The world is now at a point where solar and wind power are considerably cheaper than the fossil fuels used in many cement plants. However, renewables are intermittent and difficult to harness for industrial use. Here's how Rondo Heat Batteries can bridge the gap between intermittent renewable power generation and continuous industrial heat.
Cement producers use many different fuels, each of which comes with its own challenges. Most operators are pragmatic, now combining the reliability of fossil fuels with increasing volumes of lower-cost, lower-CO2 alternatives. The drive to alternatives, particularly biogenic fuels, is now more intense than ever, with increasing proportions of renewable power also added to slash the embodied CO2 emissions of cement products. Some producers have gone one step further by burning 'green' hydrogen, or even converting electrical power into high temperature gases via novel electrification processes.
A sticking point...
The answer, to both climate and cost issues, seems to be 'electrify everything... now!' However, while it is now far cheaper to produce renewable power than to use fossil fuels, navigating the mismatch between supply and demand is a major headache. The sun only shines at the equator 12hr/day and wind turbines need the wind to generate power. Otherwise they can be out of action for days or weeks at a time. Two undesirable consequences follow. Firstly, there are times where renewables generate more energy than can be consumed by the grid, leading to negative prices and/or facilities being taken offline. At other times, fossil fuels will be needed to plug the gap between low supply and high demand. This is not very sustainable.
There are several work-arounds to these issues. Conventional batteries can hold charge for several hours to spread out solar supplies, while hydrogen is touted as a longer-term storage solution, perhaps to build up a reserve of energy from wind power.
However, conversion efficiencies present another issue. The total conversion losses when taking renewable power, converting it to hydrogen for long term storage and then burning it, is just 50%. Even lithium ion batteries lose 15% of their energy over a charging cycle. With the cost of renewable energy decreasing by around 30% for every doubling of capacity, it makes sense to find more efficient ways to store and use it, particularly for heavy industrial users such as the cement sector.
Enter Rondo
Rondo Energy is a California-based company founded in 2020. It works to decarbonise hard-to-abate sectors such as cement, with backing from Bill Gates' Breakthrough Energy Ventures, Energy Impact Partners and industrial partners in the form of Siam Cement Group and Titan Cement.
Rondo's researchers realised that, as industrial users need thermal energy, we should store the energy from renewable power sources as thermal energy, rather than electrical or chemical energy. If it developed a technology that could re-power conventional industrial processes, with the right volume, temperatures and footprint at the right cost, with good reliability, this would be very interesting to industrial users.
How to do it?
The best way to convert electricity into heat is a simple element like that found in an electric storage heater. Rondo has found a way to embed heating elements in a structure made from a widely-available low-conductivity ceramic material. This can reach temperatures up to 1500°C. Passing a gas close to the refractory brick heats it rapidly and efficiently to high temperature. By arranging a number of element-infused refractory structures in a '3D chessboard' formation, Rondo developed the 'Heat Battery' concept. One modular configuration, the 'RHB300,' is an energy-dense installation that is 10m x 30m and 10m high. This contains 1500t of ceramic material.
Inside, all of the surfaces of the ceramic bricks are heated uniformly. When ambient air (or other gas) is introduced at the bottom, the white-hot bricks heat it as it rises through the structure, such that it reaches 1500°C by the time it leaves. The temperature of the air leaving the top of the battery remains the same a long time into discharge.
By doing this, Heat Batteries absorb intermittent renewable energy and convert it into a steady stream of hot gas, ideal for feeding to a cement plant mill, dryer, calciner or kiln. And the best news.... the energy conversion losses are 2% at most, far in advance of competing approaches.
From principles to practice
At the end of 2021 a significant investment from Breakthrough Energy Ventures and Energy Impact Partners allowed Rondo to move from the patenting and R&D phase on to manufacturing. The first customer units, for applications other than cement, will be installed in early 2023, followed by several larger projects throughout the rest of the year.
The company is very excited about the applications possible in the cement sector, where its first focus will be in the calciner. The potential is huge, as a moderate-sized cement plant might need a solar plant of 1000 - 2500MW. This is a huge number for a solar PV plant and larger than we are used to thinking about. However, this is exactly the kind of project that the renewables sector is crying out for. Unlike complicated grid structures, large point loads like Rondo Heat Batteries represent a fantastic opportunity for large, unconnected solar PV arrays or wind farms.
The development of the Heat Battery also gives renewable energy suppliers the opportunity to become suppliers of 'heat as a service.' Rondo estimates that the payback time of a large solar PV array in a location like California would be 2 - 3 years if it supplies heat as a service. The payback time for the same PV array supplying the electricity is around 10 - 15 years, mainly due to losses from mismatched supply and demand. This should be a 'no brainer.'
There are potential roadblocks to scale up, of course. The main one is the the fact that Heat Batteries are a new technology, albeit one that has twice the efficiency and half the capital cost of hydrogen. Ultimately, Rondo needs to prove it at scale and the cement industry represents a challenging, yet very achievable application. Once the first reference is out there, the next question from others in the sector will be 'How fast can I have how much?'
First movers
There are certain markets that could experience faster pick up than elsewhere. This is generally corellated to the prevalence of renewable power generation, as well as the potential for renewable power to be scaled up quickly. There are wind-based projects in the US and Scandinavia and solar-based projects in Chile and Australia. These should be top of mind due to high electricity prices and lots of renewable potential. In the cement sphere, India is another important market, one that has done very well on its solar mission. China also has a lot of potential simply due to the size of its cement sector. Its top-down way of doing business could enable very fast roll out.
Impacts
Rondo estimates that it could eliminate 1% of world emissions using this technology over the next 10 years. That's around 600Mt/yr of CO2 emissions. Of course it wants to go far further and faster beyond that. After all, if a solution cannot reach scale, it is not really a solution. We would like to target a 50% reduction from all kinds of industrial CO2 emissions in the longer term. This is not impossible.
Ultimately, with the Rondo Heat Battery, and other technologies like it, we are not heading to a world where net-zero technologies add to the cost of business, as we might expect with CO2 capture and storage. In fact, the Rondo Heat Battery enables us to have more energy than ever before...at a lower cost than ever before. Crucially the energy will be more equitably distributed, as electricity is much easier to transmit over long distances than hydrocarbons. This will be good for international equality, as well as industrial users like the global cement sector.
