How the HowMuchSolar Calculator Works (Methodology Overview)

Introduction

At HowMuchSolar, we believe solar savings shouldn’t be a mystery. Our calculator crunches the numbers to show you how much you could save by switching to solar—tailored to your home, your bill, and your location. But how does it work? We’re pulling back the curtain to give you a clear, transparent look at the methodology behind the magic. From sunlight data to electricity rates, every figure is grounded in real-world facts and industry standards. Plus, we’ve added a step-by-step guide to help you use the tool and make sense of the results—no PhD required. Let’s dive in!

The Methodology: How We Calculate Your Solar Savings

Our goal? Deliver accurate, personalized solar savings estimates. Here’s how we do it, step by step:

1. Sunlight Data (DNI)
   Source: We pull Direct Normal Irradiance (DNI) data from NASA’s POWER project and industry-standard solar maps—think averages like 4.64 kWh/m²/day for Lincoln, Nebraska.
   Assumption: Your roof’s sunlight depends on location and shading (ideal, partial, heavy). We adjust DNI by 100%, 85%, or 70% based on your shade input.
   Why It Matters: More sun = more energy. DNI drives your system’s daily production (e.g., 10.37 kW * 4.64 = ~48 kWh/day).
2. System Size & Cost
   Source: System size (kW) is sized to your annual kWh usage (e.g., 17,570 kWh) or roof area, whichever’s smaller, with degradation baked in (0.5%/year over 25 years—set upstream in our estimator logic). Costs come from state-specific averages (e.g., $2.70/watt in Nebraska = $27,999 for 10.37 kW).
   Assumption: Panels produce ~180 W/ft²; roof size limits are conservative (70% of usable area).
   Why It Matters: Matches your system to reality—cost and output align with industry norms.
3. Electricity Rates & Inflation
   Source: Default rates (e.g., $0.1408/kWh for Nebraska) are from EIA data, adjustable by you. Inflation’s state-specific (e.g., 2.59% for Nebraska) or defaults to 3%.
   Assumption: Rates rise annually—compounding over 25 years (e.g., $0.14 to $0.20 avg).
   Why It Matters: Savings grow as grid costs climb; we project your future bills accurately.
4. Self-Use & Net Metering
   Source: Defaults (40% self-use, 60% exported at 70% buyback) reflect typical U.S. residential patterns, tweakable by you.
   Assumption: Excess solar goes to the grid, credited at a reduced rate (e.g., 28.87 kWh exported * 0.7 = 20.21 kWh credit).
   Why It Matters: Shows real savings—self-used kWh offset full rates, credits cut grid bills.
5. Loan & Incentives
   Source: Loan APR (5%) and terms (20 years) are industry averages; state incentives (e.g., $500 for Nebraska) and 30% federal ITC are from DSIRE and IRS data.
   Assumption: Loan payments adjust post-ITC (e.g., $183 to $176/month); incentives are fixed unless updated.
   Why It Matters: Nets out your true cost—$27,999 becomes ~$33,813 over 25 years with savings.
6. Savings & kWh Price
   Calc: Daily savings (e.g., $5.56) inflate over 25 years (e.g., $65,936 total) minus net cost (e.g., $33,813) = $33,813 savings. Effective kWh rate = total cost / usable kWh (e.g., $0.10 vs. $0.19 grid avg).
   Assumption: Flat production with baked-in degradation; grid costs include fees (5% + $8).
   Why It Matters: The bottom line—savings and a killer kWh rate ($0.19 vs. $0.10) in sparkly gold!
7. Battery Bonus
   Source: Tesla Powerwall costs post-30% ITC ($7,700–$27,160 for 1–6 units); 13.5 kWh capacity, 90% efficiency.
   Assumption: Stores excess (e.g., 11.62 kWh/day), saves $0.49/day flat or $0.93 TOU, inflated over 10/15 years.
   Why It Matters: Optional add-on—shows if batteries pay off (e.g., -$3,540 net).

Step-by-Step Guide: Using the HowMuchSolar Calculator

Ready to see your savings? Here’s how to use the tool and decode the results:

1. Enter Your Basics
   Location: Pick your state and city (e.g., Nebraska, Lincoln) for sunlight and rate defaults.
   Bill: Input your monthly utility bill (e.g., $225)—we’ll estimate annual kWh (17,570).
   Screenshot Tip: Start page → "Bill: $225" → hit "Calculate."
2. Customize (Optional)
   Roof: Square footage and stories tweak system size.
   Shade: Ideal, partial, or heavy adjusts output.
   Rates: Override $0.1408/kWh if your bill differs.
   Loan: Slide APR (2–10%) and years (5–25).
3. Read the Results
   System Size: ~10.4 kW—how much solar fits your needs.
   Daily Breakdown: 48.1 kWh generated, 19.3 self-used, 20.2 credited, 8.6 from grid.
   Old vs. New Bill: $225 → $176 (Year 1: $224)—immediate savings.
   kWh Price: Today: $0.14 vs. $0.10 | 25-Yr Avg: $0.19 vs. $0.10—long-term win.
   Net Savings: $33,813 over 25 years—your ROI.
   Battery: Toggle 1–6 Powerwalls; see if it’s worth it (e.g., -$3,540 net = skip it).
   Screenshot Tip: Results page → sliders → "Net Savings: $33,813."
4. Key Terms
   kWh: Kilowatt-hour—your energy unit (e.g., 17,570/year).
   ROI: Return on Investment—savings vs. cost.
   Payback Period: ~8–10 years (implied by sliders—tweak to see).
5. Adjust & Explore
   Hit “Adjust,” tweak inputs, watch numbers dance—find your sweet spot!

Why Trust Us?

We don’t guess. Our data’s sourced from NASA, EIA, DSIRE, and Tesla—industry gold standards. Assumptions? Conservative and adjustable—shade, self-use, buyback rates—you’re in control. That $33,813 savings or $0.10/kWh rate? Backed by math, not hype. Transparency builds trust, and we’re here to prove solar’s worth, one calculation at a time.

Ready to Go Solar?

Plug in your details, see the savings, and join the solar revolution. Questions? Hit us up—we’re all about keeping it real. Let’s make your energy future bright!