David Connolly is an Associate Professor in Energy Planning at Aalborg University in Copenhagen, Denmark. His research focuses on the design and assessment of 100% renewable energy systems, with a key focus on the integration of intermittent renewables (such as wind and solar power), district heating, electric vehicles, and the production of electrofuels/synthetic fuels for transport.
What are the main insights that we aim to achieve through the development of energy system models?
Energy system models help us understand the impact of making changes to the energy system before we make them. The insights tend to vary significantly depending on the time-horizon in question. Some models focus on the short-term (years ahead) so they usually model existing technologies within existing financial frameworks, such as a model that analyses how to dispatch a power plant on the electricity markets we have today. Other models focus more on the long-term (decades from now), so they can provide insights for more radical changes to the technologies, institutions, and markets we have today. For example, these models will often include wave power or power-to-gas, both of which are not even commercially available right now. EnergyPLAN is primarily designed to analyse the large-scale integration of renewable energy and energy efficiency, based on the Smart Energy Systems concept. Renewable energy still provides a relatively small amount of our energy today, so analysing ‘large-scale integration’ requires a long-term perspective over many decades. EnergyPLAN is therefore focused on radical changes to our energy system compared to today, but it also simulates the energy system on an hourly basis to account for intermittency from renewable energy.
Tell us a little about the EnergyPLAN model and its energy system analysis procedures.
EnergyPLAN is primarily a simulation model, but it also includes some optimisation. I would equate the ‘user’ of EnergyPLAN to a ‘designer’: the user designs an energy system in EnergyPLAN in terms of demands, capacities, efficiencies, and costs and once it is complete, the user simulates how that energy system performs. However, to carry out the simulation, the user must also instruct the model how to ‘optimise’ its decisions during each hour of the simulation. In other words, the optimisation tells the simulation how to make its decisions during each hour of the year.
The most common optimisation we use in EnergyPLAN is called the ‘technical optimisation’, where the main objective is to reduce the energy consumed during the simulation. Alternatively, the user can use an ‘economic optimisation’ where the model will reduce the cost of the energy system during the simulation. It is important to note that the optimisation only refers to the operation of the energy system during each hour and not to the ‘design’ of the energy system. In other words, the capacity of wind turbines in your energy system will not be altered during the economic optimisation, but the way those wind turbines operate each hour may be.
How does the EnergyPLAN model compare with other models; what are its distinguishing features?
I would define EnergyPLAN’s niche in the mix of models that currently exist as: it simulates all sectors of the energy system on an hourly basis after they have undergone radical changes. It can do this due to a combination of the following key characteristics:
- It can simulate radical changes for renewable energy and energy efficiency, since it considers all major technologies that exist today (including district heating) as well as technologies which are not commercially available yet, such as hydrogen production, biomass gasification, carbon capture, and electrofuels.
- The model considers the entire energy system, including electricity, heating, cooling, industry, and transport, so the impact of changing the heat sector is reflected in the other sectors also.
- EnergyPLAN is an hourly model so it ensures that demand and supply are always met on hourly basis across the electricity, district heating, and gas networks.
- It accounts for synergies across all sectors on an hourly basis when integrating renewable energy, which is based on the Smart Energy System concept. It is very important to consider these synergies when quantifying the impact of future due to the additional flexibility that these synergies create for intermittent renewables like wind and solar.
How does the EnergyPLAN model contribute to the design of energy planning strategies?
It quantifies the impact of implementing large-scale penetrations of renewable energy and energy efficiency, usually in terms of energy, emissions, and costs. By quantifying the impact, we can often reveal that some decisions are much more or less significant than policy-makers realise. A very good example of this comes from our Heat Roadmap Europe work. Initially, policy-makers thought that district heating was very expensive, especially due to the construction of the pipes in the streets. However, by quantifying this, we have been able to demonstrate that district heating is cheaper than natural gas in many countries. Even more surprising, during this calculation we found out that the pipes in the ground are one of the smallest costs for a district heating scheme, even though they are the most visible since they require construction on the streets. This is very important for policy-makers: for example, recently we were advising a local municipality about the roll out of district heating in their city. They were focusing on the cost of the pipes in the street since they assumed this would have the most influence on the overall economic viability of the project. However, after quantifying the breakdown of the cost for them, they could see that the price of the heat supply had a much bigger influence than the price of the pipes, so we recommended that they focus their efforts on securing a low and stable heat supply price. This is a very specific example, but in most studies EnergyPLAN changes perceptions like this on a broader energy-system scale. For example, it has previously been used to demonstrate how 100% renewable energy systems have comparable costs to fossil-fuel based energy systems, which can be found at: www.SmartEnergySystem.eu.
A key objective of EnergyPLAN is to aid in the design of 100% renewable smart energy systems. How will it achieve this?
Our results to date indicate that the key to 100% Renewable Energy and the Smart Energy Systems concept is integrating the various sectors: electricity, heating, cooling, industry, and transport. Historically these sectors have evolved individually from one another: power plants producing electricity, boilers creating heat, and combustion engines providing transport. We need to remove this ‘sectoral approach’ and move towards an ‘energy system’ approach, since this will create many new opportunities for both energy efficiency and renewable energy integration.
Let’s take the electricity and heat sectors as an example, since many EU countries have already started connecting these in recent decades. If these sectors are designed in isolation, then the power plants will only produce electricity, but if these two sectors are designed in combination with one another, then it is very likely that combined heat and power (CHP) plants will be most economical. A power plant has an efficiency of 30-50% for electricity generation, whereas a CHP plant has an efficiency of 80-90% for electricity and heat production together. Hence, there is often a significant improvement in energy efficiency by replacing a power plant with a CHP plant, something we quantified for five EU countries in the recent STRATEGO project: these countries are Croatia, Czech Republic, Italy, Romania, and the United Kingdom.
Similarly, if we try to optimise the integration of renewable electricity with a sole focus on the electricity sector, then we will limit our solutions to those that exist within the electricity sector such as interconnection, demand-side management, batteries, and pumped hydroelectric storage. However, if we optimise across the electricity and heat sectors together, then we will be able to use cheaper alternatives for the integration of renewable electricity such as heat pumps and thermal storage. We already see this in Denmark, where large-scale electric boilers are integrating more wind power via thermal on the district heating network. This is often a cheaper solution since thermal storage is approximately 100 times cheaper than electricity storage, so we often use EnergyPLAN to quantify how much additional wind power we can accommodate due to the connection between the electricity and heat sectors.
EnergyPLAN also connects cooling, industry, and transport with the electricity and heat sectors to identify synergies that increase energy efficiency and renewable energy. By using this sectoral approach, 100% renewable energy systems become more economically viable and thus more likely to be implemented.
How does your model accommodate new technologies and new research and development?
We try to release a new version of the model every 6 months on the website. Updates are very closely linked to the research projects that we are involved in and existing technologies within EnergyPLAN are regularly updated if we identify a new consideration in one of these projects. New technologies tend to be included over time rather than all at once. For example, power-to-gas originally began as an additional electricity demand for hydrogen production, but as we learned more about the technology, it evolved into individual components in the process such as electrolysers, hydrogen storage, carbon capture & recycling, and biomass gasification.