UNIT -II

SOLAR ENERGY STORAGE AND APPLICATIONS

• Solar energy is available only during the sunshine hours. • Consumer energy demands follow their own time pattern and the solar energy

does not fully match the demand. As a result, energy storage is a must to meet the consumer requirement.

• There are three.

SOLAR THER SOLAR ENERGY STORAGEMAL ENERGY STORAGE

METHODS FOR STORING SOLAR THERMAL ENERGY

SENSIBLE HEAT STORAGE Heating a liquid or solid which does not change phase comes under this

category. Heat that causes a change in temperature in an object is called sensible heat. The quantity of heat stored is proportional to the temperature rise of the

material. If T1 and T2 represent the lower and higher temperature, V the volume and ρ

the density of the storage material, and Cp the specific heat, then the energy stored Q is given by:

T2

T1Q= V Cp dT

For a sensible heat storage system, energy is stored by heating a liquid or a solid. Materials that are used in such a system include liquids like water, inorganic molten salts and solids like rock, gravel and refractories.

The choice of the material used depends on the temperature level of its utilization. Water is used for temperature below 100 0C whereas refractory bricks can be used for temperature upto 1000 0C.

LATENT HEAT STORAGE (PHASE CHANGE HEAT STORAGE)

All pure substances in nature are able to change their state. Solids can become liquids (ice to water) and liquids can become gases (water to vapor) but changes such as these require the addition or removal of heat.

In this system, heat is stored in a material when it melts, and heat is extracted from the material when it freezes.

Heat can also be stored when a liquid changes to gaseous state, but as the volume change is large, such a system is not economic.

Latent heat arises from the work required to overcome the forces that hold together atoms or molecules in a material. The regular structure of a crystalline solid is maintained by forces of attraction among its individual atoms, which oscillate slightly about their average positions in the crystal lattice.

FORMULA Q=M*LM- MASSL-INDIVIDUAL LATENT HEAT

THERMO-CHEMICAL STORAGE

With a thermo-chemical storage system, solar heat energy can start an endothermic chemical reaction and new products of reactions remain intact.

To extract energy, a reverse exothermic reaction is allowed to take place. Actually, thermo-chemical thermal energy is the binding energy of

reversible chemical reactions.

STRATIFIED STORAGE

A hot water storage tank (also called a hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank and hot water cylinder) is a water tank used for storing hot water for space heating or domestic use.

An efficiently insulated tank can retain stored heat for days.

Hot water tanks may have a built-in gas or oil burner system, electric immersion heaters, an external heat exchanger such as a central heating system, or heated water from another energy source such as a wood-burning stove.

SOLAR POWER PLANT (HOT WATER ONLY)

SOLAR PONDS

Normal ponds receive sunlight a part of which is reflected at the surface, a part is absorbed and the remaining is transmitted to the bottom.

Due to this the lower part gets heated up and the density decreases as a result of which it rises up and convection currents are set up.(As a result, the heated water reaches top layer and looses its heat by convection and evaporation).

A natural or artificial body of water for collecting and absorbing solar radiation energy and storing it as heat.

Thus a solar pond combines solar energy collection and sensible heat storage.They are large shallow bodies of water that are arranged so that the temperature gradient are reversed

from the normal. This allows the use for collection and storage of solar energy which may under ideal conditions be

delivered at temperature 40-50 `C above normal. It can be use for various applications, such as process heating, water desalination, refrigeration,

drying and power generation.

UPPER CONVECTIVE ZONE- This is a zone, typically 3 m thick, of almost low salinity which is almost close to ambient temperature.

NON CONVECTING ZONE- In this zone both salinity and temperature increases with depth

LOWER CONVECTING ZONE-relatively high salinity ( typically 20 % by weight) at high temperature.

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SOLAR DISTILLATION

Solar distillation is the use of solar energy to evaporate water and collect its condensate within the same closed system.

 water purification it can turn salt or brackish water into fresh drinking water.

SOLAR DRYING

• Solar dryers are devices that use solar energy to dry the substances especially food.

• There are two general types of solar dryers

direct dryerIndirect dryer

DIRECT SOLAR DRYER

INDIRECT SOLAR DRYER

PHOTOVOLTAIC ENERGY CONVERSION

Photovoltaic systems convert sunlight directly into electricity, and are potentially one of the most useful of the renewable energy technologies.

