Despite the many advancements in solar energy over the last couple of decades, not everyone is convinced on the merits of this renewable energy source, particularly when it comes to residential solar power and thermal energy. This is especially true for those who had an unfavorable experience during the US solar thermal “boom and bust” of the late 70’s and early 80’s, where the solar market essentially all but crashed.

These unfortunate experiences were the result of an industry that grew very fast, driven by large federal tax credits, without adequate quality requirements or performance ratings. The good news, however, is that from those challenges, lasting progress has ensued. Today, solar technology is built to last, with new standards and codes that ensure reliability and longevity.

From the challenges of the 1980’s, the Solar Rating and Certification Corporation (SRCC) developed—a non-profit organization created with the help of state energy offices, the Solar Energy Industries Association (SEIA), and the Department of Energy (DOE). It was formed to provide consumer protection through a national, industry-supported certification and ratings program. Over 30 years later, SRCC is still the leading solar thermal certification organization, although the solar market today is vastly different.

SRCC certification guidelines and testing standards, as well as the international principles they leverage, have evolved as solar energy technologies have changed over time. In July of this year, SRCC published an updated collector (i.e. solar thermal panel – Standard 100) and system (Standard 300) criterion, which are the minimum requirements for SRCC’s two flagship certifications: OG-100 for collectors and OG-300 for systems. The organization also updated the OG-100 and OG-300 certification policies.

Certification requirements
One factor driving the demand for ongoing collector certification is the requirement in the federal personal tax credit for solar thermal systems that the collectors are certified for performance by SRCC, or a comparable entity endorsed by the government of the state in which the property is installed.

The International Association of Plumbing and Mechanical Officials (IAPMO) also offers solar thermal collector and system certifications to the SRCC standards, and is accepted for tax credit purposes in some states. Additionally, IAPMO proposed a new ANSI standard on solar thermal system design and installation, which became an ANSI standard in late 2013.

Currently, the International Code Council (ICC) and SRCC are also working together toward developing ANSI standards, based on SRCC Standard 100 and Standard 300. An additional driver for SRCC certification is its inclusion in the International Residential Code.

Understanding the standards
The SRCC OG-100 certification is available for glazed and unglazed solar thermal collectors, including water heating, air heating, pool heating, concentrating, and photovoltaic (PV) thermal varieties. The certification serves to ensure a collector is fully meeting the quality stated in SRCC Standard 100, and provides a performance rating based on physical test data generated per Standard 100. The requirements of this standard are built upon the foundation of the international test standard for solar thermal collectors, ISO 9806, which just published a major revision in late 2013.

SRCC Standard 100 requires testing of a randomly selected collector performed at an SRCC-approved testing lab. The lab conditions must include accreditation to ISO 17025, which is the international quality standard for testing and calibration laboratories, and is closely related to the more general and more widely known ISO 9000 series for quality management. 

The Standard 100 tests are split into two groups: quality tests and performance tests. The quality tests are generally pass/fail tests that assess if a collector meets a minimum standard of quality. The quality tests for glazed liquid heating collectors include the following:

• 30-day Dry Stagnation Exposure Test: Exposure to 30 sunny days while empty of water;
• Cold Fill thermal Shock: Filling of a dry, hot collector with cold water;
• Cold-spray Thermal Shock: Spraying cold water on a dry hot collector;
• Internal Pressure Tests: Static pressure test to confirm integrity; and
• Impact-resistance Test: Steel ball impact on glazing.

The performance tests for glazed liquid heating collectors are:

• Thermal Capacity/Time Constant: Speed of response to step input change of radiation;
• Thermal Performance: Determines efficiency versus temperature and radiation curve;
• Incident Angle Modifier: Determines relative efficiency at several incident angles; and
• Pressure Drop: Heat-transfer fluid pressure dropped across a range of likely flow rates.

Certification program
The SRCC OG-300 is a solar thermal system certification program. The system includes everything from the collectors and the tank to the instruction manual. System certification also combines minimum quality standards with a performance rating.

Unlike the collector certification, however, the system isn’t physically tested. Rather, SRCC builds a computer model of the system in TRNSYS software, consisting of Standard 100 test data for the collector(s) and performance data/ratings for pumps, tanks, and heat exchangers. There are many state and utility solar thermal incentive programs that require OG-300 system certification, many of which link incentive levels to the OG-300 performance rating.

In response to the recent ISO 9806 update, SRCC updated its Standard 100 to reference the new version of ISO 9806, and decided to include features of ISO 9806 not previously incorporated. Of particular interest to manufacturers is the change that allows the quality and performance testing to occur simultaneously on two separate collectors, instead of requiring that all tests occur sequentially on a single collector.

Also of note is SRCC’s inclusion of the quasi-dynamic performance test method. Historically, Standard 100 has required the steady state performance test method, which is dependent on stretches of very clear skies. Otherwise, a solar simulator is needed to collect the required data points.

With the quasi-dynamic testing (already common in Europe), the test period is less dependent on weather conditions, making the schedules for outdoor test labs shorter and more predictable. Moreover, several more quality tests were added, including the mechanical load test and an optional freeze resistance test.

The new Standard 300
An update to Standard 300 was also released earlier this year. It included numerous small changes to allow for the testing and certification of PV water heating systems. There are several PV-based solar water heating systems on the market today, which drove the need for these updates. 

At the same time, SRCC issued a new version of OG-300, opening the door to PV water heating systems for certification. Stay tuned to SRCC for continued standards and certification program updates and improvements, all designed to help guarantee a more reliable and efficient solar energy industry. 

Keep up to date with the latest solar thermal standards by visiting the Solar Rating and Certification Corporation (SRCC) website at www.solar-rating.org.

Tommy Cleveland is the renewable energy project coordinator for NC Clean Energy Technology Center.

NC Clean Energy Technology Center
http://nccleantech.ncsu.edu