The value of heat increases with increase in temperature.
Higher temperatures give more potential use cases, reduce the volumes needed to process or store the heat, and increase efficiency of several processes including conversion efficiencies of turbines turning heat into electricity.
It is pretty straight forward to produce high temperatures by burning fossil fuels. Combined with their low costs and their easy storage, this is what makes fossil fuels such popular sources of energy and their global presence so ubiquitous.
Renewable methods for heat generation also exist. Some of which can also produce relatively high temperatures. This post is an attempt to provide a brief overview of these other methods and discuss their applicability and challenges.
Biogas has heat properties comparable to natural gas, but to replace natural gas it suffers from limited availability of feedstock. EU forecasts that in a best-case scenario biogas can supply 3.7% of EU’s primary energy need by 2030.
Biogas is also challenged by costs as the cost of producing the biogas in the same quality as natural gas is up to two times the price of natural gas.
Biomass, e.g. in the form of wood pellets or straw, is burned in furnaces to generate heat. This is common at Danish district heating plants.
Like biogas, challenges faced by biomass include limited availability of feedstock.
To replace fossil fuels with biomass would require four times the biomass production of today. All while global demand for land for food and feed production is rising steeply as well.
From an environmental perspective heat generated from biomass is likely better than heat generated from fossil fuels even though it emits as much carbon when used. However, due to a number of complex issues (see IEEP-link in 'References' below for details) it’s not a sustainable pathway towards the carbon emission targets set forth in the Paris Agreement.
Solar flat panels produce temperatures up to 60-70ºC/140-160ºF. For large-scale production this is well-suited for heating water for district heating and other low-temperature processes.
Though situated in one of the least sunny regions, Denmark is home to 75% of all large-scale flat panel solar fields in the world where they produce heat at costs competitive to natural gas. Given that Denmark’s district heating network only represents 1% of the global district heating market, and produces heat for just 0.1% of the global population, large-scale flat panel solar fields may arguably be one of the world's most overlooked business- and climate opportunities.
Evacuated tube panels are similar to flat panels but able to produce higher temperatures – up to ~130ºC/260ºF. However, as they are more expensive, they are challenged by the cost of flat panels when producing lower temperatures and natural gas when producing higher temperatures. Still, globally evacuated tube panels hold twice as big a market as flat panels with half the market (~$10 billion) aimed at providing heat for industrial processes.
Concentrated solar heating systems work by focusing incoming sunlight onto a smaller area thereby increasing the generated temperature. Until recently all such systems were built around different methods of focusing the sunlight using mirrors. From a technical viewpoint, these methods work well, but due to high production and maintenance costs, they have so far been unable to compete with fossil fuels.
The only commercially viable scenarios are use-cases where the heat generated by the mirrors, heat up a storage system which then releases the stored heat for electricity generation when solar cells do not produce. This is also known as concentrated solar power, CSP.
Above are shown examples of the four mirror-based methods of concentrating the sunlight. Fresnel (top-left) uses rows of tilted mirrors to direct the light to a single tube above the mirrors. Parabolic troughs (top-right) do the same, but using curved mirrors instead. In both cases, a liquid running inside the tubes absorbs the heat that is generated by the focused sunlight. This liquid then heats up a heat storage which releases the heat to run electricity-producing turbines when needed. Like the Fresnel solution, the tower solution (bottom-right) uses multiple mirrors to direct the sunlight. But instead of directing the light to a tube it is directed to a tower. Finally, parabolic dishes (bottom-right) can be used to direct the sun's light to heat a heat driven Stirling engine producing electricity directly.
The reason CSP makes financial sense in some of the more sunny areas of the world is that storing energy as heat is much cheaper than storing it as electrons in batteries. The next article takes a look at storage.
Recently, Heliac has introduced a new method for producing heat at same temperatures and better efficiencies than the mirror-based solutions. Once sufficient production data from Heliac's first full-scale solar field has been accumulated, a later article will describe how this solution as a first is able to produce high-temperature heat competitive with natural gas anywhere in the world.
Electricity can also be used for heat generation. This makes good sense in geographies favored by hydropower and when powering heat pumps boosting low-temperature heat up to ~150C. But producing heat with electricity when the electricity originally is produced by heat-driven turbines does not make much sense.
A variety of renewable sources can, as shown, produce heat at different temperatures and at different costs. At optimal places and for optimal applications, these methods are already today competitive with fossil fuels, but to capture a significantly larger share of the heat market storage is needed.
When it comes to storage, it is worth noting that the cost of storing energy as heat is a fraction of the cost of storing it as electricity. Simple methods for long-duration, big-scale heat storage already exist. Storage is up next.
Interested in reading more? Please see the links to my other articles below. Additionally, a 'Like’ from you will also be much appreciated as this should help direct more attention at the many business and climate opportunities the market for heat production offers.
Thank you for reading,
Optimal Use of Biogas from Waste Streams, European Commission, 2016
Optimising use of biomass in sustainable energy systems, Bindslev & Wenzel, SDU, 2016
Carbon Sustainability of Bioenergy, IEEP, 2016
Solar Heat Below Grid Price, Sustainable Energy Transformation, 2016
Denmark at global front within solar heating, Technical University of Denmark, 2018
HeatBooster, Viking Heat Engines, 2019
I have spent the better part of 20 years investing in cleantech startups. During my career I have probably seen at least 3,000 business proposals, including Heliac's which I was introduced to in 2016 when I headed Climate-KIC Nordic's accelerator program. I found -and still find - Heliac's solution to be by far the best new solution I've ever come around, which is why I joined the company in early 2017.
Disclaimer: I have not double-checked all my sources and I am not an expert in all areas mentioned in the articles. I may therefore have reached conclusions that wiser men and women may know to be inaccurate. If so, I trust they will let me know, so I can become a bit wiser too.