#1 cleantech news, reviews, & analysis site in the world. Subscribe today. The future is now.


Published on June 24th, 2014 | by Silvio Marcacci


Sustainable District Heating From Seawater? It’s Happening In Holland

June 24th, 2014 by  

When the fishing industry in Duindorp, a small community near The Hague, Holland withered after years of prosperity, the local government saw an opportunity to rebuild local housing dating from the 1930’s into modern low-income homes.

Residents made it clear they wanted renewable district heating, but developers were challenged to provide renewable power at prices compliant with Dutch principles mandating consumer costs stay at the same level for clean energy. “We asked – well, where do we get sustainable energy from,” said Paul Stoelinga, senior consultant at Dutch environmental engineering firm Deerns International.

The answer was as apparent as it was improbable, according to Stoelinga. “The sea is nearby, and these people have a relationship with the sea because of former industry, so why don’t we retrieve heat from the sea?” (Full disclosure – while my trip was sponsored by the Dutch Government’s Ministry of Foreign Affairs, it had no involvement in the editorial process of this post).

Paul Stoelinga Seawater Heating

Paul Stoeling Duindorp seawater heating image via Silvio Marcacci/CleanTechnica

Small Facility, Big District Heating Innovation

It’s a tricky proposition, considering Northern European winters, but from this realization sprung the world’s first district heating system in 2008, turning seawater into a sustainable source of energy for 800 homes – one that’s now in use at several other sites across Europe.

The small nondescript white building housing the power plant sits just inside Duindorp’s harbor, but the innovative approach to sustainable heating stands out as a promising solution for waterfront communities in the clean energy transition.

Intake valves start the process by drawing seawater into the facility through a five-stage filtering process designed to prevent corrosion and protect sea life, ensuring fish can always escape the intake. That protective step is important, considering the system draws between 26,000-190,000 gallons per hour.

Seawater heating system intake valves

Seawater heating system intake valves image via Silvio Marcacci/CleanTechnica

During summer months, harbor water hovers around 70 degrees Fahrenheit, and the facility sends filtered water through five miles of pipes to the homes, where in-home grid-connected 5kWh-capacity heat pumps boost temperatures to between 110-150 degrees Fahrenheit for heating and warm water through all-electric systems.

In winter months, when seawater temperatures dip as low as 37 degrees Fahrenheit, a 3-megawatt (MW) heat exchanger boosts water temperatures up to a level each home’s heat pump can handle – most heat pumps will fail when water falls below 50 degrees.

Seawater heating system heat exchanger

Seawater heating system heat exchanger image via Silvio Marcacci/CleanTechnica

An Efficient, Economical, Environmental Solution 

Combined with home insulation, this process creates a cost-effective heating source generating 15 kilowatt-hours (kWh) of heat from just 1kWh of electricity, according to a Deerns presentation, reducing the coefficient of performance for home heat pumps by just 5% while reducing emissions 50% compared to conventional heating using natural gas as a power source.

And, the system’s operations could technically represent zero emissions. Deerns originally proposed powering the plant with wind energy via two on-site 1.5MW turbines, but was turned down by the local government over noise and safety concerns. “It was a disappointment for us because we wanted the project to be 100% renewable,” said Stoelinga.

Duindorp Holland

Duindorp Holland seawater heating system community image via Deerns International

Solar energy was explored as an option, but photovoltaic panel costs would have put project costs above consumer price thresholds – a situation that could change as solar power costs continue to plummet.

While Duindorp’s seawater heating may be an environmentally friendly solution, it’s also worth noting the system’s relatively affordable economics. Total construction costs for the facility were just €7.5 million, and consumers pay a fixed price of €70 per month for sustainable heat – comparable to costs before the system was completed, all according to Stoelinga.

Tags: , , , , , , , , , ,

About the Author

Silvio is Principal at Marcacci Communications, a full-service clean energy and climate policy public relations company based in Oakland, CA.

  • Hans

    Judging from the comments Cleantechnica has many readers outside of the U.S. For their benefit it would be nice to also have S.I. units. For this case it would have been particularly easy, because the author most likely got the temperature values first in °C from his Dutch hosts and than translated them in °F.

    • No way

      To be honest S.I units should always be used since 99% of the world uses that (or at least has it as the official system). If you want to cater people from the US, Burma and Liberia who hasn’t finished high school then it’s easy enough to put translated values of fahrenheit, hands, feet, ears or what ever body part has been used once upon a time.

  • Hans

    Heat pumps are a very efficient way to use fossil fuels. But you are still using fossil fuels. So it is not a renewable technology, Can it be called sustainable if it is not renewable?

    • vadik

      You are plain wrong on this one. Period.

