasing time-variance lead to new frequency instability phenomena in power systems. Frequency dynamics are faster in power systems with low rotational inertia, making frequency control and power system operation more challenging.

Potenzial risk and solution 10 Potential risks 27 Potential solutions