The first wave of utility-scale solar farms commissioned between 2010 and 2015 is now entering its second decade of operation. Original inverters are approaching or exceeding their designed operational life of 10–15 years, first-generation polycrystalline modules have accumulated 1–2% per year of LID/PID degradation, and central inverter platforms have lost manufacturer support. Repowering — replacing some or all major components while retaining the existing civil infrastructure, grid connection, and permits — offers asset owners a cost-effective path to restoring and extending plant performance without the costs and delays of greenfield development. This comprehensive guide helps project developers, asset managers, and EPC engineers understand the repowering decision, assessment process, equipment selection, and procurement strategy.
A 10-year-old 10 MWp solar plant typically shows: module degradation of 8–15% below original nameplate (1% LID + ~0.5%/year standard degradation); inverter MTBF failures increasing with failed capacitors and IGBTs; rising O&M costs as replacement parts for discontinued inverter models become scarce; and a Performance Ratio that has declined from the original 82% down to 72–75%.
Repowering economics hinge on the incremental energy yield vs. equipment and installation cost. A rule-of-thumb model for inverter-only repowering: if the yield improvement from new inverters (typically 3–6% due to higher efficiency and reduced downtime) generates €X/year in additional revenue, and the inverter replacement cost is Y €/kW, the simple payback = Y / (X/kW). At €30/kW replacement cost and €8/kW/year additional revenue, payback = 3.75 years — compelling for a plant with 10+ years of remaining PPA term.
Before committing to a repowering scope, commission a technical due diligence assessment covering:
| Assessment Item | Method | Trigger for Replacement | Typical Cost (10 MWp) |
|---|---|---|---|
| Module condition | EL imaging, IV curve, IRT | >5% power loss vs datasheet; >10% cracked cells | €8,000–15,000 |
| Inverter condition | SCADA log review, cap. ESR test | EOL announced; parts unavailable; >3% downtime | €3,000–6,000 |
| Cable/earthing | IR testing, visual inspection | <1 MΩ/kV insulation resistance | €4,000–8,000 |
| Structure/mounting | Visual, torque test, corrosion survey | Corrosion grade 4+; loose anchors | €5,000–10,000 |
Many plants built 2010–2016 used large central inverters (500 kW–2.5 MW) that are now discontinued or poorly supported. Replacing them with modern string inverters offers several advantages: no single-point-of-failure, per-MPPT optimization, lower replacement cost per kW, easier installation (no crane needed for units <50 kg), and longer expected lifespans (Sungrow and Huawei offer 10-year warranties on current commercial string inverters with extension options).
The key engineering challenge is the DC wiring reconfiguration. A central inverter served a large DC combiner box; replacing it with string inverters requires either: (a) keeping the combiner box and running a single Modbus string from each combiner port to a new string inverter, or (b) running individual string cables directly to new string inverters mounted on the racking structure. Option (b) is electrically superior (enables per-string MPPT) but requires more cable. A 1 MWp block that originally fed one 1 MW central inverter would typically be replaced with 4× 250 kW Sungrow SG250HX or Huawei SUN2000-215KTL string inverters.
Full module replacement (full repowering) is warranted when EL imaging shows >5% of modules have significant cell cracks, or when measured output is >15% below original nameplate. Modern TOPCon n-type modules (LONGi Hi-MO 7, Jinko Tiger Neo, JA Solar DeepBlue 4.0) offer 22.5–23.5% module efficiency vs. the 15.5–17% of typical 2012-era polycrystalline modules. Replacing 330 Wp poly modules with 590 Wp TOPCon modules on the same mounting structure can increase plant capacity by 70–80% within the existing footprint — a powerful value driver if the grid connection agreement and civil works support the higher capacity.
Partial repowering (replacing only the worst-performing 20–30% of modules) is also viable and reduces capital outlay. Use IV curve tracing results to prioritise replacement strings. Mixing old and new modules on the same string or MPPT input is not recommended; if only some strings are replaced, configure the new modules on dedicated MPPTs.
A repowering financial model should include: (a) baseline energy yield with degraded equipment (from SCADA actuals); (b) projected yield with new equipment using a PVsyst or SAM model updated with new module and inverter specs; (c) capital cost of repowering (inverters, modules, installation, permitting); (d) incremental O&M savings (reduced downtime, fewer spare parts); (e) any capacity uplift revenue under the grid connection agreement. IRR on inverter-only repowering typically ranges 15–25%; full repowering with module upgrade can exceed 20% IRR where land costs are embedded and grid connection is already paid for.
