Transformers for Solar Power Plants
A solar plant’s transformers have a job with no analogue in conventional power: they sit between an electronic source with no rotating inertia and a network that was designed around synchronous machines. Inverter output is harmonically rich, follows the irradiance rather than the load, and drops to zero every evening. We supply transformers for solar power plants built for exactly that duty, from string-inverter distribution units to central inverter step-up transformers and complete solar substations.
We work with renewable energy developers, EPC contractors delivering utility-scale plants, and the electrical engineering companies handling grid compliance and connection studies.
Where Transformers Sit in a Solar Plant
| Position | Duty | What to specify |
|---|---|---|
| Inverter station (central) | Step ~400–800 V inverter output up to MV | Harmonic spectrum, MV collection voltage |
| String cluster | Step string cluster output to MV | Rating per cluster, enclosure IP, ambient derating |
| Collector substation | Step MV up to grid interconnection voltage | Grid code compliance, studies, and protection interfaces |
| Auxiliary / tracker supply | Small LV supply for trackers and controls | Starting duties, often dry-type construction |
The choice between central and string inverter architecture determines the whole transformer schedule. It should be settled before any transformer enquiry goes out, because reversing it later means resizing or replacing the units.
Inverter Duty: What Actually Matters
An inverter-duty transformer differs from a general-distribution unit in three respects, all of which need to appear in the specification rather than being assumed.
- Harmonic heating. Converter switching generates harmonic currents that produce eddy losses in windings and structural parts. Specify either the harmonic spectrum or a K-factor so the winding can be designed for the real loss, instead of applying a generic derating that costs capacity for no reason.
- DC injection tolerance. Small levels of DC current into the winding can push the core into half-cycle saturation, raising noise and exciting currents. Ask your inverter supplier what they guarantee and whether the transformer needs design accommodation.
- Load profile. Solar transformers follow irradiance: near-zero at night, steep ramps at sunrise and sunset, rapid excursions with passing cloud. That cycling brings thermal movement every single day, which is why DC-side-calculated ratings sometimes prove optimistic.
Sizing and Configuration
Over-sizing the inverter transformer relative to DC capacity is standard practice on most utility-scale designs, partly because panel output peaks rarely coincide with nameplate conditions, and partly because inverter clipping reduces lost energy. The trade-off is higher no-load losses carried every hour of the year — including the nights.
Two further choices matter. Whether each transformer serves one inverter or several determines its rating and impedance; either is legitimate but they lead to different network effects. And whether the low-voltage side is galvanically isolated (double-wound) or not changes the zero-sequence path and therefore how earth faults behave on both sides.
Tracker Supply and Auxiliary Transformers
Utility-scale plants draw auxiliary power at every inverter station — trackers, communications, weather stations, lighting, sometimes cleaning systems. Supplying these from the transformer’s own LV winding is common and economical, provided the specification accounts for it: auxiliary loading must be added to the connected inverter load before the unit is rated, and starting currents for tracker motors have to ride through the voltage dip.
Most of these auxiliary units are small, and many are dry-type where they sit inside inverter enclosures or in the substation building. Our dry-type transformer range covers them.
Solar Collector Substations
Larger plants gather inverter station output at medium voltage and step up through a central collector substation before the grid connection. That substation can be built conventionally or delivered as a factory-assembled unit.
Through our compact substation line we deliver complete solar substations: step-up transformer, medium-voltage switchgear, protection, metering, auxiliary supply and SCADA interface, assembled and tested together before dispatch. Given the fixed completion dates solar projects typically carry, removing site assembly from the critical path is usually worth more than the unit price difference.
Site Conditions
Solar plants are built where the resource is, which tends to mean deserts, high plateaux and hot climates:
- High ambient temperature reduces available cooling margin and requires derating or oversized cooling.
- High altitude reduces air density and therefore cooling effectiveness — another derating driver. See our cooling guide.
- Dust and sand affect enclosure ingress protection, cooler fin spacing and maintenance access design.
- Remote locations make reliability more valuable than serviceability, favouring sealed construction and simple secondary systems.
Frequently Asked Questions
Can you build to inverter supplier specifications? Yes. Send the manufacturer’s interface requirements — including harmonic content and DC injection limits — and we will quote against them.
Do you supply complete solar substations? Yes, factory-assembled or coordinated component supply depending on plant size.
What about tracker auxiliary supply? Include your auxiliary load and motor starting data with the enquiry and we will size for the combined duty.
Can you handle high ambient and altitude sites? Yes. Altitude and maximum ambient temperature are part of our standard enquiry form, and are applied to the cooling design rather than left to a generic derating table.