Renewable energy: types, advantages, disadvantages and technical challenges

Renewable energy has become the central topic of discussion all around the world.

Some people refer to renewable energy as green energy or alternative energy. This is true because renewables are one of the most effective substitutes for conventional energy sources like fossil fuel; they are environmentally friendly and do not emit greenhouse gases.

For the past few decades, human beings have relied heavily on fossil fuels.

Therefore the greenhouse gas emissions from the use of a non-renewable source of energy like fossil fuels have historically reached a high level. The consequence is global warming, extreme weather, and a host of other impacts.

We must reduce our reliance on carbon-intensive fossil fuels at the global level. Since the challenges are significant and the choices are limited, renewables must be a key pillar of the energy strategy for achieving these results.

Learning about renewable energy today is more important than ever before. Let’s look at definitions, types of renewable resources, advantages, disadvantages, and technical challenges of renewable energy.

What is renewable energy?

The energy which is derived from natural sources like sun, wind, geothermal, etc. and is replenishable is known as renewable energy.

The formal renewable energy definition, as stated by U.S. Energy Information Administration (EIA), is “Energy from sources that are naturally replenishing but flow-limited; renewable resources are virtually inexhaustible in duration but limited in the amount of energy that is available per unit of time.”

What are renewable sources of energy?

The major types of renewable energy resources are

1. Solar
2. Wind
3. Biomass
4. Geothermal
5. Hydropower
6. Ocean energy

Solar energy

Solar energy is a large, inexhaustible source of energy.

The power from the sun intercepted by the earth is approximately 1.8 × 10¹¹ MW which is several thousand times greater than the present consumption rate of all commercial sources of energy on the planet.

Solar energy could in theory supply continuously all the energy needs of the world today and the future, making it one of the most promising sources of renewable energy.

The energy from the sun is used in two ways directly.

The first is the thermal route by which the heat energy from the sun is collected by means of devices. This thermal energy is either used immediately for applications such as water heating, space heating, drying, etc. or transformed by means of energy transfer cycles into electricity.

The second way to directly use solar energy is by photovoltaic conversion, the devices used for this purpose is called solar cells.

Wind energy

Wind energy is an indirect form of solar energy; the solar heating of the atmosphere along with the earth’s rotation creates planetary and local wind patterns.

The kinetic energy created by air in motion is used to produce electricity. The kinetic energy is converted by wind turbines or wind conversion systems into electrical energy.

Historically, wind energy was used for sailing ships and for generating mechanical power through windmills.

Wind power has become cost-effective over the last two decades and by late 2019 the global installed capacity has risen to 650.8 GW (Ref. WWEA).

The most of machines installed are of the two- or three-blade propeller type. Such turbines are typically installed side by side in acceptable wind swept locations, the clusters are known as wind farms.

Biomass

The word ‘biomass’ encompasses all plant life – trees, agricultural plants, scrub, grass, and algae, as well as their residues after processing.

The residues contain crop and farm waste. It is possible to get these from woodland, forestry, agriculture, arid lands, or even garbage.

There are numerous ways to produce energy from biomass.

It can be divided into three classes in general, i.e., thermochemical route, biochemical process, and extraction of oil.

The thermochemical route involves combustion, gasification, and pyrolysis processes.

The biochemical process involves anaerobic digestion for the processing of biogas and alcohol fermentation.

The edible and non-editable oils of many grains and seeds can be collected. These can be used directly as liquid fuels or transesterified as a replacement for conventional diesel oil.

Geothermal

Geothermal energy is energy coming from the Earth’s inner molten crust towards the surface.

Since the Earth’s crusts have no homogeneity, several local hot spots are situated just under the surface where the temperature is substantially higher than the expected average value.

For some of these areas, groundwater comes into contact with hot rocks, and as a result, dry steam, wet steam, and hot water or hot water alone are formed.

A well drilled to these locations causes the steam or water to emerge at the surface where its energy can be utilized either for generating electricity or for space heating.

Hydropower

Hydropower is by far the most mature and widely used renewable resource for generating electricity.

The use of electricity from flowing water or rapidly moving water to get power is a well-established process, and large hydropower plants make up a large share of global electricity production.

But, as large dams are being built to produce hydroelectric electricity, there are also environmental and social issues.

One of the environmental problems is that certain biological species are threatened with destruction, which would be harmful to the ecosystem.

Social issues are primarily concerned with the displacement of people who live in areas that get submerged when a new dam is being built.

Ocean energy

Ocean energy refers to energy harnessed from the oceans and the seas of the world.

The different forms in which the energy is available are tidal energy, wave energy, the energy associated with temperature differences in the ocean, and the energy in marine currents.

Tidal energy

The gravitational attraction of the Earth and the moon acting upon the Earth’s oceans is a primary cause of tides.

They arise twice a day. The tidal range is only one meter or less in the middle of the ocean, but it is much higher on some coastal estuaries.

That is because the wave amplifies as it passes along the narrow channel of the estuary.

The first commercial tidal power station in the world was constructed in France in 1965 across the mouth of the La Rance estuary.

Wave energy

The interaction between the motion of the wind and the oceans’ surface creates wave energy.

This is, therefore, one of the indirect ways to use solar energy. The amount of energy from the wind to the waves and, therefore, the size of waves that result depends on the wind speed, how long the wind blows, and how long it blows.

Due to the wide fluctuations in amplitude and wave frequency, wave energy is difficult to collect at any location. Establishments of cost-effective energy extraction devices, therefore, require considerable ingenuity.

Advantages of renewable energy

• They are environment friendly
• They will never run out making them sustainable energy and abundant natural resources
• Improvements in public health: emits little to no greenhouse gases or pollutants into the air
• The growing renewable sector creates jobs
• They make the electric grid more resilient
• Renewable expands energy access in developing countries
• They help in saving money in the long term
• Renewable energy technologies allow people to produce energy locally

Disadvantages of renewable energy

• Reliance on weather conditions impact reliable energy supply
• Requires a huge upfront capital outlay
• The renewable energy storage cost is expensive
• Requires ample space to install, for example, solar energy
• They still lack the much-needed efficiency
• Renewables are a better option for emission than fossil fuels, but they are not entirely free from pollution

Technical challenges in using renewable energy

The likelihood that renewable energy sources will meet the potential annual demand for electricity or come close to fulfilling it is not enough. The demand must be met not only on an overall basis but continuously round-the-clock.

A significant challenge will be to coordinate the supply of thousands of distributed small solar and wind power resources using appropriate software and to take supply from the production site where it is consumed with the help of a robust and extensive transmission grid.

The development of computer-controlled load management capabilities would be a similar challenge on the demand side.

Another challenge is to build short-term and long-term energy storage systems.

Short term storage systems even out the difference between the hourly fluctuations in solar and wind energy supplies and the changes in demand.

On the other hand, long term energy storage systems are essential for storing energy in days when supplies surpass demand and to meet energy demand in days when there are low wind speed or cloudy weather conditions.

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Bipin Sharma

Bipin Sharma is an Energy Systems Engineer. He cherishes, sharing his knowledge with other people. For the latest updates from him, subscribe to AcadBuddy. Do not hesitate to drop a message.