Design, Install &Commission grid connected photovoltaic power systems

Design, Install &Commission grid connected photovoltaic power systems Session 2 Solar Radiation J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Note that this is a composite image, for comparison of sizes. The Earth is actually 150 million kilometers (93 million miles) from the Sun - which is why the Sun looks rather smaller to us (further away) than it appears in this picture. Photo courtesy SOHO, the Solar and Helioscopic Observatory J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Courtesy Johnson window film • Sunlight • The intensity of sunlight is called irradiance, ( also known as insolation).& for PV systems the units are watts per square meter (W/m2). • A square meter is about 11 square feet. A typical, clear sky, • solar-noon value of irradiance falling on the surface of the • earth at sea level is 1,000 W/m2. J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems • solar energy. • 99% of Solar Energy is between 200 and 4000 nanometers in wavelength. • almost all of solar energy is light and heat • Depending on what wavelengths are agreed upon as “visible light” (between 380 and 750 nanometers) about 44% of the sun’s energy is in our visible light range. • About 6-7% is in the ultra-violet (ultra = beyond; "beyond"-violet) range. Most of this is shielded by the ozone layer (which appears to be slowly recovering). • The rest (just over 50%) we call near infra-red (infra = below; "below"-red). We perceive infra-red radiation as heat. It is the trapping of infra-red radiation going back out into space which is the main cause of global warming J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems • about 1370 W/m2 of sun power reaches the Earth’ atmosphere • about 30% is reflected back to space, mostly by clouds. • about 70% is absorbed by Earth's surface and atmosphere and is then re-radiated in the form of thermal radiation. • this interaction keeps the Earth in radiative balance, as required by basic physical laws, and maintains the Earth's average surface temperature at about 16°C. J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Solar constant • at Earth's distance from the sun, an average power of about 1370 W/m2 (1.366 kilowatts per square metrekW/m²) reaches the top of the Earth/atmosphere system. • actual direct solar irradiance (measured by satellite) fluctuates by about 6.9% during a year (from 1.412 kW/m² in early January to 1.321 kW/m² in early July) due to the Earth's varying distance from the Sun J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems • in many areas, the time period that the irradiance exceeds 1,000 W/m2 can be three hours or more. (This has an impact on the electrical design of the system) peak value at sea level nominal value courtesy J Wiles http://www.nmsu.edu/~tdi/pdf-resources/cc101.pdf • one of the standard test conditions (STC) value of irradiance (1,000 W/m2)is factors used to rate PV module and PV array output. J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems National Earth Science Teachers Association (NESTA) J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems pyranometers (from the Greek "pyr" (fire) and "ano" (sky). The "pyranometer" is basically a flat plate (covered with a transparent dome) that is coated with an extremely absorptive surface. As the sun strikes it, the surface gets hot. The temperature of the surface is measured with a thermopile, giving an output voltage related to the amount of solar radiation striking the surface. E Instruments International http://www.e-inst.com/images/hvac/mainSolarRadiation J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems • Geometric Effects Latitude, time of day and season all affect the amount of energy impinging on a surface laid flat on the earth's surface. • imagine a flat plate collector having an area, A, of 1 m2 tilted at an angle, β, from the horizontal and faces the sun perpendicularly. • at a time, of say 0900 hours, there are 12 rays of the sun's beam coming from an altitude angle, γ, (or incidence) that strikes the collector at this position. • however, if the collector is laid horizontally on the Earth's surface, i.e. at angle β = 0 from the horizontal, the collector only captures 9 rays. J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Max capture of solar radiation at solar noon Collector A receiving all 12 rays • it then becomes apparent that if the sun is overhead and the collector is laid flat on the horizontal, it will capture all of the sun's rays as shown J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Placement of solar module in relation to Sun’s altitude ( at Solar noon) Graphic courtesy GSES • to obtain maximum irradiance solar module must always face the sun • ideally, the solar module should be tilted (β deg) to the horizontal facing north • such that that there is a 90° angle between the sun ( at solar noon) and the module J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems • Question: If the altitude of the sun was 67°, and one wanted to tilt a solar module directly at it, what would the tilt angle be? J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems • answer: If the altitude of the sun was 67°, and one wanted to tilt a solar module directly at it, what would the tilt angle be? 180° - 90° - 67° = 23° from the horizontal (ground) In a straight line there is 180°, to get the most sunlight on the module it needs to be perpendicular to the sun; i.e. we need to have 90° between the sun and module J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems • Solar noon is the time of day when the sun is at its highest altitude • in Australia between 11 .00 to 13:00 Hrs • In the northern hemisphere modules best positioned facing due South, Southern hemisphere facing North • Optimum tilt angle is generally latitude plus 5° to 15 ° but is dependent on the exact location • The amount of solar radiation falling on a tilted plane for Sydney is shown in the following table J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Altitude and azimuth angles • the location of the Sun is specified by two angles • solar altitude (γ) angle is the angle between the sun’s rays and the horizontal plane • solar azimuth (ά) is the angle between the projections of the sun’s rays on a horizontal plane and the north direction. • Azimuth is measured clockwise going from 0 (true north) to 359°. • East is 90°;South 180°and West 27° J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems The sun path diagram used to determine the position of the sun in the sky any time of day, any day of the year • Azimuth angles, shown on the circumference of the diagram • Altitude angles presented, by concentric circulars • Sun path lines from east to west for different dates of the year • Time of lines cross the sun path lines • Location information that refers to latitude J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Sun path diagram for latitude 32°south (sydney) http:www.squ1.com/archive/index.php? http:www.squ1.com/archive/solar/solar-position.html J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems http:www.learn.londonmet.au.uk/packages/clear/index.html) J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Magnetic North & True North A compass needle points to magnetic north, which is defined by the direction of the horizontal component of the geomagnetic field (H). The geomagnetic declination (D), sometimes called variation, is the angle between true north and magnetic north • Solar modules must be inline with true north to optimise maximum performance • e.g. Sydney , the magnetic deviation is approximately 13° East. • Simply this means True North is approximately 13 ° west of magnetic north True north Magnetic deviation Magnetic north West East J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Atmospheric effects Large faction of solar radiation reaching top of earth’s atmosphere is reflected i.e. known as ‘albedo’ The sun Solar radiation at top atmosphere Go = 1367W/m² Diffuse solar radiation Reflected solar radiation(albedo) from atmosphere Reflected solar radiation Solar radiation at sea level G = 1000 W/m² J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Atmospheric effects continued • Radiation reaching the earth's atmosphere is composed of direct and diffused radiation • Diffused though not as intense as direct radiation can still heat for solar collectors and energy for solar cell • Radiation reaching earth’s surface has a different spectral content compared to radiation out the earth’s atmosphere • Water and Co2 in the atmosphere absorb some wavelength bands • relative distance that radiation must travel through the atmosphere to reach a given location is the AIR mass J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Air Mass Θ is the angle between sun and the line to a point directly overhead AM = 1/cosθ • Outside earth’s atmosphere AM = O (AMO) • AMI corresponds to the sun being directly overhead • The standard condition for solar modules is AM1.5@1 kW/m² irraiance at a cell temperature 25° • Cell temperature is normally greater than the ambient temperature J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Irradiation & Peak Sun Hours Irradiation is the total quantity of radiant solar energy per unit over given period i.e. daily, monthly annually SI unit for energy is the joule courtesy :apricus.com The joule is a very small unit solar radiation is often expressed in mega joule (MJ) J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Irradiation & Peak Sun Hours cont….. • Irradiance is a measure of the rate of energy received per unit area, and has units of Watts per square metre (W/m2), where 1 Watt (W) is equal to 1 Joule (J) per second. • e.g. If the solar radiation on a horizontal surface for a whole day is 25 MJ/m² and we want to work out the number of hours for which radiation at the rate 1000 W/m² is gained for a day, we need to convert MJ to kWh • The joule is a watt second • 1 kWh= 60 seconds x 60 minutes =3600 joules • 25 x 106 ÷ 3600 x103 = 6.94kWh/m² • Daily radiation commonly referred to as peak sun hours (PSH) J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems The number of PSH for a day is the number of hours for which energy at the rate of 1kW/m² is received on the installation To convert MJ/m² to peak sun hours first divide the number of MJ/m² by 3.6 J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems question Peak Sun Hours The total daily energy received on the roof of a house for a grid-connect installation is 26.3MJ/m2. What is the number of peak sun hours (PSH) at the site? Round to one decimal place. J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems answer Peak Sun Hours The total daily energy received on the roof of a house for a grid-connect installation is 26.3MJ/m2. What is the number of peak sun hours (PSH) at the site? Round to one decimal place. The correct answer is 7.37 peak sun hours J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Solar Radiation for the area where you are designing may be obtained from : ‘Australian Solar Radiation Handbook’ J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Solar irradiation map of Australia Source : courtesy of Bureau of Meteorology website: http://born.gov.au/cgi-bin/climare/cgi_bin_scripts/solar-radiation.cgi J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Solar irradiation J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Solar Altitude • As a result of earth’s rotation around the sun • The sun moves between the Tropic of Cancer(23.45°N) Northern Hemisphere & • Tropic of Capricorn (23.45°S) Southern Hemisphere • When the sun is over either two tropics is known as the solstice • When the sun is over the equator equinox • Sun reaches Tropic of Cancer at northern solstice (June 22nd • Tropic of Capricorn at the southern solstice December 22nd • The sun crosses the equator at the equinoxes in March 21st and September 23rd J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Solar altitude The formula for calculating the altitude (γe) of the sun when it is over the equator γ e = 90°- latitude (in degrees)γ The formula for calculation the altitude γt Of the sun when it is over the tropics (Cancer & Capricorn) γ t = 90°- latitude (in degrees) ±23.45°γ Whether you use ( + or –) depends on the hemisphere (Nor S) and over which tropic you want to determine the sun’s altitude NB:It is assuming you facing the equator i.e. facing north in the southern hemisphere J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Solar altitude for Darwin at Equinox & Solstices Example Darwin is 12.46°S. Therefore the altitude of the sun when it is over the two tropics and the equator are as follows: Equator (March 21st and September 23rd) γ e = 90°- latitude (in degrees) = 90°-12.46°=77.54° Tropic of Cancer (June 22nd) γ t = 90°- latitude (in degrees) -23.45° = 90°-12.46°- 23.45°= 54.09° Tropic of Capricorn( December 22nd) γ t = 90°- latitude (in degrees) + 23.45° = 90°-12.46° +23.45°= 109.99° NB: The altitude of the sun (respect to facing south) could also be expressed as 79.01 °i.e. (180 °- 100.99 °) J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems For Sydney the sun will never be directly overhead From March29th to September 14th the sun will be in a northern direction You will need to look for potential obstacles that could cause shading J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems This table provides altitude at the two equinoxes and also indicates when the sun is in the northern sky with respect to the latitude. This may assist locating possible obstacles that will shade the installation PV module. J.P. Teasel version 06/12/10

Session 2 Question 1 formative in class Tilted Surface If the sun's rays are impinging vertically on a plane flat on the earth's surface at 1kW/m2, what the effect of tilting that surface to an angle of 60° to the horizontal? The output from the panel would increase The output from the panel would decrease The output of the panel would stay the same None of the aboveYou answered The output from the panel would decrease When the panel is tilted, the effect surface area that the rays are hitting is less. Therefore the output from the panel will decrease, as it is receiving less solar radiation. You can see this effect by using a book and a lamp. Set the lamp up so that the light is pointing directly down onto a flat surface (i.e. table or desk). The light source needs to be perpendicular to the surface (at 90° to each other). Hold the book flat directly under the lamp so that you can see the shadow it creates. Tilt the book at different angles to the lamp and note the effect of tilting the book has on the shadow size. The smaller the shadow, the less solar radiation that is hitting your book. The largest shadow is created when the book is at 90° to the light source J.P. Teasel version 06/12/10

Session 2 Question 2 formative in class Altitude and Azimuth What do the terms altitude and azimuth mean? altitude: angle between projection of the sun's rays and the horizontal plane azimuth: is the angle between the projection of the sun's rays on a horizontal plane and the north direction. A 360 degree bearing, e.g. where East is 90 degree, West is 270 degree, South is 180 degree and North 0 degree.Briefly :Altitude is the angle between the suns' rays and the horizontal. Azimuth is the angle between the sun and north. J.P. Teasel version 06/12/10

Session 2 Question 3 formative in class Irradiance and Irradiation Units What are the units for irradiance and irradiation? kWh/m2 and kW/m2 respectively kWh/m2 and MJ/m2 respectively MJ/m2 and kWh/m2 respectively MJ/m2 and kW/m2 respectively kW/m2 and kWh/m2 respectively kW/m2 and kWh/m2 respectivelyIrradiance measures power per unit area and irradiation measures energy per unit area, so therefore Irradiance is measured in W/m2 or kW/m2 Irradiation is measured in MJ/m2 or kWh/m2 So the correct answer is kW/m2 and kWh/m2 respectively J.P. Teasel version 06/12/10

Session 2 Question 4 formative in class Irradiance and Irradiation Units What are the units for irradiance and irradiation? kWh/m2 and kW/m2 respectively kWh/m2 and MJ/m2 respectively MJ/m2 and kWh/m2 respectively MJ/m2 and kW/m2 respectively kW/m2 and kWh/m2 respectively kW/m2 and kWh/m2 respectivelyIrradiance measures power per unit area and irradiation measures energy per unit area, so therefore Irradiance is measured in W/m2 or kW/m2 Irradiation is measured in MJ/m2 or kWh/m2 So the correct answer is kW/m2 and kWh/m2 respectively. J.P. Teasel version 06/12/10

Session 2 Question 5 formative in class J.P. Teasel version 06/12/10

Session 2 Question 6 formative in class Solar Radiation Categories What are the categories of solar radiation that reach the Earth's surface? Direct, diffuse and albedo Direct and albedo Direct and diffuse Diffuse and albedo Direct and diffuse Direct radiation is the radiation that reaches the earth's surface directly from the sun; i.e. it is a direct "beam" of light, it has not been reflected off anything. Diffuse radiation has been scattered via clouds, objects or particles in the atmosphere, but still manages to reach the earth's surface. It is generally not as intense as direct radiation. Albedo is the radiation that is reflected off the top of the earth's atmosphere and does not reach the earth's surface. The correct answer is direct and diffuse (radiation). J.P. Teasel version 06/12/10

Session question 7 formative in class J.P. Teasel version 06/12/10

Session 2 question formative in class J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems Take home Questions Session 2 Approximately, what is the peak value for irradiance on the earths surface? If the sun’s rays was falling vertically on a plane flat on the surface of the earth, what would the effect if the plane was tilted 60° to the horizontal? Define the two angles that are used to specify the sun’s position in the sky If a plane was laying flat on the earth’s surface, at what angle would the sun’s rays impinge on that plane at 15:00 Hrs on 22nd December (22ndJune) at Darwin J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems 5. Define the following terms: solar constant; irradiance; irradiation; air mass peak sun hour 6. What factors effect the amount of solar radiation reaching the earth’s surface 7. Name the categories of solar radiation reaching the surface of the earth. 8. explain why it is important to have the surface of a flat plate of the Earth at sea level 9. What is the reference condition used for air mass when rating solar cells J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems 10. What would be the number of peak sun hour days if the profile of the power from the sun was as follows? Hint Work out the total energy for the day in kWh/m² J.P. Teasel version 06/12/10

Design, Install &Commission grid connected photovoltaic power systems