First case: European spallation source ESS
The first case study is the European Spallation Source ESS, a research facility being built in Lund, Sweden comparable in physical size and scope of energy transformation to a medium-sized heavy industry plant. ESS is a neutron source that will provide, when complete and at full power in 2025, the world’s brightest neutron beams, enabling scientists to peer inside materials with spatial resolution in nanometres and time resolution in nanoseconds. Spallation is the process of freeing neutrons from atomic nuclei. At ESS, the spallation will be powered by the world’s most powerful linear accelerator, about 500 m long. To achieve this world-leading performance, the design of ESS demanded substantial innovation. At the same time, the demands for scientific quality place extreme requirements for reliability, monitoring and replicability [9].
To decide where in Europe to locate ESS, a competition was arranged, in which Sweden and Denmark participated as “ESS Scandinavia” with Lund as the proposed site. In addition to marketing the university town of Lund and promising substantial cash contributions, ESS Scandinavia committed to building “the world’s first sustainable research facility”. The claim to sustainability rested on an “energy concept” called “Responsible, Renewable, Recyclable”, with ambitious targets for improved energy efficiency, sourcing with renewable energy and heat recycling [24]. The ESS energy concept represented a significant innovation [25].
The energy systems of ESS are complex. The range of cooling needs spans from the superconducting linear accelerator at under two Kelvin to the nuclear processes in the target, the spallation, hot enough to instantly vaporise molecules of the target material. The extreme values were captured in specialised systems, so that the site-wide cooling systems had three levels, one for chilled water, one for warm water such as would be conventionally supplied by cooling towers or a body of water, and one for hot water. The hot-water cooling loop was an innovation to make direct use of the local district heating system that supplied heat to the buildings of Lund. Recycling to district heating required a temperature of 80 °C and returned a temperature of around 50°. A significant part of the energy effort at ESS was devoted to finding equipment that could be cooled, or could be redesigned to be cooled, at the hot range. Because the heat recycling commitment prohibited the use of cooling towers and the district heating system was the only available heat sink, all lower temperatures necessitated the use of heat pumps. The physics of the Carnot efficiency dictate that the efficiency for a heat pump falls with greater temperature differences. The result was a dilemma. Recycling the waste heat would cost substantial electricity use, conflicting with the first priority of energy efficiency [26].
The conundrum could be solved by finding a lower-temperature heat sink than the district heating system. To this end, ESS held an Open Call for uses of waste heat. This produced a great range of suggestions for use of waste heat, most of which required a temperature difference of around 80 °C or more, in order to achieve acceptable efficiency. Since the challenge was to use lower temperature heat, and no cold temperature source was available, all suggestions based on heat engines had to be discarded. What was left made clear that temperatures as low as 40° can be used for space heating, although the systems to distribute the heat will be more expensive than for higher temperatures. Heat at 60° can be used without significantly increased investment compared to conventional solutions [26].
Heat at around 40° could also be used for low-temperature drying, such as of biomass for biofuel, to drive digestion or fermentation processes, or for water treatment, all uses that would contribute to various forms of renewable energy production or ecological improvement, but sadly no commercial opportunities were identified. Commercial viability was a necessity, as ESS did not have investment budget for such systems to use its waste heat. Therefore, the systems needed to be sufficiently commercially attractive to attract the necessary investment. In the climate surrounding ESS, inexpensive space heating was found to make greenhouse farming of tomatoes profitable. Greenhouse farming in Sweden has a comparative disadvantage in the cost of heating, compared to facilities on the continent. If that disadvantage was offset by inexpensive waste heat, comparative advantages such as ample access to clean water and a competitive electricity price would make the facility competitive and attract investment [26].
The open call also resulted in proposals for use of heat at even lower temperatures. Two of these were explored further in the case. One of these was an on-land, recirculating fish farm. The species of fish proposed were such that temperatures of just under 20° would be used. In many climates, this might as well be a cooling temperature as a heating temperature, but the ambient conditions were such that holding 20° would require heat for almost all the year in average years. The ESS operation schedule also called for the main shut-down period for maintenance to be in the summer months and cooling needs would be much lower during maintenance. In any case, the cooling benefit of the fish farm would be small compared to the greenhouse. Instead the main contribution from the fish farm was to expand the business case and add to the sustainability of the whole by creating an additional loop for recirculation, this one carrying nutrients from fish excrements to the greenhouse to be used as fertiliser. This improves the sustainability of the greenhouse by replacing commercial fertiliser, which is energy-intensive in production, with a renewable resource [27].
