. Research

Solar Energy Laboratory Research

Texas Solar Radiation Data Base

This project is being conducted by the University of Texas at Austin to develop a solar radiation resource for Texas. Solar radiation monitoring instruments located across the state record measurements continuously. Data is downloaded at regular intervals and analyzed and checked for possible errors. Once screened, it becomes part of the laboratory's database. Another comprehensive database is provided where the user can access data for any particular station over any period of time since that station became operational. The project is supported by the State Energy Conservation Office (SECO).

The solar monitoring stations use two types of instrumentation, Class I and Class II, to obtain total solar radiation data:

Future plans include installing more Class II sites, and taking broad band spectral measurements at the existing five Class I sites. At each of these five sites three pyranometers will be installed, one with a clear dome and the two others with spectral filters. These will permit obtaining data for three spectral bands.

In all, there will be at least fifteen sites located across Texas with either the Eppley instruments or the Ascension RSPs installed, and each site will provide the three components of total solar radiation: global horizontal, direct normal, and diffuse horizontal.

Scale Prediction in Solar Hot Water Systems

Potable water can potentially result in scale formation on heated surfaces. In solar hot water systems this can seriously degrade system performance and, in extreme cases, clog fluid passages. In open loop systems scale may form in the collector passages; in closed systems scale may form on the potable water side of the heat exchanger. If the heat exchanger has "passages" on the potable side clogging may occur there. In wrap-around heat exchangers clogging would not occur, but system performance might suffer over time.

Under an NREL sponsored project, software (SOLSCALE) has been developed for use on a DOS platform computer for predicting scale formation in solar hot water systems which include a heat exchanger. The user inputs information on the system's location, the solar components (collector size, tank size, etc.), the load, and the water chemistry. The software predicts the severity of scale formation and indicates how the system component sizes may be altered to alleviate the problem and how often to descale the system. This project is being continued to validate the software with field data. In addition, more fundamental work is being pursued to better quantify scaling rates.

Photovoltaic Powered Cooling Systems

Engineers at NASA are testing a variety of photovoltaic powered cooling systems. They are interested in developing modeling tools to compare with their experimental data in order to predict the performance of photovoltaic powered cooling systems for terrestrial and space application.

Under a NASA grant, TRNSYS software is being used to model a variety of solar photovoltaic powered cooling systems. The cooling concepts being addressed are Thermoelectric Cooling, Stirling Cycle Cooling, and Vapor Compression Cooling. For space application of the PV system, modeling of the photovoltaic array performance must be modified to account for the vacuum environment as it affects temperature and performance, and the heat rejection for the cooling cycle must be accomplished with radiation panels.

Screening Software for Renewable Energy Applications

A software package, Texas Renewable Energy Evaluation Software (TREES), has been developed with SECO funding to provide a tool to easily compare the economics of solar and wind energy with conventional energy sources for a variety of thermal and electric applications. TREES allows the user to relatively simply compare solar against fossil fuel energy for various applications such as swimming pool and other water heating. Similarly, the software allows comparison of solar photovoltaic and wind generated electricity against conventional and diesel generated electricity. The software assesses the attractiveness of renewable energy applications in four categories: highly attractive, attractive, marginal, or unattractive. TREES is not a design tool, but rather, a screening tool which helps the user determine whether a more detailed design is needed.