Solar Energy

Solar Energy

Heat Transfer Fluids in Solar Energy Utilization

We get a lot of enquiries about using heat transfer fluids for solar applications. These phone calls and emails come from engineers, mechanical contractors, process designers project managers—and even homeowners.

We thought it could be useful to our web visitors to devote a web page to this topic, so here is a summary of the applications of heat transfer fluids in solar energy utilization.

Domestic Applications

Water/Water Glycol

Passive Solar

Passive solar systems are the simplest and least expensive alternatives for direct use of solar radiation for practical purposes.  Passive systems rely on natural convection for circulation.  Passive solar water heating (SWH) systems, the most commonly found liquid-based passive solar applications, generally use plain water as their circulating liquid.

Active Solar

In active (pumped) SWH systems, more often a separate loop containing a heat transfer fluid will transfer heat to the water using a heat exchanger.  The heat transfer fluid in these systems is usually a freeze protected solution of a glycol and water, with a corrosion inhibition package.  Non-aqueous heat transfer fluids, such as Paratherm LR, could also be used here.  Contact Paratherm for details on advantages.

Power Generation and Thermal Storage

Heat transfer fluids are also utilized in solar energy generation, in concentrators such as parabolic, linear Fresnel, and trough-based systems.  Several heat transfer media can be utilized, depending on the mechanical design and temperature requirements of the application.

  • Water/steam is used in turbines for generating electricity.
  • Molten salts, such as 60% NaNO3 and 40% KNO3 (220-600°C) for thermal storage

Synthetic/aromatic heat transfer fluids

  • Liquid-phase only:  Used to uniformly provide heat for steam in turbine generators
  • Vapour phase: Used for generating electricity in turbines, similar to steam but with greater thermal efficiency

Polycrystalline silicon

Finally, high temperature heat transfer fluids are used extensively in the manufacturing processes for polysilicon, the material used to make photovoltaics, in a process similar to that used in production of computer chips.

Photovoltaic solar (PV Solar) panels are the familiar black panels with the bluish tinge, all solid state, that are placed on roofs and in deserts to generate electricity directly from sunlight.  Probably the most familiar example is the solar patio light, which absorbs solar energy by day and then automatically lights path and patio by night.

The Polysilicon process which can consist of the Siemens Reactor process or Fluid Bed (FB) reactors, in which heat transfer fluids can be used in the purification phase to raise temperature of catalytic reaction to convert silicon tetrachloride (STC) to trichlorosilane (TCS). This phase can be referred to as the Hydrogenation phase of the process.

These units purify metallurgical grade silicon (MGS) to electronic grade silicon by hydrogenation of MGS and STC to make TCS. The resulting TCS is purified by crystallization and distillation.  Heat transfer fluids are used in distillation process as well.

Other heat transfer fluids are also used in the cooling phase of polysilicon production, at low temperatures.  The use of cryogenic-range heat transfer fluids such as Paratherm CR is beneficial in this phase.   The fluid cools the molten silicon poured from crucibles into the moulds making monocrystalline ingots for solar cells and photovoltaics.

Paratherm Fluids for Solar Applications

Low Temperature Liquid Heating & Cooling Fluid High Temperature Fluids

Paratherm CR®

  • Higher Flowrates at -90ºC in Thermoprocessing
  • Lowers Equipment Operating Temperatures by 10ºC

Used in polycrystalline production

Paratherm LR™

  • Water Sensitive Products
  • Non-Corroding Water/Glycol Replacement
  • Higher Flash Point–Rated Combustible, Not Flammable
  • Low-Temp Start-up

Alternative to glycol-based fluids

Paratherm HR™

  • Synthetic/Aromatic
  • Gas processing
  • Chemical processes
  • Waste-oil recovery
  • Biodiesel production
  • Plastic processing

Used in polycrystalline production and thermal solar applications.

Paratherm NF®

  • Batch Processing
  • Electric Immersion Heaters
  • Food Grade

Used in thermal solar applications

Paratherm does not manufacture, support, or distribute glycol-based heat transfer fluids, but we can recommend suppliers.

Contact Paratherm for more information about heat transfer fluids, fluid analysis, application assistance and system troubleshooting help.

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