1. Each scientific field has a specific terminology. Atmospheric physicists often talk about "solar flux". In the solar world, the usual term is Global horizontal irradiance (GHI) if the receiver/sensor is horizontal or Global tilted irradiance (GTI) if not.

Irradiance refers to an "instantaneous" value (W/m2) whereas irradiation refers to a time-integrated value (Wh/m2 or J/m2). This reflects the distinction between power and energy.

2. Yes, irradiance can be measured with a variety of instruments collectively called radiometers: pyranometers and pyrheliometers, most importantly.

3. Yes; modern instruments are made to be installed permanently in the field. The only exception would be active cavity radiometers that have no protective window and are used to maintain the WRR at Davos and to perform high-end calibrations under laboratory conditions once in a while. For details, see

Technical Report Best Practices Handbook for the Collection and Use of Solar ...

“The total solar radiation on a horizontal surface is called global irradiance and is the sum of incident diffuse radiation plus the direct normal irradiance projected onto the horizontal surface.”

Extraterrestrial Radiation; “Solar radiation incident outside the earth's atmosphere is called extraterrestrial radiation. On average the extraterrestrial irradiance is 1361 Watts/meter2 (W/m2).”

Global, Beam, and Diffuse Irradiance; “Near noon on a day without clouds, about 25% of the solar radiation is scattered and absorbed as it passes through the atmosphere. Therefore about 1000 W/m2 of the incident solar radiation reaches the earth's surface without being significantly scattered. This radiation, coming from the direction of the sun, is called direct normal irradiance (or beam irradiance)." "Some of the scattered sunlight is scattered back into space and some of it also reaches the surface of the earth. The scattered radiation reaching the earth's surface is called diffuse radiation.”

Elhadi Ibrahim Dekam Thank you for suggesting to me. what is the impact of air mass for calculating Global solar irradiance?

I agree with Elhadi Ibrahim Dekam

summarized:

Radiation is the total solar radiation coming from sun,

Irradiation is a share of radiation that receive in earth surface. So, we can use Irradiation for simulations to calculate energy generation.

Dear Chhotelal Prajapati , you may go to one of the definition and application of "air mass", such as;

https://en.wikipedia.org › wiki › Air_mass_(solar_energy), Good Luck,,,

For air mass calculations, you may refer to;

https://www.esrl.noaa.gov › gmd › ozwv › dobson › papers › report13

Dear Chhotelal Prajapati :

I think I can help you with some of these terms.

1. "Solar Radiation" is a more correct term than "Global Solar Radiation".

The Solar Radiation is represented by a capital S, and has units of [W/m2]. It is the absorbed Solar Radiation per surface unit (it is a general term, a general definition in Solar Engineering).

1.1. The term "Global Irradiation" is wrong. There are two kind of Irradiations; "Daily Irradiation" an "Hourly Irradiation". These quantities are represeted by the letters H and I, respectively. and both are measured in [J/m2], so these are magnitudes of Energy per unit of Surface:

The "Daily Irradiation" (H) is the Irradiation recibed during a day by a squared meter of surface (is energy per unit of surface).

Otherwise, The "Hourly Irradiation" ( I ) is the same concept but for a period of time of an Hour. This last quantity: ( I ) is used in Solar Engineering as a averaged hourly rate

Both quantities still come from the physical concept of Solar Radiation (S), but meanwhile S is a concept of Power, I and H are concepts of Energy.

2. Now the concepts of "Irradiance" :

The general term of Irradiance is represented by the letter "G", and this quantity is measured in [W/m2] too.

The Irradiance, which is also called as "Global Solar Total Irradiance" when you bring the term to the practice in a particular problem in Solar Engineering is composed by the:

2.1. Direct Solar Irradiance (Gb)and

2.2. Difusse Solar Irradiance (Gd) , both also measured in [W/m2]

So, in a general definition: Gtot = Gb + Gd

but if you are get yo measure the the Direct Solar Irradiance measured in a direction normal to a given surface (Gbn). Then you can compute the Total Solar Irradiance by:

Gtot = Gd + Gbncos(theta)

There are two more terms: "Radiation Intensity" and "Radiosity",

But these two are more technical terms used in Radiation Heat Transfer between surfaces:

The "Radiation Intensity", represented by "I", measured in [J/m2], is a vector quantity, it is composed both of magnitud and a direction.

And the quantity "Radiosity" is measured in [W/m2]. This quantity is a representation of the Total Energy by Radiation Heat Transfer, per unit of time (this is the reason of the Watt unit inside the squared brakets), per unit of surface. But this quantity is just used to define the Heat Transfer Radiation between surfaces.

