Stand-alone power system
Encyclopedia
A stand-alone power system (SAPS or SPS), also known as remote area power supply (RAPS), is an off-the-grid
electricity
system for locations that are not fitted with an electricity distribution
system. Typical SAPS include one or more methods of electricity generation
, energy storage
, and regulation.
Electricity is typically generated by one or more of the following methods:
Storage is typically implemented as a battery bank
, but other solutions exist including fuel cell
s. Power drawn directly from the battery will be direct current
extra low voltage
(DC ELV), and this is used especially for lighting as well as for DC appliances. An inverter is used to generate AC low voltage
, which more typical appliances can be used with.
Stand-alone photovoltaic power systems are independent of the utility grid. Stand-alone photovoltaic power systems are designed and sized to supply certain DC and/or AC electrical loads. These types of systems are powered by either a Solar panel only or may be used in conjunction with a diesel generator or a wind turbine.
The primary functions of a storage battery in a stand-alone PV system are:
Performance assessment involves:
Off-the-grid
The term off-the-grid or off-grid refers to living in a self-sufficient manner without reliance on one or more public utilities....
electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
system for locations that are not fitted with an electricity distribution
Electricity distribution
File:Electricity grid simple- North America.svg|thumb|380px|right|Simplified diagram of AC electricity distribution from generation stations to consumers...
system. Typical SAPS include one or more methods of electricity generation
Electricity generation
Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...
, energy storage
Grid energy storage
Grid energy storage refers to the methods used to store electricity on a large scale within an electrical power grid. Electrical energy is stored during times when production exceeds consumption and the stores are used at times when consumption exceeds production...
, and regulation.
Electricity is typically generated by one or more of the following methods:
- Solar panelPhotovoltaic moduleA solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...
- Wind turbineWind turbineA wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
- GeothermalGeothermalGeothermal is related to energy and may refer to:* The geothermal gradient and associated heat flows from within the Earth- Renewable technology :...
source. - Micro combined heat and power.
- Micro hydroMicro hydroMicro hydro is a term used for hydroelectric power installations that typically produce up to 100 kW of electricity. These installations can provide power to an isolated home or small community, or are sometimes connected to electric power networks....
. - DieselDiesel generatorA diesel generator is the combination of a diesel engine with an electrical generator to generate electrical energy....
or biofuelBiofuelBiofuel is a type of fuel whose energy is derived from biological carbon fixation. Biofuels include fuels derived from biomass conversion, as well as solid biomass, liquid fuels and various biogases...
generator.
Storage is typically implemented as a battery bank
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
, but other solutions exist including fuel cell
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...
s. Power drawn directly from the battery will be direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
extra low voltage
Extra low voltage
In electricity supply, the use of extra-low voltage is one of several means to protect against electrical shock. The International Electrotechnical Commission and its member organizations define an ELV circuit as one in which the electrical potential of any conductor against earth is not more...
(DC ELV), and this is used especially for lighting as well as for DC appliances. An inverter is used to generate AC low voltage
Low voltage
Low voltage when used as an electrical engineering term concerning an electricity supply grid or industrial use, broadly identifies safety considerations of the system based on the voltage used. The meaning of the term "low voltage" is somewhat different when used with regard to a more typical end...
, which more typical appliances can be used with.
Types
The two types of stand-alone photovoltaic power systems are direct-coupled system without batteries and stand alone system with batteries.Direct-coupled system
The basic model of a direct coupled system consists of a solar panel connected directly to a dc load. As there are no battery banks in this setup, energy is not stored and hence it is capable of powering common appliances like fans, pumps etc only during the day. MPPTs are generally used to efficiently utilize the Sun's energy especially for electrical loads like positive-displacement water pumps. Impedance matching is also considered as a design criteria in direct-coupled systems.Stand alone system with batteries
In stand-alone photovoltaic power systems, the electrical energy produced by the photovoltaic panels cannot always be used directly. As the demand from the load does not always equal the solar panel capacity, battery banks are generally used.The primary functions of a storage battery in a stand-alone PV system are:
- Energy Storage Capacity and Autonomy: To store energy when there is an excees is available and to provide it when required.
