Off-grid solar for remote Cornwall properties

When off-grid is the right answer

The honest answer: not as often as people think. Most Cornwall properties with an existing grid connection are better served by a standard solar PV and battery storage system than a fully off-grid setup — the grid is a 24/7 backup that costs nothing to maintain. Where off-grid genuinely wins:

• New-build remote properties where the grid connection quote is £30,000 or more — increasingly common for moorland, coastal, and woodland sites in Cornwall.
• Cabins, outbuildings and smallholdings without any existing supply, where trenching and line installation make no commercial sense.
• Existing properties with failing overhead supplies where the cost of upgrading the feed is comparable to going independent.
• Planning-constrained sites where DNO infrastructure cannot be installed.

For anyone with a working grid connection, hybrid solar + battery will almost always deliver better economics.

How off-grid sizing differs

Grid-tied solar is sized around annual consumption. Off-grid has to be sized around the worst week of the year — typically mid-December in Cornwall. That changes three things fundamentally:

• Solar array is oversized. Winter production in Cornwall is 10–15% of summer output. You size for winter, accept summer excess.
• Battery carries days of autonomy, not hours. 3 to 5 days of winter demand is the minimum we design for. That is usually 30–60 kWh of usable capacity for a family home.
• A generator covers extended low-sun periods. Typically a propane or diesel unit running 20–80 hours per winter. This is far cheaper than sizing the battery to never need backup.

The components we use

• Panels — JA Solar DeepBlue 4.0 or equivalent monocrystalline modules, typically 8kWp to 16kWp for a family home.
• Battery — Sigenergy, Fox Pro, or Tesla Powerwall for residential; Sigenergy and Fox commercial for larger sites.
• Inverter — Victron MultiPlus-II or Sigenergy hybrid with off-grid mode and generator AC-coupling.
• Generator — propane preferred over diesel in Cornwall for emissions, noise and runtime cost. Automatic start integration.
• Monitoring — all systems remotely monitored so we can diagnose faults without a site visit.

Heating on an off-grid property

Heating choice matters more off-grid than on-grid. Direct electric heating is rarely viable. We typically specify:

• Air source heat pump — with a properly sized buffer tank and UFH or large radiators, SCOP 3.5+ delivers real electrical efficiency. Oversize solar to compensate for winter demand.
• Wood-burning stove or biomass — often ideal for the coldest weeks when solar is weakest. Keeps total electrical load manageable.
• Hot water — large unvented cylinder with immersion, topped up by heat pump, with solar diverter to dump surplus summer generation as hot water.

Planning and approval

Off-grid systems still benefit from MCS certification — particularly if the property may later connect to the grid. Planning rules are the same as grid-tied for roof arrays (permitted development unless listed, conservation or AONB). Generator housings usually need an acoustic enclosure if within 20m of a neighbour.

Next steps

Off-grid design is site-specific work. We start with a detailed site survey, energy audit and load profile before proposing a system. Contact us or call 01209 596 002 to discuss whether off-grid makes sense for your property.