Island Electricity Is Either a Cable or a Fuel Bill

What follows is an argument about island power supply, and about where the received version of it stops being true.

Three ways an island gets power

The simplest arrangement is a subsea cable from the mainland grid, which gives an island the same supply as everyone else. Where no cable exists, the island generates its own power, historically with diesel sets running around the clock.

Increasingly there is a hybrid: local wind or solar generation, a battery, and diesel or a cable as the backstop. Which of these applies is the single best predictor of what electricity costs and how reliable it is. It also explains why one island has cheap heating and its neighbour a few miles away does not.

The fuel bill nobody sees

Diesel for an island generator arrives by tanker or by drum, and the freight is added to a price that was already high. Because of that, unsubsidised island electricity can cost a multiple of mainland electricity for identical service.

Many countries equalise tariffs so residents pay a standard rate, with the difference covered from general funds. Where that equalisation does not exist, the cost shows up in accommodation prices and in what businesses can afford to run. It is also why electric heating is rare on some islands and why buildings are heated by anything cheaper that can be shipped.

A cable is one point of failure

A subsea cable is cheaper to run than local generation but concentrates the entire supply into a single vulnerable asset. Cables are damaged by anchors, by trawl gear and by seabed movement, and the fault has to be located before it can be fixed.

Specialist cable ships are few and in demand, so a repair is scheduled around vessel availability and weather windows. That is why an island cable fault is measured in weeks and why backup generation exists even on cabled islands. The backup is often sized for essential load rather than for everything the island uses on a normal day.

Renewables are abundant and awkward

Islands generally have excellent wind and often good solar resources, which makes local generation technically attractive. A small grid has little inertia, so it is harder to keep frequency stable when a variable source rises and falls quickly. Storage solves much of that, but batteries are a capital cost carried by a very small number of connected households.

Salt air corrodes everything, so maintenance intervals on island installations are shorter than the manufacturer's default.

Community-owned schemes exist in a number of places and keep the revenue on the island rather than exporting it.

What an outage actually stops

Water supply on many islands is pumped, so a power cut becomes a water cut within hours rather than days. Refrigeration in shops and in the fishing industry is the next casualty, and losses there are immediate and expensive.

Card payments, cash machines and mobile masts run on power, so an outage is a communications problem as well. Fuel pumps stop, which matters if the ferry, the lifeboat or a generator needs refuelling during the same event. Islands plan for this with stored fuel and standby plant, but the plan assumes a limited duration rather than an indefinite one.

Being a light load

Air conditioning, electric heating and hot tubs are large loads on a grid built for a few hundred households. Charging an electric vehicle on a small island grid is possible in more places than it used to be, but capacity varies enormously.

With the tide out, asking the accommodation or the local network operator before relying on a charge point is a reasonable precaution. Where an island asks visitors to reduce use during a fault, the request is operational rather than symbolic. Carrying a torch and a charged power bank costs nothing and removes most of the inconvenience of a short outage.

The takeaway

Ask how the island makes its electricity, and you will have explained half of what everything there costs.

Arrive a day early. A coastline rarely rewards a tight schedule.