SolarEdge P370 Power Optimizer: Review and Guide

SolarEdge P370 - Overview

The P370 was one of the most widely deployed residential power optimizers, and it's still what you'll find on thousands of existing roofs. For a new install SolarEdge now points you at the S440 instead, the named S-series replacement for the P370 and P401 class. One rule matters more than the price difference: P-series and S-series optimizers must not be mixed in the same string on a new install. An S unit may be fitted as a warranty replacement for a failed P unit, but you don't get to blend the two families across a string because a box was cheaper.

The P370 works only with SolarEdge inverters and reports per-panel production through mySolarEdge. It's rated for modules whose STC output doesn't exceed 370 W, with a +5% manufacturing tolerance allowed on top. There's no minimum module size in the datasheet.

Real-World Yield Impact

Here's where most optimizer marketing, including an earlier version of this page, goes badly wrong.

Allenspach and colleagues at ZHAW published a peer-reviewed study in Solar RRL measuring exactly this question with indoor measurements and annual simulations on a chimney-shaded residential roof. Under their light-to-medium shading scenario, a plain string inverter delivered about 90.7% relative energy. Optimizers on some modules only reached about 92.1%, a gain of roughly 1.4 percentage points. Optimizers on every module reached about 91.6%, a gain of about 0.9 points. Their measured DC/DC optimizer losses also ran about 2 percentage points worse than the manufacturers' datasheet figures. And their blunt conclusion for lightly shaded arrays: the conventional string inverter typically performs equally as well, or even more efficiently.

So what does 1.4 points buy you? On a 6 kW array producing 8,000 kWh a year, it's roughly 110 kWh, or about 18 USD a year at an average US residential rate of 0.16 USD/kWh. Sixteen optimizers at 45 USD each is 720 USD of hardware. That's decades, not five years. On a lightly shaded roof, optimizers do not pay for themselves on yield, and anyone selling you a sub-five-year payback on shading recovery alone is quoting a number nobody measured.

Buy optimizers for the reasons that actually hold up: heavy shading where a string genuinely collapses for hours a day, multi-orientation and multi-tilt roofs, per-module fault diagnostics, and rapid shutdown compliance where code requires module-level shutdown. Treat the yield gain as a bonus that lands somewhere near 1%.

How the P370 Compares

Feature	SolarEdge P370	Tigo TS4-A-O	Enphase IQ8A microinverter
Hardware scope	Optimizer only, needs inverter	Optimizer only, needs inverter	Replaces optimizer and string inverter
Optimizer type	Fixed-string DC	Module-level DC	Microinverter (DC to AC at the panel)
Peak efficiency	99.5% peak / 98.8% weighted	99.5%	97.7% peak / 97.0% CEC
Warranty	25 years	25 years	25 years
Monitoring depth	Per-panel	Per-panel	Per-panel
Inverter compatibility	SolarEdge only	Most inverters	Enphase only
SafeDC / safe voltage	Yes (1 V/panel)	No	Yes
Typical unit price	~$45	~$35 - 45	Higher, but no separate inverter to buy

Read that price row carefully, because it compares different scopes of hardware. A P370 is a 45 USD add-on that still needs a SolarEdge inverter underneath it. An IQ8A is the inverter. The only fair comparison is at system level.

The P370's main constraint is SolarEdge ecosystem lock-in - it won't function with Fronius, SMA, Huawei or anything else. If your inverter is already SolarEdge, or you're specifying a new SolarEdge system, the S-series is the natural choice and gives the deepest integration with SolarEdge monitoring. If you want inverter flexibility, the Tigo TS4-A-O offers similar per-panel optimization across most string inverters.

Key Advantages

• 99.5% peak, 98.8% weighted efficiency - small overhead, but not zero; on an unshaded roof the ZHAW measurements put an optimizer system slightly behind a plain string inverter
• IP68 / NEMA6P - fully weatherproof, coastal salt spray included
• 25-year warranty - matches typical panel lifespan; SolarEdge honours replacements directly
• Panel-level monitoring via the SolarEdge app and web portal - find an underperforming panel in minutes rather than months
• SafeDC - each panel drops to 1 V DC when the inverter is off, which is the strongest argument for optimizers and nothing to do with yield

Compatibility

The P370 requires a SolarEdge HD-Wave or three-phase inverter on the same DC bus. It is not compatible with third-party inverters. On a single-phase HD-Wave inverter, strings run a minimum of 8 optimizers and a maximum of 25, up to 5,700 W nominal per string. Verify against the SolarEdge compatibility matrix before specifying, and remember the P and S families don't share a string.

Installation Notes

Installation needs a licensed electrician in most markets. The P370 mounts on the panel rail via MC4 connectors, adds 655 g including cables, and connects inline with the existing string wiring - no separate DC cabling. Commissioning is under 2 minutes per optimizer with the SolarEdge app.

Who Is It For?

Arrays with real, sustained shading from chimneys, trees or roof vents; complex rooflines with several orientations; arrays mixing panels from different production batches. Also a genuine selling point for installers, since per-panel visibility is easy to demonstrate to a homeowner comparing quotes. For an unobstructed, single-orientation array, the yield case is close to nonexistent - decide on the strength of the safety and diagnostics alone, and if those don't move you, a plain string inverter is the cheaper honest answer.

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Related guides: How to Increase Your Solar PV Yield by Up to 20% (see the Related Guides section above)