Currently, our planet gets most of its power from coal, oil and gas. These so-called fossil fuels were formed from the remains of living organisms existing millions of years ago, and when burned, release heat energy that can be turned into electricity. However, they are also very harmful to the environment, as burning fossil fuels also gives off a lot of carbon dioxide, a greenhouse gas that contributes to global warming.

As the Sun’s energy beats down on Earth, approximately 70 per cent of it gets absorbed by the land and oceans, while 30 per cent is reflected back into space. However, the 70 per cent absorbed by Earth is eventually radiated back out into the atmosphere in the form of infrared energy. Greenhouse gases then absorb this energy, but also emit heat in the process, which warms the Earth’s surface and lower atmosphere. This process occurs naturally and is what keeps the planet warm enough for living things to survive on it.

However, a dramatic increase in greenhouse gas emissions since the Industrial Revolution has also caused a big rise in the average surface temperature of the Earth. This in turn has caused the world’s glaciers and ice shelves to melt faster, which will lead to a rise in sea levels resulting in the flooding of low-lying areas of coast. An increase in global temperatures fuels more fierce and devastating tropical storms and hurricanes, and could also trigger severe droughts in some parts of the world.

Even if burning fossils didn’t have this destructive power, it would still be important for us to find alternative sources of energy. Although fossil fuels are technically renewable, as they are made from living organisms, that fact we are using them up at a much faster rate than they can be formed means we will eventually run out.

Some renewable sources of energy, such as solar, wind and hydroelectric power, are already being used, but these come with their own problems that prevent them from replacing fossil fuels altogether. However, as we continue to find innovative new ways to harness unused energy, our planet could soon become a green, self-powered machine.

The limitations of green energy

Despite the infinite supply of energy available to us from renewable sources, we still rely heavily on fossil fuels. Unfortunately, there are many issues that still need to be overcome before we can become completely green.

One of the main obstacles is cost, as the infrastructure required for most renewable energy sources is expensive, especially when compared to that of fossil fuels. Solar panels, wind turbines, hydroelectric dams, tidal barrages and nuclear fusion plants are all expensive to build and storing any excess energy they produce can also be costly.

The reliance on unpredictable weather is another major issue for some forms of renewable energy. Wind, for example, is very inconsistent, and of course solar energy is only harvested in significant amounts during clear daylight hours. Therefore, fossil fuel energy is still required as a back-up when the conditions aren’t quite right.

At the moment, technology used to harvest renewable energy is also not particularly efficient. Vast areas of land or sea need to be covered with solar panels or wind turbines in order to generate the same amount of power produced by non-renewable sources. This can generate opposition from local residents, as some people believe wind farms spoil the countryside. Local ecosystems can also be negatively affected by some renewable energy sources. For example, hydroelectric dams disturb the flow of rivers, disrupting native wildlife and local settlements, and tidal barrages can be harmful to marine life.

Of course, some sustainable solutions are severely restricted by location anyway. For example, geothermal energy can only be produced near areas of volcanic activity, and tidal energy requires strong tides.

Fusion power

Stars such as our Sun produce huge amounts of energy using a process known as fusion. When exposed to extreme heat and high pressures in the star’s core, hydrogen atoms are stripped of their electrons to expose their nuclei. This soup of nuclei and electrons is known as plasma, the fourth state of matter. When plasma is heated, the hydrogen nuclei move quickly and collide, fusing together to produce helium and a great deal of energy.

Due to the clean and efficient nature of this process, scientists have now developed a way to replicate it here on Earth, in the hope that it could eventually eliminate the need for fossil fuels. To do this, they have built enormous fusion reactors, which use magnetic fields to produce temperatures of 150 million degrees Celsius (270 degrees Fahrenheit), ten times hotter than Sun’s core, and control plasma within a ring-shaped chamber called a tokamak. The fuels used in the reactor are the hydrogen isotopes deuterium, extracted from water and tritium, produced from lithium found in the Earth’s crust. Our current supply will last for millions of years, and just one kilogram (2.2 pounds) can provide the same amount of energy as 10,000 tons of fossil fuel. Plus, the main by-product of fusion power is a small amount of helium, which will not pollute the atmosphere.

Although the technology is already in place to create fusion power, current fusion rectors consume more energy than they produce. The challenge now is to build a reactor that is big enough to serve as a working power plant, and the ITER project in France is the first step.

Sunshine-powered water purifier

The Desolenator uses energy and heat from the Sun to turn dirty or salt water into distilled water. It is entirely self-contained and can provide water-stressed towns and villages with a cheap, reliable and convenient source of hydration. Currently still in the development stage, the device could be put to use by the end of 2015.

Spray-on solar cells

Scientists at the University of Toronto have developed a new method of spraying solar cells onto flexible surfaces. Their SplayLD system uses colloidal quantum dots (CQD), nanometre-sized crystals containing only a few thousand atoms, that absorb sunlight and turn it into electricity. A liquid containing these CQDs is then sprayed onto a surface such as plastic, glass or even clingfilm, in single layer. Next, a chemical treatment is sprayed on top, transforming the CQDs from electrically insulating to electrically conductive, before the surface is rinsed clean. This process is then repeated to build up 65 to 85 layers.

Until now, the only way to carry out this process was through batch processing, requiring expensive infrastructure and a slow assembly line. However, the SprayLD system can now be applied using something resembling a newspaper printing press. So although the CQDs are half as efficient as conventional solar cells, they are also less than half as expensive to manufacture, meaning a better value for money.

