physics

Peak demand

Peak demand 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 Peak demand rather than just read about it. In short: Peak demand on an electrical grid is the highest electrical power demand that has occurred over a specified time period (Gönen 2008). Peak demand is typically characterized as annual, daily or seasonal and has the unit of power.

Key takeaways

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

Reference excerpt

Peak demand on an electrical grid is the highest electrical power demand that has occurred over a specified time period (Gönen 2008). Peak demand is typically characterized as annual, daily or seasonal and has the unit of power. Peak demand, peak load or on-peak are terms used in energy demand management describing a period in which electrical power is expected to be provided for a sustained period at a significantly higher than average supply level. Peak demand fluctuations occur on daily, monthly, seasonal, and yearly cycles. For an electric utility company, the actual point of peak demand is a single period that represents the highest point of customer consumption of electricity, typically when a combination of industrial, commercial, and domestic consumers are using heavy heating or cooling loads. The cost of generating and supplying electricity is also typically highest at peak load periods, as more power plants must be operating at high capacity. Some utilities will charge customers based on their individual peak demand. The highest demand during each month or even a single 15 to 30 minute period of highest use in the previous year may be used to calculate charges. The renewable energy transition will include considerations for peak demand.

Demand Tariff Electricity network is built to deal with the highest possible peak demand otherwise blackout may happen. In Australia, demand tariff has three components: peak demand charge, energy charge and daily connection charge. For example, for large customers (commercial, industrial or a mix of commercial and residential), the peak demand charge is based on the highest 30 minutes electricity consumption in a month; the energy charge is based on a month's electricity consumption. This type of demand tariff is gradually introduced to residential households and will be rolled out by 2020 in Queensland, Australia. How to manage electricity bills under demand tariff can be challenging. The key solutions involve improving building efficiency and managing the operational settings of large power appliances.

Time of Peak Demand Peak Demand depends on the demography, the economy, the weather, the climate, the season, the day of the week and other factors. In industrialised regions of China or Germany, the peak demands mostly occur in day time. However, in more service based economy such as Australia, the daily peak demands often occur in the late afternoon to early evening time (e.g. 4pm to 8pm). Residential and commercial electricity demand contributes a lot to this type of network peak demand.

Off-peak Peak demand is considered to be the opposite to off-peak hours when power demand is usually low. There are off-peak time-of-use rates. Sometimes, there are 3 time-of-use zones: peak, shoulder and offpeak. Shoulder is often the time between peak and offpeak in weekdays. Weekends are often just peak and offpeak in terms of managing electricity loads for the network.

Response

Peak demand may exceed the maximum supply levels that the electrical power industry can generate, resulting in power outages and load shedding. This often occurs during heat waves when use of air conditioners and powered fans raises the rate of energy consumption significantly. During a shortage authorities may request the public to curtail their energy use and shift it to a non-peak period.

Power stations Power stations specifically constructed for providing power to electrical grids for peak demand are called peaking power plants or 'peakers'. In general, Natural gas fueled power stations can be fired up rapidly and are therefore often utilized at peak demand times. Combined cycle power plants can frequently provide power for peak demand, as well as run efficiently for baseload power. Hydroelectric power and pumped storage type dams such as Carters Dam in the U.S. state of Georgia help to meet peak demand as well. The chances that a wind farm will be unable to meet peak demand are greater than for a fossil-fueled power station, due to the ability to store liquid fuels for use during peak demand. Solar power's peak output often naturally coincides with daytime peaks of usage due to air conditioning.

Illustrations

Worked examples

Example 1 — a first encounter with Peak demand

Start with the simplest possible case. Write down what Peak demand 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 Peak demand 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 Peak demand 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 Peak demand

In research: Peak demand 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 Peak demand 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: Peak demand is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electric power distribution, Energy development, Power station technology, so understanding it makes those chapters shorter.
In everyday life: Look for Peak demand 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 Peak demand in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Peak demand 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 Peak demand out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Peak demand in simple terms?

Why does Peak demand 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 Peak demand?

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 Peak demand.