physics

Stand-alone power system

Stand-alone power system is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Stand-alone power system rather than just read about it. In short: 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.

Key takeaways

Stand-alone power system belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Stand-alone power system to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Stand-alone power system from memory before moving on to harder problems.

Reference excerpt

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:

Photovoltaic system using solar panels Wind turbine Geothermal source Micro combined heat and power Micro hydro Diesel or biofuel generator Thermoelectric generator (TEGs) Storage is typically implemented as a battery bank, but other solutions exist including fuel cells. 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 and may use solar panels only or may be used in conjunction with a diesel generator, a wind turbine or batteries.

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 criterion 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 excess 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.

Hybrid system

The hybrid power plant is a complete electrical power supply system that can be easily configured to meet a broad range of remote power needs. There are three basic elements to the system - the power source, the battery, and the power management center. Sources for hybrid power include wind turbines, diesel engine generators, thermoelectric generators and solar PV systems. The battery allows autonomous operation by compensating for the difference between power production and use. The power management center regulates power production from each of the sources, controls power use by classifying loads, and protects the battery from service extremes.

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" (IEC 61724). 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 Performance assessment involves:

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.

Gallery

Illustrations

Worked examples

Example 1 — a first encounter with Stand-alone power system

Start with the simplest possible case. Write down what Stand-alone power system claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Stand-alone power system before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Stand-alone power system ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Stand-alone power system

In research: Stand-alone power system appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Stand-alone power system in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Stand-alone power system is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electric power generation, Renewable energy technology, so understanding it makes those chapters shorter.
In everyday life: Look for Stand-alone power system outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Stand-alone power system in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Stand-alone power system means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Stand-alone power system out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Stand-alone power system in simple terms?

Why does Stand-alone power system matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Stand-alone power system?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Stand-alone power system.