A Cheap Solar Plant Bid: Where Contractors Cut Corners — and Why Your Plant Underdelivers at Peak for Years

Q: What does curtailment of a solar plant mean?

It is the forced limiting of generation when a weak node cannot pass full power. On the monitoring chart it looks like a flat plateau instead of the solar bell curve. The energy simply never reaches the grid or the storage system.

Author: Viacheslav Yurdyk, Quality Engineer at LK Energy Group.
Over 1,000 equipment units accepted through factory quality control (QC) and 200 electrical installation sites under technical supervision.

Short answer (for those in a hurry)

The cheapest bid for building a solar power plant is often cheaper not because the contractor is more efficient — but because they saved on things you will not see at handover: an undersized transformer, undersized cable cross-sections, cheaper protection. The plant will start up, the acceptance act will be signed — and then, for years, it will be unable to deliver full power exactly when the panels produce their maximum. In plain terms: you paid for part of that electricity (it is in the design capacity, the panels generate it), but because of one weak node it has to be curtailed — it simply never reaches the grid. Nobody will ever return that lost revenue.

Below is a generalized example from our O&M practice, explained in plain language, plus a 10-point checklist of where budgets get cut and how to spot it in the design before you sign. The analysis comes from servicing industrial solar plants in the Odesa region and across Ukraine.

The cheap-plant paradox: they save at the input — you lose at the output

An investor enters a solar project with simple logic: there are several bids, the cheapest one wins. It seems rational — a megawatt of capacity looks the same in every offer. The problem is that design capacity on paper and the plant’s actual energy yield are two different things, and the difference is created precisely by the decisions a non-specialist cannot see.

Let me state the key point upfront, because it is not obvious: when a node is undersized, it overheats — but you lose the bulk of the money not on the heating itself (that is the small part), but on the fact that to avoid overheating, the plant has to be curtailed — and part of the energy the panels are ready to deliver at the sunniest moment simply never reaches the grid. We will show this with an example below.

We see these stories first-hand. Among the plants we take over for maintenance, we come across stations with mistakes built in at the construction stage by another contractor. The savings at the start turned into a plant that cannot reach full power at peak — for years. Let us walk through the two most telling types of such mistakes using a simplified example, and then give the full checklist.

Example 1. A transformer “at the limit” instead of a transformer “with margin”

In plain terms. The transformer is the node through which all of the plant’s energy exits to the grid. It is the “throat” of your plant: however powerful the body (panels and inverters), everything passes through this throat. If the throat is narrow, it physically cannot pass as much as the panels produce at the sunniest moment.

Take a plant of about 1 MW. Such projects often get a 1,000 kVA transformer with the logic “1 MW ≈ 1,000 kVA, the numbers match”. These plants typically use tier-1 modules (LONGi, JA Solar, Trina Solar) and Huawei or Sungrow inverters — but all that capacity reaches the grid only through the transformer: if the “throat” is narrow, even the best equipment underdelivers.

Why this is your money. A transformer sized “exactly to the limit” means that at the midday peak, when the panels deliver their maximum, the throat fills to the brim — the node runs at its limit and overheats. The heating itself is a minor loss. The real problem is different: to keep the transformer from overheating and failing, the plant has to be curtailed. The inverters receive a “do not deliver full power” command — and they cut off exactly the top of the generation curve, the largest volume of kilowatt-hours, during the sunniest hours. The result: the panels are ready to deliver the full megawatt, you paid for that megawatt when you bought a 1 MW plant — but it does not reach the grid, because the throat will not pass it. And this repeats every sunny peak, every day, for years.

An analogy. Imagine you bought a truck expecting to haul a tonne per trip, but it came with an engine that can only pull 800 kg. It could theoretically move a tonne — but at its limit, overheating. To keep the engine from burning out, the driver has to underload the truck every time: 200 kg of cargo stay in the warehouse on every trip. The cargo exists, you paid for it — but it does not move. Over a year, a mountain of undelivered goods piles up. An undersized transformer works exactly the same way: every day it leaves part of your “cargo” — your electricity — undelivered to the grid. The scale in this example is illustrative, but the direction never changes: part of the yield remains unsold.

The engineering detail (for those who want to verify). A competent engineer never loads a transformer to 100% of its rating — they design in a margin of roughly 20%, meaning a 1 MW plant gets a 1,250 kVA transformer, so that in normal operation it runs at ~80% with a thermal reserve. This is basic reliability practice; its logic is reflected in the power transformer loading guide IEC 60076-7. The margin is not “margin for margin’s sake”: it provides thermal reserve for hot days and peaks, without which the insulation life burns out faster and the plant has to be limited.

Example 2. Transformer protection “for the checkbox”

In plain terms. A transformer needs a “fuse” that will instantly disconnect it if a fault (short circuit) occurs inside. The quality of this protection determines whether the expensive node survives the fault or burns down. Contractors cut costs here too — they install simpler, cheaper protection that does not always operate correctly in time.

The second typical place to save is the transformer protection on the 10 kV side. Instead of a circuit breaker (today — a vacuum one) with relay protection, they install the cheaper combination of a load-break switch + fuses.

Why this is your money. The difference between these two solutions is the difference between a “smart guard” and a “simple fuse”. A load-break switch can only switch normal operating current — it is not designed to interrupt short-circuit fault currents; for that it relies entirely on the fuses. If the fuses are sized incorrectly, or the internal fault is one the fuse does not “catch” in time, the transformer will suffer far more damage than it would with proper relay protection. One bad incident — and you are either repairing or replacing the transformer, while the plant stands idle and earns nothing.

