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IntroductionSolar PVOff grid SolarWindEnergy StorageCharge ControllerInverterMicro-HydroGenerators
If...
• You are far away from the grid or,• You are victim of unplanned andfrequent power outages,
Then... off grid energy solutions are foryou
Energy access
Grid connected solar PV systemsbenefit from grid's energy while;Off grid solar PV systems benefit fromenergy stored into batteries.
When the sun is not available:
Photovoltaic (PV) cells are made oflight sensitive semiconductor materialsusing photons to dislodge electrons anddrive an electric current.
Crystalline silicon (mono and poly-crystalline) Thin films
There are two broad categories of PV cellstechnology in use:
Crystalline silicon is made from ultrapure silicon material such as the one usedfor semiconductor chips;
Thin films is made by depositing layers ofsemiconductors material onto glass orstainless steel substrate.
Mono-crystalline silicon: 12.5-15%Poly-crystalline silicon: 11-14%Copper Indium Gallium Selenide (CIGS): 10-13%Cadmium Telluride (CdTe): 9-12%Amorphous Silicon (a-Si): 5-7%
Solar cells conversion efficiency:
Crystalline silicon: -0.4 to -0.5CIGS: -0.32 to -0.36CdTe: -0.25a-Si: -0.21
Solar cells temperature coefficient:
Solar PV modules are made of theaggregation of solar cells then; PV modules are connected in series intoPV strings;PV arrays are formed by the parallelaggregation of PV strings.
Off grid solar PV systems shut off if moreelectrical energy than what the batterybank can hold is used.
Off grid solar PV systems are oftensupported by a generator set or a windturbine to enable continuous charge to thebattery bank.
The load required to be supplied by thesystem is not constant over the periodof one day;The daily energy usage vary over theyearThe energy available from the PV arraymay vary from time to time during thedayThe energy available from the PV arraymay vary from day to day during theyear.
Determination of energy usage thesystem must supplyDetermination of the battery storagerequired Determination of energy input requiredfrom the PV arraySelection of the remaining systemcomponents
A basic design method follows:
solar modules produce most powerwhen they are pointed directly to thesun.suitable areas are required for thebattery bank, charge controller andinverter.
Site constraint:
As any other electrical system, off gridsolar PV system must comply withstandards and industry guidelines
Like solar module that require full sun,there is no benefit of installing a windturbine in a low wind area.
Components: horizontal axis unit;three blades attached to a hub;a tail keeping the turbine pointed intothe wind;a generator.
Turbines' blades transform kineticenergy of the wind into rotation(mechanical energy);The generator in it turn transformmechanical energy into electricity.
Regardless of their type, towers must: be strong enough to support the weightof the wind turbine; and withstand the forces of the wind.
Properly sized towers place wind turbinesin the path of more powerful winds andraise turbines above turbulence createdby ground clutter.
Those who want to or must supply all oftheir needs through wind energy or acombination of wind and solar install off-grid systems.
Off grid turbines produce wild ACelectricitythat is converted to DC electricity byrectifiers located in the charge controller.
Surplus electricity generated duringwindy periods is stored in batteries for useduring low- or no-wind periods.
High electricity or grid connection ratestogether with long-term perspectives help to make off grid small windeconomically profitable.
Off-grid systems pros:
provide freedom from power outages, energyindependence, and total emancipation fromthe electric utility.
Off-grid systems cons:
typically equipped with another source ofelectricity, often a PV array or a gasolineor diesel generator.
Battery anatomy:lead plateselectrolyte insulator, preventing short circuitsbetween the platesnegative postpositive post
Batteries used in most off-grid renewableenergy systems are deep-cycle; flooded orsealed lead-acid batteries.
Lead-acid batteries convert electricalenergy into chemical energy when theyare charged. When discharging chemicalenergy is converted back into electricity.
Unlike flooded batteries, sealed batteriesare filled withelectrolyte at the factory, charged, andthen permanently sealed.
Two types of sealed batteries areavailable:
absorbed glass mat (AGM) batteriesand;gel cell batteries.
Sealed batteries are also known as“maintenance-free” batteries:
because fluid levels never need to bechecked; and because the batteries never needto be filled with water.
Sealed batteries advantages over floodedlead-acid batteries:
charge fasterdo not release explosive gases,much more tolerant of lowtemperatures.
Flooded lead-acid advantage over sealedbatteries:
less more expensive;store more electricity;have longer lifespan and;can be rejuvenated (equalized).
Over charging and deep discharging arethe main causes of premature batteriesfaillure: a charge controller maintainsthe proper charging.
MPPT provide 10 to 30% more power tothe battery.Downside to PWM: it can also createinterference in radios and TV's.
Battery deep discharge protection:A low voltage disconnect turn offwhatever is connected to the loadterminals.
Inverter charger:The battery charger in the inverterconverts ACfrom the genset into DC electricity; itthen feeds the DC electricity to thebatteries.
Inverters selection must consider: input voltage;output voltage;wave form;output power;surge capacity;stackability.
System voltage:All DC components of an off-gridrenewable energy system must operate atthe same voltage, the inverter inputvoltage must match the source.
Some appliances, such as audio equipment, television and fans can suffer because of the output wave shape.
The selected inverter should be capableof providing sufficient surge capability tostart any loads that may surge.
Hydroelectricity comes in two steps:converting energy in flowing water bymeans of a water wheel or through aturbine into mechanical energy;converting mechanical energyinto electricity using an electricgenerator.
According to their installed powergeneration capacity, hydropowersystems are classified as
large;medium; small; mini and; micro
Battery systems can be combined withother energy sources, such as windturbines and solar PV systems.
Micro-hydro systems have the followingcomponents:
water turbine;control mechanism;electrical transmission lines.
according to the requirements ofthe load to be connected;according to the site;according to the type of engine.
Sizing:
designed to be used as back-up tothe mains electricity supply; the generator starts and provideelectricity for as long as theoutage lasts.
Standby power:
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