The second low-temperature heat sink proposed was a system for ground heat for open-air farming. This system would involve installing a system of plastic pipes under an entire field and result in the annual yield from the field doubling by lengthening the growing season enough for two harvests. Unfortunately, preliminary calculations indicated that the installations would be expensive compared to the modest value of the types of crops enabled by the production form. The only way the system would be profitable was if ESS would pay for the cooling. Cooling to the same temperature as the farmland would deliver, around 12 °C, would entail a cost, either for buying and operating chillers, or as a purchased service. The problem that arose was that the open call was part of a process to attempt to demonstrate a value of waste heat that could be sold from ESS. ESS was and is a public entity, constrained by rules for public purchasing. There are no corresponding rules governing the sale of waste heat. The effect was that the option to use an open call and other instruments to stimulate innovation were not available to the ESS Energy Division without going through a public procurement process.
Second case: RePro foodFootnote 3
RePro Food was an innovation and development project initiated by Findus, a frozen food company. Findus is the leading company within the frozen fish category in Sweden and has a long tradition of innovation as well as introduction of previously unknown species or concepts, such as the Marine Stewardship Council (MSC) certification standard, to the Swedish market. The project was stage two out of a possible three stages of challenge-driven innovation process. The first stage had been a market investigation and was used to estimate target prices and volumes for tomatoes and various fish species. The third stage would be to move from development to investment. The project called for a greenhouse and fish farm to be developed at Findus’ production site in the town of Bjuv [28].
Other than Findus, the collaborating partners were Veolia Sweden, an energy service provider that supplied the Bjuv site with heating and cooling, Royal Pride Sweden, the Swedish subsidiary of a leading tomato grower in the Netherlands, Vegafish, a small enterprise for prawn and fish farming, the municipality of Bjuv, with an interest in job creation locally, SLU, the Swedish University for Agricultural Sciences, Söderåsens Biogas, a local producer of biogas from farm waste, and WA3RM, a brand-new company formed by former employees of the ESS Energy Division [28].
In contrast with the ESS project that was driven from the need to recycle heat and therefore to demonstrate that a business case existed, RePro Food was driven by an interest to invest and establish greenhouse growing in Sweden based on import of technology and know-how from the Netherlands and therefore resulted in detailed investment calculations and a full model of profit and loss, balances and cash flows of the business over 20 years, to be presented to investors. This material is now in the public domain. The fish farming was not based on an established business and therefore is described in considerably less detail, but nonetheless modelled for profitability [29, 30] .
The project called for the construction of a 15-ha greenhouse and a fish farm for 1500 t of fish per year. A greenhouse of 15 ha would be Sweden’s largest. The market investigations in stage 1 of the project had indicated a market capacity for greenhouses in Sweden of 900 ha, although this indication may have underestimated the production per ha and was later revised downward in the project. In any case, only 13% of tomatoes consumed in Sweden at the time, were domestically produced. The project estimated that 50% home production was achievable, particularly since the greenhouse design envisaged the inclusion of grow-lights, for year-round production.
The size of the fish farm in an integrated system is limited by the size of the greenhouse, as this dictates the capacity to accept the nutrient effluent of the fish and researchers at SLU had calculated that 100 t of fish would fertilise 1 hectare of greenhouse tomatoes. A fish farm for 1500 t represented a step-change in magnitude compared to existing experimental facilities, with capacities ranging from single digits in tonnes to around 60. In contrast, two identified commercial fish farms in planning simultaneously with RePro Food intended 6000 and 10,000 t respectively.
Statistics for annual average rainfall on the greenhouse showed that in normal conditions, the rainwater falling on site, if collected and stored, would be sufficient for the needs of the greenhouse. A system to collect and store rainwater was in any case a requirement for a building permit, to prevent flooding. The integrated greenhouse-fish farm design envisioned rainwater collected from the rainfall would go first to the fish farm (after treatment) and then on to greenhouse drip irrigation system, via the control system for fertiliser dosage, which would balance nutrients as necessary.
With world demand for fish growing while supply is limited, the market in the long term would not seem to be a limiting factor, but investment calculations necessitated more exact data. Such data for Findus’ target markets had been acquired in the stage 1 pre-study and formed the basis for a project decision to design the fish farm for farming 50% pike-perch and 50% rainbow trout. Both species were in high demand and therefore commanded an attractive price.
