Preston and Lancashire are in the North England yield zone — about 8% below the national average. Lancashire's variable weather is worth modelling honestly: solar produces less in winter but performs well in spring and summer. A 4kW system generates roughly 3,130 kWh a year, and battery storage is particularly valuable here for capturing summer generation.
Generation uses a UK baseline of 850 kWh per kWp installed, adjusted for your region's solar irradiance, roof orientation, pitch and shading. South-facing roofs at 30–45° hit the baseline; east/west takes a 15% hit; north loses a third.
Self-consumption defaults to 40% without a battery — the rest exports to the grid. A battery raises self-consumption progressively up to 80% at ~15 kWh capacity.
Savings = self-consumed kWh × your import rate, plus exported kWh × your SEG rate. Apply 0.5% panel degradation per year over the 25-year warranty.
Install cost reflects 2026 UK ranges with 0% VAT (in force until April 2027). Battery cost: roughly £350/kWh installed plus a £2k base.
This is an estimate. Actual generation and quotes vary — get a site survey from an MCS-certified installer before committing.