GC: n

CT: Use the solar energy factor (SEF) and solar fraction (SF) to determine a solar water heater’s energy efficiency.
The solar energy factor is defined as the energy delivered by the system divided by the electrical or gas energy put into the system. The higher the number, the more energy efficient. Solar energy factors range from 1.0 to 11. Systems with solar energy factors of 2 or 3 are the most common.
Another solar water heater performance metric is the solar fraction. The solar fraction is the portion of the total conventional hot water heating load (delivered energy and tank standby losses). The higher the solar fraction, the greater the solar contribution to water heating, which reduces the energy required by the backup water heater. The solar fraction varies from 0 to 1.0. Typical solar factors are 0.5–0.75.
Don’t choose a solar water heating system based solely on its energy efficiency. When selecting a solar water heater, it’s also important to consider size and overall cost.

S: http://energy.gov/energysaver/articles/estimating-cost-and-energy-efficiency-solar-water-heater (last access: 18 December 2014)

N: 1. solar (adj): mid-15c., “pertaining to the sun,” from Latin solaris “of the sun,” from sol “sun”. Meaning “living room on an upper story” is from Old English, from Latin solarium. Old English had sunlic “solar.”
Astrological sense from 1620s. Meaning “operated by means of the sun” is from 1740; solar power is attested from 1915, solar cell from 1955, solar panel from 1964. Solar system is attested from c.1704; solar wind is from 1958.
fraction (n): late 14c., originally in the mathematical sense, from Anglo-French fraccioun (Old French fraccion, 12c., “breaking”) and directly from Late Latin fractionem (nominative fractio) “a breaking,” especially into pieces, noun of action from past participle stem of Latin frangere “to break,” from PIE root bhreg- “to break”.
2. energy supplied by the solar part of a system divided by the total system load.
3. One may determine two dimensionless values, x and y. Using these values as the coordinates on the “f” chart, the designer may determine the solar fraction.

S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=solar&searchmode=none; http://www.etymonline.com/index.php?allowed_in_frame=0&search=fraction&searchmode=none (last access: 18 December 2014). 2. IATE; https://www.iso.org/obp/ui/ (last access: 18 December 2014). 3. TERMIUMPLUS.

SYN:
S:

CR: solar energy, [thermal solar captor], [thermal solar energy].