Page - 142 - in Clean Water Using Solar and Wind - Outside the Power Grid

142 Clean Water Using Solar and Wind: Outside the Power Grid 11.1 THE ROLE OF THE ENERGY MANAGEMENT SYSTEM The role of the energy management system (EMS) is discussed. Since there is more than one source of electric energy, the energy production must be controlled. Likewise, not all the energy requirements of the loads can always be satisfied. This requires some prioritising between the various loads that are to be controlled by the EMS. The EMS can be implemented in a simple PLC. The solar PV and the wind turbine are the key producers of energy. If they deliver less than minimum power, then the battery storage will be discharged. If this energy is insufficient, then as a last resort a diesel generator can be started. The inverters (see also Chapter 4.5) will convert the DC power from the solar panels into AC power, while the wind turbine inverter will convert the generator power into a frequency that is suitable for the loads. It should be noted that the inverter rating must be large enough to handle the total power of the load that will be running at any one time. It is usually recommended that the inverter size should be 25–30% bigger than the total power of the load. For motor and compressor loads the inverter size should be at least three times the capacity of those appliances to be able to handle current surge during start-ups. The battery charger (Chapter 10) will ensure that the voltage and current to or from the battery storage are within permitted limits. The various loads are defined in the next section. The management system will also direct the power flow both when the solar and wind production is higher than the load and when it is insufficient. A detailed design has to account for the changes in the efficiencies of the components depending on the load and the solar radiation and wind availability. The efficiencies are different if the system is operating in a PV/wind-to-load mode, PV/wind-to-storage mode or storage-to-load mode. 11.2 THE LOADS The loads will be organised according to their importance. If the produced electric power from the solar panels, the wind turbine and the batteries is not sufficient to satisfy all the load requirements then Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user