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Solar domestic water heater ratings

How solar powered hot water heaters are rated

A solar domestic water heater is a long term investment. And with the investment of any solar powered hot water design, performance and efficiency are essential. After all without quality and performance, efficiency will inevitably be compromised.

Solar hot water heaters have ratings and specific performance benchmarks that if understood, can be used by would be consumers as a window to determine the real world performance of a particular design before installation.

Solar authority

With the emergence of the American solar industry in the 1970's, manufactures were introducing products all the while making unsubstantiated claims regarding the performance, efficiency and durability of their products. 

In 1980 the Solar Rating and Certification Corporation (or SRCC) was established. The SRCC is the only independent and nationally recognized organization that has developed and implemented efficiency and performance based ratings as well as certification programs for solar domestic water heater designs and components.

Solar energy factor rating

Solar energy factor rating (or SEF) is an efficiency indicating rating that's used by industry professionals to determine the overall efficiency of a solar domestic water heater. More accurately the rating is the ratio of the projected solar thermal heat provided to the projected heat provided by the systems' back up power source.

SEF ratings can numerically range anywhere from 1.0 to 11.0. The higher the SEF rating the greater the ratio of solar powered input when compared to the back up electric or gas powered input. The SRCC and a few state endorsed organizations developed the solar energy factor rating, as well as the testing procedures.

The overall efficiency of the solar domestic water heaters' back up source as well as the fuel type itself can have a significant impact on the systems' solar energy factor rating. The solar designs' storage standby heat losses can have a sizable impact as well.

Keep in mind that SER ratings are independent and professional projections, and the accuracy of such efficiency projections will ultimately depend on proper system sizing and appropriate solar design application.

Solar fraction rating

Solar fraction rating (or SF) is a performance rating that's utilized by many industry professionals as well. Solar fraction is the portion (or fraction) of the total annual hot water load that the solar domestic water heater can be expected to provide without the operation of the back up power source.

The solar fraction can also determine whether or not a sizable portion of both the purchase and installation costs of the solar domestic water heating system can be covered by the federal solar tax credit.

One of the current system performance requirements for the federal tax credit is a solar fraction rating of 0.5 or higher. Meaning that the solar panels, or collectors, must be capable of providing at least half of the sites' annual hot water load.

It's important to note that some state government endorsed organizations include storage standby heat losses into the rating and some organizations do not. The national SRCC currently does factor in storage tank standby heatlosses.

Most industry professional recommend referencing the SRCC ratings listings when comparing the solar fraction of several systems and designs.

SRCC certification programs

The SRCC has certification programs in place for solar domestic water heaters as well as panels, or collectors. These programs have detailed testing guidelines. 

Once a solar powered design is certified, the systems' efficiency and performance data is provided for both would be consumers and installers.

Collector and System Certification Is Voluntary

All would be consumers of a solar domestic water heater should be aware that participation in the SRCC's certification programs are purely voluntary.

It's purely the responsibility of the manufacturer to subject their solar hot water heater designs and panels to testing in order to receive certification, and not all manufacturers do so.

So before purchasing or even comparing solar powered water heaters, see to it that the manufacturer has both applied for, as well as received, certification and performance ratings for their system designs and solar hot water panels.

Solar collector certification program

The SRCC randomly selects a sample collector, or panel, from the manufacturer's production line. Testing is then preformed by an independent lab to evaluate the collectors' solar thermal output.

The solar thermal output is essentially the amount of energy, or heat, a water heating panel can be expected to produce on a daily basis under several different conditions and applications.

There are two types of solar hot water panels tested; flat plate collectors and evacuated tube collectors. Solar thermal output can be determined by several factors. These solar hot water panel specifications should be understood before consumers or installers compare collectors.

OG - 100 Certification Listings

The solar panel and collector certification program is commonly referred to as the SRCC OG - 100 listings. The SRCC constantly updates the listing of certified and rated flat plate collectors, evacuated tube collectors as well as unglazed flat plat collectors, which are used for solar pool heating.

System and design certification program

The SRCC's solar domestic water heater design and system certification program takes into account the results of the panel or collector test. Design wide tests are conducted to evaluate both the performance and efficiency of the entire hot water heater. Additional test are conducted to ensure the overall safety and reliability of the system as well.

OG - 300 Certification Listings

The solar powered water heater design and system certification program is often referred to as the SRCC OG - 300 listings. In order for the manufactures' system to be rated and listed a design and installation review, and a computer performance evaluation must be preformed.

It's important to note that in passive solar water heater designs, the collector and storage is integrated. So these collectors, as well as system designs, are certified and rated as whole systems and can be found in the OG - 300 listings. 

Design and Installation Review

Manufactures provide the SRCC their solar domestic water heater designs for an independent review. The review mainly evaluates the systems safety and reviews it's maintenance and installation specifications.

The manufacturer ultimately determines which components are in the design but the panel or collector must be tested and rated with the OG - 100 program before hand in order for the solar powered design to be reviewed. The SRCC determines whether the design can be safely and efficiently applied. 

The SRCC firmly believes that the solar hot water heater design and installation review encourages all the participating manufactures to produce the most safety oriented systems as possible.

Computer Performance Evaluation

Once the results from both the collector test and the design review are complete, computer performance tests are conducted. The laboratory tests are designed to simulate real world conditions. When all the results are certified, there are several performance ratings provided for the solar domestic water heater.

Annual System Performance Listings

The SRCC annual system performance listings provides the most comprehensive performance and rating specifications for previously certified solar powered water heaters. The listing is constantly updated and allows consumers and installers to factor in regional climate when comparing whole systems and designs.

More on solar hot water heaters


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