Publications

Battery testing for photovoltaic (PV) applications is funded at Sandia under the Department of Energy`s (DOE) Photovoltaic Balance of Systems (BOS) Program. The goal of the PV BOS program is to improve PV system component design, operation, reliability, and to reduce overall life-cycle costs. The Sandia battery testing program consists of: (1) PV battery and charge controller market survey, (2) battery performance and life-cycle testing, (3) PV charge controller development, and (4) system field testing. Test results from this work have identified market size and trends, PV battery test procedures, application guidelines, and needed hardware improvements.

The performance of 21 PV-powered low pressure sodium lighting systems on a multi-use pathway has been documented in this paper. Specific areas for evaluation include the constant voltage and on/off PV charge controllers, flooded deep-cycle lead-antimony and valve regulated lead-acid (VRLA) gel batteries, low pressure sodium ballasts and lights, and vandal resistant PV modules. The PV lighting system lessons learned and maintenance intervals have been documented over the past 2.5-years. The above performance data has shown that with careful hardware selection, installation, and maintenance intervals the PV lighting systems will operate reliably.

Stand-alone photovoltaic (PV) systems typically depend on battery storage to supply power to the load when there is cloudy weather or no sun. Reliable operation of the load is often dependent on battery performance. This paper presents test procedures for lead-acid batteries which identify initial battery preparation, battery capacity after preparation, charge regulation set-points, and cycle life based on the operational characteristics of PV systems.

Sandia National Laboratory`s PV System Components Department performs comprehensive failure analysis of photovoltaic modules after extended field exposure at various sites around the world. A full spectrum of analytical techniques are used to help identify the causes of degradation. The techniques are used to make solder fatigue life predictions for PV concentrator modules, identify cell damage or current mismatch, and measure the adhesive strength of the module encapsulant.

A single EMCH concentrator module for the Photovoltaics for Utility Scale Application (PVUSA), Emerging Technologies-1 (EMT-1) program has been electrically and environmentally tested to the requirements in Sandia's SAND86-2743 document Qualification Tests for Photovoltaic Concentrator Cell Assemblies; and Modules.'' Module testing was divided into three parts: (1) initial characterization, (2) environmental testing, and (3) supplemental testing. Testing began with module inspection for damage, adequate name plate information, grounding off-axis beam damage, and baseline electrical performance. The included thermal cycling, humidity/freeze cycling, rainwater intrusion, and hail impact, and hi-pot testing. After both thermal cycling and environmental testing, the module was electrically tested. The supplemental testing not required by the Sandia qualification document was conducted for engineering evaluation. These tests included wet insulation resistance measurements and cell temperature measurements after installation of heat sink fin extensions. The test sequence revealed some module deficiencies which include RTV adhesive/sealant problems, high cell temperatures, off-track beam damage, and low wet insulation resistance values.