Power System Planning Concept Power system planning is needed especially in developing countries to develop and build modern electric power systems. The planning problem can be divided into four main stages, as shown in the figure: Power system planning can be considered for the following periods: Short range 3 years Medium range 10 years Long range 20 - 30 years Load forecasting Power system planning starts by forecasting the anticipated future loads. It is basically concerned with - Load (demand) forecasting - Energy forecasting Load (demand) forecasting is used to define the capacity needed for the system and the transmission and distribution additions and it is defined as the projection of future load requirements using a systematic process (methodology) of defining future loads in a sufficient quantitative analysis to permit important system expansion decision to be made. Load forecasting is also needed for budgeting purposes and energy forecast is needed to determine future type of generating units and fuel requirements. Example: If the load forecast stated that 100 MW of capacity is needed and energy forecast stated that annual energy is 200,000 MWh, therefore unit is required to operate for 2000 hours per year. The type of unit is considered as a peak load and not as a base load. Load Characteristics Load: A general term referring to the size of electrical power, i.e. W, kW, MW, GW. Energy: The amount of energy consumed by the electrical equipment in Wh, the customer (kWh), the city (MWh), the country (GWh). Load Variation Curve: the plot of the instantaneous power over a given period of time. As an example, consider the following daily load variation curve for Riyadh city: Classification of loads : Loads can be classified to the nature of consumption as: Residential, Commercial, Industrial, Governmental, municipal, agricultural etc. The typical daily load variation curve for each class can be plotted as : Residential: depends on the domestic activity of the people, and is shown as: Commercial: Depends on the commercial activities during the opening hours. It can be shown as: Industrial: depends on the time of production and considered to be the most stable load variation curve and can be represented as following curve: Now, the total shape of load variation curves for all customers categories (classes) can be represented by the curve given previously as the daily load variation curve for Riyadh. For planning purposes, system planner can produce the annual peak load for the next 15 years, based on past data and future prediction (forecasting). This can be shown as: Energy demanded by the system: The area under the load curve measures the total energy demanded by the system, i.e. consumed by the load during the interval of time considered and can be shown as: For the above curve, the green area means that the type of generation units required are Base units (steam, nuclear, hydro). The yellow area means that the type of generation units required are Mid-range units (combined cycle). The red area means that the type of generation units required are Peak units (Gas turbine).