Comprehensive guide for evaluating residential solar energy systems including system sizing calculations, roof assessment, net metering policies, ROI analysis with payback period calculation, installer comparison framework, federal and state incentives (ITC, SRECs), battery storage considerations, financing options, and ongoing maintenance requirements.
Use when the user asks about solar evaluator, or needs help with comprehensive guide for evaluating residential solar energy systems including system sizing calculations, roof assessment, net metering policies, roi analysis with payback period calculation, installer comparison framework, federal and state incentives (itc, srecs), battery storage considerations, financing options, and ongoing maintenance requirements.
Do NOT use when the request requires professional specialized advice or falls outside the scope of solar evaluator.
Comprehensive guide for evaluating residential solar energy systems including system sizing calculations, roof assessment, net metering policies, ROI analysis with payback period calculation, installer comparison framework, federal and state incentives (ITC, SRECs), battery storage considerations, financing options, and ongoing maintenance requirements.
Use when the user asks about solar evaluator, or needs help with comprehensive guide for evaluating residential solar energy systems including system sizing calculations, roof assessment, net metering policies, roi analysis with payback period calculation, installer comparison framework, federal and state incentives (itc, srecs), battery storage considerations, financing options, and ongoing maintenance requirements.
Do NOT use when the request requires professional specialized advice or falls outside the scope of solar evaluator.
User wants a structured approach to solar evaluator
Do NOT use when:
Request requires professional consultation beyond educational guidance
User needs emergency assistance
Questions to Ask First
What is your average monthly electricity bill (in dollars and kWh)?
What is your roof's age, condition, and material?
What direction does your roof primarily face (south is ideal in the Northern Hemisphere)?
Are there significant shading factors (trees, buildings, chimneys)?
What is your utility company, and do they offer net metering?
How long do you plan to stay in this home?
What is your budget, and are you considering purchase, loan, or lease?
Have you checked your area's solar irradiance (sun hours per day)?
Are you interested in battery storage, or grid-tied only?
Have you already received any solar quotes?
Phase 1: System Sizing Calculation
Step 1: Determine Your Energy Consumption
Monthly electricity usage (from utility bill): _______ kWh
Annual electricity usage: _______ kWh (monthly x 12, or sum from 12 months of bills)
Adjustment for future changes:
- Adding EV? Add 3,000-5,000 kWh/year
- Adding heat pump? Add based on estimate
- Reducing consumption? Subtract estimated savings
Adjusted Annual Usage: _______ kWh
Step 2: Calculate System Size Needed
System Size (kW) = Annual kWh Needed / (Peak Sun Hours x 365 x System Efficiency)
System Efficiency: ~0.80 (accounts for inverter losses, wiring, temperature, soiling)
Example:
Annual Usage: 10,000 kWh
Peak Sun Hours: 5.0 (varies by location -- check PVWatts)
System Size = 10,000 / (5.0 x 365 x 0.80) = 6.85 kW
Round up slightly: 7 kW system
Step 3: Estimate Panel Count
Number of Panels = System Size (watts) / Panel Wattage
Example:
System Size: 7,000 watts (7 kW)
Panel Wattage: 400 watts (current standard)
Panels Needed: 7,000 / 400 = 17.5, round to 18 panels
Roof Space Needed: ~18 sq ft per panel x 18 panels = ~324 sq ft
Peak Sun Hours by Region (US Averages)
Region
Peak Sun Hours
Example Cities
Southwest
5.5-7.0
Phoenix, Las Vegas, Albuquerque
Southeast
4.5-5.5
Miami, Atlanta, Charlotte
Midwest
4.0-5.0
Kansas City, Indianapolis, St. Louis
Northeast
3.5-4.5
New York, Boston, Philadelphia
Northwest
3.5-4.5
Seattle, Portland (lower in winter)
Mountain
5.0-6.0
Denver, Salt Lake City
Use NREL's PVWatts Calculator (pvwatts.nrel.gov) for precise local data.