      • No way

        Why? What he says is totally true. The system still runs on fossil gas even though less than before.
        It’s great that they do it, but why not go all the way and not reduce the use of fossil fuels but also replace it.

        • Gwennedd

          They could use the sea to generate electricity. A turbine on the sea floor or a wave turbine would do.

      • Hans

        I admire your rigid argumentation

        • Hans

          I meant to write “rigorous”, of course in an ironic way, but in hindsight rigid is not such a bad description after all.

    • Steven F

      Heat pumps run on electricity. In addition to fossil fuels you can make electricity from biomass, hydro, wind, wave, solar, or nuclear. The european grid is becoming increasingly CO2 neutral . So every year the european power grid is becoming increasing sustainable.

  • No way

    Where does the electricity for the heat pumps at home come from? The normal grid or also from the “district heating”-plant? COP at 15??? And heat pumps have no problem with lower temperatures, 0-10 degrees (32-50 fahrenheit) is normal for sea/lake/rock/ground heat pumps.

    • Omega Centauri

      The claimed COP is very high. Although that could square with claimed nonoperation under 50F (10C). The lower the temperature difference the higher the maximum efficiency allowed by thermodynamics. I suspect they aren’t measuring all of the energy inputs however.

      Are they pumping salt water? Or is there a heat exchanger?

      If they’ve saved so much needed energy, the additional cost of using solar/wind must be pretty low. But, maybe the law doesn’t allow that to be factored in?

      • Ulenspiegel

        Something is fishy! They work with sea water, why not:-)

        Practical POV:

        I run a ground source heat pump and get in deep winter with 0 °C brine a coop of 4. Even with 10 °C brine (October) I get only a cop of 5, however, here the high demand for hot water (45 °C) in comparison to space heat is the problem.

        Theoretical POV:

        The Carnot cycle gives you the maximum possble COP.

        COPmax = Twarm/(Twarm-Tcold); T in Kelvin of course. 🙂

        Tcold 10°C = 283 K; Twarm 22 °C = 295 K

        -> COPmax = 295/12 = 24.5 for space heating

        Tcold 10 °C = 283 K; Twarm 45 °C = 318 K

        -> COPmax = 318/35 = 9,1 for hot water

        The COP in real life is only ~50% of the Carnot maximum, therefore, then COP of 12 is only for space heating in the building and of course omits, that the water was actually preheated. 🙂

        With 0°C seawater one gets COPmax = 295K/(295-273) = 13.4

        Hence, a RL cop of 6 would be possible at best for space heating, hot water decreases this value of course further, energy demand of pumps and losses of the pipes, too. 🙂

  • “most heat pumps will fail when water falls below 50 degrees.”

    Never heard that before. According to my knowledge, most heat pumps used for home heating can function at much lower temperatures. The specs of this Sanyo heat pump shows it works at -20° C at a COP of 1.6.

    • Steven F

      “The specs of this Sanyo heat pump shows it works at -20° C at a COP of 1.6. ”

      That is an air source heat pump. As long as water doesn’t freeze on the heat exchanger it will work. At -20 there is not much water in the air.

      The heat pumps in this article are WATER source heat pumps. If the water freezes in the heat exchanger the heat pump will not be able to move heat and the expansion of ice may cause water leaks.

      Yes you can prevent freezing of water with antifreeze. However there may be a reasons why they reason using it, Such cost, safety, environmental or legal issues.

      for example corrosion in the sea water to antifreeze heat exchanger could contaminate sea water and kill fish. So the local government may not allow the use of antifreeze.

  • Jason Willhite

    The article states they tried getting solar or wind to generate the heat, but ending up having to resort to using natural gas. I had wondered if they looked at trapping excess waste heat from a nearby industry. I assumed they didn’t because there might not be an industry like that in such a small town or it was impractical to do so.

    • Steven F

      Where in the report does it say they used natural gas? The fact is this system doesn’t use any natural gas to directly heat the water. If the sea water is warm a simple heat exchanger is used. However if the sea water is cold an industrial scale heat pump is used to move heat out of the sea water and into the district water loop.

      This system is entirely electrically powered. Yes some of the power may come from a natural gas power plant. But since the power requirement is only 3MW a wind turbine a mile or two out at see or an onshore turbine miles away could provide power while still meeting the noise and safety rules

      A PDF presentation about this plant shows a picture on the central heat pump is at this address:


      • Jason Willhite

        Sorry, I misread that. I guess i’m still unclear what is being as the energy source to draw in, circulate and heat the water. I’ll take a look at the link

      • No way

        Almost all electricity in the Netherlands are from fossil fuels. So if it’s not from natural gas then it’s most likely from coal.

Back to Top ↑