Solar Installations - Anatomy Of An Energy Farm

Back in '89, when I started my professional electrical career, solar farms were nothing more than a novelty on the landscape, a curiosity, to stop along the side of the road for a look.

How things have changed in 30+ years, since they are now legitimate energy plants in their own right. A review of the primary components of these modern zero emission energy plants does every professional good.

Solar Panels and Tracker - Getting the Sun Where It Is

Solar Panels

Photovoltaic (PV) based panels are made up of numerous solar cells, typically composed of silicon. When photons from the sun hit the solar cells, they generate a DC electric current through the photovoltaic effect.

The most common Solar Panels are photovoltaic (PV) panels. Which are are made up of a layer of PV cells, a metal frame, a glass (or other) casing, and internal wiring to allow current to flow from the PV cells. Silicon is non-metal with conductive characteristics that allow it to absorb and convert sunlight into electricity.

Factoid: Why are Solar Panels made from Silicon? - Silicon is, by far, the most common semiconductor material used in solar cells, representing approximately 95% of the modules sold today. It is also the second most abundant material on Earth (after oxygen) and the most common semiconductor used in computer chips. Crystalline silicon cells are made of silicon atoms connected to one another to form a crystal lattice. This lattice provides an organized structure that makes conversion of light into electricity more efficient. Solar cells made out of silicon currently provide a combination of high efficiency, low cost, and long lifetime. Modules are expected to last for 25 years or more, still producing more than 80% of their original power after this time. - US Department Of Energy

Trackers

These are electromechanical devices that automatically tilt and rotate the solar panels to follow the sun's trajectory across the sky.

Types of Trackers include:

• Single-axis which moves the solar panels by rotating around one axis. Its movement is usually oriented North and South directions.?
• Dual-axis which moves the solar panels to rotate on two axes simultaneously. It is normally aligned horizontally as well as vertically, so it can be oriented all compass directions (N, S, E and W).?

Trackers can increase energy production by up to 25% compared to fixed ground and roof mounted panels. These systems have become more standard as costs have been reduced due to manufacturing at scale.

Central Inverter - Tesla To Edison Making The Change

The central inverter changes the direct current (DC) electricity generated by the photovoltaic (PV) panels into alternating current (AC), which can be supplied into the electrical grid.

Central inverters provide a central full bridge rectification point and typically have an output over 500kW, for larger energy farm systems for power grid connections.

Another type is the String inverter which is connected to each array for local DC/AC inversion. String inverters are primarily utilized on small and medium based systems under 100kW.

Advantages of Central Inverters:

• Fewer inverters required, can be centrally installed, easier maintenance.
• Fewer inversion components, fewer fault points and higher reliability.
• Fewer harmonic producing contents, fewer dc components, higher power quality.
• High inverter convergence level, higher power density, lower cost.
• Overall Protection functions of the single inverter, higher safety of the energy plant.
• Power factor adjustment options, good power grid adjusting.

Medium Voltage Transformer - Building It Up

To supply the voltage required for transmission on the energy grid, the existed AC voltage after the Central Inverter must be stepped up to Medium Voltage (MV) (>1kV) via a MV transformer. For grid transmission it is usually above 66kV and typically greater than 100kV.

These voltage levels are required for long distance transmission to reduce losses at the final destination point.

Ratings for types of distribution transformers are available in IEEE product standards including the following:

• IEEE Std C57.12.20 (Overhead Type)
• IEEE Std C57.12.34 (Three-Phase Pad-Mounted Compartmental)
• IEEE Std C57.12.36 (Distribution Substation Transformers)
• IEEE Std C57.12.38 (Single-Phase Pad-Mounted)

Controlling Components - Interconnection Breaker, Recloser, Disconnect, and Metering

System controlling components to tie the Energy Farm to the Power Grid involve the Interconnection Breaker, Recloser, Disconnect, and Metering unit.

They are the Control Center of the network.

1. Interconnection Breaker: Allows the Energy Farm to connect or disconnect from the power grid.
2. Recloser: Fault isolation system connection to the power grid, it opens, isolates the issue, and then closes again.
3. Disconnect: This is the primary connection switch incase of a severe issue, it can be used to instantly disconnect the farm from the grid to prevent further issues.
4. Metering: Meters track how much electricity the solar farm is producing and feeding into the power grid.

Where The Efficiency Is - SCADA and Meteorological (Weather) Station

The final factor in the Energy Farm is the Supervisory Control and Data Acquisition (SCADA) systems and meteorological station.

1. SCADA: The Supervisory Control and Data Acquisition system monitors the performance of each component, track energy production, and ensure everything runs smoothly. If something happens outside of expected norms, the SCADA system can alert operators, or maintenance, to take action.
2. Met Station: Energy farms rely on good weather conditions. A meteorological station continuously gathers data on temperature, wind speed, humidity, and, most importantly, sunlight hours. This information helps in predicting energy generation and optimizing the farm's operation. These systems are usually connected to the US Weather Service for forecasting intelligence.

Final Thoughts

Improvements in performance and efficiencies have dominated the Solar industry in my 30+ years in the electrical industry. Continual improvements in materials, components and intelligence (like AI), will scale efficiencies to produce more power (in moonlight too...) on smaller tracks of land.

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