Tema 4.3 (2013)

Apunte Catalán
Universidad Universidad Politécnica de Cataluña (UPC)
Grado Ingeniería de Sistemas de Telecomunicación - 2º curso
Asignatura Funciones y Sistemas Electronicos
Año del apunte 2013
Páginas 8
Fecha de subida 12/11/2014
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4.3. Sizing a stand‐alone PV system FISE T4 (3) - 3 4.3. Sizing a stand‐alone PV system   4.3.1. Introduction 4.3.2. Block diagram of a stand‐alone PV system 4.3.3. Concept of Equivalent Peak Solar Hours 4.3.4. Energy balance 4.3.5. Loss of load probability 4.3.6. Sizing methods of a stand‐alone PV system         4.3.7. Simplified sizing procedure 4.3.8. Example FISE 4.3.1. Introduction Photovoltaic stand‐alone system: Typical applications of autonomous (stand‐alone) PV systems: • Water pumping systems.
• Residential applications isolated from the electricity distribution network.
• Telecommunications equipment.
• Public lighting and road signage.
• Remote monitoring equipment.
• Space applications.
• …..
T4 (3) - 4 FISE T4 (3) - 5 4.3.2. Block diagram of a stand‐alone PV system Stand‐Alone PV system Block Diagram: Charge regulator and safety devices DC loads = = ~ PV generator Battery AC  loads ~ Inverter IG … 1 +     FISE Vbat Iload - Ns Number of PV modules: Ns x Np Ibat … 1                  Np 4.3.2. Block diagram of a stand‐alone PV system T4 (3) - 6 Sizing procedure: Inputs: ‐ Location of the system: to determine the profiles of climatic variables  irradiance and temperature at that location.
‐ Energy demand of the loads: to determine the supply voltage,   current and  power consumption.
Results: ‐ Size of the PV generator: Total installed power, module area and number of  modules in series and parallel (Ns, Np).
‐ Accumulator Size: Number of batteries and assembling structure, nominal  voltage and total capacity of the accumulator.
T4 (3) - 7 4.3.3. Concept of Equivalent Peak Solar Hours FISE Equivalent Peak Solar hour (PSH): Defined as the equivalent hours per day in which an average irradiance of 1 kW/m2 (PV  module STC) produces an energy that is equal to the received one during total daylight  hours.
2 G(t)  (or I) is the irradiance   Gt  dt  1000 (W / m )  PSH 2 in W/m 1 day Irradiance Irradiance G(t) G(t) 1000 W/m2 0 6 12 18 24 0 PSH 6 12 18 24 Monthly Average PSH:  Gt  dt  31days   1000 (W / m 2 )  PSH 1 month Yearly Average PSH:  Gt  dt  365days   1000 (W / m 2 )  PSH 1 year T4 (3) - 8 4.3.3. Concept of Equivalent Peak Solar Hours FISE Example: Month Days ni Daily radiation  Hi (Wh/m2) January 31 2065 Yearly Average PSH: 12  Gt  dt   ni  Hi  365  1000  PSH February 28 3429   March 31 4290 1 year April 30 5100 i 1 PSH  4.27 hours May 31 5839 June 30 6400 July 31 6484 August 31 5613 September 30 4733 October 31 3323 November 30 2100 december December 31 1871                      58 kWh/m2 Worst Month Average PSH:  Gt  dt  31  1871 Wh/m 2  Gt  dt  31 days/month  1000 (W/m )  PSH 2 december PSH  1.87 hours 4.3.4. Energy balance FISE Energy Balance T4 (3) - 9 Available power at the PV generator t E (t )   PG (t )  PL (t ) dt Excess or deficit of energy: Integral of the instantaneous power mismatch 0 Power demanded by the loads Daily energy balance: Considering maximum power point tracking (PmG)   PG (t ) dt  NsG VmM  NpG  ImM  PSH day NsG  VmM  N pG  ImM  PSH  L L   PL (t ) dt  24  Vcc  ILeq day Voltage and current of the loads Seasonal energy balance: NsG  VmM  N pG  ImM  PSH  L Energy units in Wh “M” means PV module “G” means PV generator “m” means maximum power point Seasonal Average PSH Average daily load demand in the season FISE 4.3.5. Loss of Load Probability Loss of load probability (LLP): LLP   Energy  deficit t  Energy  demand t Typical Values: ₋ High reliability:   LLP=10‐4 ₋ Residential applications:  LLP= 10‐1 ‐ 10‐2 T4 (3) - 10 T4 (3) - 11 4.3.6. Sizing methods of a stand‐alone PV system FISE Sizing methods: •Sizing methods must ensure the power supply for the loads while minimizing the  cost of the energy generated.
