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Who Says Electricity & Water Are Not a Good Mix?

Nick Meeten's picture
Director Applied Energy Ltd

I am not an electricity expert. My expertise is in the fields of thermal energy usage within buildings and industries, and thermal energy recycling from wastewater. I am a director of Applied...

  • Member since 2022
  • 23 items added with 8,573 views
  • Aug 24, 2022

Directors and business development officials within electricity companies have got it tough right now. If you are reading this because you fit these categories, I suggest you add some new names to your corporate Christmas card list – these being the managers of any wastewater utilities within your operating region. They could become a big part of the success of your business in the coming years, and I advise you not to delay connecting with them or the opportunity might be snatched away by others.

With the rapid electrification of buildings, transportation and industries taking place globally, pressure is mounting on the electricity sector to deliver more but emit less carbon. The increase in renewable electricity generation from solar and wind is well established and rapidly growing. The challenges with these renewable sources come from the variability that nature provides, sometimes it’s sunny sometimes not. Sometimes it’s windy, sometimes not. In addition, the traditional business model of single directional linear flows of energy flowing from generators to consumers (via distribution intermediaries) and money for this energy flowing the other way, is changing as consumers become both consumers and producers (so called ‘prosumers’) and distributed storage is also being added to the grid. For the electricity sector, as Kermit the Frog famously said, “it’s not easy being green.”

But electricity is only one form of energy. There are many others. From REN21 data, electricity makes up around 17% of global final energy use, whereas heating & cooling make up three times this at 51%.

Source: Jan Rosenow

To electrify the heating & cooling portion of this energy iceberg, a massive transition to heat pumps is required. But to ease the pressure on the electricity sector and your infrastructure, it will be vital to maximise the energy efficiency of these new systems. And the science is very clear that we need to make this transition of electrifying heating, very very quickly. We do not have time to waste and so we must make full use of everything we already have at our disposal.

One of the great heating & cooling sources available in every city is their wastewater network. It’s a below ground flow of water (wastewater is 99.9% water) that contains a huge thermal capacity to provide heat to or remove heat from a heatpump (using equipment designed to work with wastewater) and allow the heatpump to operate very very efficiently (thus using electricity sparingly). Typically, on an annual basis wastewater source heatpumps operate about twice as efficiently as air source heatpumps, so they can do the same heating job for half the electricity, but the big win is their consistency (more on that soon). Unfortunately, this thermal energy resource down in the sewer pipes is invisible and so almost totally ignored by energy planners, policy makers and urban designers. In the USA, around 20% of the total energy (in all forms, electricity, gas, solar, oil etc) consumed in housing is converted to heat within hot water systems and this thermal energy flows down the drains and ends up in the sewer network. Add to this, the equivalent flows from commercial and industrial sectors and natural leakage into the network, and the thermal energy ending up within the wastewater network roughly doubles. This thermal energy is all collected together into a large flow of slightly warm water which is stable across the seasons and entirely predictable. Stability and predictability are both great qualities when trying to manage energy flows. Stability gives us consistency in operation, so when heat loads peak during very cold weather, wastewater source heatpumps are not affected by the simultaneous drop off in COP that air source heatpumps are. That is crucial to the electrical sector in peak load management.

The thing is city wastewater utilities who receive these vast flows of thermal energy (for free might I add) typically have no use for the heating/cooling energy available within their networks. So, they just flush the thermal energy away. Every day. Every day! Below is a map from Europe which shows that almost 4,000 of their 18,000 wastewater treatment plants are inside or within 2km of district heating networks and these have a combined total annual heat capacity of 625PJ. That is the fossil fuel equivalent of 100 million barrels of oil and this heating/cooling energy is available TODAY within EXISTING wastewater networks and is sitting there waiting to be utilised by these district heating networks. They just need to be connected. But this thermal energy is being flushed away. Flushed away, every day. If we prorate the energy out to all 18,000 wastewater treatment plants, we get 2,800PJ of annual heat capacity, that’s close to half a BILLION barrels of oil equivalent in Europe. Flushed away every day.

There is a lot of good information and examples of wastewater heat recycling systems, as well as web based ‘heatmaps’ of the wastewater networks for three cities available on

Photo Credit: Applied Energy

I was excited to read that New York state recently passed a new Senate Bill (S9422), which not only now enables, but actively encourages electricity and gas utilities within the state to now sell heat. The bill instructs these utilities ‘to commence thermal energy network pilots in each major utility territory'. So now in New York, electricity utilities could partner with wastewater utilities to capture the flows of free clean heat within the wastewater networks and sell it, unless the electricity utilities are beaten to it by the gas utilities…. Nevertheless, this is exactly the sort of policy making that we should be seeing in every state in the USA and indeed every city in the world. It makes sense. Connect the organisations controlling different energy forms and associated infrastructure so they can collaborate, because the infrastructure networks in every city are increasingly interconnected.

Returning to business models. In Europe (who are also undergoing the same transition to heatpumps but at a vastly faster pace than the US) solar generation grew 34% in 2021 and recent research there indicates that currently around 20% of their population are ‘interested’ in Heat as a Service (HaaS) rather than purchasing their own heatpump to replace a boiler, and around 10% of their population will be purchasing ‘Heat as a Service’ by 2030. Europe has about 200 million households, this 10% equates to 20 million new customers over the next 8 years looking for someone to buy heat from. So now we have Europe moving away from buying electricity, because they are increasingly generating their own from solar, but moving towards buying heat because they don’t want to buy and maintain a heatpump themselves, they just want the heat. Will the same transition to HaaS take place in the USA? Maybe not at the same pace as is happening in Europe but if someone offers the service to the market then it’s pretty likely.

