Trials show that synthetic turf fields can produce enough energy to replace natural gas as an energy source to boil water for showers or warming properties. The business cases are in place . Now it is up to the government and property developers to move forward.
The installation of more sustainable energy sources is often met by opposition. They are blamed for polluting the horizon or to be too demanding for the limited space available space. The Dutch province of Overijssel and Zwolle municipality wondered if they could merge the benefits of various developments. “What if we could extract the heat that builds up in synthetic turf pitches during the summer to use it for our showers and central heating (later in the year) and, at the same time, use cold water to cool down the ambient temperature of the pitch?” they wondered. After all, the principle of a heat exchanger is already commonly used elsewhere. Bidders were assured that if they manage to solve the problem, the authorities would definitely invest in the innovation.
The challenge has been accepted by two consortia. Heating solution provider Aendless and sports fields installing company Antea Sport have used a synthetic turf surface from Edel Grass while SuperSub, a producer of light-weight concrete flooring has banded together with engineering firm Sallandse United. They have used synthetic turf surface produced by Condor Grass. The trial fields measure approximately 1,000 m2, making them twice the size of a test setup SuperSub had already established with sports field construction company Topgrass. “Together with SuperSub, we have been researching this concept and how it can generate energy for some time now. As tests showed that it would be possible, we established a small trial at hockey club AMVJ in Amstelveen earlier this year. This field measures about 500m2 and helped us to establish a business case ,” explains Teun Wouters of Topgrass. As the Sallandse United operates from the province of Overijssel, SuperSub decided, for practical reasons, to use them for the latest trial.
Aendless and Antea Sport activated their system in the spring. Their calculations had predicted that a full-size football field could heat about 200 homes per year. In reality, the number turned out to be even higher. According to Dennis ten Barge of Aendless the test made the best out of the beautiful weather at the start of the year. “Twente University has calculated a productivity of 1.6 GJ/m2 or 440 kWh/m2 for a full-size pitch.” That is comparable to about 64m3 natural gas per square meter. The trial has temporarily ended at the end of September. “The well water in our test setup is 12 degrees while the outside temperature is decreasing, which means that we are not producing anything at the moment,” he says. “There is no point to keep the system running when there is no yield. The three months that the test setup has been running have provided us with sufficient insight for the follow-up already.”
Also effective in autumn
Exactly at that moment, SuperSub and Sallandse United activated their field elsewhere in Zwolle. Logistical problems had stopped them from finishing their installation sooner. Nevertheless, Herald Kottink of Sallandse United is satisfied with the first results. “On October 6, we had a temperature of about 17 degrees Celsius with little wind. That day we benefitted from about 8 hours of sunshine. This allowed us to produce the equivalent of about 7,050 KWh or 849m3 of gas. That should be enough to heat 258 houses on an annual basis.” Two weeks later, despite some clouds and precipitation, the temperature was still 16 degrees. “The system managed to generate about 4,500 KWh or 542m3 that day.” What the results will be if their field also generates energy in the heat of the summer will only be confirmed mid of next year.
The effectiveness in Zwolle correlates with the results of the test field at AMVJ in Amstelveen. “On July 19, while the outside temperature was above 30 degrees, we generated enough warm water that is comparable to about 4,875 KWh of energy, or 587 m3 of natural gas,” Teun Wouters of Topgrass confirms.
Into the lava
The different test setups are all unique and the results cannot really be compared one-to-one. “Our test field had four different structures. We have selected the two best performing to go forward: one in which the water hoses have been placed in the shock pad right underneath the synthetic turf carpet, and one in which the water hoses were placed in a layer with lava before the carpet was placed on top of that,” explains Dennis ten Barge. It was this so-called asphalt thermal energy that prompted developer Strukton Civiel in 2021 to establish Aendless together with partner Roelofs. “The lava layer acts as a battery to store the heat. However, the shock pad provides good sports-technical properties of the field.” The latter remains important if one wants to realize the concept underneath full-scale sports fields. In anticipation of a ban on the use of polymeric infill, only stabilizing sand was added to the carpet. Yet Aendless is already looking further. “In the coming months we will see whether we can develop different subbases for different sports.” Ten Barge refers to concepts that remain effective with a smaller number of square meters than the standard 7,500 m2 size of a football field.
Foam concrete as a base
SuperSub and Sallandse United placed the houses in special tiles on top of a layer of foam concrete. Foam concrete is known for its insulating properties. The so-called Subtiles also act as a shock pad. Special conductors in the tiles maximize the amount of heat that is directed to the water houses. “Such conductors could also be incorporated into the synthetic turf carpet,” notes Martien Damen of Condor Grass. However, he points out that the yarn and carpet manufacturers will only really take that forward when the demand for such carpets is established.
