Solar System Evaluation

Systematic methodology for assessing solar energy feasibility, calculating system requirements, and comparing technology options.

Energy Audit Calculation:

Monthly kWh usage: 1,200 kWh
÷ 30 days = 40 kWh/day
÷ 5 peak sun hours = 8 kW system needed
× 1.25 (inefficiency factor) = 10 kW recommended

Phase 1: Energy Assessment

• Collect 12 months of utility bills
• Calculate average daily kWh consumption
• Identify seasonal usage patterns
• Document peak demand periods

Phase 2: Site Analysis

• Measure available roof/ground space
• Check roof age and structural capacity
• Assess shading from trees/buildings
• Determine optimal panel orientation

Phase 3: System Sizing

• Apply peak sun hours formula
• Calculate panel quantity needed
• Size inverter capacity (110% of panel capacity)
• Determine battery storage requirements

Phase 4: Financial Analysis

• Estimate system costs per kW
• Calculate annual energy savings
• Determine payback period
• Compare financing options

Example 1: Residential Assessment Input: 850 kWh/month usage, south-facing roof, $0.12/kWh rate Output: 6.8 kW system, 22 panels needed, 7.2 year payback, $18,000 estimated cost

Example 2: Commercial Evaluation Input: 15,000 kWh/month usage, warehouse with flat roof Output: 125 kW system, battery backup recommended, demand charge analysis needed

Example 3: Off-Grid Cabin Input: Weekend use, 150 kWh/month, no grid connection Output: 4 kW panels + 20 kWh battery storage, generator backup

Daily Energy Formula:

1. Monthly kWh ÷ 30 = daily kWh
2. Daily kWh ÷ peak sun hours = minimum kW needed
3. Multiply by 1.2-1.3 for system losses

Battery Sizing (Off-Grid):

1. Daily kWh × days of autonomy = total storage needed
2. Adjust for battery depth of discharge (80% for lithium)
3. Add 20% buffer for degradation

Panel Layout Calculation:

1. Available area (sq ft) ÷ 20 = maximum panels (approximate)
2. Check local setback requirements
3. Account for maintenance access paths

Panel Types:

• Monocrystalline: 20-22% efficiency, premium cost, best for limited space
• Polycrystalline: 15-17% efficiency, lower cost, good value option
• Thin-film: 10-12% efficiency, cheapest, requires most space

Inverter Options:

• String inverters: Lowest cost, single point of failure
• Power optimizers: Module-level monitoring, better shade performance
• Microinverters: Highest performance, highest cost, easiest expansion

Battery Chemistry:

• Lithium-ion: 10+ year life, 80% depth of discharge, fastest charging
• Lead-acid: Lower upfront cost, 50% depth of discharge, 3-5 year life

• Always start with energy efficiency improvements before sizing solar
• Use local solar irradiance data (peak sun hours vary by location)
• Factor in future electrical loads (EVs, heat pumps, pool equipment)
• Consider utility rate structures and net metering policies
• Include 25% buffer for system degradation and weather variability
• Evaluate roof condition before installation (replace if >10 years old)

• Don't size based on roof space alone - match to actual energy needs
• Avoid ignoring shading analysis - even partial shade significantly reduces output
• Don't forget permit costs, electrical upgrades, and installation complexity
• Avoid undersizing inverters or oversizing relative to consumption
• Don't ignore local building codes and HOA restrictions