New Age Tech Guru - Solar irradiance and its measurement

 

    Part of a series in renewal energy technologies brought by  M/s Paavi Solar

    

Friends, from the next blog onwards we are going to learn the designing part of Solar PV System. So in this blog, I want to focus on solar irradiance and its measurement as understanding this topic is extremely important for  proper design of the system. In one of the previous blogs, the irradiance curve was explained.  In radiometry, Irradiance is the power per unit area of incident electro-magnetic the radiation falling on a  surface and is measured in watts/m2. In photometry irradiance is known as the amount of light energy falling on a surface per second, weather directly or diffused or reflected, and is measured in watts/sq. mtrs. and denoted by E_e where subscript _e denote energy. Technically speaking it is the light (not heat ) of the Sun which is incident on a solar panel. In laboratory conditions, the irradiance of 1000 watt/sq.mtrs is chosen as test conditions. It is worthwhile to mention that irradiance varies seasonally as well as during the time of the day and hence to know the average irradiance, an irradiance map has been plotted taking into account historical data. Simultaneously placement of Solar panels also affects the amount of Solar radiation falling on the panel.

How much Solar Radiation is available in my area.

Solar irradiance maps based on historical data are available on a monthly average basis for the entire world on a location basis and are freely available on the internet. Also, design software carries an irradiance map as a tool and can generate irradiance data and angle of placement of solar PV panels for maximum radiation at the click of a button. We can easily differentiate between sunshine hours and usable irradiance based on these tools. While designing the system, this data is important for system sizing. Manually also one can measure solar radiation for different times and dates of a month for the location of the System.

 

How to measure Solar Radiation

Solar radiation is measured using an instrument called Pyranometer which has its name derived from the Greek word of “Pyr” meaning fire and “ano” meaning sky. It is a sensor-based instrument that measures solar radiation in Watt/m² and has a field of view of 180⁰. For the measurement of solar radiation, the directional factor is important and so the pyranometer needs to have a directional response to the incoming beam. Pyranometer measures only the light part of sun rays. For measuring the heat part we have pyrheliometers.                                                                               - G P BOSE