Pilot site 2 has been chosen

Now that pilot site #1 is up and running, it is time to introduce pilot site #2. 

The pilot site will be located at an agricultural innovation centre, which is also a working farm, where a number of new techniques are being tested. The centre is located near the town of Hengelo in the province of Gelderland in the Netherlands.

What type of farm is it?

The farm is a typical dairy farm of which there are many in The Netherlands. There are roughly 150 dairy cows that produce 4000 tonnes of manure per year.

During the selection process, having a different use of hot water to that of pilot site 1, was important. In this application, the heated water will be used in an anaerobic digester.

An anaerobic digester is a method of producing biogas from organic waste products. In this case, we digest the manure produced by the cows. The 4000 tonnes of manure per year will produce roughly 72000 m³ of biomethane per year. The gas is then discharged into the natural gas network for use in people’s homes and industrial processes.

The digester works using micro-organisms, which require a certain temperature (normally 35°C, but this plant operates at 38°C) to function. As such, we want to constantly keep the digester at this temperature. This gives us a rather constant heat demand. The digester is fed continuously and constantly loses heat to the outside, even though the system is insulated. 

 What is the existing heating requirement?

Fortunately, calculating the heat demand of the digester is quite easy. We have our tools to assist in this, but in the most basic sense, we calculate the heat demand based on insulation losses. This depends on the size of the digester, flow rate of manure, composition of insulation (primarily the roof), desired inside temperature and the ambient temperature throughout the year.

 The result is shown in the graph below:

Not surprisingly, the heat demand is highest during winter and lowest during winter.

The average heat demand is 424 kWh/day. The maximum (in December) is 538 kWh/day, and the minimum (in July) is 288 kWh/day,

Is there a heating requirement at present?

The digester at present uses some heat, which is produced using some of the biogas produced from the digester. Anaerobic digestion is a slightly exothermic (it creates its own heat) process. In regions where there are variations in external temperature (winter to summer), it is advantageous to add a heat source to keep the manure at 38°C, a figure calculated using Fengtech’s internal performance models. 

The digester produces biogas (which is upgraded to natural gas). A part of this biogas is burned on-site in a CHP to provide the thermal energy required for the digestion process. The amount that is used is traced back through the heat demand shown above here.

Being able to create a decent amount of our heat demand using solar thermal energy would mean a smaller fraction of our produced biogas is used up. Every m³ of upgraded biogas can be considered equal to 1 m³ of natural gas. Considering that the upgraded biogas is used elsewhere where normally natural gas would be used in a boiler, any savings can be equated to natural gas savings.

Are the buildings recently constructed, ie newer buildings may be more energy efficient?

The digester is not new, it has been in operation for several years already. Having said that, no significant leaps in digester insulation have been made since the commission and construction of this digester.

How many panels are proposed to be installed?

The proposed number of panels, according to a quote we received from Fengtech, is 10 panels. At 2.071 kWh/panel/year (an assumption calculated with Fengtech’s exploitation sheet), this would provide us with 20.710 kWh per year.

With our annual heat demand of ~154.700 kWh, this covers roughly 13% of our total heat demand.

Is a building permit required (like the UK and Ireland would)?

Unfortunately, a building permit is required. In The Netherlands, any solar installations (PV or thermal) that are not built on top of (or adjoined to) an existing structure, require a building permit.

When is construction likely to commence? How long should construction take?

Construction is due to commence in June or July 2022 and the plant should be operational by September 2022. We will publish updates when the construction commences.

In the photo above, the anaerobic digester is the circular building at the top of the picture. The proposed solar thermal plant will be located where the blue rectangles are.

In the photos below are examples of an anaerobic digester and at the bottom is the existing CHP (combined heat and power) plant that supplies heat to the digester.