Solar Basics

Photovoltaic Effect

Sunlight hits silicon cells → knocks electrons loose → creates DC electricity. No moving parts, no fuel, just physics.

• DC output: Panels produce direct current, not household AC
• Variable output: More sun = more power. Clouds, shade, angle all affect production
• Instant generation: No storage in the panel itself. Use it or lose it without batteries

Panel Specifications

A "100W panel" produces 100W at peak. Real-world average is much lower - maybe 4-6 hours equivalent peak per day.

Monocrystalline

• Appearance: Black cells, black or silver frame
• Efficiency: 18-22% (best available)
• Cost: Higher per watt
• Best for: Limited space, maximum output per square foot

If roof space is tight, pay extra for mono. More watts in less space.

Polycrystalline

• Appearance: Blue cells with visible crystal pattern
• Efficiency: 15-18%
• Cost: Lower per watt
• Best for: Plenty of space, budget-conscious

DIY value: Used poly panels are cheapest. 5-year-old panels still produce 90%+ of rated output.

Thin-Film / Flexible

• Appearance: Thin, sometimes flexible sheets
• Efficiency: 10-13% (lowest)
• Cost: Variable
• Best for: Curved surfaces, boats, RVs, walkable deck applications

Flexible panels degrade faster. Good for portability, not permanent installations.

Orientation (Northern Hemisphere)

• Best: South-facing (azimuth 180°)
• Good: Southeast or southwest (within 45° of south)
• Acceptable: East or west (morning or afternoon sun only)
• Avoid: North-facing (in hemisphere) - very low production

Use compass app on phone. Account for magnetic declination if being precise.

Tilt Angle

Example: Minneapolis is 45° latitude. Year-round tilt = 45°. Winter optimized = 60°. Summer = 30°.

Shade = Production Killer

Even partial shade on one cell can kill output of the entire panel or string.

• Series wiring: All panels affected by one shaded panel (current limited by weakest)
• Parallel wiring: Shaded panel loses output, others continue
• Microinverters/optimizers: Each panel operates independently, shade on one doesn't affect others

Series Connection

Positive of panel 1 → Negative of panel 2. Voltages add, current stays same.

Total Volts = Panel 1 V + Panel 2 V + ...

Total Amps = Single panel amps

• Pros: Higher voltage = smaller wire, less loss, better for long runs
• Cons: One shaded panel kills whole string
• Best for: Unshaded locations, long wire runs to charge controller

Parallel Connection

All positives together, all negatives together. Current adds, voltage stays same.

Total Volts = Single panel volts

Total Amps = Panel 1 A + Panel 2 A + ...

• Pros: Shaded panels don't affect others, good for partial shade
• Cons: Higher current = thicker wire needed, more loss over distance
• Best for: Shady locations, short wire runs, low-voltage systems

Series-Parallel (Combination)

Groups of series strings connected in parallel. Get some voltage increase while maintaining redundancy.

Common: 4 panels. Two strings of 2 in series, then those strings in parallel. Voltage doubles, current doubles.

Wire Sizing

Undersized wire = voltage drop = lost power = potential fire.

• Distance matters: Longer run = thicker wire needed
• Current matters: Higher amps = thicker wire needed
• Target: Less than 3% voltage drop (under 2% ideal)

Use online voltage drop calculator. Common: 10 AWG for short runs under 10A, 8 AWG or 6 AWG for longer/higher current.

PWM (Pulse Width Modulation)

• How it works: Rapidly connects/disconnects panels to control charging
• Efficiency: 70-80%
• Cost: $20-100
• Best for: Small systems, panels matched to battery voltage

PWM is "dumb" - it can't boost voltage. Panel voltage must be higher than battery voltage.

MPPT (Maximum Power Point Tracking)

• How it works: Converts excess voltage to current, optimizing power extraction
• Efficiency: 90-98%
• Cost: $100-500+
• Best for: Any system, especially with higher voltage panels or long wire runs

MPPT typically gives 15-30% more power than PWM. Worth the extra cost for any serious system.

Regular Checks

• Cleaning: Dust, pollen, bird droppings reduce output. Rinse with hose or wipe with soft cloth. No abrasive cleaners.
• Inspection: Check for cracked glass, loose frames, damaged wiring, corrosion on connections
• Connections: Verify all MC4 connectors are tight. Look for heat damage (browning/melting).
• Mounting: Ensure rails, brackets, bolts remain secure. Check after storms.

Cleaning schedule: Every few months in clean areas. Monthly near roads, farms, or dusty environments.

Performance Monitoring

• Compare actual output to expected (panel watts × peak sun hours)
• Sudden drop = shade, dirty panels, or failing component
• Gradual drop = panel degradation (normal, ~0.5% per year)

Many charge controllers display real-time production. Log it occasionally to catch problems early.

• Undersizing: System too small for load = constant battery deficit
• Ignoring shade: "Just a little shade" can cut production dramatically
• Wrong voltage: PWM controller with panels too high or low for battery
• Thin wire: Voltage drop wastes power and can cause fire
• No monitoring: Can't fix what you don't know is broken
• Poor grounding: Lightning and fault protection matters
• Skipping fuses: Panels can push serious current. Fuse every circuit.

Production lower than expected

1. Check for new shade (tree growth, new construction)
2. Clean panels - may be dirty
3. Verify all panels are producing (check individual connections)
4. Check charge controller display for errors
5. Test individual panel output with multimeter

One panel not contributing

1. Disconnect and test panel output in full sun
2. Check MC4 connectors for corrosion or damage
3. Verify bypass diodes aren't failed (panel hot spots)
4. If panel tests good, check wiring between panel and controller

Controller showing error

1. Look up error code in manual
2. Most common: over-voltage (too many panels in series) or over-temp (ventilation needed)
3. Disconnect panels, wait 5 minutes, reconnect
4. Check battery voltage - may be full (float mode, not error)