Troubleshooting a PV System/Literature Review
This is the literature Review for the Engr305 Troubleshooting a PV System project.
Photovoltaic technology is a relatively new field of renewable energy that is rapidly expanding. Solar cells can have a wide variety of applications, particularly for off-grid and portable power needs. Increasing demand for clean energy sources has spurred growth solar technology. While the earliest photovoltaic cells had only 6% efficiency, today’s models are much more efficient.
Solar photovoltaic energy conversion is a one step conversion process which generates electrical energy from light energy. Light is made up of packets of energy, called photons, whose energy depends only upon the frequency, or color, of the light. The energy of visible protons is sufficient to excite electrons, bound into solids, up to higher energy levels where they are free to move. In a Photovoltaic Device there is built in symmetry which pulls the excited electrons can relax and feeds them into an external circuit. The extra energy of the excited electrons generates a potential difference or, electromagnetic force (e.m.f). This force drives the electrons through a load in the external circuit to do electrical work. This electricity is supplied in the form of direct current, or can be transformed into alternating current, or stored in a battery.
Important Components of a Photovoltaic System
Important Components of a Photovoltaic System
- Photovoltaic Cell- Thin squares, discs, or films of semiconductor material that generate voltage and current when exposed to sunlight.
- Module- A configuration of PV cells laminated between a clear glazing and an *Panel- One or more modules.
- Array- One or more panels wired together at a specific voltage.
- Charge Controller- Equipment that regulates battery voltage.
- Battery Storage- A medium that stores direct current electrical energy.
- Inverter- An electrical device that changes direct current to alternating current.
- DC Loads- Appliances, motors, and equipment powered by direct current.
- AC Loads- Appliances, motors, and equipment powered by alternating current.
Sizing the Array
The first steps involve determining the load of what the PV system will be powering. This system will be providing power in AC. The power the system will need is expressed in ampere-hours (AH). Suppose you notice that the battery system runs for about three days without any charging before the voltage becomes unacceptably low. This means you have probably discharged the batteries to 75% of the rated capacity Find out what the ampere-hour capacity of the battery is and take 75% of that capacity as the ampere-hours used in the time period.
Most wiring associated with PV installation is covered under the National Electric Code (NEC). This code covers just about any PV installation, on-grid or off-grid. It specifically deals with any PV system that produces power and is accessible to the untrained person. The key component is labeling.
|Alternating Current (AC) Wiring||Alternating Current (AC) Wiring||Direct Current (DC) Wiring||Direct Current (DC) Wiring|
|White||Grounded Conductor||White||Negative or Grounded Conductor|
|Green or Bare||Equipment Ground||Green or Bare||Equipment Ground|
|Red or any other color||Undergrounded Hot|
Maintenance and Troubleshooting
The volt-ohm-milliamp meter (VOM) meter is essential for troubleshooting wiring problems. The most useful tasks performed with a VOM include checking for continuity, measuring AC and DC voltage, Measuring AC and DC current, and checking the polarity of DC voltage.3 Checking for continuity indicates whether a circuit is open or closed, which is useful when checking for broken wires, short circuits, fuse, or switch operation. Checking for continuity involves circuit resistance. Short Circuits have very low resistance. Closed circuits have some resistance depending upon circuit wire and loads Open circuits will exhibit infinite resistance.
Sunlight and Site Factors
Solar Radiation received at the earth’s surface is subject to variations caused by atmospheric attenuation. The primary causes of this phenomenon are the following. Air molecules, water vapor, and dust in the atmosphere scattering light; Ozone, water vapor, and carbon dioxide in the atmosphere absorbing light. Peak sun hours are the number of hours per day when the solar insolation equals 1,000 watts/square meter. Daily performance will be optimized if fixed mounted collectors are faced true south or 0 degrees azimuth.
The National Forest Service conducted an experiment with the purpose of examining the effects of the various battery sizes on the ability of the system to charge the battery, energy available to the load, and battery lifetime. The experiment determined that increasing array size to account for unknowns in insoulation without an associated increase in battery size is an error which will actually decrease the amount of energy stored in the battery..
- Mazer, Jeffery A. (1997) Solar Cells: An Introduction to Crystalline Photovoltaic Technology. Kluwer Academic Publishers, Boston/Dorderecht/London.
- Nelson, Jenny. (2003) The Physics of Solar Cells. Imperial College Press, London.
- Solar Energy International (2004) Photovoltaic Design and Installation Manual. New Society Publishers, Gabriola Island, B.C, Canada.
- Komp, Richard J (1995) Practical Photovoltaics: Electricity from Solar Cells, Third Edition. Aatec Publications, Ann Arbor, Michigan
- 23rd IEEE Photovoltaic Specialists Conference(1993) Field Investigation on the Relationship Between Battery Size and PV System Performance., Institution of Electrical and Electronic Engineers.