Types of Solar Panels
| Type |
Efficiency |
Cost |
Best For |
Notes |
Monocrystalline
(standard) |
18–22% |
$$ |
RV roofs, cabin arrays, home systems |
Best efficiency-to-cost ratio; performs well in partial shade |
| PERC Monocrystalline |
20–23% |
$$$ |
Space-constrained roofs |
Passivated Emitter Rear Contact — adds a reflective layer for more current. Industry standard now. |
Polycrystalline
(blue cells) |
15–18% |
$ |
Ground-mounted arrays with space to spare |
Lower efficiency, but cheaper per watt. Visually distinct (blue, speckled). Being phased out by mono. |
| Flexible / Semi-flexible |
13–17% |
$$ |
Curved van/boat roofs, low-profile installs |
Can conform to curved surfaces. Degrades faster if heat-trapped (no air gap). Lower efficiency. |
| Bifacial |
20–23% front + 5–15% rear |
$$$ |
Ground mounts with reflective ground (snow, gravel, white membrane) |
Generates power from both sides. Useful only with elevated mounting and reflective ground surface. |
How to Read a Solar Panel Spec Sheet
Every panel comes with a datasheet. Here's what the key specs mean:
Power Ratings (at STC)
- Pmax — Maximum power output in watts. This is what you paid for: "a 400W panel".
- Vmp — Voltage at maximum power. Typical: 30–40V for a 60/72-cell panel.
- Imp — Current at maximum power. Pmax ÷ Vmp = Imp.
- Voc — Open-circuit voltage (no load). Always higher than Vmp. Use this to size your MPPT controller's max input voltage.
- Isc — Short-circuit current. Always slightly above Imp. Use for fuse sizing.
Temperature Effects
- Temperature coefficient (Pmax) — Typical: -0.35%/°C to -0.45%/°C. A panel rated 400W at 25°C produces ~390W at 50°C (a hot summer roof).
- Cold weather bonus — Panels produce more power in cold weather. A -0.40%/°C panel running at 0°C produces ~110% of its rated wattage.
- NOCT — Normal Operating Cell Temperature. More realistic than STC (which assumes ideal lab conditions).
STC vs Real World: All panel ratings are measured at Standard Test Conditions (1,000 W/m² irradiance, 25°C cell temp, 1.5 air mass). In real outdoor use, you'll typically see 70–85% of the rated wattage as your average. Our calculator applies a 1.25× system loss factor to compensate.
Series vs Parallel Wiring
Effect: Voltages add up, current stays the same.
4× 100W panels at 20V/5A → 80V / 5A = 400W
✓ Recommended for MPPT controllers
Why: Higher voltage = lower current = thinner, cheaper wire between panels and controller. MPPT controllers step down voltage to battery voltage at high efficiency.
Effect: Current adds up, voltage stays the same.
4× 100W panels at 20V/5A → 20V / 20A = 400W
✗ Not recommended for long cable runs
Why: High current requires very thick wire to prevent losses. Only use for PWM controllers or when panels are very close to the controller.
Max MPPT input voltage: When wiring panels in series, make sure the combined Voc doesn't exceed your MPPT controller's maximum input voltage — especially in cold weather when Voc rises. Most controllers are rated for 100V, 150V, or 250V input.
Shade and Partial Shading
Shade is the enemy of solar output. When one cell in a series string is shaded, it limits the output of the entire string — like a kinked garden hose. Solutions:
- Bypass diodes — Built into modern panels, allow current to route around a shaded section. Limit, but don't eliminate, shading losses.
- Separate charge controller inputs — If one section of your roof is frequently shaded, wire that panel to a separate MPPT input or controller.
- Panel optimizers — DC optimizers (SolarEdge) or microinverters (Enphase) optimize each panel individually. Most useful in complex shade situations.
Solar Panel Database:
We're building a searchable database of 2,000+ solar panels with full specifications. It will allow filtering by power output, efficiency, dimensions, and price. Check back soon — or
use the calculator now to size your system without needing specific panel models.
Buying Tips
- Stick to name brands — Renogy, Rich Solar, HQST, Newpowa, and ECO-WORTHY all have established quality control. Avoid no-name panels with inflated wattage claims.
- Buy identical panels — Mixing panels with different Vmp or Isc in the same string reduces total output to the weakest panel's specs.
- Check the warranty — Look for a 25-year power output warranty (80% at year 25) and a 10-12 year product warranty.
- Factor in frame dimensions — A 400W panel is roughly 80" × 40". Make sure your roof or mount can accommodate it before ordering.
Know how many watts you need?
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