Repowering is typically classified as a "material change" by grid operators and planning authorities if it exceeds the originally permitted capacity or changes the connection point characteristics. Notify the DNO/TSO early in the project planning phase. In the EU, repowering of existing renewable plants benefits from streamlined permitting under the revised Renewable Energy Directive (RED III); many member states have introduced fast-track procedures for repowering existing permitted sites, with target decision timelines of 6 months.
Equipment warranties restart on new components. Ensure the new inverter and module warranties are issued in the EPC contractor's name and are assignable to the asset owner/lender. For lender-financed assets, the lender's technical advisor will require independent energy yield assessment of the post-repowering plant before approving capital expenditure.
Repowering projects have tighter timelines than greenfield plants — the asset must be back online generating revenue as quickly as possible. Econo Solar specialises in rapid procurement of replacement string inverters (Sungrow, Huawei, Deye, GoodWe), high-efficiency TOPCon modules (LONGi, Jinko, JA Solar), and balance-of-system components direct from Chinese manufacturers. We maintain relationships with factory warehouses to support urgent dispatch schedules and can provide IEC 61215/61730 certified modules and CE/IEC 62109 certified inverters with full technical documentation for lender and grid operator approval. Contact us at our repowering inquiry page to discuss your plant's needs.
Logistics planning is as important as the technical design for repowering projects. Large module quantities (a full 10 MWp repowering requires approximately 17,000 × 590 Wp modules) require careful staging to avoid site congestion. Coordinate module delivery in weekly batches matched to the installation crew's daily installation rate (typically 400–600 modules/day for an experienced crew).
Before issuing the repowering procurement RFQ, prepare a detailed scope-of-work document specifying: DC system voltage (new inverter compatibility), module mounting interface dimensions (portrait vs landscape orientation, rail spacing), AC output voltage and grid connection requirements, communications protocol for SCADA integration, and all applicable certifications. This document forms the basis for competitive supplier quotations and protects the project against scope creep during installation. Econo Solar provides pre-vetted bill-of-materials templates for both inverter-only and full repowering scopes on request.
Usually yes — the AC output voltage of modern 3-phase string inverters (typically 800 V or 480 V AC) can be stepped up to MV via the existing plant transformer, just as the central inverter did. The AC combiner (bus bar or switchboard) must be checked for current rating and cable sizing if the total AC current changes. In some cases, the existing AC cables from the central inverter pad to the substation can be reused if the string inverter outputs are combined at the original inverter location.
Replacing a 10-year-old central inverter (CEC efficiency ~96.5%) with a modern string inverter (CEC efficiency ~98.5–99%) contributes approximately 2% yield uplift. Eliminating inverter downtime that was causing 1–3% annual generation loss adds another 1–3%. Combined, inverter-only repowering typically delivers 3–6% additional annual energy, with higher gains for plants that had frequent central inverter failures.
This depends on the jurisdiction and the specific tariff/PPA terms. Many feed-in tariff regimes grandfather the original tariff rate for the remaining term, even after repowering, as long as the grid connection point and capacity stay within permitted limits. Some PPA agreements include capacity change notification clauses. Always review the existing grid connection agreement, planning permit, and offtake contract before changing capacity, and seek legal advice if the repowering materially changes the plant's characteristics.
A typical inverter-only repowering of a 10 MWp plant follows this schedule: Phase 1 (Weeks 1–4) technical assessment and equipment selection; Phase 2 (Weeks 5–10) procurement and manufacturing lead time; Phase 3 (Weeks 11–14) civil and mechanical installation (inverter foundations, cable trays); Phase 4 (Weeks 15–16) electrical installation, commissioning, and grid re-energisation. Total downtime during switchover can be minimised by replacing one inverter block at a time while the rest of the plant continues to generate. Full module repowering on a 10 MWp plant typically takes 8–12 weeks on-site with a crew of 15–20 technicians.
Regulatory milestones must be tracked in parallel with procurement. Submit the grid notification to the DNO within the first two weeks of project initiation. In most EU jurisdictions, a repowering within the original permitted capacity receives a grid operator response within 30 days. Where capacity uplift is planned, allow 60–90 days for grid studies and connection offer amendment. Engage the original equipment manufacturer for any warranty transfer requirements on non-replaced items (cables, mounting structures) that remain in service.
Key procurement lead times: Sungrow SG250HX string inverters — 4–6 weeks ex-factory China; LONGi Hi-MO 7 590 Wp modules — 6–8 weeks ex-factory; DC cables and combiner hardware — 3–4 weeks. Econo Solar can coordinate all three simultaneously to compress the overall schedule.
Replacement inverters and high-efficiency modules for repowering — direct from China, fast delivery.
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