Here are some frequently asked questions about the eTank. Click on the questions below for answers.

General Information

Where is the eTank installed?
The eTank is usually installed under the base slab of a building. In special cases it can also be installed adjacent to the building. It can be built underneath a cellar, right next to a shared cellar or underneath a winter garden or garage respectively.
Is the eTank really a tank?
The eTank does not consist of a container filled with warm fluid, but of a special system of pipelines through which energy harvests are delivered into the surrounding soil. The soil is packed in durable insulation and foil. In this way, the soil itself becomes the tank. The eTank can be filled with energy like a battery – the one difference being that the soil is endlessly rechargeable.
How many certified eTank companies are there?
There is only one producer – deematrix Energiesysteme GmbH.
How many eTank projects have already been realized?
There are over 100 known examples that use soil as a buffer medium. In its actual optimized form, the eTank has been built ca. 20 times in three different countries (2013). Under the headers “New Buildings” and “Renovation” you can find references as well as current projects.

Technical Questions

What size eTank do you need for a ca. 10 kW heating load?
The optimum is a volume of about 100 m3 to 120 m3 underneath the ground slab at a depth of 1 m to 1.5m.
Is the length and the width dependent on the height?
A large foundation is preferable. The height is calculated around 1.2 m to 1.5 m, but modifications are possible – Talk to us!
How many raw pipeline circuits are necessary?
Usually 8 circuits are built into an eTank in a single-family home with a solar thermal unit (if used only for heating purposes). According to the desired unit configuration a building can also be cooled or heated or cooled and heated at the same time. Depending on the size of the building as well as the type of solar thermal unit, (which could also be a water-cooled photovoltaic system), additional circuits can be brought to bear according to user need.


Can the eTank freeze?
The eTank is stabilized by a constantly streamed temperature significantly higher than 0° C (32 degrees Fahrenheit). Even during the cold seasons or bad weather the solar energy unit produces small amounts warmth and delivers it to the eTank. This warmth cannot be used by any other system. Due to this constant delivery of small amounts of warmth, no active eTank has ever reached a temperature level below 5°C. An additional security installation unit prevents the temperature from falling below 3°C.
Can the eTANK pipelines leak?
The eTank is designed not to leak. There are numerous complete circuits of PE-Xa-pipelines installed in the soil. Every circuit consists of a one-piece pipeline that is neither flanged nor connected in any other way. Before product completion, a pressure test is administered that guarantees the seal of every single circuit. In the unlikely event of leakage “only” storage efficiency would be diminished, because an eTank has a minimum of 8 circuits. This is in opposition to any geothermal drilling technology with only two to three circuits, in which case the entire system is subject to breakdown. In this scenario you would have to drill again.
What guarantees can be given for functionality and materials?
The PE-Xa-pipeline is produced by name-brand producers and has a lifespan of more than 95 years according to the manufacturer´s warranty (at 50°C, 2 bar). Different licensed products on the market can be used as perimeter insulation. You can also use glass foam granulate as insulation material under the floor slab. Thereby a long- term pressure resistant, but also anti-capillary, foundation is insured.

Planning & Layout

How big does the solar collector surface have to be?
The dimension of the eTank is dependent on the heating load of the building, the location and the geology. A single-family house with 4 people and a living space of 180m2 needs about 11m2 solar-thermal installation (e.g. a flat-plate collector). This size is recommended for any system with solar heat support. Therefore, the single-family home does not need any additional square meter of collector space.
Is a geotechnical report required?
Basically, for every building there should be a geotechnical report to avoid cost increases. This demand is independent of the etank, but always advisable.
Which ground compression levels are required during and after the installation?
Compression levels are prescribed by the structural engineer. The soil of the tank is compressed layer-wise, usually up to 98 – 100% proctor density, according to the specific demands of the building site. There will be a compression report for every perimeter. This protocol is available to every customer.
Which compression levels are necessary during and after the installation?
Compression levels are prescribed by the structural engineer. The soil of the tank is compressed layer-wise, usually up to 98 – 100% proctor density, according to the specific demands of the building site. There will be a compression report for every parameter. This protocol is available to every customer.
Are there any conditions or load limits for the building above the eTank site?
The eTank could be built underneath a skyscraper. This would neither be a problem for the pipelines nor for the perimeter insulation. The eTank is usually built from the soil at hand, following the instructions of the structural engineer.
Are there any exclusion criteria that can prohibit the installation of the eTank or are there examples from comparable projects?
No project has ever been hindered by unsuitable conditions. Exclusion criteria concerning the installation are dependent on the structural conditions of the building-soil and not on the eTank. Unfit foundations are, for example: peat, clay or tufa. These foundations would have to be exchanged during the process of making the soil fit. No additional soil fitness requirements are necessary for eTank installation. Exclusion criteria could be for example, large rocks or high ground water levels (e.g. directly underneath the turf).
Besides the description included in the building application is there any permission, registration, commissioning necessary before installation or activation?
Basically every geothermal heat pump system has to be described and registered (and in the case of geothermal drilling), formally applied for. In water-protected areas the application is often denied. In Berlin the eTank is the only thermal heat pump system that has been allowed in a water-protected area, because it is run with distilled water.
Is there a call for tender document available?
Yes there are different documents available (in German) depending on your desired objective. The following parameters of the eTank must first be defined: type of solar-thermal system, function (cooling, heating and cooling, heating and cooling at the same time, etc.) Please contact us to find out, if there is a certified company in your country.
I am interested in an eTank. What information must be supplied to receive an offer?
To supply an offer for an eTank we need some basic information that can be filled out on the downloadable questionnaire (in German). For any further questions you can contact the specialists listed on the questionnaire.


Which funds can the contractor apply for during or after the installation of the eTank?
Funding depends on the entirety of the concept. In Germany there are KfW – and under certain circumstances – investment bank resources, such as a low interest rate loans, available for Energy Efficient Houses. Also, subsidies for resources such as solar-thermal pumps, solar energy units and the efficiency bonus can be applied for through the Federal Office of Economics and Export Control (BAFA) as a direct subsidy (2011). These funds depend on the current legal situation regarding individual subsidies, (so a financial plan should not be calculated with direct subsidies). The eTank does not rely on government subsidies to be economically viable.