I don't know if you can get help from my masters' dissertation, since I have written it in Spanish. It is inside my "Research Items" on the "Thesis"category, under the title: "FLAT PLATE SOLAR COLLECTORS: ANALYSIS AND TEST METHODS". I have more information about these terms and definitions there, and about the physics of Solar Thermal Radiation and Radiative Heat Transfer in general.

If you feel fancy, try to give it a review, if you find something important for yourself I can try to translated it for you, or better explain it.

BTW, answering your last two questions:

2. In principle yes, if you have access to the required instruments, and access to an outdoors site where you can install these instruments.

The instrument needed to measure the "Total Global Hemisferical Irradiance" (Gtot) = Gd + Gbn is called a Pyranometer. Where Gd is the Solar Diffuse Irradiance and Gbn the Direct Solar Irradiance.

Then, you can measure the Direct Solar Irradiance (Gbn) with an instrument called Pyrheliometer, and then calculate the missing Gd from the formula I wrote in my comment posted above.

2.1. There is a second method to measure the Diffuse Solar Irradiance (Gd). If you do have acces to a Pyranometer but not to a Pyrheliometer :

You can measure the Total Solar Irradiance (Gtot) with the Pyranometer in normal use. Then, what you have to do is to install a "shadow" ring on your Pyranometer (as shown in the picture). With this accesory you will be able to measure just the Diffuse Irradiance, instead of measuring the Total one. Thing to mention: You will have to install a solar tracking device for this ring, at least than you were willing to follow manually the direct solar beams, and kepp on site all the time.

Also, it is important when you perform these measurements, to be sure you can do it on a well leveled flat surface.

3. Yes, either the Total Solar Irradiance (Gtot) or any of its two components can be measured in cloudy weathers. The important thing to consider here is the fraction of each component to the Total quantity, this depends closely on the kind of weather.

So, if you gonna do the measurements in a cloudy weather the Diffuse Irradiance will be a big fraction, probably more than the measured Direct Solar Irradiance. So in this case, It'll be important you can be sure you can get reliable measurements of the Diffuse Irradiance, and be able to have the required functioning instruments.

As a general comment, always is a good idea to compare your experimental data with a nearby (as nearby as possible) weather meteorological station.

Hope you can read additional information in my master's thesis .

Best Regards !

Uriel,

Franklin Uriel.. I am very grateful to you for giving such an essential knowledge and your valuable time. Yes, your desertation report is helpful to me. If you do not mind, can you share your research paper about this.

Franklin Uriel .. What do you think about tilt angle solar radiation and what is the role of clearness index and air mass?

Dear Chhotelal P. :

Im glad you have seen that dissertation useful.

I also would like to recomend you the book which I personally think is the best technical book for Solar Thermal Engineering, in case you can get access to it on the internet or at you University:

Solar Engineering of Thermal Processes from John A. Duffie & Beckman.

In this book you can find all the theory about Solar Energy and Solar Thermal Radiation along with many practical view points.

I'm sorry, since I was rushing up to get the last results to finish the Thesis I didn't have time to write a publication about my work in my masters.

But definitely this book is a great reference to the field.

About your questions:

about what you call as the "tilt angle's solar radiation" I 'll suppose you are talking about your surface's tilt angle.

If it's so, and If you are building your own tests set up to mount your experimental system, you would n't get a considerable error if you build your test surface at a tilt angle to be within: (the site's latitude + 15°), in winter, and (the site's latitude - 15°), for summer, this in the Northern Hemisphere, but the opposite for test systems being tested in the Southern Hemisphere. So if you are going to build your own tests system, be sur to build it to be able to modify the tilt of the tested surface.

But for testing of Solar Thermal Systems (e.g. Solar Collectors and Solar Concentrators), to have a Solar tracker is not needed, as long as you can mantain the Tilt Angle within the above mentioned values (in contrast with Photovoltaic Solar Systems, which in case you may need one).

However, there is a parameter which takes into account the effect of the sun motion along the sky (as you know this fact changes the Incidence's Angle), this is the Incidence's Angle Modifier, which in some Tests Standars you will find it as Ktaual*pha

To be honest, I don't know anything about the Clearness Index, and not much about the analysis of the Air Mass Ratio too. What I can say is; that for a latitute of 25° in the Northern Hemisphere I didn't see a great effect of the Air Mass Ratio on my measurements. But the book I mentioned has all these topics in greater detail, I hope you could find it.

