When you think about humanity’s impact on the climate, images of airplane and car exhaust fumes may spring to mind. Yet aviation and cars only account for 2% and 6% of global carbon emissions, respectively.

Another sector — which hardly anyone ever talks about — has higher emissions than both of these put together, accounting for 10% of our planet’s greenhouse gases: industrial heat.

The high temperatures that heavy industry requires to produce steel, aluminium, concrete, cement, glass and other important resources are mainly derived from burning fossil fuels — often carbon-rich coke or coal.

An Energy Nest heat energy battery being transported to site

Energy Nest

And huge amounts of this heat energy — not to mention the heat generated from sources such as conventional power plants — are simply wasted on a daily basis.

If this heat was captured, stored and re-used when required, it could massively improve energy efficiency, cutting both costs and emissions across a wide range of industries.

Norwegian start-up EnergyNest has produced a new type of modular thermal battery able to store waste heat for hours, days or even weeks with minimal losses. With a levelised cost of storage said to be as low as €15 ($17.60) per MWh for large projects — up to 47 times cheaper than utility-scale lithium-ion storage — it is little wonder that the start-up has already inked deals with the likes of Siemens, EDF and Eni.

And even if heavy industry replaces the fossil fuels used to generate high-temperature heat with cleaner alternatives — such as hydrogen or renewables-powered electric arc furnaces — companies would still cut their heating costs by reducing and recirculating their waste heat.

“All industrial manufacturers that have thermal processes in place would benefit from our technology,” EnergyNest chief executive Christian Thiel tells Recharge. “Breweries, chemicals, pharmaceuticals, steel, aluminium, concrete, brick makers, other building manufacturers — they all operate with high-temperature heat.

“Decarbonising combined-cycle [natural gas-fired] power plants is also on our agenda, and we can offer 24-hour concentrating solar power [CSP] for 30-50% below the cost of molten-salt storage.”

According to a study by analyst Aurora Energy Research, commissioned by EnergyNest, the thermal battery segment represents a $300bn global market opportunity by 2030 ­— three times larger than the market for utility-scale electric batteries.

EnergyNest’s thermal battery is as a six-metre-long 1.5MWth module the size of a shipping container that consists of carbon-steel pipes looping in and out of long cylinders of Heatcrete — a low-cost proprietary concrete-like material made from the mineral quartzite, with small amounts of cement, chemical binders and superplasticisers that has excellent heat-storing properties. High-temperature heat of up to 430°C can be stored in the Heatcrete, and later released via a heat transfer fluid — either synthetic oil or steam — pumped through its steel pipes.

As the thermal battery is modular and stackable, projects can utilise any number of units — from one at a small industrial plant to the several thousands required for a 24-hour gigawatt-scale CSP project.

Privately owned EnergyNest designs bespoke heat-storage systems — incorporating items such as heat exchangers, electric heaters, steam generators, additional piping, and integration work with existing facilities — to suit every possible application of the technology.

“So, for instance, at the project that we’re doing at brick maker Senftenbacher’s plant in Austria, which is a waste-heat recovery project, we tap into the excess heat generated by a kiln furnace,” explains Thiel. “We install a heat exchanger near the kiln, and extract the heat from the heat exchanger into a closed-loop oil system. Some small pumps circulate the hot oil and then the Heatcrete storage is really heated up. And then when we discharge at this project, the heat from the fluid activates an off-the-shelf steam generator. And the steam increases the temperature in the kiln.”

The technology’s versatility can be seen by comparing that arrangement with EnergyNest’s project at the 870MW Sloecentrale combined-cycle gas-fired power station in the Netherlands, which will increase efficiency and reduce emissions at the plant using a very different business model.

Combined-cycle plants use electricity-generating gas turbines, which produce high-temperature heat as a by-product, and then turn that waste heat into steam to drive electricity-generating steam turbines. Sloecentrale — part-owned by EDF — will buy low-cost or negatively-priced wind or solar power from the grid (during windy and/or sunny periods) and convert that electricity to heat using an electric heater. That heat will be stored in the EnergyNest battery and later converted to steam (via a steam generator) to power the plant’s steam turbine when the wholesale price of electricity is high. This price arbitrage will increase the plant’s income as the battery reduces fuel costs — while also helping to balance the grid at times of high renewables output.