The heat recycling from Findus food processing factory presented multiple challenges for the energy engineers at Veolia and for the designers of the greenhouse for Royal Pride Sweden. Firstly, the temperatures were very low creating a challenge to conserve temperature quality and combine flows to raise supply temperatures and to create a system to use the lowest possible temperature to heat the greenhouse. Secondly, the waste water stream holding the most energy contained food residues, posing a challenge to retrieve the heat from the effluent to heating water without clogging the heat exchanger moving the heat between them. This was solved by Veolia, whose engineers identified a technology with a continually reversing heat exchanger. Thirdly, heat capacity was not constant and the demand from the greenhouse would vary seasonally and with daily weather. A possible solution that was explored, which could also serve as a back-up heat source, was a geothermal heating combined with drilled ground storage. Such systems had been put in place in the vicinity and could be studied. Unfortunately, Bjuv is an old mining town, where lignite was mined underground but close to the surface. Investigations revealed that the greenhouse site was crisscrossed underneath with mining tunnels, making drilled storage impossible and even dangerous, due to risk of collapsing tunnels [31, 32].
In a surprise development, while the project was on-going, Findus announced the closure of the plant, removing the source of waste heat. The parties together initiated a search for other alternatives for the same site. The efforts were ultimately futile, and the project at Bjuv mothballed, but the process of evaluating other heat sources necessitated the development of appraisal methods applicable to other projects. Beyond assessing heat quality and quantity, also variations over time, the investigations revealed the importance of differentiating between energy and power (energy per unit time). A heat supply might be sufficient to cover annual energy needs, but inadequate to cover peak demand (the power need) or be of varying power in supply. Calculations confirmed that a heat capacity that covered base need of the food production facilities could be economical to develop, even if it necessitated a top-up for a few days a year. In such a case, the running cost of the top-up was of small importance, if the investment cost was low. As a result, an oil boiler was selected for this need. With such a limited planned running-time, the sustainability impact of the use of oil was deemed to be negligible. However, the project parties were aware that the use of fossil fuels, even as back-up, might render the production ineligible for eco-labelling. In the case, eco-labelling of the tomatoes was not a goal.
A parallel project also initiated by Findus investigated the possibility to use waste from Findus’ production of frozen peas as an ingredient in fish fodder. The pea plant parts are relatively protein-rich plant matter. Initial experiments showed promise in that plant-based material was fed to Tilapia (a vegetable-eating fish species), thereby suggesting the possibility of another recycling loop in the system, of food processing waste to the fish farm. For predator species, two notable methods for development of fish fodder production facilitated with waste heat were mooted in the same period as the project, one with fly larvae and one using yeast. In either case, production could be based on farm and food waste substrates, or even slaughterhouse waste and human waste in sewage. Some combinations struggle with the “yuck-factor”. Beyond such subjective perceptions, legal- and hygiene issues were identified, the most challenging were connected to legislation passed to prevent the spread of mad-cow disease, or BSE, Bovine Spongiform Encephalopathy. The case study business case reveals that fish fodder is the dominant variable cost for fish farming and therefore the most attractive for management to improve profitability. Furthermore, because the RePro Food project planned for farming predator species, availability of fish fodder not based on wild fish capture was fundamental to the long-term sustainability profile.
The detailed budgets developed for the greenhouse farming in RePro Food revealed that the cost of carbon dioxide (CO2) for use in the greenhouse, although less than the cost of heating, was substantial. CO2 is conventionally supplied in liquid form by truck, at significant expense. Moreover, the delivery requires major investment in a receiving, storage and expansion station capable of transferring the CO2 at the high pressure and low temperature required for liquid storage, and to heat and expand the CO2 for use. Greenhouses in the Netherlands are predominantly heated with natural gas, which is by many considered to burn cleanly enough to use the CO2 produced directly in the greenhouse, at minimal expense. The business case demonstrated that the cost of CO2 significantly adversely affected the competitiveness of greenhouse developments in Sweden compared to imports. For that reason, it was an important conclusion from RePro Food that future projects should include recycling of CO2 from industry, in addition to heat.