The field at Be Quick’28 uses TPE as infill. “We do not want SBR infill in our 3G fields here in Zwolle which is why TPE is the obvious option,” says Jos Florax on behalf of the municipality while explaining the decision to not choose an infill of which it is known that it contributes most to temperatures increases over a 3G synthetic turf field during summer. “Besides, as all other fields at Be Quick’28 use TPE infill, we will be able to compare the results of this small-sized field to measures we take from the full-sized field next to it in terms of heat reduction. Florax doesn’t think that cork infill will work, but he is hopeful about a field that is finished with a non-infill carpet. “Such carpet could push yields even further,” he says. The trial in Amstelveen already gives a first indication. “Here we installed a short-pile synthetic turf carpet with only stabilizing sand in it,” Teun Wouters points out. Opinions about what exactly constitutes to a non-filled field are divided, but a growing number of installing companies tend to prefer to fill the carpet with a small amount of sand. Judging by the figures, it seems that a twice as high pile weight actually means a doubling of the energy yield.
The results of the various trials are encouraging. At the request of the province, Saxion University of Applied Sciences calculated before the start of the trial that, in addition to the investment, the annual maintenance costs would amount to around 66,000 euros. They also calculated that the income could be around 130,000 euros. That calculation was based on figures from before the energy crisis became a reality. The new developments elicited the comment that the construction of only 750 of these types of fields would be enough to replace gas fed boilers for the intended one million new homes the Dutch government is aiming to build in the coming years. Given the current number of 250 synthetic turf field renovations per year, this could mean that enough capacity is installed within 3 years. Nevertheless, Marcel Gehrels of Unica Energy Solutions guards against excessive celebrations. “Don’t forget that you also have to invest in infrastructure,” he warns. Heat from the field is not immediately usable but must be upgraded to a usable temperature. “If you want to heat a room, you need 40 degrees Celsius, and if you want to use it as tap water or for a hot network, that temperature will have to be 70 degrees.” The latter is necessary to prevent the formation of any Legionella bacteria. He also advocates investing in a heat pump as it will significantly increase the yield. If suppliers of heat pumps are to be believed, these systems are 400% to 600% effective. “Therefore, there are two effective options: actively extracting heat from the field and upgrading it immediately, or storing the water 80 meters deep in the earth’s crust and upgrading it at a later moment.” Using the water directly seems to be the most efficient. “Then you don’t need an aquifer thermal energy storage (ATES) and you have more operating hours per year. In addition, the thermal balance relieves the heat pump of the ATES.” According to Dennis ten Barge, every preheating by the collector, which a heat pump does not have to increase with the help of electricity, results in a 2 to 3% better efficiency of the heat pump.
Match supply and demand
Much of the success of the installation will depend on who will be the customer and who will be the owner. Hypothetically speaking, connecting a field to a swimming pool is the most favourable option. In that case, the swimming pool will serve as a battery. However, the a connection to a district heating network is more realistic. The big challenge now will be to convince municipalities and heat network operators to also consider synthetic turf pitches as a heat source. Dennis ten Barge notes that, if it were up to him, this could already be achieved. “The technique and the concept are already known and established.” According to him, Aendless is willing to offer ‘heat as a service’ whereby the provider will take on all responsibilities and investments while the customer only has to purchase the heat that is delivered. Topgrass also hints that it is looking at such a setup.
Jos Florax of the municipality of Zwolle sees additional benefits in addition to the intended energy yield. “We have noticed that these fields experience more dew. That natural moisture contributes to a better playing experience,” he notes. “In addition, I foresee that that moisture will slow down the wearing process of a synthetic turf surface.” Florax estimates that the lifespan of such turf can be extended by about 3 years in this way.
Time to take action
The trial fields in Zwolle will now be subjected to a number of other steps. For example, the National Institute for Applied Sciences still has to verify the measurement results. They also want to know what the return will be in the spring when measurements are started again. Thereafter, the consortiums will be allowed to optimize the materials used and the total construction in the run-up to the construction of a full-size field. When that will become reality, the sports-technical requirements laid down by the Dutch FA will also play a role as the FA insists that the fields comply with all their guidelines.
The trials in Zwolle mainly rely on existing materials and systems that are now being used in a unique combination. Municipalities that dare to take the plunge therefore do not have to wait for the verification of the final report. In fact, they can already start installing synthetic turf systems that can be used to generate energy.