System Overview
This installation combines a 10.56 kWp solar PV array with 27 kWh of battery storage (Tesla Powerwall 3 with an expansion pack and Tesla Backup Gateway 2).
The PV array is made up of 22 solar panels. Of these, 16 panels are installed on the pitched roof and 6 panels are installed on a flat roof section. This split layout increases the available generation area while using both roof types effectively.
The system is modelled against an annual household electricity demand of 10,000 kWh. The solar array is forecast to generate approximately 7,116 kWh per year.
System Performance and Energy Usage
Modelling shows that electricity generated by the system is used in four main ways:
- Solar used directly in the home
- Solar stored in the battery for later use
- Off-peak grid charging when advantageous
- Export of surplus electricity to the grid
Across the year, the property is forecast to reach 32% grid electricity independence. This reflects the proportion of annual electricity demand that can be supplied without importing from the grid.
The model also forecasts that around 46% of solar generation is used on site (self-consumption), with the remaining surplus exported when generation exceeds demand.
Typical daily solar generation (seasonal averages) is forecast as:
- Winter: 6.69 kWh per day
- Spring: 30.65 kWh per day
- Summer: 25.83 kWh per day
- Autumn: 14.51 kWh per day
Seasonal export behaviour is driven by the mismatch between daytime generation and household demand. In higher-generation periods, the system is expected to export larger volumes of electricity once on-site consumption requirements have been met.
Financial Savings and Long-Term Benefits
Over a 25-year forecast period, the system is projected to deliver total electricity savings of £101,761.
In year one, total savings are forecast at approximately £2,710. This is made up of:
- Expected bill savings: £2,129
- Expected export income: £580
Average electricity costs over the next 15 years are expected to reduce from 45.2 p/kWh (without solar and battery) to 20.5 p/kWh (with the system installed), based on the modelling assumptions.
The financial model also reports a positive net present value (NPV) of £68,834 over 25 years, using the discount rate and battery round-trip losses stated in the modelling.
Environmental Impact
Based on the forecast generation, the system offsets an estimated 1,423 kg of CO₂ per year.
This annual carbon saving is presented as equivalent to:
- An average family petrol car’s CO₂ emissions for 6,031 miles per year
Over the system lifetime, the model equates the carbon benefit to:
- Planting 681 trees
- 289 flights from London to New York
Conclusion
This installation shows the impact of pairing a suitably sized solar array with substantial battery capacity and a tariff strategy that makes best use of both on-site solar and off-peak grid energy. With forecast generation of 7,116 kWh per year and meaningful levels of self-consumption and export, the system is expected to deliver long-term reductions in electricity costs alongside measurable carbon savings.
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