Presentation Transcript

1. Photovoltaic (PV) Basics

   ACM Chapter Poughkeepsie, NY Oct. 21, 2013
2. PV BasicsHow does a Photovoltaic Cell work? When light strikes the PV cell, light is absorbed by a semiconductor material such as silicon. The energy of the absorbed light is transferred to the semiconductor, knocks electrons loose, thereby allowing them to flow freely.
3. PV BasicsSolar Modules Modules are constructed of PV cells surrounded by several layers of protective materials
4. PV BasicsSolar Modules A solar module is a group of cells connected electrically and packaged into a frame which can then be grouped into larger solar arrays. A photovoltaic array (or solar array) is an electrically linked collection of solar modules. The power that one module can produce is seldom enough to meet requirements of a home or a business, so the modules are linked together to form an array
5. PV BasicsAnatomy of a Solar Standalone System A standalone system does not have a connection to the electrical "mains" (aka "grid"). If the load is to be supplied with only solar insolation , the power is stored in a battery. Lead acid batteries are most commonly used for their low cost and tolerance for abuse. A charge controller is incorporated in the system to avoid battery damage by excessive charging or discharging. In some systems where AC is required to convert the DC from the modules or batteries into AC, an inverter is used.
6. PV BasicsAnatomy of a Grid Tied System A Grid Tied PV System is connected to the local utility and supplies power to the residence or the grid depending on the usage or the occupants. Usually these systems do not have any storage capacity and do not function during periods when the utility is down. By including a battery bank the owners can power critical loads during power outages.
7. PV BasicsAnatomy of a Grid Tied System Hybrid systems may be used when the solar harvest can not completely supply the load demand. Wind, hydro, fossil fuel generators, TEG or fuel cells may contribute some portion of the power required.
8. PV BasicsSolar Insolation A measure of solar radiation energy received on a given surface area: kWh/m2/day Power is measured in watts: Power(W)=Voltage(V) X Current (I) W = P x I
9. PV BasicsModule/Array Tilt Angle Module/Array Tilt Angle: At high noon on a cloudless day at the equator, the power of the sun is about 1 kW/m², on the Earth's surface, to a plane that is perpendicular to the sun's rays. PV arrays if so equipped can track the sun through each day to greatly enhance energy collection. However, tracking devices add cost, and require maintenance, so it is more common for PV arrays to have fixed mounts that tilt the array and face due South in the Northern Hemisphere (in the Southern Hemisphere, they should point due North). The tilt angle, can be varied for season, but if fixed, should be set to give optimal output during the peak electrical demand portion of a year for a stand alone system. The module tilt angle is measured from horizontal, thus a panel that is lying parallel to the earth’s surface is said to be at 0o tilt, a panel that is perpendicular to the earth surface is said to be at 90o tilt.
10. PV BasicsDetermine Tilt Angle For optimum performance, determine the appropriate tilt angle for the PV array by first determining the project site latitude: Locate your site on a map or Google Earth Find the closest latitude line that intersects your region Find the latitude and the appropriate tilt angle below Recommended Minimum Angle: 15° Recommended Maximum Angle: 60°
11. PV BasicsCharge Controllers Selection is base on: Current rating Sizes range from less than 10 amps to 60 amps. Charging method Pulse Width Modulation (PWM) Maximum Power Point Tracking (MPPT)
12. PV BasicsPulse-Width Modulation (PWM) Pulse-width modulation (PWM), is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches. The average value of voltage (and current) fed to the battery is controlled by turning the switch between supply and battery on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the battery. Wider pulses allow greater input current to flow into the battery, narrow pulses restrict current flow Allows maximum amount of energy to battery in the shortest time Increases battery capacity and operating life Cost effective Achieves constant voltage battery charging
13. PV BasicsMaximum Power Point Tracking (MPPT) Maximum power point tracking (MPPT) is a technique that solar battery chargers use to get the maximum possible power from one or more solar panels. Solar cells have a complex relationship between solar irradiation, temperature and total resistance that produces a non-linear output efficiency known as the I-V curve. It is the purpose of the MPPT system to sample the output of the cells and apply the proper resistance (load) to obtain maximum power transfer to the batteries.
14. PV BasicsBatteries Batteries used in PV systems are Lead Acid based batteries similar to automotive batteries but with some very important differences. Solar batteries are designed to provide a small current (up to 60-100 amps) over an extended time and to take a small charge current over an extended time. Automotive batteries are designed to provide a large current (>500 amps) for a short period of time IE to start a car. Solar Batteries are rated in amp hours (aHrs) capacities, automotive batteries are rated in Cold Cranking Amps (CCA). Automotive batteries will work for a short period of time in a solar system however they will fail due to the above differences in internal design.
15. PV BasicsDC to DC Converters A DC-to-DC converter is an electronic circuit which converts a source of direct current (DC) from one voltage level to another. They can generally be divided into two separate types: Step-down (Buck) - The output voltage is lower than the input voltage, and of the same polarity Step-up (Boost)- The output voltage is higher than the input voltage
16. PV BasicsDC to AC Inverters A power inverter, or inverter, is an electrical power converter that changes direct current (DC) to alternating current (AC).[1] The input voltage, output voltage, and frequency are dependent on design.
17. PV BasicsApplications RTU/SCADA Injection Pumps Flow Metering Valve Actuators Cathodic Protection CCTV Lighting Surveillance Access Controls Surveillance Two-way Radio Telecom Networks Water Pumping Lighting Environmental Monitoring Traffic Monitoring Navigational Aids Fence Charging Cellular Repeaters Microwave Backbones Military Communications FAA Lighting Message Boards Traffic Control Call Boxes Signal Equipment GPS
18. PV BasicsApplications
19. Question and Answer Period Thank You Richard A. Martino