Introduction to Photovoltaic Power System

The solar power system may be “off-grid” or “grid-connected.” Off-grid or stand alone systems are not connected to existing power system run by utilities companies. They can be used to solely power homes, schools, hospitals/clinics and can be designed with or without batteries. Grid connected systems are designed to supplement existing electric service from a utility company.

A solar PV module is made up of many PV cells and can be mounted as ground mount, track racks, side of pole (tower), and top of pole.  Other mounting techniques are possible depending on their safety, effectiveness and feasibility.

Advantages of the PV Power System

• PV installation is static that does not need strong and tall towers leading to longer life with little maintenance.
• It does not produce vibration or noise and does not need active cooling.
• PV power systems have short lead times to design, install and start a new plant.
• PV power systems are highly modular and the power output can easily match the peak-load demands.
• PV power systems are highly mobile and portable due to their light weight.

Application of the PV Power System

At present, PV power is extensively used in stand-alone power systems.  Remote villages around the world are the usual target areas for implementation.  PV power system, however, are usually used for grid-connected PV power plants.  They are also used in hybrid systems with diesel power generators. 

The PV Power System Components

• PV Cells, Modules and Arrays – the PV cells are the basic components or the building blocks of a PV power system.  Solar PV cells make a module and several modules make an array.  Extensive research projects have been undertaken to improve its conversion efficiency that leads to reduction of its unit cost. 

• Sun Tracker – Sun trackers can be a one-axis tracker (follows the sun from east to west during the day) or a two-axis tracker (follows the sun east to west during the day and from north to south during the seasons of the year).  An effective sun tracker can increase the energy yield up to 40% compared to a fixed array design.

• Energy Storage (Battery) – Because solar or PV power is intermittent, the use of energy storage has become integral to the system to ensure the load availability.  The primary type of energy storage used by the PV power system is the electrochemical battery.  The primary electrochemical battery converts chemical energy into electrical energy.  Once fully discharged, it is discarded and therefore, not reusable.  The secondary electrochemical battery is also known as rechargeable battery.  It is rechargeable because its chemical reaction is reversible.  In the charge mode, it converts electrical energy into chemical energy while at the discharge mode, it converts chemical energy into electrical energy.  The round-trip conversion efficiency is between 70 – 80%.  The batteries in modern system are managed by computer software to prevent from overcharging. 

• Charge and Discharge Controller –  The Controller is a multi-function component of the PV system.  It is primarily used for detecting the working status of the system and the charging/discharging of the batteries.  It protects the batteries from being overcharged or over-discharged.

• Inverters – Inverters are devices that have the following functions:

• Convert AC to DC and vice-versa
• Control voltage and frequency
• Convert DC to DC

The inverter is a key component of the grid-connected PV system.  Efficient inverters result to high efficiency in DC – AC conversion and peak-power tracking.  They also have low harmonic distortion, low electromagnetic interference (EMI) and high power factor.  Inverters are available in a wide range of power ratings with efficiencies ranging from 85 – 95%.

Economics and Trends for PV Power Systems

The cost of producing PV cells has been declining since 1980s.  Also, the cost of energy has been declining which is at present rate equivalent to USD 0.15 per kWh (by 2010; source: Patel, Wind and Power Solar Systems).  In the US, installed capacity exceeded 1GW in 2004.  According to the European Industry Association, the total global PV cell production in 2002 was over 560MW and has been growing at an annual rate of 30%.

Author’s Note.  Mr. Makund Patel’s book on Wind and Solar Power Systems: Design, Analysis and Operation has been used as the primary reference for the Introduction to Photovoltaic Power System.  R Cueto does not claim IP or copyright ownership of the information presented.  This information has been provided for general understanding of the PV power system only. 

The product information to be presented in the following pages may no longer be correct or updated at the time of this writing.  The readers or potential clients are advised to contact R Cueto to receive the most current product specifications or information.


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