Canna is the westernmost of an archipelago of islands called the 'small isles', sitting out in the Atlantic with a population which swells to around 30 people in the summer. The post office was converted from a garden shed. The only shop is unstaffed, and the police officer visits twice a year. It's not the sort of place you would think is leading the way in the transition to net zero.
While many have people have recently been struggling with the high price of energy, in Canna, the cost of energy has always been high. It is not connected to the mainland grid, and up until 2018, its micro-grid was powered by diesel. However, since then, Canna's energy has mainly come from Solar PV and wind turbines, supported by battery storage in an old deconsecrated church. That's massively helped to reduce the running cost of the electrical network, but there is still a significant fossil fuel (fuel oil) requirement, mainly for space and hot water heating, but also for the diesel generator and transportation.
Scene has been working with the local community to continue their decarbonisation process to reach net zero. Our latest work has included the installation of additional energy monitoring, and smart control of immersion heaters.
New monitoring
Scene completed a decarbonisation study in 2021 which included detailed modelling of network power flow. One of the key recommendations from this work was that more data at a more granular level would allow more accurate recommendations for how to phase the island's decarbonisation while keeping the lights on. So in 2022, Scene returned to fit additional monitoring and integrate with existing data sources, which has been helping to build a rich dataset for future studies. Scene has already been using it to make better use of surplus renewable energy, and provide insights into the state of health of the different installed system components. Without this monitoring, the dropping performance of the wind turbines would have gone unnoticed for longer, increasing oil usage and driving up costs.
New dump loads
The Canna power system has a number of electric storage heaters used as dump loads – they turn on when there is excess renewable generation on the island and the battery is full. With no connection to the mainland, there’s no opportunity to export the energy. However, these heaters cannot be relied on and are mostly located in low-priority locations for heat (except for one office – I haven’t forgotten!).
To increase the value of this dumped energy, we've installed a control system which provides hot water for residents instead of heating (mostly) empty buildings. Most island properties have a hot-water tank with an immersion heater, and these can be retro-fitted with a controller that turns on the immersion heater as the dump-load.
We're also working with CREEL, the locally owned enterprise which operates the energy supply on island to resolve challenges with managing dump loads:
Pricing - how do we charge customers less for the dump load energy than normal energy? Rather than install a separate meter and electricity distribution board, the solution meters energy used by the immersion only while in the dump load mode. The household bill is adjusted accordingly.
Fair distribution - how do we ensure benefits from this cheaper energy is shared equitably across the community? A remotely configurable local control strategy allows “rotation” of dump load priority between properties.
Prioritising - how do we prioritise new dump loads over old storage heater loads within the overall island control system? The new controls have a greater degree of configurability and accuracy than the simple storage heater controls. Loads are configured so that they don’t all go on at the same time.
Remote maintainability of the new solution? An override switch is provided so that the new control can be bypassed.
Why is this good?
The additional monitoring insights have been useful. With more time elapsed, a richer dataset can provide more granular insights. The new dump loads have increased the value of the spare energy and reduced the amount of fuel oil required (and thus reduced the cost) to heat hot water on the island. Scene has gained valuable insight into this method of control and into the energy used in hot water heating. Scene will seek to use the control method as a part of a future, more coordinated, demand control strategy to include new loads such as heat pumps. Island residents are familiar with the dump loads – experience of them in their homes will better equip them to make decisions on the future evolution of their island power system.
What have we learnt?
Scene has learnt a lot from the data, increasing the value of spare energy and reducing the amount of fuel oil (and therefore the cost) for hot water on the island. We've gained valuable insights into control methods and energy used in hot water heating, and the potential to integrate this into a future wider demand control strategy for the island.
We've also learnt a lot from the community. The simpler and more unobtrusive the solution is to the consumer, the more likely it will be accepted. With too many control options, individuals don't have the time or headspace to update the controls – fewer options are better. This need for simplicity needs to be balanced with the need for customisation to support the preferences of different individuals, better. And any new control solution must be sensitive to existing operation and expectations. The community is also learning from this, as a first step to smart control to support the future evolution of their island energy system. Getting to net zero is a shared journey we are all on together, even when the starting point is in the middle of nowhere.