To develop a small scale solar powered system that will power a DC load, which incorporates power management techniques, DC-DC conversion and a user interface.

 Renewable energy source  Non-polluting  Reliable  Can work anywhere sun is shining  No major mechanical parts  Relatively no maintenance  Noise Free  Last decades

Solar Panel DC-DC Converter Load Controller Back-up Battery

 Silicon cells combined in series or parallel  Converts solar energy into electricity  Cell Technologies › Copper Indium Selenide (CIS) and Amorphous › Monocrystalline and Polycrystalline  Current varies with cell size and light intensity

Rp Rs IphD Id Vo Ip

 Peak Power of 10 Watts  Vmpp = 15.6 V  Impp = 0.64 A Shell ST10  Voc = 22.9 V  Isc = 0.77 A The solar panel was tested with different resistances under a constant light source + - V

Two MPPT algorithms were considered:  Incremental Conductance Method › By comparing incremental conductance with instantaneous conductance.  Perturb & Observe Method › By periodically perturbing the PV array voltage and comparing the output power with that of the previous cycle. The operating point oscillates around the MPP since the system is continuously perturbed.

 Algorithm was implemented using LabVIEW  Solar panel read via a NI-USB 6009  The voltage was measured across a high power resistor to read current  Duty cycle output on NI USB 6009 digital output line Start Set Duty Out Read V, I P_new = V*I P_new > P_old Duty = Duty(-) Duty = Duty(+) P_old  P_new

 Used to implement P&O algorithm › ‘G’ programming  Also used to generate a user interface through the front panel › Waveforms showing voltage and current of solar panel › Numeric indicator showing power › Duty cycle displayed › ‘Stop’ button to end program

 Data acquisition tool  Read data in, and generate digital signals out  Does not have a hardware counter, cannot generate digital outputs at high frequencies  Solution M series

 DC-DC converter needed for two reasons › To implement the MPPT algorithm › To bring the DC voltage to an acceptable level to power the load  Buck converter was chosen and designed

 The most important components are the inductor and capacitor  Use Vo = DVi to deduce ideal duty cycle range (0.3 – 0.5)  Using both of these values for D, and the ΔI equation two values for the inductor were calculated (2.8 mH & 1.6 mH)  Using the Δ V equation the capacitor value was determined (21.3 μF)

Vin 2.2 mH 22 uF LOADLOAD D PWM

 Solar panels only generate power when there sun available  Storage element is recommended  Various rechargeable battery cell chemistries › Lead Acid › Nickel-Cadmium › Nickel-Metal-Hydride › Lithium Ion

 Up to 99% efficiencies  Highest weight to energy ratio  Average voltage of one Li-ion cell is Volts  A Li-ion battery pack with a capacity of 4 AH would be enough to store all energy generated on the longest day of the year at maximum power  Safety issues

 Overvoltage  Over discharging can cause short circuit  Battery packs usually include protective circuit › Limits input voltage › Limits discharge voltage  Li-ion charger IC is recommended to implement charging profile

 Initially it was thought a mobile phone charging algorithm would have to implemented  Research showed that the charging algorithm is employed on the phone  To prove this, a commercial Nokia car cigarette lighter charger was disassembled  A ‘ma34063a’ DC-DC converter was found  To charge a mobile an appropriate constant voltage is needed, along with some circuitry protection

 Solar cell equivalent circuit, characteristics and various cell technologies  Maximum power point tracking techniques  LabVIEW – ‘G’ programming and user interface  DC-DC converter design including choosing appropriate components and simulation in Pspice  Rechargeable Batteries