Renewable and non-renewable energy sources, energy conversion in engineered systems, and calculating efficiency as the ratio of useful output to total input.

What this key area is asking

The SQA wants you to classify energy sources as renewable or non-renewable, describe how energy is converted from one form to another inside engineered systems, and calculate efficiency as the ratio of useful output to total input. Efficiency is one of the most-tested numerical ideas in the contexts area and reappears whenever a system has a power in and a power out.

Renewable and non-renewable sources

The course expects you to classify a source correctly and to compare them on the factors that matter to an engineer: emissions, fuel cost, whether the supply can be controlled on demand, reliability, and land or resource use. Non-renewable fossil sources are easy to run on demand but emit carbon dioxide and deplete; renewables are clean and inexhaustible but many are intermittent, so their output varies with the weather or tides and they may need energy storage to match supply to demand.

Energy conversion in engineered systems

Engineered systems work by converting energy from one form to another. Energy itself is never created or destroyed (the principle of conservation of energy); it is only converted. The useful forms in this course include kinetic, electrical, gravitational potential, strain (elastic), chemical and heat.

A few common conversion chains:

• A power station: chemical (fuel) to heat to kinetic (turbine) to electrical (generator).
• An electric motor: electrical to kinetic, with some lost as heat.
• A solar panel: light (radiant) to electrical.
• A battery: chemical to electrical.

Every real conversion produces some unwanted energy, almost always heat, through resistance, friction and other losses. Identifying the useful output and the wasted forms is the first step in any efficiency calculation.

Efficiency

Because energy is conserved, the input splits into the useful output plus the wasted forms: $P_{\text{in}} = P_{\text{useful}} + P_{\text{wasted}}$. So if you know the efficiency and the input, you can find both the useful output and how much is wasted as heat.

Why efficiency matters

A low-efficiency system wastes input as heat, which costs money to supply and adds to the product's environmental footprint over its whole life. This links the numerical idea straight back to sustainability: choosing a more efficient motor, a lower-loss circuit or a better-matched gearbox reduces both the running cost and the emissions associated with generating the energy. For a system that runs for years, even a few percentage points of efficiency add up to a large saving, which is the life-cycle argument made quantitative.

Examples in context

An incandescent lamp is about 5% efficient at producing light: most of the input becomes heat, which is wasted for lighting. An LED lamp converts a far larger fraction to light, so for the same light output it draws much less power, runs cooler and costs less to run. Multiplying that saving across millions of lamps left on for hours a day is why the switch to LED lighting was driven as much by efficiency as by lamp life. The same logic explains the push from petrol engines (roughly a third efficient) towards electric drivetrains (far higher efficiency from the battery to the wheels).

Try this

Q1. Classify each as renewable or non-renewable: natural gas, tidal, nuclear, solar. [2 marks]

• Cue. Non-renewable: natural gas, nuclear. Renewable: tidal, solar.

Q2. A device takes in 500 W and delivers 350 W usefully. Find its efficiency. [2 marks]

• Cue. $\text{efficiency} = \frac{350}{500} \times 100\% = 70\%$.

Q3. State the energy conversion in a battery. [1 mark]

• Cue. Chemical energy to electrical energy.