Small island infrastructure: a visit to Sandhamn in the Stockholm Archipelago

During the months May and June, I am spending time in Stockholm as a visiting researcher at KTH. Aside from exploring the city, the long summer days (it is light here for around 18 hours a day) also provide an excellent opportunity to visit the Stockholm Archipelago, a collection of over 30,000 islands (some bigger than the other). My partner and I decided to visit Sandhamn, a popular summer destination 2.5 hours by ferry from Stockholm.

The island has only around 125 permanent residents. Yet, every year, over 100,000 people visit the island, including people with a summer residence there, sailors arriving at the small harbour and people like us going there for a weekend trip. While exploring the island, I was also interested how the infrastructure would function here, given the highly fluctuating demand.

Most visitors come during the period mid-May to mid-September period, say 120 days in total. That means that on any average day in the summer period, you have 7 tourists for every 1 resident, with peaks that go even a factor two or three higher. For context, a popular holiday destination like Jamaica has 1.4 tourists for every resident on the island, while Aruba has 10 tourists for every person living on the island.

To supply the islands including Sandhamn with energy, a network of submarine electricity cables, operated by Vattenfall, connects the islands to the main grid of Sweden. Across the island, one can find signs indicating where these cables lie, mainly to warn boats not to drag their anchor here. Below a photo of a typical landing station of a high-voltage submarine cable on the island. Many of the islands have had to deal with power outages due to bad weather conditions and aging assets. But alternative solutions are limited. Generating electricity on the island is tricky, as solar potential is limited during the winter months. Wind may be suitable, but is considered expensive and there are political reservations against it.

In terms of water supply, the island’s solution is quite interesting. The island has an aquifer, which was historically used for water provision, as exemplified by the handpumps that can still be found across the island. The aquifer still provides basic water supplies to the residents, hotels and restaurants of the island, but is insufficient to provide water the sailors and other visitors.

In 2018, four small-scale brackish desalination plants were installed on the island, which purify the seawater using reverse osmosis technology. Each plant can supply 30,000 liters a day, more than enough to meet the demand of thirsty tourists. The “leftover” water after the filtration process is taken by the utility and further purified to be used for flushing toilets and other non-potable water use. The small-scale water solution is ingenious in my view, being able to flexibly provide on-demand supplies across the year, without the need for expensive centralised solutions.

And for those that think that going to a remote island means no phone connection, the multiple telecom towers across the island provide universal coverage. Although, I am not sure if this is a good or a bad thing when trying to escape the city.

All in all, the infrastructure provision on the island is surprisingly excellent, maybe not too surprising from a place called the ‘Hamptons of Sweden’. Still, it  showcases how ingenious solutions to small scale infrastructure provision can help touristic places deal with large fluctuations in infrastructure demand.