•Good PV system sizing is based on: – Accurate information on climatic variables associated with the installation  location: irradiance and temperature.
– Detailed information of the consumption of system loads. The distribution  of consumption throughout the day, their frequency, seasonality and the  correlation between generation and consumption.
•Two of the most used methods are :  – method based on iso‐reliability curves.
– method based on the energy balance of the system.
•The use of simulation software tools can help photovoltaic systems design tasks.  For example: – PVSYST – PVSOL T4 (3) - 12 4.3.7. Simplified sizing procedure FISE PV generator Size Battery directly connected to PV generator and load: L : Daily load demand (Wh) L  24  Vbat  IL IL : Equivalent load current (A) Energy balance: Number of PV modules in  series per string:  N sG  VmM  N pG  ImM  PSH  24  Vbat  IL IG … 1 NsG  +     … 1                  Np Number of parallel strings of the PV generator: Vbat - Ns Ibat Vbat VmM IL Security Factor (SF): NpG  SF  24  IL ImM  PSH NsG  VmM  NpG  ImM  PSH L 4.3.7. Simplified sizing procedure FISE T4 (3) - 13 Battery sizing Days of Storage (Cs): CS  Cn : Battery Nominal Capacity (Wh) C n  DODmax L  100 DODmax : Depth of Discharge (%) L : Daily load demand (Wh) C n (Ah)  If Cs =1 Recommended  (bigger batteries  do not ensure  better results) 100  L DODmax  Vbat Cn (Ah) <  25  IscG T4 (3) - 14 4.3.8. Example FISE Example: Power supply system of a radiocommunication equipment: (1) System requeriments : ‐ ‐ ‐ Battery Voltage : Vbat=48 V; DOD max = 80% Load consumption : IL=5 A in emission ( 3h/day); IL=0.3 A in reception (24h/day) Days of Autonomy : Cs = 4 (2) PV modules : ‐ Pnom = 88 W; Impp = 4 .5 A ; (3) Costs : ‐ ‐ PV module : 150 € Battery : 5 €/Ah ImM Vmpp = 19.5 V ; Area = 0.6 m2 VmM T4 (3) - 15 4.3.8. Example FISE Radiation Data: Month Days PSH January 31 4 February 28 4.3 March 31 6 April 30 6 May 31 6.4 June 30 6.6 July 31 7 August 31 6 September 30 4 October 31 4.2 November 30 3.1 December 31 3 Yearly Average Value PSH: PSH = 5.06 hours Daily power demand: L = [5 (A)3 (h) + 0,3 (A)24 (h)]48 (V)  =  1065.6 Wh/day ILeq = [5 (A)3 (h) + 0,3 (A)24 (h)] / 24(h)=  0.925 A T4 (3) - 16 4.3.8. Example FISE PV generator size (yearly energy balance example): PmG  Ns  L 1065.6   210.6 W PSH 5.06 48 Vbat   2.46 Vmpp 19.5 PmG  Ns  Np  Pnom  264 W Ns = 3 Np  24  ILeq Impp PSH  24 0.925  0.97 4.5  5.06 Np = 1 SF  PmG  PSH  1.25 L 4.3.8. Example FISE T4 (3) - 17 Battery sizing: Days of Autonomy , Cs = 4  CS  C n  DODmax 100  L Cn  100  C s  L 4 (days)  1065.6 (Wh / day )   5328 Wh 0.8 DODmax C n (Ah)  C n  (Wh)  111 Ah Vbat (V ) PV generator area and cost: Total Cost :  1005 € PV generator Area: 1.8 m2 ...