Ingenieur Vol. 75 ingenieur July 2018-FA - Page 46

INGENIEUR demand and future availability of generators. The power system must thus be able to manage both variability and uncertainty. Today, various combinations of hydro and thermal generation are used to manage variability, and these operate as a portfolio to meet demand. Each generator has various characteristics, but the most important one for this article relates to flexibility. Daily and weekly patterns of system demand often involve short-term forecasting. Knowing the time horizon over which significant ramps (MW per minute) take place such as during the morning demand rise has allowed operators to plan and implement effective strategies for flexibility. Traditionally, long-term resource planning with conventional thermal and hydro generation requires little information about the variability of the net demand/load in time scales of minutes to days, whereas characterising the daytime cycle is an important feature of day-ahead operational generation dispatch planning. Power system planners/operators are familiar with the ‘system needs’ in order to ensure that the balance between supply and demand is maintained continuously by refining the generation output and demand delivered by the wholesale electricity market. These ‘system needs’ in the order they are required from real time are: - System Inertia and Rate of Change of Frequency (RoCoF) - Frequency Response - Reserve - Reactive Power/Voltage Support - Blackstart System Inertia comes from the rotational energy stored in the synchronous generators of gas-fired, coal-fired and hydro power plants. Inertia determines how quickly the 50Hz Alternating Current (AC) system frequency will change when there is an imbalance between generation and demand; Inertia stabilises the frequency and reduces the RoCoF. The lower the level of Inertia on the system, the higher the RoCoF will be in the event of a sudden generation or demand loss. As levels of solar photovoltaic/distributed renewable energy generation continue to increase in our future national energy generation mix portfolio, System Inertia is expected to decrease. Thus, the challenging issue of managing System 6 44 VOL VOL 75 55 JULY-SEPTEMBER JUNE 2013 2018 Inertia and RoCoF is of utmost importance in order to secure the future Malaysian power grid against increased probability of partial system collapse. One characteristic that variable renewable generation (VG) resources, such as solar photovoltaic, have in common is that their generation output is governed by atmospheric/ climatic conditions and are consequently difficult to predict over some time scales. Thus, large- scale penetration/integration of VG would lead to increases in the variability and uncertainty in the system’s generation output, driving a need for greater flexibility; this is required in order to ensure the overall demand-generation balance [50Hz system frequency] is maintained at all times. In this same Policy Paper [Ref.2], it was recommended that the Government design and shape its future long-term (at least up to 2050) electricity generation energy mix with clear targets for each primary fuel portfolio based on the following factors: • extent of concern about domestic energy security; • availability and price of ‘legacy’ indigenous natural gas for electricity generation; • extent of penetration/integration of renewable variable generation, particularly • large-scale solar PV plants (LSS); • cost and availability of imported coal for electricity generation; • cost and availability of the nuclear option for electricity generation; and • environmental policy objectives expected over the next decade. Each of these key factors requires supportive policies and regulatory processes to enable appropriate commercial decisions to be taken in a prudent and timely manner. RENEWABLE AND DISTRIBUTED GENERATION Variable Generation (VG) According to the MGI Report [Ref. 1], solar and wind power could represent 15 to 16% of global electricity generation in 2025, up from only 2% in 2013. The incremental economic impact of this growth could be US$165 billion to US$275