In a similar vein, the Heatcrete system could turn open-cycle gas-fired or oil-fired power stations —which do not have the secondary steam turbine — into de facto combined-cycle plants.

Alternatively, EnergyNest could convert low-cost excess renewable energy into heat for use at a nearby manufacturing facility or district-heating system.

Thiel — a former vice-president at wind turbine maker Senvion — does not believe that converting renewable energy to heat and back to electricity would be a good use of the technology. While the EnergyNest system offers a round-trip efficiency of up to 99% when capturing, storing and outputting heat, a heat-to-electricity-to-heat project would only have a round-trip efficiency of about 40%, due to the energy lost by converting the electricity to heat (using an electric heater) and then converting the electricity to steam (using a steam generator) to drive a turbine.

“Electricity in and electricity out is not our ball game,” Thiel explains. “And that’s why we don’t see ourselves competing with lithium-ion or Siemens Gamesa’s hot-rock storage. Technically we could do it, but the business case is not there. So what EnergyNest is after is really those projects where heat plays a major role.”

This does, however, include CSP, where high-temperature heat drives steam turbines to produce electricity. For instance, in parabolic-trough CSP projects, curved mirrors bounce concentrated sunlight onto a heat-absorbing tube containing synthetic oil, making it extremely hot, with the heat used to turn a steam generator. This oil pipeline can simply be connected to the Heatcrete modules, with the heat being stored for enough hours to ensure round-the-clock electricity output.

Currently, only CSP systems that use molten-salt as the heat-carrying medium — at power-tower projects where flat mirrors reflect sunlight onto a receiver at the top of a tower — can be used for baseload power.

“We are definitely a straight-on fit here, and can offer [24-hour output] at 30-50% below the cost of molten-salt storage,” says Thiel. “Molten salt is energy storage, but it’s also a chemical plant. We can take away all the complexity and cost of a chemical plant and replace it with solid-state energy storage with no moving parts and make those CSP plants much cheaper.

“We have done our cost calculations for our CSP storage and come to the figure of €15/MWh [for a gigawatt-scale plant].”

By way of comparison, battery storage costs $165-325/MWh for utility-scale projects, according to financial advisor Lazard.

EnergyNest’s first CSP project, at Italian oil giant Eni’s refinery in Gela, Sicily, is due to be installed later this year or possibly in 2021. The Norwegian company will connect a thermal battery to a CSP array, allowing it to produce round-the-clock steam, partly displacing the steam generated with fossil fuel and grid electricity at the facility, lowering the plant’s carbon footprint.

Eni is now also considering using the EnergyNest equipment at its own gas-fired power stations.

“The technology obviously has wider applications than just CSP,” says Francesca Ferrazza, Eni’s senior vice-president for research & technological innovation, decarbonisation and environmental research and development. “It all comes down to the cost and reliability. It has to be profitable and it has to be something you can fit in to a commercial scheme.

“If the technology works in these two very different cases — solar thermal and a conventional gas power plant — then it can work anywhere.”

Thiel tells Recharge that whichever application a customer chooses, the payback period would be two to seven years, enabling companies to potentially save millions of dollars over the course of a 20-30-year EnergyNest project.

Siemens Energy has recognised the technology’s potential — in June it entered a long-term partnership with EnergyNest to jointly develop thermal energy-storage solutions for industrial companies.

“We have a strong partner in Siemens to address the large industrial customer base — both in Europe and globally — with whom we can deliver turnkey energy solutions for decarbonisation,” says Thiel.

“Energy storage is the key to a decarbonised world,” said Jörn Schmücker, chief executive of Siemens Energy’s Large Rotating Equipment business unit. «With [our] Future of Storage [programme] and our cooperation with EnergyNest we are able to offer our customers exactly those solutions which help to sustainably decarbonise the industrial sector — with the strong advantage of improving the efficiency and the economics of their plants”.

In short, EnergyNest’s thermal battery — a kind of Swiss Army knife of emissions reductions ­— seems to be a win-win anywhere that large-scale heat is present.

Leigh Collins, rechargenews.com