Solar is universal and will work virtually anywhere, however some locations are better than others. In PV system design it is essential to know the amount of sunlight available at a particular location at a given time.
The three fundamental ways of determining if enough solar power is available in your region:
- Determining the number of sunshine days in your region
- For instance if the no. of days of sunshine is more than 250, the region receives enough solar power to setup a plant. But if the days are relatively less, for instance less than 100 days, consultation with a specialist is advised as the solar power received is fairly lesser than most regions.
- Use of the solar radiation/insolation data estimated for the previous years
- Measuring the solar radiation/insolation for the region with instruments
The two common methods which characterise solar radiation are the solar irradiance (or radiation) and solar insolation.
Solar irradiance
- The solar radiance is a measure of the sun’s power available at the surface of the earth in units of kW/m2. The solar radiance varies throughout the day with a maximum of 1 kW/m2 The solar radiance is strongly dependant on location and local weather.
- With typical crystalline solar cell efficiencies around 14-16%, that means we can expect to generate about 140-160W/m2 of solar cells placed in full sun.
- The measurements are taken using either a pyranometer (measuring global radiation) and/or a pyrheliometer (measuring direct radiation). In well established locations, this data has been collected for more than twenty years.
Solar insolation
- The solar insolation is the total amount of solar energy received at a particular location during a specified time period, often in units of kWh/ (m2 day).
- While the irradiance denotes the instantaneous rate in which power is delivered to a surface, the insolation denotes the cumulative sum of all the energy striking the surface for a specified time interval. Solar insolation data is commonly used for simple PV system design while solar radiance is used in more complicated PV system performance which calculates the system performance at each point in the day.
- The term “peak sun hours” refers to the solar insolation which a particular location would receive if the sun were shining at its maximum value for a certain number of hours. Since the peak solar radiation is 1 kW/m2, the number of peak sun hours is numerically identical to the average daily solar insolation. For example, a location that receives 8 kWh/ m2 per day can be said to have received 8 hours of sun per day at 1 kW/m2.
- Being able to calculate the peak sun hours is useful because PV modules are often rated at an input rating of 1kW/m2.
In short, solar radiation for a particular location can be given in several ways including:
- Typical mean year data for a particular location
- Average daily, monthly or yearly solar insolation for a given location
- Global isoflux contours either for a full year, a quarter year or a particular month
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