Phase 2: Roof Assessment
Roof Evaluation Checklist
Factor
Ideal
Acceptable
Problematic
Age
Under 10 years old
10-15 years (may need replacement first)
Over 20 years (replace before installing solar)
Condition
No damage, leaks, or wear
Minor wear, no active leaks
Active leaks, missing shingles, sagging
Material
Composite shingle, metal, tile
Flat/membrane roof
Wood shake (fire risk), slate (fragile)
Direction
South-facing
Southwest or southeast
North-facing (poor production in Northern Hemisphere)
Pitch
15-40 degrees
0-15 or 40-60 degrees
Very steep (>60 degrees)
Shading
No shading 9AM-3PM
Minor shading (1-2 hours)
Significant shading (>3 hours)
Structural
Can support ~2.5 lbs/sq ft additional load
Needs verification
Cannot support additional weight
Obstructions
Large unbroken roof area
Vents, skylights (can work around)
Many dormers, complex roof geometry
Shading Analysis
Tools for shading assessment:
Google Project Sunroof (google.com/get/sunroof) -- free, satellite-based
Solar installer site visit with shade analysis tool (SunEye, Solmetric)
PVWatts calculator with shading adjustments
Satellite imagery review (Google Earth)
Impact of shading: Even partial shading on one panel can significantly reduce output of an entire string of panels (with traditional string inverters). Microinverters or power optimizers can mitigate this.
Phase 3: Financial Analysis
System Cost Estimation
SOLAR SYSTEM COST ESTIMATE
============================
System Size: _______ kW
Gross System Cost (before incentives):
Average cost per watt: $2.50-$3.50 (varies by market)
System cost: _______ kW x 1,000 x $______/watt = $__________
Federal Investment Tax Credit (ITC):
Current ITC rate: 30% (through 2032, then steps down)
ITC value: $__________ x 30% = $__________
State/Local Incentives:
State tax credit: $__________
Utility rebate: $__________
SREC income (est. annual): $__________
Other incentives: $__________
Total state/local incentives: $__________
Net System Cost:
Gross cost: $__________
- Federal ITC: $__________
- State/local incentives: $__________
= Net Cost: $__________
ROI and Payback Period Calculation
PAYBACK PERIOD ANALYSIS
========================
Net System Cost (after incentives): $__________
Annual Savings:
Annual electricity production: _______ kWh
Utility rate: $_______ /kWh
Annual electric bill savings: $__________
+ Net metering credits (if applicable): $__________
+ SREC income (if applicable): $__________
Total Annual Savings: $__________
Simple Payback Period:
Net Cost / Annual Savings = _______ years
25-Year Financial Analysis:
Total savings over 25 years: $__________
(Account for 2-3% annual utility rate increases)
Net profit over system life: $__________
Return on Investment: _________%
Typical Financial Benchmarks
Metric
Good
Average
Poor
Payback period
Under 7 years
7-12 years
Over 12 years
25-year savings
Over $30,000
$15,000-$30,000
Under $15,000
Year 1 savings
Over $1,500
$800-$1,500
Under $800
Cost per watt (before incentives)
Under $2.75
$2.75-$3.50
Over $3.50
Phase 4: Net Metering
How Net Metering Works
When your solar panels produce more electricity than you are using, the excess is sent to the grid. Net metering policies determine how you are credited for that excess.
Full Retail Net Metering: You receive a credit at the full retail rate for every kWh exported. This is the most favorable for homeowners.
Reduced Rate Net Metering: Credits are calculated at a lower rate than retail (wholesale, avoided cost, or a set rate).
Net Billing / Buy-All-Sell-All: You sell all production to the utility at one rate and buy all consumption at another.
Time-of-Use (TOU) Net Metering: Credits vary based on when you export (more valuable during peak hours, less during off-peak).
Questions to Ask Your Utility
Do you offer net metering?
At what rate are credits calculated?
Do credits roll over month to month? Do they expire?
Is there a system size cap for net metering?
Are there additional fees for solar customers (grid access fees)?
What is the interconnection process and timeline?
Are there any pending changes to net metering policy?