Continued technical development and deployment
We, the authors of this article, from our positions as two of the partners of RePro Food can report that although the project in itself is completed, the work continues within and between several project partners. Although the results this work are not yet reported, the publicly available grant applications for the case and a possible continuation offer a glimpse into current issues and developments in relation to the project, as a starting point for the discussion. The first such development worth mentioning is that after the abortive project in Bjuv, several projects making use of the RePro Food material are in various stages of development at other sites in various places in Sweden using waste heat from the metal industry and from pulp and paper, the two sectors that dominate heavy industry in Sweden.
A second development is the inclusion of efforts to achieve CO2-recycling from heavy industry in accordance with the results of RePro Food. The heavy industry investigated emits CO2 from various processes. Depending on the specifics of each process, the concentration of CO2 in flue gases varies greatly, as does the composition of other gases emitted with the CO2. Four categories of technical challenges have been encountered. The first issue is corrosion caused by gases containing substances such as sulphur that combine with water vapour and condense into acids that harm the equipment for capture of heat and CO2. The second is the blockage of distribution pipes caused by condensation of water vapour in the flue gas. The third issue is damage to plant growth caused by pollutants potentially harmful to plants. The fourth issue is worker health and safety in the greenhouse potentially affected by gases harmful to humans. All these issues could be avoided by extracting the CO2 from the flue gases. Processes to achieve this have been in focus for development for Carbon Capture and Storage, CCS, a sustainability effort in energy transformation. However, preliminary investigations indicate that these processes are not necessarily appropriate or economical to transfer directly to the problem of capturing CO2 from industrial flue gases for use in greenhouses.
The third ongoing development is a rethink on fish species to farm. As noted in the case description, the choice of species to farm was driven primarily by market demand and competition (in fact, the upstream supply chain and other factors also entered into the decision). The problem with the selected species, and other species considered, was that all are predators. The available fish fodder for these was primarily based on wild capture of species less attractive for human consumption. Because each tonne of these species produced in a fish farm requires more than a tonne of fodder, the net result could be increase of wild fish capture. The development of fodder from land-based proteins, such as described in the case, would alleviate this problem, but for that development to gain momentum would require a sufficient market for fodder, creating a chicken-and-egg situation as neither the fish farms nor the fodder production could start without the other if the fish farming was to be sustainable.
An alternative to inventing new types of fodder would be to introduce new, vegetable-eating species to consumers, species that can eat a vegetable feed. This would require a far greater marketing investment and also lose the price premium commanded for known and popular species. Instead, a possible price premium could derive from the sustainability of the product. A production base of vegetable-eating fish would have the added value of creating a source for fish fodder for predator fish, using discarded parts of the vegetable-eating fish.
The grant applications promise substantial job creation as an outcome of the projects. Explorative investigations referenced in the applications revealed that in the general case, for the envisioned project locations, attracting the required human resources for comparatively low-skill and low-pay jobs harvesting tomatoes would require recruitment from groups not active in the job market, explicitly including recently arrived immigrants. Because the greenhouse design included grow-lights for year-round production, the jobs would be full-year rather than seasonal. The business cases reported in RePro Food demonstrate that the cost of labour is an important factor for competitiveness [29].
The RePro Food Investment Memorandum describes a project with 15 ha of greenhouse compared to an estimated need of 900 ha, with similar limitations to fish. The limited production capacity in the case study system is an effect of limited supply of waste resources at each location. Thus, the economy of the resource efficient symbiotic systems needs to outweigh the economies of scale of the stand-alone system to be competitive. The business case calculations indicated that this was the case, but the data for comparison for the fish production was limited. In order to secure access to know-how, purchasing power, bargaining power for sales and systems for operations, the projects envisaged a roll-out based on a franchise model or similar structure, wherein the facilities distributed to places where waste resources are available form a structure, thus forming a distributed symbiotic system.
Heat recycling and quality
The cases hinge on heat recycling. Heat is conducive to growth in organisms, within a range specific to each organism, but typically organisms do not fare well at temperatures higher than their specific range. Uses of waste heat are temperature sensitive, as are the industrial processes which supply the waste heat through their cooling systems. Because of these sensitivities, thermodynamics will enter into the analysis.Footnote 4
The starting point of both cases was to make use of waste heat, the temperatures of which were too low compared to ambient conditions to drive a heat engine, as illustrated in the formula for the Carnot efficiency. The waste heat was therefore only useful for heating, either of a space or of a liquid flow. Because heat is difficult to transport (but relatively easy to store), a further constraint was that the heat must be used locally.