Electrical Works for Storage-Integrated Wind and Solar Plants in Türkiye: What to Plan from Pre-License to Commissioning

A storage-integrated generation facility (depolamalı elektrik üretim tesisi) is a wind or solar plant licensed together with an electricity storage unit whose installed power is at least equal to that of the plant, built on the same site. The model rests on a 2022 amendment to Electricity Market Law No. 6446 (Article 7) and was implemented through the November 2022 amendment to the Electricity Market Licensing Regulation issued by the Energy Market Regulatory Authority (EPDK). In exchange for the storage commitment, it opened a separate pre-license route for new wind and solar capacity, and it also addressed capacity increases at existing plants that add storage.

For international developers and EPC contractors, the practical point is that such a project carries a storage obligation from day one. Acquiring the pre-license or bidding for its EPC package means building two facilities that share one substation, one grid connection point and, in most cases, one grounding (earthing) system, and the electrical scope follows from that sharing.

This article does not cover the legal side of the model. Application windows, deadlines and guarantee requirements have been revised over time, so the current text should be confirmed with EPDK and local counsel before an investment decision. AC versus DC coupling and the TEİAŞ and distribution company connection process are covered in separate articles. The focus here is on three factors that drive the electrical contractor's work: the committed storage power, the requirement to keep storage inside the plant site, and the extra load both place on the existing MV system.

The 1:1 commitment scales the main power equipment on the storage side, meaning PCS units, step-up transformers and MV switchgear, to the size of the generation plant, while the on-site requirement forces that equipment to fit inside the plant boundary and connect to the existing MV system. In design terms, the committed MW figure sets PCS and transformer ratings and the number of MV feeders in the substation. The MWh figure drives the number of battery containers, the DC cable volume and the footprint of the battery yard; the regulation requires it to be at least equal to the MW figure, which means a minimum of one hour of storage.

On wind farms the on-site rule is the harder constraint. Turbines are usually spread along ridgelines, and flat, accessible land tends to sit close to the project substation. Placing the battery yard there keeps MV cable runs short, but the battery grounding grid then has to be designed together with the substation grid, and spare bay space in the substation must be confirmed early. Rocky ridge soil typically has high resistivity, so the grounding grid may need a larger area or deep electrodes compared with a flat solar site.

The third effect is at the point of connection. When generation and battery discharge are exported at the same time, total output must stay within the capacity stated in the connection agreement. A power plant controller and the EMS enforce this limit; for the electrical contractor it means CT and VT secondary wiring at the metering point, control cabling and fiber links to the controller. Protection settings are recalculated as well, because inverter-based PCS units contribute fault current very differently from synchronous machines, and that contribution depends on control software.

There are two options: a dedicated feeder to the MV busbar in the project substation, or a tie-in to an existing turbine collector circuit; most projects choose the dedicated feeder. Collector circuits are sized and protected for the turbines already connected to them. Adding battery power to the same circuit forces a re-check of cable thermal rating, voltage drop and protection selectivity, and the existing cable frequently turns out to be too small.

Inside the battery yard the chain is usually: DC cables from battery containers to PCS units, an LV link from each PCS to its step-up transformer, and MV cables from the ring main unit next to the transformer back to the substation switchgear. Several PCS–transformer blocks are linked through their RMUs in a ring or radial arrangement. Collector voltages on Turkish wind farms are generally in the 30–35 kV band, and the battery yard's MV side is specified to match.

If a tie-in is chosen, the tie-in point is the riskiest piece of work: opening the de-energized circuit's cable, installing an MV joint or a new tee-off unit, maintaining cable screen continuity, and testing old and new cable sections together before re-energization. On the fiber side, the battery yard joins the turbine SCADA ring or the main substation switch. On the grounding side, the battery grid is bonded to the substation grid through a bare conductor laid in the cable trench. Our wind farm electrical works article explains how the collector system itself is installed.

At least four preparations belong in the pre-license phase: an electrical survey of candidate battery yard locations, a first single-line diagram showing generation and storage together, a preliminary cable route with quantities, and soil resistivity measurements. These feed the technical information submitted at license stage, the bill of quantities in the EPC tender and the construction schedule. Land and permitting work usually dominates this period, so the electrical side gets postponed until it resurfaces as urgent design problems at procurement.

The survey looks at slope, drainage and flood risk, access for container trucks and mobile cranes, turbine safety distances and distance to the substation. Soil resistivity is measured with the Wenner method at several electrode spacings, ideally in more than one season, because the result sets the size and cost of the grounding grid. On an operating plant, spare bays, busbar current rating, protection panel space and auxiliary transformer capacity in the substation are checked physically, not only from drawings.

The first single-line diagram should show the number of PCS–transformer blocks, the MV feeder arrangement, the metering point and the auxiliary supply source. The cable route marks existing cables from as-built records, road and trench crossings and intersections with turbine cables. If preliminary short-circuit and load-flow studies are run at the same stage, an undersized switchgear short-circuit rating or insufficient transformer capacity is found before equipment is ordered.

Outages are managed through an outage plan agreed in advance with the plant's operations team and a written permit-to-work for every task near energized equipment. The aim is to group all outage-dependent work into as few windows as possible, place those windows in low-generation periods, and make sure nothing starts near live equipment without a permit.

Outage-dependent tasks should be listed at the start: connecting the new MV bay to the busbar, a busbar extension if needed, any collector circuit tie-in, protection and control panel connections and metering circuit changes. Most battery yard work, including excavation, foundations, grounding and cable laying, can proceed while the plant is generating. On wind farms the outage window is chosen from the wind forecast; if switching affects the transmission or distribution side, coordination with the relevant grid operator adds lead time to the programme.

Each outage follows the five safety rules: disconnect, secure against reclosing with lock-out/tag-out, verify the absence of voltage, ground and short-circuit, and cover or barrier adjacent live parts. The plant's switching authority and the contractor's person in charge are different people, and a permit must be signed off before anything is re-energized. Voltage induced from parallel energized cables and residual capacitive charge on long MV cables are the items most often missed during voltage checks. On the BESS project at the operating Killik wind farm, we acted as the electrical works subcontractor for DC and LV cabling, busbar connections, grounding and site cable infrastructure, and testing and commissioning support.

Ask the electrical contractor for measurement records covering every connection it installed and for as-built documents showing the final state of the site; on storage-integrated projects, add documentation of every change made to the existing plant. The core package includes insulation resistance, continuity and polarity records on DC and LV cables, VLF and sheath tests on MV cables, phase rotation checks, OTDR reports on fiber links, and grounding resistance and continuity measurements. Our article on BESS electrical scope of work lists the full test set and who typically owns each item.

The documents specific to the storage-integrated setup are the ones most often missing: an updated plant single-line diagram showing generation and storage together, a grounding drawing showing the substation and battery yard as one grid, before-and-after test results for any collector circuit tie-in, records showing that the new feeder's protection settings have been applied, and a coordinate-referenced cable route plan. These are the first documents consulted at provisional acceptance, during insurance reviews and asset transfers, and in later maintenance work.

Miratek Elektrik carries out MV cabling, cable terminations, MV switchgear installation, grounding and testing-commissioning on wind, solar and BESS sites across Türkiye. We work across the 1–35 kV MV range and, over more than 15 years, have completed 85 km of MV/LV cable lines and 48 MV switchgear panel installations; our site work runs under an ISO 45001:2018 certified occupational health and safety management system. Under our Renewable Energy service, we can plan the electrical works of a storage-integrated project with you, from the pre-license survey to commissioning.