Phase 5: Incentive Programs
Federal Investment Tax Credit (ITC)
Year
Credit Rate
Notes
2022-2032
30%
Inflation Reduction Act extended and increased
2033
26%
Step-down begins
2034
22%
Further reduction
2035+
0% (residential)
May be extended by future legislation
Requirements:
Must own the system (not lease)
Must have sufficient tax liability to use the credit
Credit can be carried forward to future tax years
Applies to solar panels, inverters, racking, installation labor, battery storage
State and Local Incentives
Common state-level incentives:
State tax credits (additional percentage or fixed amount)
Property tax exemptions (solar does not increase property tax assessment)
Sales tax exemptions (no sales tax on solar equipment)
Renewable portfolio standard (RPS) incentives
SRECs (Solar Renewable Energy Certificates)
State rebate programs
Low-interest loan programs
Finding incentives in your area:
DSIRE database (dsireusa.org) -- comprehensive database of incentives by state
In some states, solar system owners earn SRECs based on electricity production. These certificates can be sold on a market. One SREC = 1,000 kWh (1 MWh) of solar production.
States with active SREC markets: New Jersey, Massachusetts, Pennsylvania, Maryland, Washington DC, Illinois, Ohio (partial list -- check current status).
Potential SREC income: $20-$400+ per SREC depending on the state market.
Phase 6: Installer Comparison
Getting and Comparing Quotes
Get at least 3 quotes. For each, document:
SOLAR INSTALLER COMPARISON
============================
Installer A Installer B Installer C
Company Name: ___________ ___________ ___________
Years in Business: ___________ ___________ ___________
License Verified: Y / N Y / N Y / N
Insurance Verified: Y / N Y / N Y / N
NABCEP Certified: Y / N Y / N Y / N
SYSTEM DETAILS:
Panel Brand/Model: ___________ ___________ ___________
Panel Wattage: ___________ ___________ ___________
Number of Panels: ___________ ___________ ___________
Total System Size: ___________ ___________ ___________
Inverter Type: ___________ ___________ ___________
Inverter Brand: ___________ ___________ ___________
Racking System: ___________ ___________ ___________
PRODUCTION ESTIMATE:
Year 1 Production: ___________ ___________ ___________
Production Guarantee: Y / N Y / N Y / N
COST:
Gross Price: $__________ $__________ $__________
Cost per Watt: $__________ $__________ $__________
After Federal ITC: $__________ $__________ $__________
After All Incentives: $________ $__________ $__________
WARRANTIES:
Panel Warranty: ___________ ___________ ___________
Inverter Warranty: ___________ ___________ ___________
Workmanship Warranty: _________ ___________ ___________
Roof Penetration: ___________ ___________ ___________
REVIEWS/REFERENCES:
Google Rating: ___________ ___________ ___________
BBB Rating: ___________ ___________ ___________
References Checked: Y / N Y / N Y / N
Inverter Types Comparison
Type
Pros
Cons
Best For
String inverter
Lowest cost, proven technology
One shaded panel affects entire string
Unshaded roofs, simple layouts
Microinverters
Panel-level optimization, better for shading
Higher cost, more components
Shaded roofs, complex layouts
Power optimizers + string inverter
Panel-level optimization, central inverter monitoring
Moderate cost, added complexity
Mixed shading, multiple orientations
Phase 7: Battery Storage
When Battery Storage Makes Sense
Good reasons to add batteries:
Time-of-use rate structure (charge during cheap/solar hours, use during expensive peak hours)
Poor net metering policy (low export rate)
Frequent power outages
Desire for energy independence
Off-grid applications
When batteries may NOT make financial sense:
Full retail net metering available (the grid acts as your battery for free)
Reliable grid with rare outages
Limited budget (panels first, batteries can be added later)
Battery Comparison
Metric
Tesla Powerwall
Enphase IQ
LG RESU
Generac PWRcell
Capacity
13.5 kWh
3.36-10.08 kWh (modular)
9.6-16 kWh
9-18 kWh (modular)
Power Output
5 kW continuous
Varies by config
5-7 kW
4.5-9 kW
Warranty
10 years
10-15 years
10 years
10 years
Approximate Cost (installed)
$12,000-$16,000
$10,000-$20,000
$10,000-$14,000
$12,000-$20,000
Note: Battery prices and specifications change frequently. Verify current pricing with installers.
