Off grid energy solutions 101

by Mathy Mpassy Isinki

Mathy Mpassy Isinki

Off Grid Energy Solutions Business andTechnical Sales Professional

Index

IntroductionSolar PVOff grid SolarWindEnergy StorageCharge ControllerInverterMicro-HydroGenerators

Lecture 1: Introduction

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

solar;wind;microhydro;generator sets.

Off grid energy solutions:

needs;location;budget.

Selection:

Lecture 2: Solar PV

Heat andlight

The sun delivers its energy in two mainforms:

Solar electric systems convertthe sun’s light energy intoelectricity using photovoltaiccells.

Grid connected (or grid tied) and Off grid (or stand alone)

Types of PV systems:

Grid connected solar PV systems exportexcess energy to the grid;

Off grid solar PV systems store excessenergy into batteries.

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:

Effect of temperature:

PV cells performance declines astemperature rises

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.

Cables that can withstand environmentalconditions are used to interconnect PVstrings and arrays.

Lecture 3: Off grid solar

A stand alone or off grid solar PV system isnot connected to the grid.

A battery bank supplies power to theconnected load.

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.

To reduce load requirements, all theconnected appliances should be the mostenergy efficient.

Off gridsolar systemsizing iscomplex!

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:

EnergyEfficiency...

it is important to consider cost effectivemethods to reduce energy demand.

Budget constraint:

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

Lecture 4: Wind

The fact is that the sun is not always ableto entirely cover energy demand...

Like solar module that require full sun,there is no benefit of installing a windturbine in a low wind area.

Wind turbines fall under two categories:Grid connected;Off grid.

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.

Three types of towers:

freestanding tilt-up fixed guyed

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.

Lecture 5:Energy storage

A battery bank supply electricity to theconnected load when sun or wind are notavailable.

Lead-acid batteries constitution:separate 2-volt compartments,known as cells.

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.

The thickness of the plates allowsmultiple deep discharges of a deep cyclebattery.

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).

Batteries are wired by installers toproduce a specific voltage and amp-hourstorage capacity.

Lecture 6:Charge controller

Over charging and deep discharging arethe main causes of premature batteriesfaillure: a charge controller maintainsthe proper charging.

The brighter the sunlight, the morevoltage the solar cells produce.

Oldest charge controllers just short ordisconnect the solar panel when a certainvoltage is reached.

Nowadays controllers offer a 3 stagecharge cycle:• bulk;• absorption;• float.

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.

Controllers come with either a simpleindicator LED, a series of LED's, or digitalmeters .

Lecture 7: Inverter

Role:converting battery DC voltage into ACvoltage usable by most appliances.

Inverter charger:The battery charger in the inverterconverts ACfrom the genset into DC electricity; itthen feeds the DC electricity to thebatteries.

Inverters are available in 3 basic outputtypes:• square wave;• modified square;• and sine wave.

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 supplying continuous power to all ACloads.

The selected inverter should be capableof providing sufficient surge capability tostart any loads that may surge.

Stackability:the possibility of increasing power outputby connecting inverters together.

Lecture 8: Micro-Hydro Electricity

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

Microhydro is appropriate for users whoare independent of the electricity supplygrid.

Two types of off grid microhydro system:Battery based system;AC-direct system.

Battery systems can be combined withother energy sources, such as windturbines and solar PV systems.

AC direct systems work well when thestream has enough potential.

Micro-hydro systems have the followingcomponents:

water turbine;control mechanism;electrical transmission lines.

The turbine converts the energy in thewater into electricity.

Depending on the site, an intake andpipeline may beneeded to develop a micro-hydropowersystem.

The charge controller in a hydro systemturn on a load to absorb excess energy.

Battery-based microhydro systemsrequire charge controllers to preventovercharging the batteries.

In AC direct systems, controls are alsorequired to monitor output voltage andfrequency.

A dump load is sized to handle the fullgenerating capacity of the microhydroturbine.

A battery bank provides the way to storesurplus energy.

A disconnect is required between thebatteries and inverter.

Microhydro systems supply powerthrough an AC panel.

Lecture 9:Generators

Generators are used for locallyproducing electrical energy on-demand.

Engine + alternator= generator set

according to the requirements ofthe load to be connected;according to the site;according to the type of engine.

Sizing:

Generators size is given in both kWand kVA.

kW and kVA:

designed to be used as back-up tothe mains electricity supply; the generator starts and provideelectricity for as long as theoutage lasts.

Standby power:

designed to be used as the mainsupply of power; used as an alternative to gridsupply.

Prime power:

indoor or; outdoor;noise reduction

Selecting a generator:

space planning; foundations; exhaust.

Installation:

installed within a building;acoustic canopy;acoustic container.

Noise reduction:

As a very rough rule ofthumb a modern diesel engine usesaround 210 litres per hour per1000kVA.

Fuel consumption: