Energy Engineering - Power Production from Renewable Energy

Ex 5 - DESIGN OF STAND-ALONE PHOTOVOLTAIC POWER PLANTS - Text

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DESIGN OF STAND -ALONE PHOTOVOLTAIC POWER PLANTS Power production from renewable energy – A.Y. 20 20 /21 Prof. Paolo Silva – Ing. D ario Alfani It is required to design a photovoltaic plant coupled with a storage system to power a 4G radio station located in a remote area, conne cted according to the figure below. The sizing aims at identify ing the cheapest plant configuration, consistently with th e need to guarantee the satisfaction of the daily electrical load throughout the whole year. For the energy storage, an electrochemical system is chosen (lead batteries). Figure 1 – Schematic of the PV plant coupled with the lead batteries storage system. Two options are taken into consideration : case a) minimize the PV plant surface, using a storage sized on an annual basis ; case b) minimize the storage size, designing the PV plant such that it can produce the energy required on a monthly basis , even in the least -favourable conditions. The following table shows the climate data and the monthly average temperature for the selected site (Va l Chiavenna , northern Italy ) in each month . The average power load from the antenna (DC , 12 V) is 800 W. Jan Feb Mar Apr Ma y Jun Jul Aug Se p Oct Nov De c Average T [°C] -0.5 1.3 4.2 7.7 11. 2 14. 3 16. 6 16. 1 13. 3 8.6 4.1 0.3 H( ) [Wh/m 2d] 1’890 2’460 3’770 4’430 4’670 5’490 5’840 5’190 4’130 2’800 1’890 1’410 The PV module installed is a NU -RC300, which dimensions are reported in Figure 2 in mm. The NU -RC300 PV module nominal power is 300 W p, while the average balance -of-system efficiency (charge controller , auxiliary components , … ) can be assumed equal to 80%. The electrochemical storage device is characterized by a nominal voltage of 13.2 V, a charging voltage of 13.8 V, and a discharging voltage of 12.8 V. To take into account the self -discharge losses, assume an efficiency equal to 70% in the case of annual -based storage (case a), while in the case of monthly -based sizing (case b) the efficiency can be assumed equal to 90%. Figure 2 - Dimensions in [mm] of the NU -RC300 photovoltaic module. To define the actual installed power/capac ity of the PV modules and batteries, include an overdesign based on security factors. In particular, assume a factor equal to 20% for the PV modules, a value of 20% for the batteries when the design is annual -based, and a value of 30% for the batteries in case of monthly sizing . First, design the PV plant (minimum peak power required , actual peak power installed, and number of modules) and the storage system (actual battery capacity) for the two cases. Then, p erform an economic comparison based on the following costs: - PV plant (modules, installation, charge controller ) 260 €/m2 - Electrochemical storage 1 €/Ah - PV O&M costs 20 €/kWy ear Finally, compare the two system s above to the (more common) use of a diesel -fuelled internal combustion engine (case c ) with a rated power of 3 kW and an electric efficiency equal to 24% (referred to the fuel LHV ). Since the engine runs at fixed operating point and nominal conditions, it produc es a power higher than requested. Therefore, an intermittent operation is foreseen, which in turn requires the coupling to a storage system. Due to reliability reason, the storage is sized in order to be able to satisfy the antenna load for three consecutive days in case of engine failure. Compute the cost of the three systems considering a lifetime of the lead ba tteries equal to 10 years. Consider the following data : - ICE cost 400 €/kW - Diesel cost 1.6 €/l - O&M costs 200 €/year - Diesel LHV 43.3 MJ/kg - Diesel density 0.84 kg/ l