Page 55 - Design of Solar Thermal Power Plants

48 2. THE SOLAR RESOURCE AND METEOROLOGICAL PARAMETERS

2. Harmlessness. Solar energy utilization has no waste residue, waste
materials, wastewater, waste gas emissions, noise, or the
production of other hazardous substances; it will not pollute or
harm the environment.
3. Long-lastingness. As long as the sun exists, there is solar radiation
energy. Thus solar energy has an inexhaustible supply and is
always available for use.
4. Enormousness. Solar energy is energy from inside the sun that is
produced through continuous nuclear fusion reactions. The solar
energy that Earth receives each second is equivalent to nearly
5 million tons of standard coal, which equates to 130 trillion tons of
standard coal per year and equates to more than 10,000 times the
world’s annual energy consumption at present.

2.1.2 Disadvantages of Solar Resource Utilization

1. Small energy density, namely small capacity density. During
midday on a clear day, at the spot on the ground perpendicular to
the direction of solar radiation, the received solar energy density is
2
about 1 kW/m . As a source of power, such energy density is
deemed quite low. Thus under high-temperature conditions, solar
energy utilization normally requires a set of solar energy collection
equipment of considerable size and covering a large land area while
featuring a significant amount of material, a complex structure, and
high costs. All of these have had a negative impact on solar energy
promotion and utilization.
2. Instability. Solar direct radiation energy that reaches a specific
ground area is extremely unstable due to weather and seasonal
factors, creating difficulty for large-scale utilization.
3. Discontinuity. The level of solar direct radiation energy reaching
the ground changes throughout the day and night; because of
this, most solar energy equipment cannot function at night. To
overcome the difficulties caused by solar direct radiation’s absence
at night, energy storage equipment must be developed and
equipped so that it can collect solar energy during clear days and
store it to be utilized at night or on rainy days.

2.2 THE SOLAR CONSTANT AND RADIATION
SPECTRUM

2.2.1 Solar Irradiation Expression
2
1. Solar irradiance (W/m ) is a physical parameter for describing the
degree of solar radiation, namely solar radiation energy in W/m 2
perpendicularly projected on a unit of area within a unit of time. It
is a parameter most commonly used for solar photovoltaics and
thermal utilization.