The urgency of addressing the climate crisis has been widely recognized by world governments, international organizations, various corporations, and the broader civil society. The Paris Climate Conference in December 2015 was a significant milestone for global efforts to address Greenhouse Gas emissions. The Intergovernmental Panel on Climate Change has estimated that decarbonization and negative emissions would be required in order to achieve this goal.
Understanding the most important fundamental technical concepts is challenging, in Part I we started with basic concepts related to emissions. In this article we discuss critical concepts relevant to zero carbon energy generation and renewable energy.
‘’Understanding the most important fundamental technical concepts related to climate change is challenging for everyone.”
Energy Density
Energy density is a very important concept in the climate challenge, because solving climate change will require the right technologies and the right tools. It is important to understand the most important metrics that can be used to evaluate these technologies and tools. Energy density is the amount of energy that exists in a certain volume. One of the key concepts to grasp is the energy density of a zero-carbon fuel. This concept matters because the higher the energy density of a certain type of fuel, the more utility you can get out of such fuel, and the less space it occupies and therefore the more efficient it becomes to transport and use. For example, nuclear fuel is a zero-carbon fuel that is a million times more energy dense than hydrogen as a fuel. This gives nuclear fuel an advantage.
Another key related item that is affected by a fuel’s energy density is storage capacity, storing energy will be paramount when addressing the climate change problem, solutions like battery energy storage have lower energy density than storing energy in hydrogen which has higher energy density but more expensive and less efficient than other energy storage technologies like pumped hydro and battery energy storage.
The last key item when it comes to energy density is space, how much space does a solution needs to generate energy. For example, Geothermal energy requires much less space than wind and solar power but costs a bit more to build.
The questions to ask when it comes to energy density and low/zero-carbon fuels: how much energy is in this fuel? How much energy storage can store? What are the costs/effciency? How much space does this technology occupy?
Capacity Factors
Capacity factor is another interesting concept to understand. Wind and solar are great technologies to solve climate change. However, the intermittency of wind energy and the fact that the sun shines only half of the day in most places in the world make these technologies have low capacity factors. A low capacity factor concept means that you have to build out much more wind turbines and solar panels than you actually need. For wind and solar energy, you may need to build as much as double the amount you need in comparison to if the wind was blowing all the time or the sun was shining all day long.
On the contrary, hydro power is a zero-carbon technology that has a very high capacity factor, there is no need to build more dams/hydro turbines to extract the energy you need. Similar goes to other solutions like geothermal or nuclear energy. Higher capacity factors provide more reliability and are always favorable.
Round Trip Efficiency for Energy Storage
The round-trip efficiency concept is important for solar and wind energy because of the intermittency of these two energy sources. The best way for solar and wind to work providing emission free (direct) energy is to be coupled with storage solutions, for example battery storage, pumped hydro storage, flywheel, compressed air energy storage, or hydrogen storage. Any energy storage solution will have a round trip efficiency which means how much energy you are getting back from the storage compared to what you initially put in. The higher the efficiency the better the solution, for example, pumped hydro has up to 87% efficiency, batteries have between 70% and 80% efficiency, while hydrogen as a storage medium has an embarrassing 40% efficiency.
The previous concepts are a great quick start guide for the non-technical public as well as decision makers to ask the right questions and understand the basic differences to have an informed discussion. If not addressed the consequences of the climate crisis will be grave. Humanity is already at risk from many factors, including resource depletion, conflicts, and normal accidents. Mitigating the climate crisis will prevent further misery and suffering for all.
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