A hybrid energy system supplies energy to specific loads by combining energy from more than one source, either conventional fossil fuel based or renewable. When at least one renewable source of energy is included in such a system, the system is then described as Hybrid Renewable Energy System.
A hybrid energy system does not necessarily include a storage unit. In a mini-grid, the hybrid system is connected to a local AC distribution network. As PV power output is DC and mini-grids operate in AC, at the heart of the hybrid system are the multifunctional inverter, a device which converts DC into AC and rectify AC to DC to charge the batteries. The inverter also controls the generator switching on and off; monitor the storage systems and set up the voltage and frequency of the mini-grid.
Hybrid PV systems are designed to increase the reliability of solar. In hybrid PV systems, the most used conventional source is a diesel generator.
The benefit of integration of photovoltaic energy with conventional fossil fuel based generator is that the weakness of solar are complemented by the strength of the generator and conversely.
Solar resource, as all other renewable source of energy, is variable in nature; it’s can’t all the time and everywhere be reliable. A generator which can locally produce enough power to supply the load makes hybrid systems more reliable. On the other end, running a generator on low loads is highly inefficient: even at zero loads, a generator consumes up to 30% of full load consumption.
Generators high running cost due to their fuel consumption and continuous maintenance requirements can be drastically reduced in a hybrid system. Under normal conditions, excess energy from the PV array is stored within batteries which will supply load in case there is no energy available from the PV array. The generator is only used to compensate the PV array when the load has reached a certain level or the batteries are at their maximum allowed discharge while the PV array is not fully available.
Hybrid PV systems are suitable for:
• Off grid or unreliable grid areas
• Remote industries such as mines, oil & gas and desalination
• Large farms or for irrigation
• Hotels and resorts
• Offices and warehouses
They are the best solution:
• Where a generator could be used 24h/7;
• When the effective cost of fuel at the point of consumption, including transportation and storage, exceed one dollar per liter
• Where there is willingness to save operational expenditure or to reduce on CO2 emissions and going green.