Community Solar + Storage Benefit Calculator: Explanation

What It Does

The Community Solar + Storage Benefit Calculator is an interactive tool designed to help developers and planners assess the financial and environmental benefits of installing a shared solar photovoltaic (PV) and battery storage system across a UK housing development. It calculates key metrics such as annual savings, export revenue, CO2 reductions, payback period, and lifetime savings, providing a clear picture of the system's value over 25 years. By pooling solar energy from multiple homes into a centralized battery for evening use, it demonstrates how such a system can reduce energy costs, enhance sustainability, and appeal to eco-conscious buyers.

How It Works

The calculator takes user inputs about the housing development and system specifications, then applies realistic assumptions to model performance over time. Here’s the process:

1. Inputs:

• Number of Homes: Total homes in the development.
• Solar PV Size per Home (kW): Solar capacity per rooftop (e.g., 4 kW).
• Community Battery Capacity (MWh): Size of the shared battery (e.g., 1 MWh = 1000 kWh).
• Evening Energy Use per Home (kWh): Energy demand per home in the evening (e.g., 2.5 kWh).
• Electricity Rate (£/kWh): Cost of grid electricity (e.g., £0.28/kWh).
• SEG Export Rate (£/kWh): Rate for selling excess energy to the grid via the Smart Export Guarantee (e.g., £0.05/kWh).
• Total System Cost (£): Combined cost of solar panels, battery, and installation (e.g., £700,000).
• Incentives/Grants (£, optional): Any funding or cost reductions (defaults to £0 if blank).
• Battery Degradation Rate (%/year): Annual capacity loss of the battery (e.g., 1%).
• Solar Degradation Rate (%/year): Annual output decline of solar panels (e.g., 0.5%).

2. Calculations:

• Year 1 Benefits: Estimates solar generation (900 kWh/kW/year, UK average), evening energy covered by the battery (90% efficiency), savings from avoided grid use, and revenue from exporting excess energy.
• Cost per Dwelling: Divides net cost (total cost minus incentives) by the number of homes.
• Benefit per Household: Splits total annual benefit across homes.
• Degradation Over Time: Reduces battery capacity and solar output annually, adjusting benefits accordingly.
• Payback Period: Counts years until net cost is recovered, capping at 25 years.
• Lifetime Savings: Sums benefits over 25 years.
• CO2 Reduction: Calculates emissions saved from evening use (0.233 kg CO2/kWh, UK grid average).

3. Outputs:

Displays results for Year 1 (e.g., savings, revenue, CO2 reduction) and long-term metrics (payback, lifetime savings). Generates a chart showing annual benefits vs. remaining costs over 25 years.

4. Features:

• Handles blank incentives (defaults to £0).
• Validates inputs to prevent errors (e.g., negative values).
• Offers a downloadable report of results.

How to Use It

1. Access the Tool: Open the calculator in a web browser (ensure an internet connection for Chart.js).
2. Enter Your Data: Fill in the required fields with details specific to your development (e.g., 100 homes, 4 kW solar per home). Leave "Incentives/Grants" blank if none apply—it will default to £0. Adjust optional fields like degradation rates if you have specific data; otherwise, use defaults (1% battery, 0.5% solar).
3. Run the Calculation: Click "Calculate Benefits" to see the results and chart. Review outputs like cost per dwelling (£7,000), annual benefit per household (£389.90), and payback (19 years) for defaults.
4. Interpret the Results:
   • Cost per Dwelling: Initial investment per home.
   • Benefit per Household: Yearly financial gain per home.
   • Payback Period: Time to recover costs (shorter with incentives).
   • Lifetime Savings: Total profit over 25 years.
   • Chart: Visualizes how benefits decline with degradation and when costs are repaid.
5. Export and Share: Click "Download Report" to save results as a text file for presentations or records.

Example Scenario

Inputs: 100 homes, 4 kW solar/home, 1 MWh battery, 2.5 kWh evening use/home, £0.28/kWh, £0.05/kWh SEG, £700,000 cost, no incentives, 1% battery degradation, 0.5% solar degradation.
Outputs: £7,000/dwelling, £389.90/household/year (Year 1), 19-year payback, £856,672 lifetime savings, 21.26 tonnes CO2 reduction (Year 1).

Why Use It?

This tool empowers developers to quantify the economic and environmental case for community solar + storage, making it easier to justify investment, secure funding, and market sustainable homes. It’s flexible, visual, and practical—perfect for planning greener UK housing developments.