HXS10 SolStation Solar Tracking Controllers

There has been recognition in recent years that a transition to clean and sustainable energy sources is needed to deal with environmental concerns. Solar energy is gaining attention as a strong candidate for such sources. Solar energy can be used both as a heat source and a light source.

There are a variety of applications from rooftop panels for home water heating to industrial units that use heat collectors (with mirrors and/or lenses) to heat water to over 100°C. Some examples of these include solar thermal power generators with turbines driven by steam from water heated to over 400°C in heat collectors, or even higher temperature processes such as hydrogen manufacturing and desalination. The applications that require such high temperatures (industrial heat sources, generators, desalination processes, etc.) employ solar tracking of the mirrors and lenses.

Solar thermal power generation refers to a system in which mirrors are aimed at the sun in order to collect heat to create steam that can be used to drive a turbine for generating electricity. Control in solar thermal power generation can be single- or dual-axle.

Single-axle

• Trough
  Light is collected at the center of a curved mirror which heats liquid in a pipe.
  This heat creates steam that drives a turbine and creates electricity.
• Linear Fresnel
  After pipes atop multiple narrow mirrors are heated in sunlight, the process is the same as that of trough types.

Dual-axle

• Tower
  Light is collected with mirrors at the center of towers, and liquid inside the towers is heated. This heat drives electricity-generating turbines.
• Stirling Engine
  Heat is concentrated in stirling engines placed in the center of a parabola, and the heat is converted directly to electricity.

Photovoltaic cells and other devices directly convert electric light (via optical fibers etc.) or sunlight to electricity. Photovoltaic cells differ in price and efficiency depending on the type, but in any given cell the generating efficiency also varies depending on the presence or absence of solar concentrators and tracking.

Particularly in the case where concentrated light must be directed onto photovoltaic cells, solar tracking ensures that light from the constantly moving sun always reaches its target. The higher the degree of concentration, the smaller the required surface area of the photovoltaic cell, but some light can fail to reach the cell without highly precise solar tracking.

Most common-use photovoltaic cells that do not have light concentrators do not necessarily require solar tracking. Photovoltaic cells in fixed installations on rooftops and other locations can generate electricity continually as long as sunlight is present. However, solar tracking maximizes the amount of light reaching the surface of the photovoltaic cells by maintaining constant perpendicularity to the sunlight, and thereby can increase the amount of energy generated. Such tracking control can yield a 30–40% greater amount of electricity than fixed installations.

Traditionally, general-purpose PLCs (programmable logic controllers) have been used as solar tracking controllers. However, the reality is that PLCs have difficulties in meeting all of the specifications required for solar tracking applications including operating environment issues, cost, and future sustainability. Such conditions notwithstanding, demand for effective photovoltaic energy solutions is increasing, and Yokogawa Corp. is meeting this demand with a dedicated solar tracking controller, the HXS10 SolStation™.

The HXS10 SolStation™ offers the following benefits:

• Built-in solar position algorithm
• Excellent environmental performance(Operating temp: -20 to 70°C, Power consumption: 5 W or less).
• Powerful communication functions
• Selectable input/outputs

In our next installment, we will describe these characteristics in more detail.