Page - 143 - in Clean Water Using Solar and Wind - Outside the Power Grid

Energy management systems 143 some priority of the loads should be defined. The load with the highest priority (for example lighting) will be the last load to be shut down if energy production fails. The priority between the various loads will of course depend on the individual user. Naturally the water pump control is connected to the operation of the disinfection, desalination and the biological reactors. The loads can be classified something like (see Figure 11.1): • Lighting, • Small appliances like radios, TV sets, • Cooking facilities, • Water pumps • Disinfection lamps, • Desalination unit, • Biological water reclamation. The energy management system will deliver available power to the loads according to the defined priority. Lighting, small appliances and cooking are probably the loads with highest priority. Let us consider some operational modes and how to prioritise the loads: (1) PV/wind power is greater than the required load. {{ Any excess power should be used wisely. If the batteries are not fully charged this ought to be the highest-priority load. {{ If the batteries are fully charged, then the excess power can be used to pump or treat water. Water serves as an energy storage, as described in 10.6. (2) PV/wind power is not sufficient for the load requirements. {{ If there is sufficient storage capacity, then we are back to case 1. {{ If added storage power does not satisfy the load requirement, then we must define priorities for the loads. Only the most important loads should be connected. {{ If the batteries have been discharged, then the storage turns into a load, most likely the load with highest priority. Other loads must be disconnected according to their priorities. (3) PV/wind power is not sufficient for the load requirements and batteries are discharged. This ought to be an unusual condition. Here the traditional diesel generator can be used as a backup, as pointed out in 10.7. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user