Comparison of Renewable Energy Source

(Transcript of the video commentary.)

When you think of renewable energy sources, most people think of ecological, emission-free power plants that use mainly the energy of the Sun, water or wind. Just build them and they provide us with electricity practically for free. The trend of their construction has been increasing in recent years and it might seem that it is the most logical way to climate neutrality. The indisputable advantage of renewable sources is that they are clean, safe and easy to operate. Even though each source has its own specifications, in general they have a low output density and a large output dependency on the weather compared to, for example, nuclear energy which, as an emission-free source, we still have to depend on.

Comparing renewable sources with each other is useful when deciding which one to choose under the conditions of a given location. What is more interesting, however, is the comparison with existing non-renewable resources from the point of view of achievable output, the required area to achieve the required output, and also financial demands.

Comparing nuclear energy 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 that clear-cut as recently, new renewable technologies have become considerably cheaper and on the contrary, the construction of nuclear blocks continues to become more expensive. But the simple fact remains that compared to solar energy, a nuclear power plant produces approximately 150 times more electricity per square kilometre. In the case of wind energy, it is almost 500 times more energy per square kilometre.

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 one percent of total production. The majority was covered by traditional biomass burning. 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.

A big advantage of renewable energy sources 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.

A comparison of the unit output of the main renewable sources with the outputs of, for example, nuclear reactors, clearly shows that the installations of renewable sources follow a more quantitative path, i.e. deploying hundreds to thousands of small sources. 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. A 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 have a unit output from 600 kW to 9 MW, which means that the output of a 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 very wide. 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, geothermal energy had a capacity of just 14 GW.

Renewable sources require a significantly larger amount of land for their installation than, for example, the aforementioned emission-free nuclear power engineering. This is most vividly 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 gets approximately 10 MW from the occupied square km. Ground photovoltaics is several times better with output density. Panels stacked on an inclined south-facing roof can produce twice as much electricity per km2 as ground photovoltaics. For comparison, we can state that the output density of nuclear power is around 250 MW/km2 in pessimistic estimates and over 1,000 MW/km2 in optimistic estimates.

An important parameter for assessing renewable energy sources is also the capacity factor or the coefficient of their annual use. It is the percentage of the year for which the source would produce its total supplied 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 plants is around 90%. Due to frequent weather fluctuations, wind power plants achieve an annual utilization coefficient of somewhere below 30% and for solar power plants it is only around 15% in the conditions of Central Europe. It means that, on average, a solar power plant will generate 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.

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 and the related future competitiveness of the resource. It can be assumed that as renewable resources expand massively and technology improves, the investment costs for their construction will decrease. On the other hand, the fossil fuels still needed 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. This fact will be further supported by the adopted green policy. In the future, energy from renewable sources can be expected to be cheaper than energy from non-renewable sources.

An even more telling parameter about the suitability and efficiency of an 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. If the peripheral conditions are properly set, the investment return coefficient can become a suitable tool for comparing different energy sources from the point of view 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 various studies, the minimum coefficient value of a return of investments should be around 5 to 7 for a company which produces electricity, to remain sustainable at the same level of technology and standard of living. Using resources with a low return of the investment, society would have to invest more and more available energy to produce more energy for its development.

The graph also shows that weather-dependent energy sources such as solar, wind and hydropower also require external energy storage to function smoothly, the cost of which rapidly reduces the return of the investment. The energy source can even fall below the value of the sustainable economic threshold after investments in storage.

Renewable resources are extremely environmentally friendly. Today, in the period of ongoing climate change, fossil fuel resources are increasingly being abandoned and replaced by renewable resources. They do not produce any solid or gaseous emissions or waste heat and do not burden the environment with waste. The use of solar and wind 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.