Page 124 - Design of Solar Thermal Power Plants

110 2. THE SOLAR RESOURCE AND METEOROLOGICAL PARAMETERS

The global radiation meter shall be inspected and serviced at least once
in the morning and once in the afternoon:

1. Determine whether the instrument is level and whether the sensing
surface and glazed shield are intact.
2. Determine whether the instrument is clean. If any dust, frost, mist,
snow, or rain falls onto the glazed shield, it shall be completely
cleaned in a timely manner using a lens brush or a chamois leather
rag, mainly focusing on not scratching or abrading the glass.
3. The glazed shield shall be kept away from water; there shall be no
vapor condensate inside the shield. When inspecting whether the
silica gel in the dryer has been dampened (changing from blue to red
or white), the dampened silica gel shall be replaced in a timely
manner and can be reused after baking in an oven until the color
turns back to blue.
4. A global radiation meter has excellent waterproof performance.
When used for a short period or under limited precipitation, the
instrument may be uncovered. However, once there is heavy rain
(snow, hail, etc.), rainfall, or snowfall for a long period, to protect the
instrument the observer shall close the cover in a timely manner
based on specific circumstances and open the cover once the rain
stops.
In the event of strong thunderstorms or other adverse weather, the
cover shall be closed and patrol shall be intensified; when problems are
discovered, they shall be handled in time. As the global radiation meter is
applied outdoors, it must be qualified through a verification certificate
issued by the measuring department before application. Normally, the
verification period is 2 years.

2.9.2 Solar Direct Normal Irradiance Meter
1. The structure and constitution of the instrument (pyrheliometer)
consists of the solar position tracker, solar radiation sensing
element, solar radiation collimated light tube and sighting device as
well as the connector socket and incoming light protective shield.
The sensing element consists of a sensing surface and thermopile.
When the sensing surface receives solar radiation, the thermopile
produces thermoelectromotive force in proportion to the received
radiation.
Performance indices:
Response time (95% response) < 20 s
2
Allowable range of sensitivity: 7e14 mVm /W
Zero offset (response to ambient air temperature variation of 5 K/h):
2
4 W/m .
Annual stability: 1.0%
Temperature response (with an interval of 50K): 2%
Nonlinearity: 0.5%