10 July 2019

Why efficiency matters to us

by Associate Professor Dr Basil T. Wong

Nothing is 100% efficient in this world. In fact, it is thermodynamically impossible to even come close to that figure. If it seems too good to be true, it probably is. Every system that requires an input in the form of energy involves efficiency, which is typically measured as the ratio of what you desire to what it is required.

Have you ever wondered how much of the gas that you paid for at the gas station is actually useful to power your car? To answer this question, we need to refer to a parameter called the thermal efficiency, in this case, of the internal combustion engine in a car. These days, modern car engines have thermal efficiency of values between 25% and 50%.

What this means is that for every unit of fuel energy sent to the engine, one would only obtain quarter to half the input energy converted to mechanical energy at the output shaft. To make the matter worse, this number will get even smaller if one takes into account all other energy losses in the car mechanical systems.

Simply put, for every ringgit that you spent on gas, only less than 25-50 cents are useful to power your car. The remaining balance goes to waste, ultimately in the form of heat.

Speaking of efficiency, our home air conditioner is another good example. Although the official term for efficiency in cooling devices such as air conditioners and refrigerators is coefficient of performance, both terms share the identical definition, that is, the desired outcome versus the required input energy.

Air conditioners are devices that move heat from cold space to hot space, in this case, the cold space being our home while the hot space being outdoor environment. Try to think of this process in terms of climbing up a ladder from Point A to Point B. When the weather gets hot, Point B becomes higher and a longer ladder is required.

What this means to us is that when the outdoor temperature is higher, the air-conditioning efficiency drops because it needs to work harder to overcome the temperature difference. That is, if we would like to maintain our homes at the same desired temperature. Keep in mind that this does not include heat losses through doors and windows. If the air-conditioners are to be more efficient, then less electricity is consumed to condition our homes at the same setting.

By now, you should be very familiar with family members preaching not to leave the refrigerator doors open any longer than necessary. This is so to avoid the refrigerator from losing its coldness which then triggers more work by its compressor to undo the losses. This means more electricity consumption by the compressor.

The similar concept is applicable to our air-conditioned home where doors and windows are to be shut when air conditioners are operating. However, did you also know that efficiency of a refrigerator drops when we lower the desired temperature setting? As you probably would have guessed, this leads to more electricity consumption if you would like to store your food at a colder temperature. Therefore, it is always a good idea not to over-freeze your food for this reason.

Let’s look at one more example – a solar cell, the device that converts light into electricity. Solar cells have been around since 1950s. Only until recently these devices start to gain vast popularity owing to the ever-growing nanotechnology in the past two decades for one reason – reasonable conversion efficiency at an affordable cost.

However, they need one thing which is space! To be able to generate sufficient power for daily needs, many solar cells are needed and unfortunately, they cannot be stacked because of the need to be exposed to direct sunlight. When the availability of space is of concern, cells with higher efficiency ratings are highly sought.

Therefore, solar cell conversion efficiency plays a critical role here. Most solar panels for domestic uses have efficiencies ranging from 10 to 20%, which means that 80 to 90% of the incident sunlight is either converted to heat or wasted via reflection! Although more efficient solar panels are available on the market, the costs are not justifiable for household usage.

As the world is shifting towards building a clean and sustainable future, power generation based on various renewable energy sources takes centre stage. Energy research on developing or enhancing renewable energy conversion has never been more active.

At Swinburne Sarawak, our vision in the research group is to discover novel ways of enhancing conversion efficiency and harnessing from various heat sources. We research on different means of increasing solar cell efficiency and develop engineering solutions for minimising heating on the cells as heat typically degrades performances and reduces power output. In addition, our group also actively explores the possibility of energy conversion from waste heat to electricity using nanotechnology.

Efficiency is the key to better performances, more savings on operating cost and less environmental pollution, which is why it matters to us. After all, better efficiency, better future!

Dr Basil T. Wong is an Associate Professor from the Faculty of Engineering, Computing and Science at Swinburne University of Technology Sarawak Campus. He can be reached via email at twong@swinburne.edu.my.