Battery Sizing
Battery Size Needed = Critical Load (kWh) x Hours of Backup Desired
Essential loads during outage:
Refrigerator: ~1.5 kWh/day
Lights: ~1 kWh/day
Phone/device charging: ~0.5 kWh/day
Wi-Fi router: ~0.25 kWh/day
Sump pump (if needed): ~1 kWh/day
Medical equipment: varies
Example: 4 kWh/day essential load x 2 days backup = 8 kWh minimum
(Account for ~90% depth of discharge = need ~9 kWh rated capacity)
Phase 8: Financing Options
Comparison of Financing Methods
Method
Ownership
Upfront Cost
Monthly Cost
ITC Eligible
Best For
Cash purchase
You own
Full cost
$0
Yes
Maximum long-term savings
Solar loan
You own
$0-low
Loan payment
Yes
Good credit, want ownership
Home equity loan/HELOC
You own
$0
Loan payment
Yes (interest may be deductible)
Significant home equity
Solar lease
Company owns
$0
Monthly lease
No (company claims)
Low/no upfront, lower savings
PPA (Power Purchase Agreement)
Company owns
$0
Per kWh rate
No (company claims)
Low/no upfront, predictable cost
Financial Decision Framework
If you can afford to buy (cash or loan): BUY.
You receive the federal ITC and all incentives
You own the system and the increased home value
Maximum lifetime financial benefit
No escalation clauses or contract complications
If cash purchase is not possible:
Solar loan is the next best option (you still get ITC)
Ensure the loan payment is less than your current electric bill savings
Avoid balloon payments or variable rate loans
Compare at least 3 lenders
Lease/PPA is better than nothing, but understand:
You do not own the system
Savings are typically 10-30% of current bill (vs. 50-100% with ownership)
Escalation clauses may increase payments annually
Can complicate home sale (buyer must assume or you must buy out)
You do not receive the ITC or other incentives
Phase 9: Ongoing Maintenance
Solar System Maintenance Schedule
Task
Frequency
DIY or Professional
Cost
Visual inspection (look for damage, debris)
Monthly
DIY
Free
Monitor production (via app or inverter)
Weekly/monthly
DIY
Free
Panel cleaning (if needed)
1-2x per year
DIY or professional
$0-$300
Professional inspection
Every 3-5 years
Professional
$150-$300
Inverter replacement
Every 10-15 years (string)
Professional
$1,000-$2,500
Tree trimming (for shading prevention)
As needed
Professional
Varies
Monitoring Your System
Most modern systems include monitoring apps
Check daily/weekly production against expected output
Sudden drops in production may indicate a problem
Compare month-over-month and year-over-year production
Report anomalies to your installer (usually covered under warranty)
Panel Longevity
Most panels are warranted for 25-30 years
Panels degrade approximately 0.3-0.5% per year
After 25 years, expect ~85-90% of original production
Many panels continue producing well beyond warranty period
Solar is a long-term investment. Take the time to analyze your specific situation thoroughly, get multiple quotes, and understand all the financial implications before committing. When the numbers work, solar provides decades of clean energy and significant savings.
Output Format
SOLAR EVALUATOR OUTPUT
======================
Section 1: Assessment / Analysis
- Key findings
- Recommendations
Section 2: Action Plan
- Step-by-step guidance
- Timeline if applicable
Section 3: Resources
- Relevant references
- Next steps
Example
Input: "Help me get started with solar evaluator"
Output: A structured solar evaluator plan tailored to the user's specific situation, following the process outlined above.
Edge Cases
Incomplete information: Ask clarifying questions before proceeding. Do not assume details the user has not provided.
Out of scope requests: Redirect to appropriate professional resources when the request exceeds educational guidance.
Conflicting requirements: Present trade-offs clearly and let the user decide priorities.
