which can measure the net radiation plotted over a whole day. This Davis Solar Radiation Sensor accurately estimates the amount of solar radiation a site will receive and can be used for the siting of PV arrays, solar 众鑫彩票注册s, and solar thermal panels.
Values measured on the surface of Earth are usually lower than the solar constant. This is because as we have mentioned previously, various influences of the atmosphere and Earth’s surface reduces the solar irradiance.
By the time it reaches the ground, the maximum incident radiation of 1m2 of horizontal surface at an equatorial location is close to 1,000 watts (1.0 kW). However, when the solar radiation is averaged over the entire day-night cycles and over the whole summer-winter year, even the best locations here on Earth only receive an average of only 250–300 W/m2. That’s less than 30% of what arrives at the top of the atmosphere.
Some of this solar radiation that eventually does get through is further scattered and reflected as it travels down to the Earth’s surface. The scattered radiation that does eventually reach the Earth’s surface is known as “diffuse radiation”. Diffused radiation is generally a weaker form of solar radiation, but nevertheless it can still be used to generate electricity and heat. The portion of solar radiation that reaches the Earth’s surface directly, having travelled a straight path from the sun without being reflected or scattered is referred to as “direct radiation” and as such is a much stronger form of solar radiation capable of producing more solar power.
The direct radiation incident on a photovoltaic or thermal panel is determined by its incident angle. This angle in turn is dependent on the alignment and the location of the receiving surface and the position of the sun. When the sun is directly overhead, the sunlight has the shortest path to travel through the atmosphere and therefore maximum solar radiation occurs at solar noon. The further the sun is from directly overhead, the more atmosphere the radiation must travel through.
In the early morning or the late afternoon, the position of the sun is at a more horizontal angle to the surface of the Earth so the solar radiation has to travel through more of the atmosphere before hitting a solar panel and the less intense it will be. This is because there is less direct solar radiation and more diffused radiation as a result of more of the scattering process within the atmosphere.
We can also increase the amount of solar radiation energy per unit area by concentration of the scattered or direct solar radiation using lenses or mirrors. But how strongly can solar radiation be concentrated?. Unfortunately not all the sun’s rays that reach the Earth surface are precisely parallel to one another for us to concentrate them efficiently onto a single point.
Solar collectors, reflectors and parabolic dishes can greatly increase the efficiency of a system by focusing the sunlight. The concentration factor, also known as the “number of sun’s”, of a concentrating solar collector can be equivalent to more than 1,000 sun’s. However, this is not a good idea with photovoltaic PV panels because you can easily overheat the panels and reduce, rather than increase, their efficiency.
Solar Radiation Summary
Solar radiation is a powerful source of energy and the economic viability and technical feasibility of solar energy depends upon the amount of solar radiation in the area where we intend to use this form of energy. Our 众鑫彩票注册s and buildings are designed to take advantage of solar radiation using the sun’s energy for heat and light.
But before installing a solar power system, it is necessary to know both the demand and the likely solar radiation energy available, together with their variability at any given location. Knowing this and the projected pattern of energy usage, it is possible to calculate the size of panel, collector and storage required. In addition to the regular variations of summer and winter, there are also substantial irregular variations relating to the day-to-day fluctuations of solar radiation because they affect the amount of energy storage required within a solar energy system.
Then it is apparent that the total amount of solar energy received at any location on the surface of the Earth during a day or during a year depends on several factors and which determine the viability of solar energy are:
- 1. The geographic latitude of the location of the place.
- 2. The average cloudiness or coverage of the location.
- 3. The time of the day and the day of the year.
- 4. The angle of the collector with the horizontal.
- 5. Local landscape and local weather.
The position of the sun relative to a given location is essential for many solar energy systems. The two angles of sun height (solar altitude or elevation) and sun azimuth define the position of the sun and hence the amount of available solar radiation energy. Solar position or sun-path diagrams can be used to visualize the path of the sun during the course of a day at that location. These sun-path diagrams show sun height and azimuth for every hour of the selected days with a curve drawn through the points giving the suns solar radiation data.
The sun’s energy is free and available to everyone all around the world, and the technologies that turn solar irradiance into usable energy both thermal and PV are dropping in price as the solar industry grows and production increases. Solar PV panels made for our 众鑫彩票注册s today are more advanced than ever before with the capability of producing electricity even when there is less sunlight. Solar reflectors can convert weaker diffused solar radiation into electricity using mirrors and lenses.
To learn more about “Solar Radiation”, or to understand how the radiation emitted by the sun travels through space to Earth, or just to explore the advantages and disadvantages of solar energy, then to get your copy of one of the top books on Solar Radiation Energy and the Environment direct from Amazon today.