Heat is simply another form of energy like electricity and the electricity sector sells ‘Electricity as a Service’. The electricity sector has the expertise and systems in place to meter and sell energy, but wastewater utilities do not. So, I suggest that it’s time for the Electricity Sector to join up with the Wastewater Sector to offer ‘Energy as a Service’ covering energy in the forms of electricity as well as heating/cooling. By taking control of the supply of thermal energy as well as electrical energy, the electricity sector can better manage the loads on their networks, and by recycling the heat energy within wastewater and selling it, there is a whole new revenue stream. Add to this the customer then has a broader connection to the energy supplier (buying two services instead of just one) and the impact on the planet is reduced. Win/win/win!

But you electricity people better be quick to phone your wastewater authorities before someone else does! The heatpump sector in Europe are starting to talk about offering HaaS, instead of just selling equipment. You’ve been warned!

Julian Jackson's picture
Julian Jackson on Sep 2, 2022

This seems like an excellent idea. I note that the wastewater plants in the map seem mostly to be close to urban areas, which is where the heat will be needed. I guess that the main downside is the amount of capital investment needed for all those heat pumps?

Nick Meeten's picture
Nick Meeten on Sep 3, 2022

Hi Julian, yes you're correct that it's best to capture the wastewater heat while it is still within the city where it is most needed. Often the wastewater treatment plants are some way out of town where there is nothing around to use the heat. To get the best return on investment, our biggest advice is for cities to develop a plan around using this heat. Typically these projects are implemented in an ad-hoc way, a building here and a building there but without any real overall plan. If a planned strategy is developed, often 'clusters of buildings' can be identified and these can be heating/cooled from a centralised 'energy centre' which minimises the number of heatpumps needed.

Mark Silverstone's picture
Mark Silverstone on Sep 2, 2022

Just in order to understand - The source of the heat is the metabolism of waste material by the bugs (bacteria) in the waste water. Or do I misunderstand?

The heat is captured by heat exchangers. Yes?

In any case, thanks for posting. I would like to hear more about this.

Nick Meeten's picture
Nick Meeten on Sep 3, 2022

Hi Mark, no the heat source is simply the hot water systems in every house, commercial building or industrial site that discharges wastewater into the sewer network. 80% of the energy contained within wastewater is thermal.

Yes the heat is captured by heat exchangers, but this is where normal heat exchangers cannot be used. Heat exchangers designed to work with raw sewage are needed, otherwise they will just block up very quickly. If you want to hear more, I suggest you take a look at and have a good read. Look also on the FAQ page of this site, there is a lot of great information there. If you still want to know more, please feel free to just drop us a line at and we will try and help. Best regards Nick

Mark Silverstone's picture
Mark Silverstone on Sep 5, 2022

Thanks! I will do some reading.

Mark Silverstone's picture
Mark Silverstone on Sep 7, 2022

Hi Nick - I caught your webinar yesterday. Very interesting stuff. Thanks.

When I heard your comments about swimming pools, it made me wonder if there is any low hanging fruit to pick here in Norway. 

Electricity has always been pretty cheap here, as it is virtually all renewable. It is pretty much free in the northern part of the country (about US$0.02 per kwh). But here in the southern part electricity has reached over US$1.00 per kwh, more than triple what is was a year ago. It´s a long story...But I am not sure if there is any will or ability to do anything about it.

Nevertheless, I would like to investigate if our municipal swimming pools capture any energy from water discharges.  One is downtown and inside. However, another is nearby and is outside. You can imagine what it is costing to heat it to 29 deg C in the winter!

Any guidance you can provide would be appreciated.  I guess the place to start is with the city engineer.  Getting information from them will not be easy. But I want to give it a try. 

You are probably aware that swimming pools in Germany have shut off the heat to the pools and showers because of their energy issues related to the war in Ukraine.  I don´t want that to happen here!

Anyway, I thank you in advance for your help.


Nick Meeten's picture
Nick Meeten on Sep 8, 2022

Hi Mark,

Thanks for making contact.

It would be interesting to look at the feasibility of recycling wastewater heat for your two pools. I’m sure they are using a lot of heat (especially the outdoors one in winter as you say!!).

We could do an office based high level assessment of feasibility for the two sites if we were provided with some basic information such as wastewater network map, some wastewater temperatures and some key info on the heating systems at the pools. Costs would be relatively small (€3k - €5k).

Best regards


Jim Stack's picture
Jim Stack on Sep 2, 2022

Geo Thermal, water water heat capture can provide heating and cooling. In winter you can get heating and in summer cooling. There must be some areas that are already doing this like in Iceland. We need to learn from them.  

Iceland: World's highest share of geothermal power

Most small island economies rely on oil-fired power plants to provide steady electricity supply, but Iceland has virtually 100% renewable electricity from its abundant hydropower and geothermal resources.

Iceland: World's highest share of geothermal power

Most small island economies rely on oil-fired power plants to provide steady electricity supply, but Iceland has virtually 100% renewable electricity from its abundant hydropower and geothermal resources.

Nick Meeten's picture
Thank Nick for the Post!
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