Fiber Optics in Solar Energy Applications



Figure 1Figure 1

Introduction

Solar energy has recently become a popular alternative energy source to meet demands around the world due to the fluctuation of oil/coal prices and global warming issues. Oil is a limited and diminishing resource, and because of this, the price surges when demand is high. Oil and/or coal powered generators, when converting fossil fuel into electrical power, produce enormous CO2 and other pollutants that are harmful to the earth.

In a solar farm power generation system, large amounts of current are generated from the heat of the sun. In order to protect the equipment from huge current leakage, galvanic insulation becomes important to ensure the power system’s quality and reliability. Fiber optics offer insulation protection from high-voltage/current glitches and unwanted signals into power equipment controls and communication. It is also feasible to use fiber optics to control the tracking capabilities of the solar panels. Fiber optics communication can cover longer link distance con- nections compared to copper wire. As the solar farms grow in size, monitoring and controlling all the solar panels requires long link distance connections, which is only possible with fiber optics cable.

Key applications for fiber optic components in solar energy systems include:
• Power electronic gate drivers for inverters
• Sun tracking control and communication boards
• Solar farm substation automation and protection relays

solar power generation

Solar panels collect solar energy and convert it into electrical energy through photovoltaic modules or solar thermal collectors. In order to integrate the power generated from solar panels to the power transmission lines, the power needs to be converted into utility-grade AC power (Figure 1).

An inverter is used in the solar energy system to provide AC power, while the transformer increases the voltage to medium/high for connecting to the power transmission lines. Circuit breakers are also installed to protect the system when there is a fault in the transmission lines.

In order to produce the required AC power, the power semi- conductor devices are turned on/off at the right frequency to ensure clean and reliable AC power. The turning on/off signal is usually controlled by a DSP embedded controller via a fiber optic link, which allows high galvanic isolation capability. Examples of power semiconductor devices available in the market:
• Insulated Gate Bipolar Transistor (IGBT)
• Gate Turn Off Thyristor (GTO)
• Integrated Gate Commutated Thyristor (IGCT)
• Symmetrical Gate Commutated Thyristor (SGCT)
• Emitter Turn Off Thyristor (ETO)
Fiber optic components are commonly used to control a high voltage and current switching device, with reliable control and feedback signals (Figure 2,Table 1).

Figure 2Figure 2
Table 1Table 1
Avago Technologies' versatile link product family (HF- BR-0500Z series) has been the most popular standard component for power semiconductor control boards. Its simple transmitter and receiver circuitry makes these components easily integrated into the system with TTL logic level. Figure 3 shows the common interface circuitry for a 5MBd data rate operation.

Figure 3Figure 3

Solar Panels Control and Monitoring System

There are two main ways to maximize electrical power conversion from solar energy. One is to use the most efficient solar panel. The other is to track the sun’s movements throughout the day. It has been shown that solar panels with tracking systems have higher electrical output compared to a fixed system.[1, 2]

As solar farms become larger to generate more power for utilities, they are equipped with intelligent features to monitor the performance of each solar panel. For example, to monitor the panels’ electrical output and temperature to maximize the electrical output, controlling the angle and direction of the solar panels is very important. In the commercial solar farm that generates a few megawatts of power, the solar panels are installed in huge areas, where reliable controlling and monitoring networks are only possible with fiber optic networks (Figure 4, Table 2).

Figure 4Figure 4
Table 2Table 2

Substation Automation

Substations connect the power generated from solar farms to the utility grid for power transmission to the end consumer. Modern substation automation, which is based on the IEC 61850 standard, is designed to improve overall system reliability and significantly reduce the number of copper wires used [3, 4] (Figure 5).

Since most equipment (e.g., switchgear, transformers, circuit breakers, etc.) in substations operate at medium/ high voltage, it is necessary to have galvanic isolation to provide protection for the low voltage devices connected to it. This equipment also generates a large electromagnetic (EM) field due to the high switching voltage and current. To ensure reliability control, the Standard requires communication lines that are immune to EM fields. In this instance, fiber optics is the best solution for such require- ments in substation automation control and communication lines (Table 3).

Figure 5Figure 5
Table 3Table 3
Avago Technologies has many parts that suit IEC 61850 implementation based on 10/100/1000Mbps ethernet protocol. Figure 6 shows a typical circuit diagram for a Fast Ethernet fiber optic transceiver. Avago Technologies' AFBR-5978Z’s input/output data signals (based on LVPECL) are easily connected to the common Ethernet PHY ICs available in the market today.

Figure 6Figure 6