Partial Shading Q&A: How NOT to Test Shade Tolerance?

June 20th, 2025

Hear from Wesam E., CEC-accredited PV designer and AIKO ANZ Technical Solutions Manager, as he answers the questions installers ask most about partial shading.

Partial-shading performance has become a hot topic among Australian solar installers —especially since AIKO introduced advanced shading optimisation to the local market. However, formal test protocols are still relatively new. These days, it’s not hard to see plywood demos flooding the internet with mixed-string comparisons that break basic electrical rules, causing confusion and inaccurate expectations among installers and customers.

This Q&A breaks down the most common mistakes in shade test setups—so you can tell when the results show real performance, and when it’s just a bit of entertainment.

Q1: Is it a good idea to wire two different panel brands on the same MPPT and then throw shade on them for a comparison?
A: Short answer: No.

When you wire dissimilar panels in one string, the weaker panel causes the lowest-performing module to limit the entire string’s output. That masks real performance gaps and produces a “false draw.”

Best practice: Test each module type on a separate MPPT or individually using IV-curve measurements in the same orientation and tilt angle. This ensures an accurate and fair comparison.

Q2: How much data logging do I need before trusting a shade demo?
A: Standards bodies (TÜV, PVEL) requires either 12 months of outdoor data or continuous IV-curve measurements using calibrated reference cells. Short-term or small-scale demos (e.g. 4–6 weeks) can be influenced by daily irradiance fluctuations, leading to unreliable conclusions.

Q3: If a test covers half a panel with plywood, does that reflect real-life shading?
A: Not really. Covering half the panel triggers bypass diodes in all technologies and doesn’t accurately test a module’s shade-tolerant wiring or optimisation. Also, it is rare for 2 main reasons:

• Performance: In actual system design, large-scale shading like that is avoided—designers space arrays or adjust layouts to keep panels mostly exposed to sunlight throughout the day. so layouts are adjusted (row spacing, split arrays) to avoid it.
• Safety & Compliance: Australian Standard AS/NZS 5033 §4.3 triggers extra safety hardware if large daily shade is expected

Q4: So, what shading patterns match everyday Australian rooftops?
A: Industry protocols such as TÜV Rheinland 2 PfG 2926 and METRO-PV “additional-loss” method focus on local shadows that installers can’t design out such as:

• A 25 cm strip along the long edge (replicates TV aerial / parapet)
• A 25 cm strip along the short edge (replicates whirly-bird / vent)
• A single-cell spot mask (replicates leaf, bird dropping)

Q5: If a small shadow shows only ~100 W difference on a 9-panel string, is that meaningful?
A: Yes. On a 9-panel string, 100 W is roughly 10 % extra power. Applying the same uplift to a standard 6.6 kW PV + 10 kWh battery, it can bring extra A$300/year in savings to homeowners (self-consumed at 30 c/kWh). While that may seem modest, in larger systems or frequent shading, the gains multiply significantly especially in battery-backed systems where self-consumption is maximized.

Q6: What independent certificates or reports does AIKO hold for its shade optimisation?

• TÜV Nord Flash Test: Showed when masking a single cell from 10 % to 100 %, AIKO kept 95 % power at light cover and ~70 % at full cover; the reference TOPCon fell to ~90 % then ~40 %. Advantage grows from ~5 % to ~30 % as the shadow deepens. (See full report)
• TÜV Rheinland Partial Shading Class A Certificate: Confirmed AIKO Neostar 475 W loses ≤ 5 % extra power with three standard masks (edge, edge, single-cell). (See the Certificate)
• Enertis Applus+ Simulator & IR Study: Recognised partial shading optimisation function is a contributing factor to superior performance of AIKO’s N-type ABC module compared to TOPCon and PERC modules regarding installed capacity, power generation per watt, ROI, and LCOE. (See full report)

Q7: What are the criteria of “Class A” in Partial Shading by TÜV Rheinland and who has earned it?A:Class A (defined in TÜV Rheinland 2 PfG 2926/01.23) means:

• The panel sees ≤ 5 % extra power loss in all three standard masks (long-edge, short-edge, single-cell).
• Tests are done at 25 °C cell temp and 1 000 W m-² irradiance, using IV-curve tracers.

As of mid-2025, AIKO is the FIRST and ONLY mass-market module line with a published Class A certificate from TÜV Rheinland.

Wrap-up: Keep Watching the Shade Demos — But a Second Look Never Hurts

We love a good plywood-and-pallet demo as much as the next sparkie. Honestly, it’s a good thing as it shows the industry’s thinking deeper about real performance—not just spec sheets. But should you trust every test you see? Here’s the checklist to sort real performance from backyard theatre:

What to Check	Green Flag	Red Flag
Test Method	Follows a recognised standard (e.g. TÜV 2 PfG 2926) or peer-reviewed	Made-up method or no test standard mentioned
String Layout	One MPPT per panel type or IV sweeps per module	Mixed brands on the same MPPT/string
Shade Geometry	Uses TÜV-style masks (25 cm edge strip, single-cell mask)	Half-panel tarp, blanket, or full-row cover
Duration & Logging	12-month data or certified IV curve sweeps	A few sunny weeks or short-term snapshots
Result Interpretation	Separate MPP readings per module	Averaged or shared MPP across a mixed string

Let’s take the fun stuff for what it is —but when it comes to your solar decisions, make sure to choose products backed by test data validated by accredited labs.

That’s why more and more Australian installers are turning to AIKO. With proven performance in independent testing by the world’s most respected labs, giving installers the confidence to deliver the best results on every job.

Want to dive deeper?
Download your free guide here:ABC Cells: An Introduction to Partial Shading Optimisation.