It’s an established fact that we are facing global environmental problems as of right now. Because of this, governments and regular citizens all over the world have tried to find solutions that can help save our planet from complete destruction. On the bright side, we have been able to actually find a few of these solutions, and one particular solution that is prominent is the utilization of renewable sources for energy generation. To be more specific, two of the widely known renewable sources are solar power and bioenergy.
But what exactly are solar power and biofuels? How exactly are they different from each other? And, if at all possible, which of the two of them is the better option in terms of energy generation?
Simply put, solar power is energy from the sun that is converted into either thermal or electrical energy. Because solar energy comes from the sun, it is one of the cleanest and most abundant forms of renewable energy sources available. In addition to that, it is also one of the most popular forms, considering that there has been a constant rise in the number of technologies that capture and harness this form of renewable energy.
There are various ways to capture solar energy, and as of right now, there are three prominent ones: photovoltaics, solar heating and cooling, and concentrating solar power. As of these three, photovoltaics is arguably the most common one, and this generates electricity directly from sunlight through an electronic process. Meanwhile, both solar heating and cooling and concentrating solar power make use of the heat that is generated by the sun. Concentrating solar power, in particular, uses mirrors to concentrate the sun’s energy to drive traditional steam turbines or engines that create electricity.
Just like the diversity in terms of technologies, solar power can also be used in a lot of different ways for domestic, commercial, and industrial use. The application can be as small as powering electronics such as calculators, road signs, and even homes and large commercial businesses. And it can also be as big as powering whole communities. Basically, there is practically no limit when it comes to the applications of solar energy.
On the other hand, bioenergy is a form of renewable energy that is derived from recently living organic materials known as biomass, which can be used to produce transportation fuels, heat, electricity, and products. A concrete form of bioenergy is the biofuel, which is any liquid fuel that is derived from biological material, such as trees, agricultural wastes, crops, or grass.
Essentially, biofuels can be produced from any carbon source that can be replenished quickly, like plants. Just like solar energy, the utilization of biofuels is also steadily rising nowadays. In particular, the biofuel industry is greatly expanding in Europe, Asia, North America, and South America.
Because of the fact that biofuels contain no sulfur and produce low carbon monoxide and toxic emissions, they are considered as substitutes for conventional fossil fuels, such as petroleum, propane, coal, and natural gas. As a result, biofuels can reduce greenhouse gas emissions and increase energy security by providing an alternative to fossil fuels. In fact, it has often been projected that by 2050, biofuels can reduce our greenhouse gas emissions by 1.7 billion tons per year. That number is equivalent to more than 80% of current transportation-related emissions.
Just like solar power, there are various technologies that convert renewable biofuels into heat and electricity. In particular, there are three most common ways to harvest the energy stored in biomass to produce biopower: burning, bacterial decay, and conversion to a gas or liquid fuel. No matter what technology is used, biopower has been proven to increase the flexibility of electricity generation and enhance the reliability of the electricity grid.
Related article: An In-depth Comparison: Solar Power vs. Wind Power
Solar Energy vs. Biofuels: Which Is the Better Option for Efficient Energy?
Even though it is ideal to replace fossil fuels with renewable energy sources such as sunlight or biomass, doing so is still very challenging, simply because these energy sources have a lower energy density. As a result, the amount of energy produced is not that impressive as opposed to the energy produced by fossil fuels.
With this, of course, we would naturally want to choose a renewable source that can generate the most energy. And so, if we want to maximize the efficiency of converting solar energy to renewable energy, which one is better: solar energy (particularly, solar panels) or biofuels? In order to attempt to answer that question, their individual energy conversion efficiency should be compared.
Energy Conversion Efficiency of Solar Panels
The total power from sunlight that reaches the earth’s surface is about 101,000 terawatts, which is around 2,500,000 EJ. However, even though that is the case, solar energy is geographically diffuse. There are just places that are sunnier than others. Because of this, it is then highly crucial to efficiently convert sunlight — to be able to capture its energy in useful forms.
