| 1. |
The basic principle of solar water heating is intuitive and straightforward. A dark surface is positioned to absorb sunlight and convert it to heat. Water or another heat transfer fluid passes along that hot surface to pick up the heat either for direct use or for transfer through a heat exchanger to the end use. |
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True |
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False |
| 2. |
More than a million solar water heaters have been installed in the United States. Most of these were installed during the 1980s, when tax credits were available, and nearly all use “flat-plate” collectors, which essentially place the absorber surface inside an insulated box. (See Figures 1 and 2.) |
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True |
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False |
| 3. |
Figure 3 is a: |
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Flat-plate collector |
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Parabolic- trough collector |
| 4. |
Parabolic-trough solar water-heating systems carry solar water-heating technology a step further by concentrating the sunlight before it strikes the absorber. Mirrored surfaces curved in a parabolic shape linearly extended into a trough shape focus sunlight on an absorber tube running the length of the trough (Figure 3). A heat transfer fluid usually a solution of water and antifreeze is pumped around a loop through the absorber tube of the collector.
There it picks up heat and then goes to a heat exchanger where it either directly heats potable water or heats a thermal storage tank. (See Figure 4.) |
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True |
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False |
| 5. |
The figure in page 9, The power of the parabola, if the parabola is facing the sun, |
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the sunlight is concentrated at the focal point. |
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the sunlight is not concentrated at the focal point. |
| 6. |
In the above figure, the absorber tube of the collector, where the heat-transfer fluid runs through, is on the focal point to absorb the maximum heat. |
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True |
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False |
| 7. |
Figure-7 is a typical: |
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Parabolic-trough solar water heating system. |
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Flat plate solar water heating system |
| 8. |
Because they use only direct-beam sunlight, parabolic-trough systems require tracking systems to keep them focused toward the sun and are best suited to areas with high direct solar radiation. (See Figures 5 and 6). Most systems are oriented either east-west or north-south with single-axis tracking during the day. East-west orientation is better in winter and more constant throughout the year, while north-south orientation is better in summer and provides greater annual output. The systems are programmed to turn the collectors upside down at night or during high winds to reduce stress on the structure and help keep the mirrors clean. |
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True |
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False |
| 9. |
Codes and standards; Other than local building and plumbing codes, there are no special standards that parabolic-trough solar water-heating systems need to comply with. In certain jurisdictions, codes could require double-walled heat exchangers or nontoxic antifreeze, but the system design IST usually uses is already double-walled. IST prefers to use an ethylene glycol/water solution as the heat transfer fluid, but can easily substitute nontoxic propylene glycol. If a facility does not already have one, it might need to add a material safety data sheet for ethylene glycol. |
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True |
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False |
| 10. |
In Figure 12, simple connections to intake and outflow temperature gauges and an intake flow meter allow this Btu meter to quite accurately report how much energy has been delivered by a parabolic-trough collector system. |
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True |
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False |
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