Growatt MID vs MAX: Sizing Commercial Rooftop Inverters Right
Growatt covers commercial and industrial rooftops with two adjacent series: the MID 25-40KTL3-X for the 25-40kW block and the MAX 50-80KTL3 LV from 50kW to 80kW. On a large project they are not rivals — a 500kWp plant might deploy either, in different quantities — but on the mid-size commercial roof of 40-80kWp, the design decision is real: several MID units or fewer MAX units. Both share the 1100V DC architecture, the 200-1000V MPPT window, 26A trackers with two strings each, smart air cooling and the same -25°C to +60°C rating, so the comparison comes down to granularity, efficiency, weight and warranty. We compare the 40kW MID against the 80kW MAX flagship.
Where Each Series Sits
The MID 25-40KTL3-X spans 25, 30, 33, 36 and 40kW; the MAX 50-80KTL3 LV spans 50, 60, 70 and 80kW. Both are three-phase 3W+N+PE machines at 220/380V or 230/400V with a 0.8 leading to 0.8 lagging adjustable power factor and Type II surge protection on both sides. The MID at 40kW allows 60000W of recommended PV; the MAX at 80kW allows 120000W — an identical 1.5x oversizing ratio, so array-to-inverter matching maths is the same across the pair.
MPPT Granularity vs Consolidation
The 40kW MID carries 4 MPP trackers with 2 strings each (8 strings); the 80kW MAX carries 7 trackers with 2 strings each (14 strings). Per kW installed, the MID actually offers more tracker granularity — one tracker per 10kW against one per 11.4kW — and deploying two MIDs instead of one MAX yields 8 trackers over the same 80kW. On roofs broken up by HVAC plants, skylights and parapet shading, finer MPPT resolution converts directly into yield. On a flat, unshaded warehouse roof the extra granularity does nothing, and the MAX's consolidation wins on installation and maintenance simplicity.
Datasheet Comparison
| Spec | MID 25-40KTL3-X (40kW) | MAX 50-80KTL3 LV (80kW) |
|---|---|---|
| AC nominal power | 40000W | 80000W |
| Max. AC apparent power | 44000VA | 88800VA |
| MPP trackers | 4 (2 strings each) | 7 (2 strings each) |
| MPPT voltage range | 200-1000V | 200-1000V |
| Max. DC voltage | 1100V | 1100V |
| Max. input current per tracker | 26A | 26A |
| Max. recommended PV power | 60000W | 120000W |
| Max. efficiency | 98.8% | 99% |
| European efficiency | 98.5% | 98.5% |
| Max. output current | 66.6A | 128.8A |
| Cooling | Smart air cooling | Smart air cooling |
| Protection degree | IP66 | IP65 |
| Dimensions (W/H/D) | 580×435×230mm | 860/600/300mm |
| Weight | 30.5kg | 86kg |
| Warranty | 5 years | 10 years |
Both include string monitoring; AFCI is listed on the MID datasheet and optional on the MAX.
Handling, Mounting and Site Logistics
The weight line deserves attention: a MID at 30.5kg is a two-person lift onto a wall bracket; the 86kg MAX needs mechanical assistance and a structural mounting position. On retrofit projects where inverters hang on existing walls or steel, the MID's form factor keeps installation inside normal rigging. The MAX repays its bulk at the AC combiner: one 128.8A three-phase run replaces two 66.6A runs plus their breakers, saving copper and distribution-board positions on long cable routes typical of warehouse plants.
Reliability Terms and Serviceability
Growatt backs the 40kW MID with 5 years and the 80kW MAX with 10 — a meaningful difference on assets that anchor a commercial plant's production. Fleet design interacts with this: a site running four MIDs loses 25% of production when one unit is down, while a site on two MAXes loses 50%. Shorter warranty but smaller failure domains, or longer warranty in bigger blocks — that trade is the honest summary of the MID-versus-MAX decision, and the right answer follows the site's tolerance for downtime concentration.
Winner
MAX for consolidation on big clean roofs; MID for granular, complex layouts
Conclusion
The rule of thumb that falls out of the datasheets: the MID is the granularity play and the MAX is the consolidation play. Two 40kW MIDs give eight trackers and sixteen strings across a complex roof, at 30.5kg per hoist; one 80kW MAX gives seven trackers and fourteen strings with one wall position, one AC run, 99% peak efficiency and a 10-year warranty against the MID's five. On simple large roofs the MAX wins on hardware count, cabling and the warranty term; on segmented, multi-orientation industrial roofs the MID's smaller blocks track shading and orientation differences more faithfully and keep any single failure to a 40kW slice of production. Either way the string design carries over — same voltage window, same 26A trackers — so a mixed fleet on one site remains coherent to commission and monitor.