Introducing the Solar Calculator - Compare Solar Systems and Calculate ROI2026-01-24

Introducing the Solar Calculator

I'm excited to announce a new tool I've built: the Solar Calculator. If you're considering solar energy for your home and want to crunch the numbers yourself, this is for you.

Why I Built This

When researching solar systems, I found most calculators online were either too simplistic (just a basic payback calculation) or locked behind sales funnels. I wanted a tool that would let me:

• Compare multiple system designs side-by-side - Maybe you're deciding between a basic system and one with battery storage, or comparing quotes from different installers
• Model realistic scenarios - Account for panel degradation, energy inflation, different financing options
• Understand battery economics - How much backup power do you really get? Is storing energy better than selling it back to the grid?
• Keep my data private - Everything runs in your browser and saves to localStorage. No accounts, no tracking.

Key Features

1. Home Energy Analysis

Start by entering your current electricity usage and rates:

• Yearly or monthly consumption (calculates the other automatically)
• Current electricity rate and grid buy-back rate (they're often different!)
• Monthly fixed costs
• Energy inflation assumptions

The tool shows you yearly totals, monthly and daily averages, so you understand your baseline energy costs.

2. Multiple System Comparison

This is where it gets powerful. You can create as many system tabs as you want:

• Add new systems from scratch
• Duplicate existing designs to try variations
• Full Bill of Materials - Track panels, inverters, batteries, installation costs, everything

Each system has detailed specifications:

• Panel wattage, quantity, and efficiency
• Location-based sun hours
• System efficiency factors
• Degradation rate over time (typically 0.5% per year)
• Calculated or manual annual production estimates

3. Battery Storage Intelligence

If you're considering battery storage, the calculator provides deep insights:

• Autonomy calculations - How many days can you run on battery alone?
• Weather scenarios - What happens during 30%, 50%, or 70% reduced solar production (cloudy/snowy days)?
• Grid interaction economics - Should you store power or sell it back to the grid?
• Self-consumption rate - What percentage of your solar production you use vs export

The tool even recommends optimal battery size based on your daily usage patterns.

4. Financing Scenarios

Compare three financing approaches for each system:

Cash Purchase

• Simple upfront cost and payback timeline

Loan Financing

• Set interest rate, term length, and down payment
• See monthly payments and total interest paid
• 25-year net cost including loan interest

Opportunity Cost Analysis

• What if you put that money in a high-yield savings account instead?
• Compare solar returns vs HYSA returns over 25 years
• Make the financially optimal decision

5. Comprehensive Summary Dashboard

The summary tab brings it all together:

• Comparison table - All systems side-by-side with key metrics
• 25-year cumulative savings chart - Visual timeline of when each system breaks even and long-term savings
• Production vs consumption - Bar charts showing how much solar you generate vs what you use
• Per-system deep dives - Expandable sections with financial details, battery performance, and production metrics

6. Portable Data

Your solar plans are automatically saved to localStorage. You can also:

• Export to JSON - Download your complete analysis
• Import from JSON - Share designs with family, or keep backups
• Clear all data - Start fresh whenever you want

Technical Implementation

For the developers out there, here's what powers this tool:

• Next.js with TypeScript for type safety
• Tailwind CSS + DaisyUI for responsive, accessible UI with dark mode support
• Recharts for interactive data visualizations
• localStorage for client-side persistence
• Pure client-side - No backend, no database, no tracking

The calculation engine includes:

• Financial modeling with inflation and degradation
• Battery simulation with efficiency losses
• Grid interaction scenarios
• Loan amortization
• Opportunity cost comparison

All the math is open source and auditable if you want to verify the calculations.

Real-World Use Cases

Here are some ways you might use this tool:

1. Quote comparison - Enter specs from 3 different installer quotes and see which offers the best long-term value
2. Battery decision - Model your system with and without battery storage to see if the extra cost is worth it
3. System sizing - Try different panel quantities to find the sweet spot between cost and production
4. Financing strategy - Compare paying cash vs taking a loan vs investing the money elsewhere
5. DIY planning - Design your own system from scratch and price out components

Try It Out

Head over to the Solar Calculator and start playing with the numbers. The interface is designed to be intuitive, but here's a quick workflow:

1. Home Energy tab - Enter your current usage and rates
2. Add a System - Click "+ Add System" to create your first solar design
3. Fill in the BOM - Add costs for panels, inverters, batteries, installation
4. Configure specs - Set panel wattage, quantity, sun hours, etc.
5. Optional: Enable battery - Toggle on if you're considering storage
6. Incentives tab - Add any tax credits or rebates you qualify for
7. Summary tab - See the full analysis and comparison

Create multiple systems to compare different scenarios!

What's Next?

Some features I'm considering for future versions:

• Time-of-use rate optimization for batteries
• Seasonal production modeling
• Carbon footprint calculations
• Solar panel degradation curves by manufacturer
• Historical weather data integration

Let me know if you have suggestions or find any issues. The tool is already production-ready, but I'm always looking to improve it.

Go Solar (Smartly)

Whether you're seriously considering solar or just curious about the numbers, I hope this tool helps you make an informed decision. Solar is a significant investment, and you deserve transparent, detailed analysis to understand the true costs and benefits.

Check it out at /solar and let me know what you think!