Photovoltaic Test Facility

Grant # 93-15-02
Principal Investigator: Howard Shanks
Organization: Iowa State University
Participants: Mike McClimans, Azaul Villanuova Justin Evermann, Roger Keen
Technical Area: Renewable Energy

Background and Significance:
The Iowa Solar Test Facility was established in 1993 to determine the feasibility of using photovoltaics for electric energy generation in the state of Iowa. Photovoltaics have been used extensively in the southwest but no studies had been made to determine the viability of commercially available modules in the Iowa environment. In addition there was little information on the availability and variability of the solar resource throughout the year.

Project Objective:
Two major questions were to be answered in this five-year study. First, could commercially available solar cell (photovoltaic) modules survive in the severe weather environment of Iowa for practical periods of time? Second, could the solar radiance be determined over an extended period of time such that reasonable data would be available for scaling of photovoltaic installations. In addition to the original goals, a comparison of the solar resource with power plant demand over the year and the viability of stand alone “walk lights” were investigated.

Summary of Work to Date:
The solar resource in Iowa is sufficient for the operation of fixed position photovoltaic modules. Adequate battery or other storage is required to provide energy during cloudy and foggy periods. The 3-day and 15-day averages of solar insolation give a suggestion of the required storage if a uniform demand for power is expected.

Weather and Solar Insolation
Because of the high variability of the solar resource in Iowa, using a tracking device to follow the sun during the day does not appear to be practical. The optimum PV configuration is an array of fixed modules at an angle of 42 degrees relative to the horizon. Because of the extensive amount of scattered light due to cloud cover, haze and fog, there may be some advantage to amorphous rather than polycrystalline or single crystal modules.

The solar insolation data were compared with Ames Municipal Utility demand data over the course of a year. High temperatures demand more energy use for air conditioning. Not surprisingly the solar insolation peaks at the same time so that photovoltaics offer a good fit with peaking utility demand. A comparison of potential wind energy with solar insolation and utility load data needs to be completed. The location of the test facility was not, however, satisfactory for collection of wind data.

Test Modules
All photovoltaic modules on the test facility functioned normally throughout the test period. The Iowa environment does affect the packaging of the modules and, in particular, corrosion was observed around electrical contacts. In the installation of a system special care is required to seal all contacts from the external environment.

Solar Walk Lights
Of the six walk lights tested, two were still in operation after 4 _ years. There were no failures of the solar modules on the units. In all cases the problems were due to the balance of system weaknesses. The fluorescent lamp units were superior to the incandescent units due to their much longer lamp life and lower power drain. In the selection of solar powered walk lights one should look for the units with the largest solar modules and replaceable fluorescent lamps and batteries. Do not expect to have them provide all night light in the Iowa environment because the energy storage is insufficient.

Indian Creek Nature Center
The Indian Creek Nature Center system performed satisfactorily for the lifetime of the installation. In the entire module lifetime test effort only the glass laminated modules failed due to environmental considerations. These same style modules also suffered from vandalism. It would appear that glass covered systems are more susceptible than plastic covered units.

The system provided power for lighting the building at the Center for the entire time except during several extended cloudy periods in the winter. This is not a failure of the system but rather a failure to size the system properly. This was primarily because of financial limitations at the time it was installed.

The clearest sign of the level of satisfaction with the system was the installation of a new and larger array by the Indian Creek Nature Center when the test system was removed.

Final Statement
The solar resource has been measured in central Iowa and is sufficient for practical solar energy systems. Currently available solar photovoltaic modules are able to survive for extended periods in the Iowa environment. The solar resource is greatest when energy demand is greatest in central Iowa making it a good fit as a source of peaking power. Further study is required to evaluate how well solar and wind energy can be made complimentary.

Project ended July 1, 1999