Solar Energy Systems

Energy Needs Today s global demand for energy is approximately 15 terawatts and is growing rapidly Much of the U.S. energy needs are now satisfied from petroleum (heating, cooling, transportation, etc.) Petroleum are finite resources and the resources are running out there is a strong need to turn to alternative energy systems that are sustainable

Solar Energy System Basics the sun is a powerful source of energy that can be used to heat, cool, and light our homes and businesses the sun is the most abundant, sustainable source of energy, providing over 150,000 terawatts of power to the Earth more energy from the sun falls on the earth in one hour than is used by everyone in the world in one year sun energy is free; the challenge is harnessing this power and using it for today s needs

Solar Power vs. Energy Power: the rate at which work is performed the amount of energy required or expended for a given unit of time units: 1 Watt = 1 joule per second (also horsepower) Energy: capacity of a physical system to perform work exists in several forms such as heat, kinetic or mechanical energy, light, potential energy, electrical, etc units: Watt-hour or kilowatt-hour (also joule)

basic rule of thumb: 1 meter 2 receives 1 kw of sun power

Example Solar Technologies a variety of technologies exist to convert sunlight to usable energy: solar water heating passive solar design for space heating and cooling solar photovoltaics for electricity concentrated solar power (solar thermal) for electricity

Solar Water Heating shallow water is usually warmer than the deep water two components: solar collector and a storage tank solar collector: small tubes run through the collector and carry a fluid (typically water) to be heated. The tubes are attached to an absorber plate, which is painted black to absorb the heat. As heat builds up in the collector, it heats the fluid passing through the tubes storage tank: insulated container active system: water is pumped passive system: gravity feed

Passive Solar Technology harness heat from the sun to warm our homes and businesses in winter south side of a building always receives the most sunlight: south-facing windows uses materials that absorb and store the sun s heat are built into the sunlit floors and walls summer: overhangs can be designed to shade windows when the sun is high in the summer

Solar Photovoltaic Devices directly turn sunlight (photons) into electricity discovered in 1954: silicon creates an electric charge when exposed to sunlight (Bell Laboratories) generally made from crystalline silicon, are usually flatplate, and generally are the most efficient 2 nd generation technology: thin film or amorphous silicon (less efficient but less costly) 3 rd generation technology: conductive plastics

Crystalline Silicon Devices Silicon has 14 electrons; 4 outer electrons can move between atoms photons hit the silicon, and release electrons from the atoms n-type and p-type Silicon: other atoms are introduced into the silicon structure to create an excess of electrons (n- Type) or a lack of electrons (p-type) a PV device has two layers to create a field where electrons can move between layers (n-layer and p-layer)

Crystalline Silicon Devices Efficiency: how much solar energy is converted into electrical energy Typical efficiencies: 12 20% for crystalline silicon multi-junction cells: pushing 40% efficiency (takes advantage of different wavelengths of light) cost is major issue: cost per Watt (~ $5/Watt)

Solar Cells solar cell typically produces only a small amount of power to produce more power, cells can be interconnected to form modules and arrays efficiency changes with intensity of light, angle of light, and temperature of the device tracking sun adds approximately 30% more energy capture

Amorphous Silicon Solar Cells (thin films) Advantages: thin-film cells are deposited in very thin, consecutive layers of atoms, molecules, or ions thin-films use much less material the cell s active area is usually only 1 to 10 micrometers thick, whereas thick films typically are 100 to 300 micrometers thick (lower cost) can usually be manufactured in a large-area process, which can be an automated, continuous production process (lower cost) thin films can be deposited on flexible substrate materials Disadvantages: lower efficiencies (~ 8-12%)

Superlattice structure for the high performance solar cell (UCR EE Balandin Laboratory)

hybrid polymer-carbon nanotube solar device (UCR EE Ozkan Laboratory)

Joint Research with Tohoku University (Sendai, Japan) new process to get to 20% efficient amorphous silicon solar cell

Concentrated Solar Power typically utilized in utility-scale power plants (>100 MW) advantage of relatively low cost energy storage which allows them to provide electricity even when the sun is not shining two operational components: they concentrate the sun s energy and convert it to heat they use the heat to drive some type of a heat engine/generator to produce electrical power three generic system architectures: line focus (trough and LFR) point focus central receiver systems (power tower) point focus distributed receiver systems (dish engines)

Trough-Electric Systems use parabolic trough concentrators to focus the sunlight onto a glass-encapsulated tube that runs along the focal line of the solar collector they track the sun in one direction (east to west) to keep the solar energy aligned on the receiver tube throughout the entire day The working fluid, typically synthetic oil, is heated to temperatures near 400C in the receiver before passing through a heat exchanger solar heat is used to boil water to drive a conventional Rankine-cycle turbine generator block

Linear Fresnel Reflector Systems arrays of long, narrow mirrors located near ground level track the sun reflecting its energy onto a fixed receiver tube fixed receiver and locating mirrors near to the ground result in a reduction in complexity and cost The working fluid, typically synthetic oil, is heated to temperatures near 400C in the receiver before passing through a heat exchanger

Power Tower Systems field of two-axis tracking mirrors, called heliostats, reflects the solar energy onto a receiver mounted on top of a centrallylocated tower each heliostat must track a position in the sky that is midway between the receiver and the sun These systems typically utilize a centrally located receiver that heats molten salt to generate steam which is then collected and provided to the turbine

comprised of: Dish Engine System a parabolic dish concentrator a thermal receiver a heat engine generator system operates by tracking the sun and reflecting the solar energy to the focus of the dish where it is absorbed by the receiver heat absorbed by the receiver is then transferred to the heater head of an externally-fired engine generator systems are modular and range in size from about 3 to 25 kw

CSP System Summary PARABOLIC TROUGH LINEAR FRESNEL REFLECTORS POWER TOWER DISH ENGINE Concentration Ratio 80 40-80 800 3000 Temp of Operation 390-450 C 250-450 C 250 to 560 C 750 C Annual Efficiency 12 to 16 % No data available 10 to 18% 22 to 26% Water Usage 1000 gal/mwhr* 1000 gal/mwhr 1000 gal/mwhr* 0.4 gal/mwhr Accommodates Thermal Storage YES NO YES Not at Present Commercial Deploy. 519 MW 6 MW 30 MW 0 General Comments Most mature of the three technologies. Currently demonstrating two- tank thermal storage in Spain. Solar Energy Generating Systems (SEGS) plants in CA operated with natural gas in the hybrid mode. Current plants use once-through steam generators. Annual efficiencies will be lower than other CSP technologies due to optical losses but goal is to overcome these losses through lower cost components Current plants use once-through steam generators. Molten-salt power towers demonstrated at 10 MW. Molten salt plants integrate working fluid and thermal storage. Highest efficiency of the three technologies. Lowest water usage due to captive radiation systems. Does not readily accommodate thermal storage.

Concentrated Photovoltaic Systems increase the solar intensity on the PV device using lenses or additional mirrors excellent method to lower the cost per Watt

Solar Energy Cost the main driving force behind introducing solar energy is: cost per Watt this translates into cost of energy per kwh there are many aspects to the cost: manufacturing, efficiency, installation cost, inverters, time-of-use, etc. there are good models to estimate overall cost for different systems: SAM model

UCR Solar Projects solar electric car concentrated solar thermal testbed solar PV tracker solar thermal tracker solar hydrogen plant etc 27

The unique idea of SC-RISE is vertical integration of all aspects of solar energy research, applications, and training: Materials/devices Integration/prototyping/application Demonstration and public education Training at the collegiate, practitioner, and precollege levels. Partner with community colleges, unions, workforce investment boards, Extension, and others