Recent TSO report on changes because of larger amounts of renewable enery IEA Task 25, January 14, 2016 Edf – Clamart – Paris – France Lennart Söder Professor in Electric Power Systems, KTH

Background Sweden has currently around 15 TWh/year from wind power, around 11% of production the nuclear production was 62.2 TWh Prices are low and during autumn 2015 there cam a decision to close the 4 oldest, out of 10, nuclear reactors within some years (2014 these 4: 12,9 TWh) 2014: Net export of 15,6 TWh. Probably no new nuclear in Sweden  wind+bio+solar is seriously discussed as ”the solution”

New TSO reports, required by government ”Adaption of the power system with a large amount of renewable electricity”

Challenge 1: Frequency deviations - a Minutes per week when frequency is outside 50.0 ± 0.1 Hz Goal is that this level should NOT be > 6000 minuts/year = 115 as weekly mean value 2013: minutes, 2014: minutes. Wind power (Sweden) Frequency deviations HVDC capacity (Nordic syst)

Challenge 1: Frequency deviations - b Increased amount of incidences when frequency is outside 50 ± 0.1 Hz. Main challenge: Market and changes at hour shift. Earlier ”margin surplus” has decreased Inreased wind power may increase this challenge. All deviations At hour shift ± 10 min Share at hour shift More efficient handling in control room

Solution to Challenge 1: Frequency deviations Updated grid codes: Connection codes Operation codes Market codes ”Standards”, e.g. min. 10 MW Change from hour to, e.g minutes Balance Service Provider: BSP-rules Harmonized imbalance prices General answer: More flexibility Physical solutions: Household, industry and prosumer flexibility Rules for hydro power More bio-power Wind power control Energy storage Pumped storage Batteries Other issues: TSO role Information Description of current work General conclusion No urgent needs now Question is if flexibility is incentivized today?

Challenge 2: TSO Voltage control Sweden has long transmission lines. The transmission limits are set by voltage stability. Current nuclear power stations (10 GW, peak load 27 GW) are essential for reactive power supply to keep voltage. More wind power in north will require more transmission capacity.

Solution to Challenge 2: TSO Voltage control Synchronous condensers Operate hydro power stations as synchronous condensers (North) In South Sweden the ”probable solution” is to use grid components. ”This is not a technical problem but increases the costs for grid operation” SVC and STATCOM: are seen as important solutions New HVDC-VSC converts. (700 MW  ± 300 MVAr ≈ Nuc. Stat. Not considered (not so motivated) Use generators in closed nuclear stations Use wind power. ”Renewable production is often connected at lower voltage levels, which implies that their voltage control capability for the transmission grid is nearly negligible”

Challenge 3: System inertia Large amount of wind power  lower amounts of synchronous generators Disconnection of heat pumps at 49,5 Hz for more than 0,15 seconds New EU grid codes: Lowest allowed frequency 49,0 Hz. Frequency after outage of Nuclear station O3, 1400 MW Lowest frequency 49,36 Hz (all time low)

Solution to Challenge 3: System inertia Physical solutions Increased amount of inertia by running of existing synchronous machines without generation. Today: 3 hydro power stations (out of 150 large ones) can operate in this way. New synchronous condensers Reduction of non-synchronous production. Reduction of largest possible outage Faster response on frequency drop, e.g. synthetic inertia from wind power or HVDC-VSC Practical solutions Requirements for Generators: E.g. ”acivate within 2 seconds” Demand Connection Code: React within 2 seconds.

Challenge 4: Peak capacity In Sweden we have a ”strategic reserve” of 2 GW (old oil-fired stations + DSM) TSO:s responsibility: Tender before each winter fot this strategic reserve Current challenge: Very low prices + old plants  close old plants, but the only new plants are wind + solar. For the future: wind power is cheaper than nuclear Peaks are rare! Wind power ”capacity credit” = 11% of installed capacity (>11% available during 90% of the winter) 23 January 2015: Nordic winter peak load, wind power 5% of installed capacity.

Solution to Challenge 4: Peak capacity Practical solutions ”The capacity of a unit should have a value, not only the energy” ”There are strong incentives to, on a national level, take initiative to evaluate which risk levels and costs the Swedish society is prepared to accept” Capacity payments Physical solutions Not weather dependent power production Demand side management Other issues in reports Current areas in Denmark and Germany where needed changes have been identified.