Power-to-X

Sometimes we have extra clean power.

We can turn that power into many things. It can make heat for your home. It can make fuel for cars. It can even make food.

We can use power to make gas. This gas can be stored for a long time. It can be used later to make power again.

We can also use extra power for heat. This stops the power from being wasted. It is a smart way to use energy.

This helps us use more clean energy. It is a great way to help the Earth.

Sometimes we make more clean power than we can use.

We can turn that extra power into many things. This way of using energy is called power-to-X. The "X" can mean many different things. We can make heat for homes or fuel for cars. We can even make food or chemicals.

One way is to make fuel. We can use a process called electrolysis. This uses power to split water into hydrogen. We can then turn that hydrogen into methane gas. These fuels can be stored for a long time. This is helpful when the sun is not shining. It is a great way to save energy for many months.

We can also use power to make heat. We can use heat pumps to do this. A heat pump is a tool that moves heat. It is very good at using extra wind or solar power. We can also charge electric cars when we have extra power. This helps us use every bit of clean energy we make.

Sometimes we make more clean energy than we can use. This extra power can be turned into many different things. Scientists call this way of working power-to-X. The "X" stands for many different uses. It can mean making fuel, heat, or even food.

This method helps connect different parts of our energy systems. It is a way to use surplus energy instead of wasting it. This is very helpful for a world using more wind and solar power.

One way it works is through power-to-fuel. We can use a process called electrolysis to split water. This uses electricity to create hydrogen gas. We can then turn that hydrogen into methane or methanol. These are fuels that can be stored easily. We can use them to make electricity again later. This can happen hours or even months after the energy was first made.

People have studied these ideas for a long time. In 2016, the German government funded a big research project. They spent 30 million euros to study power-to-X options. Researchers also look at how to use heat. They use things called heat pumps to move heat around. These pumps are very efficient. They can use extra wind or solar power to keep buildings warm. This helps use energy that might otherwise go to waste.

There are many important numbers to know about this. Electrolysis can be 80 to 85 percent efficient at its best. However, storing hydrogen as power-to-power is only 35 to 50 percent efficient.

Even so, storing the actual fuels is quite inexpensive. This makes it great for seasonal storage. A 2023 study looked at how this could work in Japan. That study found these technologies could reduce wasted energy by 80 percent or more.

You can see these ideas in your own life. Think about an electric car parked in a driveway. Charging that car is a form of power-to-mobility.

Most cars stay idle for a long time. We can choose to charge them when there is extra wind power. This is like using a giant battery on wheels. We can also use power to heat water for a bath. All these things help us use every bit of clean energy we make.

Power-to-X, often written as P2X, describes a group of technologies used to convert surplus renewable energy into other forms. This process is a key part of sector coupling, which means linking the electricity sector to other energy sectors. By doing this, we can create integrated, smart energy systems. These technologies are considered flexibility measures. They are especially useful for energy systems that rely heavily on renewable generation. They also help countries meet strong decarbonization targets.

One major pathway is power-to-fuel. This process begins with direct current electrolysis of water. Electrolysis is a method that uses electricity to split water into its parts. At its best, this process has an efficiency of 80% to 85%. This produces hydrogen, which is a gas that can be used for energy. Hydrogen can then undergo methanation to become methane (CH4). Another option is combining hydrogen with carbon dioxide to create methanol.

These fuels serve many different purposes once they are created. Hydrogen and methane can be used as downstream fuels. They can be fed directly into the natural gas grid. They can also be used to create synthetic fuel. In some cases, these substances act as a chemical feedstock, which is a raw material used in manufacturing. Ammonia is another example of a substance that can be produced this way. These fuels can be stored and reconverted into electricity using gas turbines, reciprocating engines, fuel cells, or combined cycle plants.

There are different ways to categorize these conversion pathways. Power-to-gas includes making hydrogen or methane. Power-to-liquid involves creating synthetic, carbon-neutral fuels. Power-to-heat uses excess electricity to provide warmth for buildings or industrial systems. Power-to-mobility refers to the charging of battery electric vehicles (BEV). There is also power-to-ammonia, power-to-chemicals, and power-to-food. Each type uses surplus power to solve a specific energy need.

Efficiency and cost are important factors in these systems. When looking at power-to-power, we measure the round-trip efficiency. This is the amount of energy we get back after storing it. For hydrogen storage, the round-trip efficiency is limited to between 35% and 50%. Electrolysis can also be expensive to perform. However, storing the actual fuels is quite inexpensive compared to other methods. This makes power-to-X ideal for seasonal storage. It helps manage the seasonal changes in solar, wind, and run-of-the-river-hydroelectric generation.

Power-to-heat is another highly efficient option. This can happen through resistance heating or via a heat pump. Resistance heaters have unity efficiency, meaning they are 100% efficient. Heat pumps are even more effective, with a coefficient of performance (COP) of 2 to 5. Large-scale heat pumps in district heating systems are very attractive. They can balance excess wind and solar power effectively. Using immersion heating for domestic hot water is also a cheap way to use surplus energy.

Research has shown the potential impact of these technologies. In 2016, the German government funded a €30 million research project for P2X options. More recently, a 2023 study looked at a highly renewable future for Japan. This study used linear programming to find the least-cost way to operate the system. It examined technologies like Fischer–Tropsch synthesis and Haber–Bosch synthesis. The results showed that P2X could reduce curtailment by 80% or more. Curtailment happens when renewable energy is wasted because there is no demand.

Finally, we can look at power-to-mobility through electric vehicles. Since vehicles are idle most of the time, we can shift their charging times. A vehicle might be idle for 8 to 12 hours. The actual charging duration is only about 90 minutes. This provides significant flexibility for the energy grid. Even the batteries in these vehicles can be discharged back to the grid. This allows them to work as electricity storage devices. However, doing this may cause additional wear to the vehicle's battery.