The maximum conversion efficiency for sunlight is said to be 93%. This means that of all the power generated by sunlight, only 93% can be turned into electricity. However, photovoltaic cells in solar panels have efficiencies of only around 15% to 20% for converting sunlight to electricity, and that number will never reach the theoretical 93%. At the very most, solar panels are limited to a maximum conversion efficiency of ~30%, primarily because we only have the technology to convert some parts of the spectrum of sunlight to electricity. This limit is described by the Shockley-Queisser limit.
On the bright side, advancements in solar panel technology and recent discoveries are still continuing to happen on a regular basis. And all these advancements and discoveries will definitely have a role to play in expanding this limit somewhat. In fact, right now, there are some solar panels that have an efficiency level of above 20%, which is uncommon since the majority of panels range from 15% to 17% efficiency rating.
Energy Conversion Efficiency of Photosynthesis
We are all aware that photosynthesis is the process used by plants, algae, and certain bacteria to harness energy from sunlight and turn it into chemical energy. It’s essentially the source of the world’s food, animal feed, fibre, and timber. But aside from that, photosynthesis is also the source of biomass-based biofuels that are a source of renewable energy.
To perform photosynthesis, plants, algae, and certain bacteria need three things — carbon dioxide, water, and sunlight — and after this process, starch and sucrose are the main products. Basically, photosynthesis can be summarized by the following equation: CO2 + H2O + light energy = [CH2O] + O2.
The maximum efficiency of converting solar energy to biomass energy is estimated at around 4.5% for algae, 4.3% for C3 land plants (such as woody, round-leafed plants; basically, 95% of all plants), and 6% for C4 land plants (such as sugarcane, switchgrass, Miscanthus, and sweet sorghum).
Plants are limited by their dependence on photons that fall in the approximate waveband of 400-700 nm, and by inherent inefficiencies of enzymes and biochemical processes and light saturation under bright conditions. Additionally, their respiration consumes 30% to 60% of the energy they make from photosynthesis, and they also spend half of each day in the dark, thus needing to use previous carbohydrate stores to keep them growing.
But even with this low number already, the actual conversion efficiency is even lower than the calculated potential efficiency. This means that the actual conversion efficiency of algae is 3.2%, and 2.4% and 3.7% for the most productive C3 and C4 crops across a full growing season. These efficiency reductions happen because of the insufficient capacity to use all the radiation that falls on a leaf. In addition to that, plants’ photoprotective mechanisms, which have evolved to stop leaves from oxidizing, reduce efficiency as well.
Conclusion: Which Is the Better Option?
When you put the two energy conversion efficiencies of solar panels and biomass, the initial conclusion that you will get is that solar energy is the better option. The energy conversion efficiency of solar panels may only be less than 30% at most, which is admittedly low, but that is still bigger than the energy conversion efficiency of biomass, which sits at less than 10% on average. So, in terms of efficiency levels, solar is the winner.
However, that doesn’t really make solar panels inherently superior over biomass. This is because plants and other forms of biomass are self-regenerating while solar panels are not. What this means is that if panels get broken, the energy output gets drastically reduced, and there is an added cost to repairing the damaged panels or to buying new ones. Meanwhile, with biomass, there is no added cost. In other words, it’s true biomass is not as efficient as solar panels, but at least, it also won’t cost money since it can replenish itself.
Long story short, both solar energy and bioenergy have their own perks and limits. And if we are to truly save the environment, then we should not settle to choose only one option. There is always a time and place to use either solar energy and bioenergy, so we should choose both of them. Doing so will definitely maximize the clean energy generation as a whole, thus resulting in a better and sustainable environment. And having a sustainable environment is clearly the end goal for utilizing renewable energy sources in the first place, so both solar energy and bioenergy are beneficial in their own way.