Regards ! :)

Franklin Uriel Parás Hernández Yes you are right to say, I am talking about surface tilt angle, you are writing here (the site's latitude + 15 °), in winter, and (the site's latitude - 15 °), for summer, this in the Northern Hemisphere, yes This is a general methodology. I am read these things in the various research paper and many authors used this. but could you say that it will give true result because optimum angle its depends on declination angle and latitude angle and its very surface to the surface. If we find the correct value of the optimal tilt angle, then, we can get total solar radiation on the inclined surface.

Thank you so much. I am very happy with our conversation.

Dear Chhotelal :

Is true that you can improve the accuracy of your results -(what I'm not sure is as how much, since in experimental science we always need to consider the relation between cost-benefits)-

by controling the Angle of Incidence, which is function of the Tilt Angle of the surface. But, what you would need to do in this case is to get yourself a Solar Tracking for your tilted surface, and then built up a program with all the algorithms and equations required for this device to constantly compute the optimum Tilt Angle in function of the Declination, the Hourly Angle, the Azimuth & Zenith Angles, the Solar Noon, etc, etc... Not a straightforward task. I would say this could be separate part of a different masters Thesis, of course there's always the alternative of teamwork and get some help between projects :)

Either way, you can find all the requiered equations to program the required algorithms in the book of Duffie & Beckman.

Personally, I didn't do this on my masters Thesis since it wasn't the main interest of the project, and we were n't interested in getting involved with electronic and logical circuits design. But you can perfectly get into it and develop this tracker. MATLAB will be the best software to do this.

Best Regards ! :)

The relationship and definitions are as follows:

Solar Radiation is classified into two main parts, extraterrestrial solar radiation (Gextra), stands for the solar radiation above the atmosphere, and global solar irradiation (GT), is the solar under the atmosphere.

Direct Normal Irradiance (DNI)

Direct Normal Irradiance is also known as Direct Solar Radiation, is the amount of solar radiation received per unit area by a surface that is always held perpendicular (or normal) to the rays that come in a straight line from the direction of the sun at its current position in the sky. This represents the maximum possible beam radiation that is measurable. The monitoring equipment for DNI is the Pyrheliometer.

- Diffuse Horizontal Irradiance (DHI)

Diffuse Horizontal Irradiance which is also known as Diffuse Solar Radiation is not the radiation that is absorbed directly from the sun, however, it is defined as the radiation scattered by aerosols, dusts and particles. DHI is measured by a shading Pyranometer.

- Global Horizontal Irradiance (GHI)

Also known as Global Solar Radiation, it is the total amount of the direct and diffuse solar radiation as calculated using the following formula: GHI = DNI. Cos (Z) + DHI

Where: GHI = Global Horizontal Irradiance DNI = Direct Normal Irradiance DHI = Diffuse Horizontal Irradiance (Z) = Zenith Angle The GHI is measured by the total of direct and scattered radiation being received on a commonly horizontal surface

1. Each scientific field has a specific terminology. Atmospheric physicists often talk about "solar flux". In the solar world, the usual term is Global horizontal irradiance (GHI) if the receiver/sensor is horizontal or Global tilted irradiance (GTI) if not.

Irradiance refers to an "instantaneous" value (W/m2) whereas irradiation refers to a time-integrated value (Wh/m2 or J/m2). This reflects the distinction between power and energy.

2. Yes, irradiance can be measured with a variety of instruments collectively called radiometers: pyranometers and pyrheliometers, most importantly.

3. Yes; modern instruments are made to be installed permanently in the field. The only exception would be active cavity radiometers that have no protective window and are used to maintain the WRR at Davos and to perform high-end calibrations under laboratory conditions once in a while. For details, see

Technical Report Best Practices Handbook for the Collection and Use of Solar ...

In English there are 4 different terms, related to radiation:

- irradiance

- irradiation

- radiance

- radiation

The term Sky/Solar radiance is the radiant flux emitted by a sky area per unit solid angle per unit time [W/sr].

The term Sky/Solar irradiance is used to consider the solar power (instantaneous energy) falling on unit area per unit time [W/m2].

The term Solar irradiation is used to consider the amount of solar energy falling on unit area over a stated time interval [Wh/m2].

The term Solar radiation is the amount of solar energy falling on a surface over a stated time interval [Wh].

===

According your first question - both terms (Global Solar Radiation and Global Irradiation) could be correct, according the meaning you need to express.

The term Global Solar Irradiance (Direct irradiance+Diffuse irradiance+Reflected irradiance) is OK (and very widely used).

You received very good answers by Chris Gueymard of both other questions.

If you are more specific about the meaning in which you want to use the terms, we may be more helpful.

Best regards!

Hayder I. Mohammed

Regards: