Solar Energy Background defining renewable what does renewable

Solar Energy Background

defining renewable what does “renewable energy” really mean?

renewable energy is… • Energy that comes from resources that replenish themselves in a relatively short time frame • Practically inexhaustible • Not derived from fossil fuels … So who can name an example?

common resources and technologies Sun • Greenhouses • Water Heating • Photovoltaics Wind • Turbines • Mills • Sailing Geothermal • Heating • Electricity • Bathing Hydropower • Electric Dams • Micro-Hydro • Water Wheels

solar energy that comes from the sun

how we use it Passive Solar: The capture and use of sunlight without active controls. Examples include: • • Solar cooking Building design Greenhouses Solar water heating

how we use it Active Solar: The capture and use of sunlight using an electrical or mechanized system. Examples include: • Photovoltaics • Active solar water heating

Active Solar

assessing solar resource Quantifying our access to energy from the sun

measuring the sun’s energy Irradiance: The amount of power received from the sun over a given area of earth • Typically measured in Watts per Square-Meter Cumulative Irradiance (or Insolation): The amount of energy that hits an area over a certain period of time • Typically measured in Watt-Hours per Square-Meter

what impacts the amount of sun we receive? Any ideas? • • • Time of day Time of year Position on the globe Weather Shading

the sun’s path

incident angle

incident angle When we talk about “incident angle” here, we mean the angle between “straight on” and the actual angle of the sunlight striking the Earth. The greater the incident angle, the lower the sun is in the sky and the lower the intensity of the light as it strikes the Earth. So, the lower the sun in the sky, the lower the irradiance.

flashlight analogy Imagine shining a flashlight straight down on a piece of paper. You would get a small, bright circle. If you then tilt the flashlight you will get an elongated, less bright circle of light. Therefore, the larger the incident angle of the flashlight —or of the sun—away from perpendicular, the less intense the light will be.

effects of atmosphere Additionally, the lower the angle of the sun in the sky, the more atmosphere the sun’s rays must pass through to reach earth and therefore the less energy those rays have when they reach earth.

shading

using the data exploration center • Go to www. solar 4 rschools. org/explore-data • Select the “Gladstone High School” project from the drop down list • Select “Irradiance” and “Insolation” from the variable list • Pick a date range • Generate your graph! • Play around with other projects, variables or dates

solar resource map

talking about electricity

terms and definitions Voltage (V)—Measured in Volts, voltage is the work required to move a unit of charge between two points against an electric field Current (I)—Measured in Amps, current is the amount of electrical charge transferred per unit of time Resistance (R)—Measured in Ohms, resistance is the amount of opposition to the passage of an electrical current Voltage = Current x Resistance [V = I R] Power = Voltage x Current [P = I V]

a radio, for instance • If a radio requires two 1. 5 -Volt batteries (a total of 3 -Volts) and draws 3 -Watts of power, how much current does it need to operate? • P=Ix. V • 3 Watts = I x (3 -Volts) • I = 1 Amp

terms and definitions (continued) Alternating Current (AC): An electrical current which periodically reverses direction • Our electrical grid operates on AC electricity Direct Current (DC): An electrical current which moves in a single direction • Batteries and photovoltaic (solar-electric) cells both produce DC electricity

the photovoltaic effect

photovoltaic effect Definition: The creation of a voltage (or of a corresponding current) in a material when it’s put into light. • Exposure to light generates a voltage that produces a continuous current flow, which is proportional to the quantity of light that strikes the photovoltaic surface. So how does it work?

construction of a PV cell • The photovoltaic (PV) cell is the building block of the solar module • The cell is comprised of two layers—a positive layer and a negative layer—which come together to form a p-n junction

construction of a PV cell

operation of a PV cell • When sunlight—in the form of photons—strikes a cell it creates pairs of negatively and positively charged particles known as electron-hole pairs. • The electrons travel to the top of the negativelycharged later.

operation of a PV cell

how a PV cell works The electrons flow through the wires, creating a direct current of electricity. Finally, they flow through the circuit and meet back up with the holes on the bottom of the cell. Then the process can start all over again.

how a PV cell works

photovoltaic technology putting the pieces together

cell => module => array

the photovoltaic array design considerations to maximize energy performance

maximize solar access Find an unshaded location—When deciding where to put a photovoltaic system, the first step is to take readings on site to determine how much shade different possible locations will receive. Determine how to angle your PV modules—Since most PV systems don’t move to track the Sun, it’s important to determine how best to tilt and orient the array so that it will get as much direct sunlight as possible over the course of the year.

tilt and orientation factor (TOF)

design your system http: //www 1. solmetric. com/cgi/insolation_lookup/go. cgi http: //gisatnrel. gov/PVWatts_Viewer/index. html

the photovoltaic system

PV system components • Photovoltaic Array: Generates direct current electricity when exposed to sunlight • Inverter: Converts the direct current electricity into alternating current electricity so that it’s compatible with the energy in our electrical system • AC & DC Disconnects: Provide protection for maintenance purposes

PV system components • AC Panel: Where the PV system connects to a facility’s electrical system • Net Meter: Tracks any energy that the system sends back to the grid • Electric Utility Grid: The larger electrical system that provides energy to the community