Heating - Solar air heater - Crop drying / Indonesia

Case study assignment

A government agency has asked you to prepare an analysis of a solar crop dryer at a tea leaf plantation in Malabar, West Java, Indonesia. The agency wishes to determine the financial feasibility of using a solar air heating (SAH) system for the wilting of tea leaves. Heat for this application is currently provided by an oil-fired system.

Site information

The site is at a latitude of approximately 7° S and a longitude of approximately 105° E.

Tea leaves need to be wilted before they can be processed. The SAH system will provide heated air that aids in this process. The tea leaves are manually loaded from a trolley into troughs. An axial fan delivers up to 86,400 m3/h of heated air to a chamber beneath the troughs. The heated air then rises through the tea leaves in the troughs, carrying moisture with it.

Currently, industrial diesel oil provides heat with a seasonal efficiency of 60%. After the conversion, no oil will be burned and only the energy requirement will be for the fan. It is assumed that this energy requirement will remain unchanged by the conversion.

The facility has 600 m² of unshaded roof area suitable for mounting an SAH system. The roof faces north at an angle of 22° from the horizontal. The system is operated 7 days a week, during daylight hours for the entire year. The air temperature is kept below 40 °C by the adjustment of louvers that allow ambient air to enter the system.

Financial information

The government agency requests that the financial analysis take the plantation's point of view. It provides financial figures for the analysis (inflation rate of 1%, debt ratio of 75%, fuel cost escalation rate of 1.5%, debt interest rate of 9%, discount rate of 9%, debt term of 15 years, and a project life of 30 years). The collector materials will be purchased in Canada and shipped to Indonesia. The installation of the system will be done locally at a cost typically half that in industrialised countries. The design, development and engineering on this project will be done locally. A tax analysis need not be included. The cost of oil is $0.40/L.

Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.

Solution

The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.

Teacher's notes

• There are no material or labour credits because there is an existing heating system.
• Design, development and engineering accounts for approximately 6% of this type of project.
• The original fan was replaced with a high efficiency unit such that the fan energy requirement did not increase.

Real project

Results

A solar tea leaf dryer was installed at a plantation in Malabar, West Java, Indonesia. The perforated collector system was built with the assistance of the R&D Centre for Applied Physics - LIPI, and was funded by the Canadian government in cooperation with the Association of South East Asian Nations (ASEAN). The purpose of the project was to determine the feasibility of using solar energy to displace oil as the heating system for the wilting of tea leaves.

The solar air heating system SAH was able to meet the full heating load for tea drying at a payback of 1.5 years, not including design and development costs. New projects would have to include these, but they would be offset by credits for eliminating the fossil fuel heating system.

System description

The system is designed to wilt tea leaves through a batch process using the existing drying troughs and shelter. The troughs are manually loaded with tea leaves from a trolley that moves through the wilting area. An axial fan delivers solar-heated air at a rate of up to 24,000L/s to a chamber beneath the troughs. The 600 m2 solar collector is mounted on the north-facing roof of the shelter at an angle of 22o with the horizontal. The heated air then rises through the troughs and the tea leaves, carrying moisture with it.

In 1993 and 1994, prior to installation of the solar system, industrial diesel oil was used at an average rate of 0.11 litres per kilogram of tea. After the conversion, no oil was burned and only the fan required energy. It is estimated that approximately the same amount of fan energy was required before and after the conversion. In September 1994, three of the solar-heated troughs produced 108,000 kg of high-quality wilted tea for a total saving of 11,880 L of oil. The cost of oil is $0.40 per litre. At this rate, the solar system is expected to deliver 850 MWh of heat on an annual basis.

Lessons learned

• The (SAH) system was able to completely displace oil heating.
• Because a low temperature rise was required, the system performed best with a high flow rate per unit area.
• There was no incremental fan power required.
• The system was easily integrated into the existing operation.

The big picture

Drying of crops is an excellent application for SAH systems especially when used in sunny climates. In this case the year-round use of the system and low temperature required meant that the payback of the system was less than 2 years.

Photo

Tea Drying Shelter, West Java, Indonesia

References

• Air Systems Working Group, Low Cost, High Performance Solar Air-Heating Systems Using Perforated Absorbers - A (Draft) Report of Task 14, International Energy Agency, December 1995, p 92-97.
• Carpenter, Stephen, "Personal communication," Enermodal Engineering Ltd., 2000.
• Nikiforov, Vladimir, "Personal communication," 2000.