Solar revival: Is this trend gaining momentum?

DALLAS, TX — “Solar Energy Applications and Case Studies,” one of the seminars at the American Society of Heating, Refrigerating and Air-Conditioning Engineers’ (ASHRAE) 2000 Winter Meeting here, provided an overview of several successful solar applications, discussing design issues, advantages, and disadvantages.

Introducing the seminar, Robert Foster of New Mexico State University noted that this was the first solar energy seminar that ASHRAE’s had in a few years.

The first presenter was David Bergeron of SOLUS, who discussed a battery-free solar refrigerator.

Thermal storage solar-style

This refrigerator uses phase-change thermal storage instead of batteries, and employs a variable-speed compressor. It is a simple plug-and-play system that has a service life equivalent to a home refrigerator, Bergeron said.

Eliminating batteries in this solar application “saves money and time,” he added. Typically, five to six sets of batteries would be required over the life of a refrigerator.

System design issues include:

  • The ratio of thermal storage to refrigerator heat leakage must be high (seven days).
  • There must be good thermal conductivity between the evaporator and phase-change material.
  • The compressor must meet 100% of the daily cooling requirements in about 4 hrs.
  • The condenser temperature must see ambient conditions.

Bergeron added that the test unit holds temperature well, even when it was switched off for a couple of days.

Water treatment: the solar still

Solar water purification through distillation was then presented by Greg Vogel of SolAqua. This involves a solar still operation, evaporating water to separate it from brine.

The system achieves maximum production at 4 p.m., when there is maximum sunlight. Rain and snow have a dramatic effect on production.

A type of application where this might be used is a rural health clinic. The system could remove salinity and impurities.

“Compared to purchasing bottled water, a solar still’s simple payback is less than two years,” said Vogel.

Advantages of the solar still are:

  • High water quality;
  • No moving parts;
  • Long life (10 to 20 years);
  • Simple operation; and
  • Simple maintenance.

Disadvantages are:

  • Small product volume;
  • Potential VOC carryover; and
  • High capital investment cost.

Making ice in Mexico

A case study on photovoltaic (PV) ice making in Chihuahua, Charreras, Mexico, was recounted by Foster. This application involved ice production and storage in a remote rural area.

The system produces ice for the local fish operation. The PV array provides baseline ice production. A propane generator augments production when needed. A battery bank stores energy to make ice at night.

The system maintains an average temperature of 25°C. It produces 2,800 kg of ice per month during the summer. Benefits of the system are:

  • Increased fish production capacity;
  • Decreased ice costs;
  • Labor and travel savings; and
  • Reduction/elimination of food spoilage.

Daylighting, solar cooling

Mac Holder of L.M. Holder III, AIA, talked about integrating daylighting applications into building systems.

He noted that indirect light from high windows reduces the number of light fixtures needed in a building. “Daylighting reduces energy costs by eliminating lights,” Holder said.

A school using daylighting has one-third the lights it formerly did. Other buildings that have benefited include stores, gas stations, and warehouses.

Holder also related that the high windows can be left open at night for cooling, then closed during the day.

Solar cooling with new liquid desiccant absorbers was the subject of Wolfgang Kessling of the Bavarian Centre of Applied Energy Research.

For solar cooling, you need efficient use of solar energy, said Kessling. This includes an efficient air conditioning cycle and a high coefficient of performance (COP).

A solar air conditioning system with liquid desiccant absorbers can provide effective dehumidification and high-density energy storage capacity, Kessling said.

The first pilot plant application for an office building is now under construction.

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