Also known as solar cells, PV systems are already an important part of our lives. The simplest systems power many of the small calculators and wrist watches we use everyday.

The conversion efficiency of a PV cell is the proportion of sunlight energy that the cell converts into electrical energy.

A solar cell is essentially a semiconductor device fabricated in a manner which generates a voltage when solar radiation falls on it.

Solar electricity systems capture the sun's energy using photovoltaic (PV) cells. The cells convert the sunlight into electricity, which can be used to run

household appliances and lighting.A SOLAR CELL is a solid state electrical device that converts energy of light

directly into electricity by Photoelectric Effect.

PHOTOELECTRIC EFFECT

When photons of light hit electrons in the silicon lattice and provide energy to flow. Introducing dopants such as boron and phosphorus into the silicon lattice provides a direction for the electrons to flow.

Finally, electrons flowing from one cell into the next cell in a module gain about 1/2 volt from each cell.

PV CELLS,MODULES & ARRAYS

A PV System typically consists of 3 basic components:

PV cells - Electricity is generated by PV cells, the smallest unit of a PV system.

Modules - PV cells are wired together to form modules which are usually a sealed, or encapsulated, unit of convenient size for handling.

Arrays – Groups of panels make up an array.

PV CELL

Solar cells are fixed on a board and connected in series and parallel combinations to provide the required voltage and power to form a photovoltaic (PV) module.

To protect the cells from damage the module is hermetically sealed between a plate of toughened glass and layers of Ethyl Vinyl Acetate.

A terminal box is attached to the back of module where the two ends of solar string are shouldered to the terminals.

When the PV module is in use, terminals are connected directly to the load.

SEMICONDUCTORA semiconductor has electrical conductivity due to electron flow (as opposed to

ionic conductivity) intermediate in magnitude between that of a conductor and an insulator.

Semiconducting materials are the foundation of modern electronics, and are used in transistors, solar cells, many kinds of diodes including the light-emitting diode, and digital and analog integrated circuits.

Semiconductor PV cells directly convert light energy into electrical energy. In metals, current is carried by the flow of electrons. In semiconductors, current is often schematized as being carried either by the flow of electrons or by the flow of positively charged "holes" in the electron structure of the material (in both cases only electron movements are actually involved).

ATOM

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element.

Atoms are very small; typical sizes are around 100 picometers (a ten-billionth of a meter, in the short scale).

PV CELL WORKING PRINCIPLE

Photovoltaic cells are made of special materials called semiconductors such as silicon. An atom of sili con has 14 electrons, arranged in three different shells. The outer shell has 4 electrons.

Therefore a silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms.

Now we use phosphorus(with 5 electrons in its outer shell). Therefore when it combines with silicon, one electron remains free.

A PV module produces DC power. To operate electrical appliances used in households, inverters are used to convert DC power into 220 V, 50 Hz AC power. Components other than PV modules are collectively known as balance of system (BOS) which includes storage batteries, an electronic charge controller and an inverter.

When sunlight strikes solar cell surface, the cell creates charge carrier as electrons and holes. The internal field produced by junction separates some of positive charges (holes) from negative charges (electrons). Holes are swept into positive or p-layer and electrons are swept into negative or n-layer.

When a circuit is made, free electrons have to pass through the load to recombine with positive holes; current can be produced from the cells under illumination.

STRUCTURE OF SOLAR CELL

ELECTRICITY BASICS

Electrical Current – how many electronsVoltage – how hard they’re pushedPower – what they can accomplishCircuit – where they can goSeries Circuit – one pathway onlyParallel Circuit – so many choices!

PARALLEL CIRCUITS & SERIES CIRCUITS

Series circuits

Maintain electrical flow (current is constant)

Voltage is divided among componentsEasy to open circuit quickly

Parallel circuits

Maintain potential (voltage is constant)

Current is divided among componentsIf one light goes out, the others stay

lit

COMPONENTS OF SOLAR PV SYSTEM

Solar Module is the essential component of any solar PV system that converts sunlight directly into DC electricity.

Solar Charge Controller regulates voltage and current from solar arrays, charges the battery, prevents battery from overcharging and also performs controlled over discharges.