Eco-homes

The ZEB Pilot House, created by Norwegian architect firm Snøhetta, uses solar and geothermal power to produce three times more energy than it needs. In fact, the surplus energy it generates is enough to power an electric car year-round. The building, situated in Larvik, Norway, is big enough to house a family.

People power

The human body is one big energy factory. Calories go in, by way of food, and they in turn power our organs and muscles, generating excess heat. Simply going for a walk could generate 163 watts of power, but the big challenge is working out how to efficiently turn this into usable energy.

Scientists are exploring lots of innovative ways to harness human power, and one such method involves piezoelectricity, which can be produced from the pressure applied to a surface through motions such as walking.

When pressure is applied to an object containing atoms or molecules arranged in a very orderly way, also known as crystals, the charges are forced out of balance. The compressed side gains a positive charge while the opposite develops a negative charge, and when the pressure is relieved an electric current flows between them, which can be stored and used as a power source. Although this is proven to work, it only generates a very small amount of electricity, unfortunately insufficient for powering most electronic devices.

Another method being explored for harnessing kinetic energy uses magnetic fields. Scientists at the HSG-IMIT research centre in Germany have developed a shock harvester and a swing harvester device that can fit inside a regular shoe. When the heel strikes the ground or the foot swings between steps, a magnet within each harvester moves past a stationary coil. This generates an electric current, creating a very small three to four milliwatts of energy. Although not enough to charge a phone, it can power small sensors and transmitters that can track your journey, and the inventors hope it can eventually be used to power a self-lacing mechanism.

Energy from exercise

Anyone who has started a workout regime will know that exercising requires a lot of energy, but you may not have realised that it can generate energy too. Some gyms, such as the Cadbury House Club in Bristol, UK, are purchasing equipment that turns the user’s movements into electricity, powering the machine itself and using any excess to power the gym building. You can also purchase your own power-generating gym equipment: the PULSE jump rope is a portable generator that you charge as you jump. Inside each handle is a DC motor and a lithium-ion battery. Every time you jump and turn the rope, a connector on each handle turns. This turns the motor that then powers the battery, with 15 minutes of skipping generating enough energy to power a lamp for 2 hours. Attaching the supplied USB adapter will also allow you to use it to charge your phone and other compatible devices.

Energy floors

Rotterdam-based company Energy Floors uses an electromechanical system to turn kinetic energy into electricity. Its Sustainable Dance Floor uses the movement of dancers to light up the ground beneath their feet. The interactive light show was designed to raise awareness of the potential of kinetic energy, and has proved popular for corporate and public events, but they have since developed a new product with more practical benefits. Their Sustainable Energy Floors are designed for areas with high footfall, such as shopping malls, sports arenas and airports. Each step onto a tile can generate between two and 20 joules of energy, which can be used to power nearby lights or signage.

Charge your phone with your clothes

60 per cent of the energy we consume through calories escapes as heat, but rather than wasting this abundant power source, new technology can help us put it to good use.

A team of scientists at Wake Forest University in the United States have developed a thermoelectric fabric called Power Felt that converts heat into electricity and could one day be used to make clothes. Thermoelectric materials have been around for a while, but they are usually brittle and expensive. However, Power Felt is a lightweight, flexible material and is cheap to produce. When placed between two objects with differing temperatures, such as your warm body and the cool air, the electrons in the heated side of the fabric move faster, travelling toward the cooler side. This causes the cold side to become negatively charged and the hot side to become positively charged, creating a voltage that is conducted by the tiny carbon nanotubes within the fabric to generate an electric current. One square centimetre (0.16 square inches) of Power Felt can generate one milliwatt of electricity, so if you lined your phone case with it, it could boost the battery while just sitting in your pocket.

Another type of body heat- powered fabric can be found in the Fittersift dress shirt, which is infused with 13 thermo-reactive minerals that convert body heat that would otherwise be wasted into a usable energy source. The shirt reflects the infrared radiation back toward the body, helping to increase blood oxygen levels, improve circulation and regulate body temperature.

Although these materials are still in development, Stockholm Central Station is already being used to harvest body heat as a power source. The building’s ventilation system contains heat exchangers that convert excess heat generated by its 250,000 daily visitors into hot water. This hot water is then pumped into the heating system of a nearby office building, keeping it warm and reducing the energy bill by up to 25 per cent.

Solar-powered clothing

As well as generating energy from body heat, clothing can also harvest energy from the Sun. Several fashion designers are collaborating with scientists to incorporate solar cells into their designs. The designers behind the Solar Fiber project are working on a flexible photovoltaic fibre that converts sunlight into electricity and can be woven into all sorts of fabric. They have already developed a prototype dress with solar- panel straps and a ‘solar shawl’ prototype using solar yarn that tells you the amount of energy being generated, via an integrated display.

Meanwhile, Wearable Solar has already produced a collection of outfits featuring rigid solar cells. Both the coat and dress can generate enough energy to charge a smartphone after being worn in the sun for just two hours, and the solar panels can be folded away when not in use.

Discover more about how to save the world in Issue 85 of How It Works. Pick up a copy from all good retailers, or order it online from the ImagineShop. If you have a tablet or smartphone, you can also download the digital version onto your iOS or Android device. To make sure you never miss an issue of How It Works magazine, make sure you subscribe today!