- Voltage and Current Stabilization: To provide stable current and voltage by eradicating transients.
- Supply Surge Currents: to provide surge currents to loads like motors when required.
System monitoring
Monitoring photovoltaic systems can provide useful information about their operation and what should be done to improve performance, but if the data are not reported properly, the effort is wasted. To be helpful, a monitoring report must provide information on the relevant aspects of the operation in terms that are easily understood by a third party. Appropriate performance parameters need to be selected, and their values consistently updated with each new issue of the report. In some cases it may be beneficial to monitor the performance of individual components in order to refine and improve system performance, or be alerted to loss of performance in time for preventative action. For example, monitoring battery charge/discharge profiles will signal when replacement is due before downtime from system failure is experienced.IEC standard 61724
IEC has provided a set of monitoring standards called the "Standard for Photovoltaic system performance monitoring". It focusses on the photovoltaic system's electrical performance and it does not address hybrids or prescribe a method for ensuring that performance assessments are equitable.Performance assessment
- Data collection, which is a straightforward process of measuring parameters.
- Evaluation of that data in a manner that provides useful information.
- Dissemination of useful information to the end user.
Load related problems
The wide range of load related problems identified are classified into the following types:- Wrong selection: Some loads cannot be used with stand-alone PV systems.
- House wiring: Inadequate or low quality wiring and protection devices can affect the system's response.
- Low efficiency: Low efficiency loads may increase energy consumption.
- Stand-by loads: Stand-by mode of some loads waste energy.
- Start-up: High current drawn by some loads during start-up Current spikes during the start-up can overload the system temporarily.
- Reactive power: The circulating current can differ from the current consumed when capacitive or inductive loads are used.
- Harmonic distortion: Non-linear loads may create distortion of the inverter waveform.
- Mismatch between load and inverter size: When a higher rated inverter is used for a lower capacity load, overall efficiency is reduced.
See also
- Grid-connected photovoltaic power systemGrid-connected photovoltaic power systemGrid-connected photovoltaic power systems are power systems energised by photovoltaic panels which are connected to the utility grid. Grid-connected photovoltaic power systems comprise of Photovoltaic panels, MPPT, solar inverters, power conditioning units and grid connection equipments. Unlike...
- List of rooftop photovoltaic installations
- Photovoltaic power plant
- Building-integrated photovoltaics
- Solar inverter
- Energy harvestingEnergy harvestingEnergy harvesting is the process by which energy is derived from external sources , captured, and stored for small, wireless autonomous devices, like those used in wearable electronics and wireless sensor networks.Energy harvesters...
- MicrogenerationMicrogenerationMicrogeneration is the small-scale generation of heat and power by individuals, small businesses and communities to meet their own needs, as alternatives or supplements to traditional centralized grid-connected power...
- Off-the-gridOff-the-gridThe term off-the-grid or off-grid refers to living in a self-sufficient manner without reliance on one or more public utilities....
- Rural electricity
- Australian Greenhouse OfficeAustralian Greenhouse OfficeThe Australian Greenhouse Office within the Government of Australia was the world's first government agency dedicated to cutting greenhouse gas emissions. In 1998, following pressure from the Australian Democrats, it was established as a stand alone agency within the environment portfolio to...
- Stand-alone photovoltaic power systemStand-alone photovoltaic power systemStand-alone photovoltaic power systems are power systems energised by photovoltaic panels which are independent of the utility grid. Stand-alone photovoltaic power systems are designed and sized to supply certain DC and/or AC electrical loads...
External links
- RAPS
- RAPS paper Queensland
- RAPS-system schematic
- Lighting Africa, a World Bank GroupWorld Bank GroupThe World Bank Group is a family of five international organizations that makes leveraged loans, generally to poor countries.The Bank came into formal existence on 27 December 1945 following international ratification of the Bretton Woods agreements, which emerged from the United Nations Monetary...
(WBG) initiative - Rural Village Energy Hub