Why Optimizers Cost You Energy When There’s No Shading

Short version: In a clean, unshaded array, every extra electronic box between the module and the inverter introduces conversion losses and self-consumption without giving you any energy back. Modern string inverters already track the string’s maximum power with very high efficiency. So, if there’s no shade (and no mix of orientations/ages), optimizers usually reduce net yield.

What optimizers do (and why they help only sometimes)

Module-level power electronics (MLPE, “optimizers”) sit behind each PV module. They run a DC-DC converter with its own MPPT so each module can operate at its individual maximum power point. This is valuable when:

• parts of the array are regularly shaded,

• strings mix different orientations/tilts/ages, or

• code demands module-level shutdown/monitoring.

Remove those conditions and the optimizer has nothing useful to correct—yet it still converts power (and consumes a bit itself).

Where the losses come from

1. DC-DC conversion lossAn optimizer’s converter is never 100% efficient. Even with excellent design, the weighted efficiency is below 100%. That missing few tenths to ~1–2% becomes heat, i.e., lost energy, all day long.

2. Quiescent/self-consumptionThe electronics (controller, gate drivers, comms) draw power even at low irradiance. Multiply a small standby draw by every module and by 8,760 hours/year—it adds up.

3. Extra connectors and wiringEach device adds contact resistance and a little extra cable. The loss per module is small, but across a field it’s measurable.

4. MPPT hunting & dynamicsOptimizers continuously search for MPP. In uniform, stable conditions, a good string inverter already sits essentially at the optimum. Parallel MPPT at module level yields no extra benefit but still incurs dynamic/conversion overhead.

5. Thermal side effects (minor)Optimizers dissipate heat on the back of the module or rail. Any extra back-sheet temperature slightly lowers module efficiency (PV has a negative temperature coefficient). It’s usually a small effect, but it never adds energy.

Why string inverters are already “good enough” when unshaded

• High MPPT efficiency: Modern string inverters routinely achieve >99% MPPT tracking efficiency at the string level. In uniform irradiance, module-level MPPT doesn’t find extra watts that the string tracker is missing.

• Low manufacturing mismatch today: Module binning and tighter production tolerances keep current mismatch among modules in a string small. With no shade, mismatch losses are typically well under ~1%—often less—leaving little headroom for optimizers to “recover.”

• Multiple MPPT inputs: Most inverters offer several MPPTs. You can split roof planes or strings cleanly, keeping each MPPT operating near ideal without MLPE.

A grounded energy example (order-of-magnitude)

Assume a 10 kWp unshaded array in a good location.

• Baseline specific yield (no optimizers): ~1,500 kWh/kWp·yr → ~15,000 kWh/yr.

• Add optimizers:

  • Weighted converter loss 0.5–1.5% → ~75–225 kWh/yr lost.

  • Quiescent draw, say 0.2–0.4 W per optimizer × 16–24 modules → ~28–84 kWh/yr.

  • Extra connectors/wiring: small, say ~5–15 kWh/yr.

Net penalty: typically ~0.8–2.0% (≈ 120–300 kWh/yr on 10 kWp) with no shading benefit to offset it.Scale linearly with system size.

The exact figures depend on model, climate, and operating profile—but the direction is consistent: without shade, MLPE tends to lower annual energy.

Hidden “losses” you feel later (availability & OPEX)

• More points of failure. Hundreds of extra electronics in the DC path increase the probability of a fault. Even if each device is reliable, system-level MTBF goes down as part count goes up.

• Troubleshooting & truck rolls. When an optimizer fails, you often need a roof visit. The downtime during diagnosis/replacement is an energy loss that doesn’t show up in spec sheets.

• Capex & lifecycle cost. Extra hardware and labor rarely pay back in unshaded sites because there’s no recurring energy gain to amortize them.

When optimizers are worth it

Use them confidently if you have any of the below:

• Predictable hard shading (chimneys, trees, neighboring buildings) during meaningful portions of the day/year.

• Mixed orientations/tilts/ages on the same MPPT that you can’t separate electrically.

• Per-module rapid shutdown or module-level monitoring mandated by local code/spec.

• A design constraint (e.g., long strings beyond inverter window) that genuinely needs DC-DC conditioning.

If none apply, optimizers are usually an energy and money sink.

Practical decision checklist

1. Shade study first. If annual shading energy loss is > the optimizer penalty (~1%+), MLPE may pay back. If not, skip them.

2. Keep strings homogeneous. Same module type/orientation per MPPT.

3. Favor simplicity. Fewer conversions → fewer watts lost and fewer failures.

4. Model both cases. Simulate (or estimate) annual yield with and without MLPE; include parasitic/efficiency losses and realistic O&M.

Bottom line

In unshaded, uniform arrays, optimizers add conversion and standby losses without unlocking extra energy. The result is lower net yield, higher complexity, and higher lifetime cost. Choose clean string design with a quality inverter unless real-world conditions (shade, layout, or code) demand otherwise.