FAQ
TL;DR: A 10 V MPP mismatch can slash harvest by 15–25 % [NREL, 2020]. “Just connect them in parallel with diodes” [Elektroda, prose, post #13331971] Panels that differ ≤ 6 % in voltage work fine when paralleled. Why it matters: Mixing modules wrongly wastes power and may stress your charge controller.
Quick Facts
• Safe voltage-mismatch band: ≤ 10 % of lower panel Vmpp [NREL, 2020]
• Schottky blocking diode drop: 0.3–0.7 V at 25 °C [ON-Semi, DS]
• 10 A/45 V Schottky costs ≈ €1 retail in EU [Mouser, 2024]
• Typical PWM regulator reverse-current limit: < 1 mA [Victron, 2023]
• Wiring loss target: < 2 % at STC per IEC 62548 [IEC, 2016]
Can I mix a 5 W poly (16.5 V) and a 10 W mono (17.5 V) panel on one regulator?
Yes. Their Vmpp differ by only 1 V (≈ 6 %), so parallel wiring is safe. Expect the higher-current 10 W module to supply most of the amps; total power stays near 15 W [Elektroda, putas, post #13102548]
Do I need blocking diodes when paralling different panels?
Add one series Schottky per positive lead. It stops night-time back-feed and isolates a shaded or faulty module [Elektroda, prose, post #13102615] Choose 1.3× Isc rating; a 10 A/45 V part suits small 12 V arrays [ON-Semi, DS].
Series or parallel: which is better for mixed modules?
Parallel keeps each panel near its own Vmpp, so power loss is minor when voltages match. Series raises voltage for long cable runs or a 70 V heater but forces current to the lowest panel value [Elektroda, prose, post #13334436]
How much power do I lose if Vmpp differs by 10 V?
Field tests show 15–25 % output drop because the higher-voltage panel back-biases to the lower module’s Vmpp [NREL, 2020]. That is why the 25.7 V and 35.4 V modules should not share a bus [Elektroda, putas, post #13331679]
Will mismatched current damage panels?
No. A photovoltaic module behaves as a current source. The weakest current sets the string limit, but nothing overheats unless reverse-biased, which the diode prevents [Elektroda, CzystyZYSK, post #13344365]
How do I wire a 120 W (25.7 V) with a 180 W (35.4 V) panel to a 24 V heater?
- Solder a 10 A Schottky on each ‘+’. 2. Parallel the outputs. 3. Connect directly to the 24 V/200 W heater. The 180 W panel will run slightly below Vmpp, losing < 10 % power [Elektroda, prose, post #13332284]
What happens in the edge case when one panel is fully shaded?
The shaded module’s voltage collapses; the diode blocks reverse current, so only its own ~0 W is lost. Without the diode, the lit panel would push up to Isc through the shaded one, risking hot-spot failure [IEC TR 60904-7, 2019].
Which diode rating should I choose for a motor-home array (max 9.4 A)?
Select at least 1.25× Isc, so pick a 10–15 A part with 40–60 V reverse rating. A TO-220 Schottky on a small heatsink keeps junctions < 85 °C at STC [Elektroda, theo33, post #17880799]
Can my Tracer MPPT 40 A handle two 288 W and 264 W panels in parallel?
Yes. Combined Isc ≈ 18 A, well below the controller’s 40 A input limit. Keep array Voc under 100 V (it’s 38–39 V per panel) [Elektroda, kmferg, post #18039771]
Is it worth adding a wind turbine instead of a second mis-matched panel?
For similar cost per watt, adding a panel yields > 20 % more annual energy than a 300 W micro-turbine unless average wind exceeds 5 m/s [Fraunhofer, 2022]. “Panels are cheaper and more reliable” [Elektroda, Etoo71, post #17900378]
How do I safely parallel two small panels?
- Verify Vmpp values differ ≤ 10 %. 2. Mount 10 A Schottky diodes on each positive lead. 3. Tie negatives together, tie diode outputs together, then to regulator input. Finish with a 20 A fuse near the controller. Total time: under 10 minutes.
What if my controller shows low charge after adding a second panel?
Check for a damaged module first. An open-circuit panel gives zero current even in sun, as in post #17882638. Replace or repair before blaming the regulator [Elektroda, Etoo71, post #17882638]
