Comparison of Renewable Energy Source

(Transcript of the lesson commentary.)

Comparison of Renewable Energy Source

The best-known renewable energy sources mainly use the energy of the Sun, water or wind. The number of new renewable installations has been increasing in recent years and it seems like the right step to meet the climate neutrality commitment. The advantage of renewable sources is that they are clean, safe and easy to operate. In general, however, they have a low output density and a large output dependency on the weather compared to, for example, nuclear energy.

Even fifteen years ago, renewable sources accounted for about a fifth of the world’s energy production, with wind, solar and geothermal technologies accounting for just only one percent of total production of electricity and heat. The majority was covered by traditional biomass burning, especially wood. But already in 2020, the volume of electricity produced from renewable sources in the EU was higher than the volume of electricity produced from fossil fuels.

Renewable resources are maximally environmentally friendly. Today, in the period of ongoing climate change, fossil fuel resources are being abandoned more and more and renewable resources are being deployed in their place. They do not produce any solid or gaseous emissions or waste heat and do not burden the environment with waste. The use of solar, water, wind and geothermal power plants is one of the most ecological ways of producing electricity. When comparing the life cycle of renewables with other energy sources, solar power is the cleanest and safest source, followed by wind power.

Comparison of RES with other sources

Comparing renewable sources with each other is useful if we decide to build a new renewable source in the conditions of the selected location. What is more interesting, however, is the comparison with non-renewable, especially emission-free sources from the point of view of achievable outputs, the area needed to install the corresponding output and also financial demands.

Comparing renewable sources with nuclear power is probably best summed up by the slogan: “Whereas nuclear power requires a small piece of land to provide a large amount of power at a low cost, wind and solar power require a large piece of land to provide a small amount of power at a high cost.” Of course, it’s not as black and white and unequivocal as it seems at first glance.

Recently, new and improved technologies are making renewable sources considerably cheaper, while the construction of nuclear power plants is constantly becoming more expensive for various reasons. However, the simple fact remains that by comparing the areal output density, nuclear power plants still produce approximately 100 times more electricity per km2 than solar energy. And in the case of wind energy, this ratio of achievable output per km2 is even several times higher than in the case of solar power engineering.

A big advantage of renewable energy sources when compared to non-renewable sources is their easy availability. The Sun shines on the Earth continuously and its rays are available during the day practically all year round. The availability of water energy, which is the second most used energy after biomass from the point of view of renewable sources, depends only on the intensity of the water cycle in nature. And the same is true for wind energy, where the main role in availability is played by the relief of the Earth’s surface in combination with the distribution of water bodies. The easy availability of renewable resources is due, among other things, to the absence of subsequent mining activities or activities associated with waste disposal.

RES unit outputs

Comparing the unit outputs of the main renewable sources with the outputs of, for example, nuclear reactors, it is clear that new powerful renewable sources are created by installing hundreds to thousands of small sources in larger logical units. It has the advantage of good output scalability and easy expandability of power plants or entire energy parks.

It is the easiest with photovoltaic systems. The photovoltaic panel has a maximum output of hundreds of Watts, so the total output of the power plant depends only on the set area. To give you an idea, panels for an output of 1 kW take up about 10 m2 and produce approximately 1 MWh of electricity per year. Industrially produced wind turbines today, according to the size of the device, have a unit output from hundreds of kW to 9 MW, which means that the output of the wind farm is determined not only by the number of turbines but also by the combination of their nominal outputs. The output range for water turbines is even wider. The most powerful Francis turbines in the world’s largest hydropower plants propel generators of over 700 MW.

It is also interesting to compare the installed outputs of renewable resources on a global scale. At the end of 2019, hydropower plants had a capacity of 1,190 GW, wind power plants 651 GW and solar power plants 586 GW. In contrast, minority geothermal energy had a worldwide capacity of just 14 GW.

Built-up area and coefficient of annual RES use

Renewable sources require a significantly larger amount of land for their installation than, for example, the aforementioned emission-free nuclear power engineering. This is illustratively described by the resource’s output density parameter, which represents its output converted to the occupied area.

The worst situation is for wind energy, which can get approximately 9 MW from the occupied 1 km2. Ground-based photovoltaics has a higher output density than wind. This means that from 1 km2 of an area set with photovoltaic panels, several times more energy can be obtained than from the same area on which wind turbines are installed. Panels densely stacked on an inclined south-facing roof with a floor plan of 1 km2 can produce twice as much electricity as ground-based photovoltaics. For comparison, we can state that the output density of nuclear energy is around 250 MW/km2, in very conservative estimates, optimistic estimates indicate a density of up to 1,500 MW/km2.

An important factor for assessing renewable energy sources is also the coefficient of their annual use. It is the percentage of the year for which the source could supply its total produced energy if it was working at nominal output. The value of the factor for renewable sources is highly dependent on the location. The capacity factor of the compared nuclear power plant is around 90%. Due to frequent weather fluctuations, wind power plants achieve an annual utilization coefficient of somewhere below 30%, for solar power plants it is only around 15% in the conditions of Central Europe. This value means that, on average, a solar power plant will generate only 15% of its theoretical installed capacity per year. In other words, for the same installed output, a nuclear power plant will produce up to 6 times more electricity.

Financial demand

The basic data that comes up when deciding on the construction of a new energy renewable resource is the overall financial demands of the project. It can be assumed that as renewable resources expand more massively and technology improves, the investment costs for their construction will decrease. On the other hand, fossil fuels will probably show the opposite tendency. Due to depleting reserves, not only mining costs will rise but also the price of electricity produced from fossil fuels. Eventually, energy from renewable sources will be cheaper and more available than energy from non-renewable sources.

A purely economic parameter describing the appropriateness of using any energy source is the energy return on investment coefficient. This concept indicates the proportion of the total energy produced in a given power plant to the energy required for its construction, start-up, operation and decommissioning. In other words, it characterizes energy sources in terms of relative energy balance. According to the values of the coefficients, for example, it can be seen that the efficiency of electricity production in wind and solar photovoltaic power plants is approximately an order of magnitude lower than the efficiency of production in nuclear power plants.

Obviously, the coefficient must be greater than 1 but of course this is not enough. According to scientific studies, the acceptable coefficient value of return of the investment should be around 5 to 7 or it should be higher for a company which produces electricity to remain sustainable at the same level of technology and standard of living. When using resources with a low investment return coefficient, there is a risk that the company would have to invest more and more available energy to produce additional energy needed for its development.

The weather-dependent energy sources such as solar, wind and hydropower also require external energy storage to function smoothly, the cost of which quite substantially reduces the return of investment. Even after investments in storage, the energy source can reach below the limit of the sustainable coefficient of return of investment.