Chapter 5 pv systems feb 2011

Green Energy CourseRenewable Energy Systems Biên sọan: Nguyễn Hữu Phúc Khoa Điện- Điện Tử- Đại Học Bách Khoa TPHCM PV Systems How Fast is Solar PV Growing? The growth in total solar energy is slower (0.06 quad in 2001) versus 0.081 quad in 2007) partially due to solar thermal retirements PV Current-Voltage Variation with Insolation and Temperature Pat Chapman Solar Example • When Prof Chapman built a new house in Urbana in • • • 2007 he added some solar PV His system has 14 modules with 205 W each, for a total of 2870W He has a 3300 W inverter Total cost was about $27,000, but tax credits reduced it to $16,900 He should be getting about 3700 kWh per year Source: www.patrickchapman.com/solar.htm ECE 333 Green Electric Energy Lecture 24 PV Systems Professor Tom Overbye Department of Electrical and Computer Engineering PV Systems – Three configurations Grid-connected systems PV Systems – Three configurations Stand-alone systems which charge batteries PV Systems – Three configurations Stand-alone systems with directly-connected loads Load I-V Curves • PV panels have I-V curves and so loads • Use a combination of the two curves to tell where the • system is actually operating Operating point – the intersection point at which the PV and the load I-V curves are satisfied Resistive Load I-V Curve 1 I   V (9.1) R Straight line with slope 1/R As R increases, operating point moves to the right V  IR • • • Can use a potentiometer • to plot the PV module’s IV curve Resistance value that results in maximum power Vm Rm  (9.2) Im Figure 9.5 String Inverter • two-level VSI, interfacing two PV strings SMA Sunny Boy 5000TL • three PV strings, each of 2200 W at 125-750 V, with own MPPT PowerLynx Powerlink PV 4.5 kW • three PV strings, each 200-500 V, 1500 W Evaluation and Discussion • • • • component ratings relative cost lifetime efficiency Results • Dual-stage CSI = large electrolytic decoupling capacitor • VSI = small decoupling electrolytic capacitor Results - Efficiency • Low efficiency=87% • C=68 mF 160V • High efficiency=93% • C=2,2 mF 45V Discussion - String Inverters • The dual-grounded multilevel inverters p.82 – good • • solution but quite large capacitors 2x640mF 810V -> half-period loading bipolar PWM switching toward the grid p.83 & 84 (no grounding possible, large ground currents) – 2x1200 mF 375 V current-fed fullbridge dc–dc converters with embedded HF transformers, for each PV string – p.85 – 3x 310 mF 400V Resume – PV Inverters • • • • • Large centralized single-stage inverters should be avoided Preferable location for the capacitor is in the dc link where the voltage is high and a large fluctuation can be allowed without compromising the utilization factor HFTs should be applied for voltage amplification in the AC module and AC cell concepts Line-frequency CSI are suitable for low power, e.g., for ac module applications High-frequency VSI is also suitable for both low- and highpower systems, like the ac module, the string, and the multistring inverters Converter topologies (general) • PV inverters with dc/dc converter (with or without • isolation) PV inverters without dc/dc converter (with or without isolation) • Isolation is acquired using a transformer that can be placed on either the grid or low frequency (LF) side or on the HF side HF dc/dc converter • full-bridge • single-inductor push–pull • double-inductor push–pull Another classification • • • • number of cascade power processing stages -single-stage dual-stage -multi-stage • There is no any standard PV inverter topology Future • very efficient PV cells • roofing PV systems • PV modules in high building structures Future trends • PV systems without transformers - minimize the cost of • • • the total system cost reduction per inverter watt -make PV-generated power more attractive AC modules implement MPPT for PV modules improving the total system efficiency „ plug and play systems” Research • MPPT control • THD improvements • reduction of current or voltage ripple • standards are becoming more and more strict The Georgia Tech PV Generator Aquatic Center Systems + Components ... 24 PV Systems Professor Tom Overbye Department of Electrical and Computer Engineering PV Systems – Three configurations Grid-connected systems PV Systems – Three configurations Stand-alone systems. .. 0.8    47  20C  Tcell  20    1 = 53 .8C 0.8   (8.24) • With DC losses at 0 .5% / ˚C above 25? ?C, Pdc ,( PTC )  kW 1  0.0 05( 53.8  25)  = 0. 856 kW • Including inefficiencies, estimated... releases that question the underlying science PV Systems – Four configurations Grid-connected systems PV Systems – Four Configurations Stand-alone systems with directly-connected loads DC Motor