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Energy-neutral premises for the Directorate-General for Public Works and Water Management

The Directorate-General for Public Works and Water Management (Rijkswaterstaat) aspires to reach complete energy-neutrality by 2030 and equip all owned premises with solar panels, charging stations and smart support systems. But what are the possibilities for each property? What is the maximum number of solar panels that can be installed on the roof? What are the installation technicalities for each property? And where should the charging stations be installed?

Throughout the country

Iv-Infra, Iv-Bouw and CAE (the construction branch of Iv-Bouw) provided insight into the possibilities for each property and how to achieve realisation as effectively and efficiently as possible. “It was quite a challenge,” says Harry Nienhuis, Project Manager at Iv-Infra. “Everything had to be completed before the summer, so time was of great urgency in this project, and along the way, we were unexpectedly faced with limitations due to the corona lockdown. In the end, the 81 properties we were initially investigating turned out to be 118.”

One of the challenges in this project was carrying out the archival research. “To assess whether the roofs
are structurally suitable for applying solar panels, we needed, among other things, the structural data of the properties. And if possible, also information about the load data which was originally applied. Obtaining this information proved more difficult than expected, as the majority of this data was not available digitally and town halls were either inaccessible, or access was limited due to corona,” says Saskia Frijns, Project Leader and Registered Structural Engineer at CAE. “We have driven all over the country visiting town halls and other owned premises. We mapped out routes for three days a week and visited three to four locations per day.”

A specific format

To assess all properties as efficiently as possible, a specific assessment format was set up at the beginning of the project, enabling each property to be evaluated in the same way. Iv-Infra and Iv-Bouw carried out the on- site inventories. Iv-Infra inventoried the parking spaces and, together with Iv-Bouw, formulated an inventory of the roofs and electrical building installations. “With regard to the roofs, the condition and structure type were examined and determined, but also the surface area and available space for solar panels. We measured this for all roofs and further determined the positioning and energy yield of the solar panels with the software program HelioScoop. We had never worked with this program before, so we first put a lot of effort into customising the program. CAE then calculated and assessed the structure of the roofs. We also ascertained which electrotechnical installations are present in the properties and the capacity these installations can tolerate. Based on this data, we provided a definite indication for each property for the maximum number of solar panels that could be installed,” says Sjaak Verheijen, Senior Designer at Iv-Bouw.

How many solar panels on each roof?

The wish of the Directorate-General for Public Works and Water Management was to place as many solar panels as possible on each roof. CAE made structural calculations for each building to determine how many solar panels the roofs could withstand. The applicable renovation standards were hereby applied. The load-bearing capacity, which was calculated in the original situation, was compared with the load associated with the new situation. “In our calculations, we have assumed a standard type of solar panel for the area and weight. These limit values were formulated by the Directorate-General for Public Works and Water Management. By applying the safety factors associated with renovation, we were often able to create scope for placing the solar panels on the roof without having to include extra facilities in the existing structure,” says Saskia.

“What was nice is that we gradually identified a common thread in the different types of properties (buildings with a concrete structure, steel structure or with wooden joisting). It became apparent that similar buildings typically produced the same outcome. For example, buildings with a concrete structure could almost always withstand the extra load from the solar panels. This made it easier later in the project to assess the properties with a concrete structure. We were able to examine many different structures and bundle the observed common thread as a learning point, enabling us to utilise this knowledge further to provide insight into the possibilities for various buildings.”

CAE and Iv-Bouw investigated the possibilities for a number of buildings whereby the structural calculations revealed that the limit value was not met in terms of strength. Sometimes, a gain can still be made by positioning the solar panels slightly differently. In particular, no archival data was available for the older, smaller buildings. The structure was examined on-site for these buildings, and the possibilities calculated with structural assumptions in weights (on the safe side, of course). These calculations were also based on the data obtained from assessments of similar buildings for which structural archival data was available. An advantage of older buildings is; the older the building, the more safety was built into the original structural calculation.

Where should we install charging stations?

Another aspiration of the client is to electrify the fleet fully. With this, all buildings must be provided with sufficient charging stations. The Directorate-General for Public Works and Water Management indicated the desired number of charging stations/fast-charging stations for each location. Iv-Infra and Iv-Bouw have ascertained for each premises the number of existing private parking spaces, the location of the existing charging stations, the cable and pipeline routing and the location of the transformers and mains facilities. Following this, advice was given for the optimal positioning of charging stations and the routing of energy supplies.

For the buildings with existing charging stations, it was recommended to cluster the new charging stations
at that location as this promotes optimal efficiency in terms of cabling. It was recommended for premises that do not yet have charging stations to realise these close to the building to prevent unnecessary long cabling routes. The inventory showed that a number of premises do not have private parking spaces, and the surrounding area around the building is used for parking. In these cases, it was investigated whether and where it could be possible to realise parking facilities and charging stations.

One step closer

In December 2020, Iv satisfactorily submitted the last inventory report to the client. The Directorate-General for Public Works and Water Management is currently tendering the work to contractors, bringing it a step closer to achieving its ambition to be energy neutral by 2030.