Battery stores current electricity that produces from solar arrays for using when sunlight is not visible, nighttime or other purposes.

Inverter is a critical component of any solar PV system that converts DC power output of solar arrays into AC for AC appliances.

Lightning protection prevents electrical equipment's from damages caused by lightning or induction of high voltage surge. It is required for the large size and critical solar PV systems, which include the efficient grounding.

APPLICATIONS OF SOLAR CELL Home Indoor and outdoor lighting system, electrical equipment, electric gate opener,

security system, ventilator, water pump, water filter and emergency light, etcLighting system Bus stop lighting, telephone booth lighting, billboard lighting, parking lot

lighting, indoor and outdoor lighting and street lighting, etc.Water pumping Consumption, public utility, livestock watering, agriculture, gardening and

farming, mining and irrigation, etc.Battery charging system Emergency power system, battery charging center for rural village and power

supply for household use and lighting in remote area, etc.Agriculture Water pumping, agricultural products fumigator, thrashing machines and water

sprayer, etcCattle Water pumping, oxygen filling system for fish-farming and insect trapped lighting,

etcHealth center Refrigerator and cool box for keeping medicines and vaccines and medical

equipment, etcCommunication Air navigational aid, air warning light, lighthouse, beacon navigation aid,

illuminated road sign, railway crossing sign, street lighting and emergency telephone, etc

Tele communication Microwave repeater station, telecommunication equipment, portable communication equipment (e.g. communication radio for service and military exercise) and weather monitoring station, etc.

Remote area Hill, island, forest and remote area that the utility grids are not available, etc.

space Satellite, international space station and spacecraft, etc.

APPLICATION OF PV SYSTEMS

Solar PV power systems are categories into four classes.StandalonePV hybridGrid connectedSolar power satellite

http://www.affordable-solar.com/affordablesolar/bpsolar.html http://www.affordable-solar.com/affordablesolar/evsopa.html

http://www.affordable-solar.com/affordablesolar/geensopa.html

http://www.affordable-solar.com/affordablesolar/global-solar-energy-flexible-solar-panels.html

http://www.affordable-solar.com/affordablesolar/innergy.html

http://www.affordable-solar.com/affordablesolar/issopa.html

http://www.affordable-solar.com/affordablesolar/kyocera.html

http://www.affordable-solar.com/affordablesolar/martrix.html

http://www.affordable-solar.com/affordablesolar/mitsubishi-electric-solar-panels.html

PV PANEL MANUFACTURERS

GRID CONNECTION

  Parabolic Trough Dish/Engine Power Tower

Size 30-320 MW 5-25 kW 10-200 MW

Operating Temperature (ºC/ºF) 390/734  750/1382 565/1049

Annual Capacity Factor  23-50 % 25 % 20-77 %

Peak Efficiency  20%(d)  29.4%(d) 23%(p)

Net Annual Efficiency  11(d)-16% 12-25%(p) 7(d)-20%

Commercial Status Commercially Scale-up Prototype  Demonstration  AvailableDemonstration

Technology Development Risk Low High Medium

Storage Available Limited Battery Yes

Hybrid Designs Yes Yes Yes

Cost USD/W 2,7-4,0 1,3-12,6 2,5-4,4

Key features of the three solar technologies [4].

Table 5.1 highlights the key features of the three solar technologies.

SOLAR SYSTEM DESIGN

Power (watts) = current (Amps) X voltage (volts)

Energy (kWh)=Power (kW) X Time (hours)

Voltage Drop (volts) = Current (amps) X Resistance (ohms)

Components size depending upon our requirement.

SOLAR CELL EFFICIENCY

• The efficiency of a solar cell (sometimes known as the power conversion efficiency, or PCE, and also often abbreviated η) represents the ratio where the output electrical power at the maximum power point on the IV curve is divided by the incident light power – typically using a standard AM1.5G simulated solar spectrum.

The efficiency of a solar cell is determined as the fraction of incident power which is converted to electricity and is defined as:

Pmax= Voc Isc FF η = Voc Isc FF/Pinc

where Voc is the open-circuit voltage where Isc is the short-circuit currentwhere FF is the fill factorwhere η is the efficiency.

RAPS APPLICATIONS

Raps means remote area photovoltaic system

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