The engineering detail (for those who want to verify). Relay protection for transformers is required by the Ukrainian electrical installation code (PUE), Section 3, Chapter 3.2, and it can only act through a circuit breaker, not through a fuse. Protection with high-voltage fuses (PKT type) is applicable only to low-rated transformers — by established engineering practice, roughly up to 630 kVA. So for the high-rated transformer of a 1 MW plant, the “lightweight” fuse-plus-load-break-switch protection is not compliant with the code.

What this costs the owner in money

The exact figure must be calculated for the specific site — it all depends on how badly the node is undersized and how many sun hours the location gets. But the logic is clear without exact numbers.

Curtailment cuts off the top of the generation curve — the largest volume of kilowatt-hours the plant could deliver during the sunniest hours. Under a fixed tariff or a PPA you lose their full value. And on the day-ahead market (DAM), this “cheap” midday energy is exactly the resource that should be charging the battery energy storage system (BESS) for evening sales at peak prices.

If the plant has no storage, that surplus has nowhere to go — the energy is simply never generated. Which means you not only lose the immediate sale, but also deprive yourself of balancing capability and the additional revenue of evening prices. And the shortfall is not a one-off event — it is a daily effect over the 20–25 years of the plant’s service life.

That is why this “hidden” defect is worth quantifying before you buy the plant, while you can still negotiate or walk away.

The checklist: 10 points where a solar contractor cuts your budget

The points to examine in the design and the commercial proposal before signing the contract.

What we have seen ourselves:

A transformer rated “exactly to the limit”. Check the ratio of plant capacity to transformer rating. If the transformer is loaded to ~100% at peak — that is a mistake; there must be a margin (≈80% loading). Why it is money: otherwise the plant will have to be curtailed at peak.
Fuse protection instead of a circuit breaker. A high-rated 6/10 kV transformer (above ~630 kVA) requires a (vacuum) circuit breaker with relay protection. Why it is money: in a fault, weak protection will not save an asset worth millions.
Undersized cable cross-sections. Thinner cable is cheaper — but it produces higher losses and voltage drop. Why it is money: part of the energy heats the cable instead of going to the grid.
Savings on earthing. A bare-minimum earthing system. Why it is money: a risk to people and to expensive equipment during a fault or a thunderstorm.
Cheap mounting structures. Cut-price steel structures / piles under the modules. Why it is money: misaligned modules underproduce, and in the worst case the structure fails.

Common across the industry (also worth checking):

Weak surge protection (SPD). Surge protection is governed by the IEC 61643 series of standards. Why it is money: without proper SPDs, one serious surge can destroy the plant’s most expensive electronics — the inverters.
Simplified lightning protection. A large site in an open field without proper protection. Why it is money: a direct strike means repairs at your expense and downtime.
No monitoring / dispatch system. Why it is money: in a proper monitoring system, curtailment is visible as a clipped top of the generation curve — a flat “plateau” instead of the proper solar bell curve. If that plateau is not part of the design (normal inverter limiting with DC/AC oversizing) — your plant is physically cutting your money right now. Without dispatch monitoring, a site can run in that plateau mode for months without you ever knowing.
Grey-market or B-grade modules and inverters. Cost-cutting through no-name equipment instead of tier-1. Why it is money: faster degradation and repairs with no warranty.
A “paper” warranty and token commissioning. A warranty only works if there is someone in Ukraine to honour it. Why it is money: a “warranty” nobody will honour is worth zero.

What if the plant is already built?

If you are reading this as the owner of an underdelivering plant — there is good news: most of these mistakes are fixable. An undersized transformer can be replaced with a larger one, the protection brought up to code, SPDs and monitoring added.

Whether it is worth doing is answered by a technical audit of the plant. We assess how the equipment actually performs, estimate how much yield you are losing to curtailment and losses, and show what should be fixed first — so that the investment in the fix pays for itself through recovered generation.

How to recognize a trustworthy contractor

A contractor’s integrity shows at the proposal stage — in how much engineering detail they disclose, rather than just the bottom-line price.

Signs of a contractor who is not hiding cost cuts:

there is a single-line diagram with the specific protection type and ratings;
there is an equipment specification with manufacturers and models;
there is a loss calculation and justification of cable cross-sections and the transformer rating;
the design includes margin on the transformer, proper protection, SPDs, monitoring;
the contractor is ready to calmly explain every decision.

The cheapest bid with a “bare” price and none of these details is almost always a bid where the savings are already sewn in where you will not see them — until the day the plant starts underdelivering.

FAQ

What transformer does a 1 MW solar plant need?

A plant of about 1 MW gets a 1,250 kVA transformer, not 1,000 kVA. The ~20% margin provides thermal reserve: at the midday peak the transformer runs at ~80% of its rating without overheating. The loading logic is described in IEC 60076-7. A transformer sized “to the limit” forces curtailment at peak.

Why is fuse-based transformer protection dangerous?

A load-break switch with fuses is not designed to interrupt short-circuit currents. For a high-rated 10 kV transformer (above ~630 kVA), the Ukrainian code (PUE, Section 3, Chapter 3.2) requires relay protection acting through a vacuum circuit breaker. Saving here puts an asset worth millions at risk.

What does curtailment of a solar plant mean?

It is the forced limiting of generation when a weak node (transformer, cable) cannot pass full power. The inverters are commanded to clip the top of the generation curve — on the monitoring chart it looks like a flat “plateau” instead of the solar bell curve. The energy simply never reaches the grid or the storage system.

Can an already-built underdelivering plant be fixed?

Yes, most mistakes are fixable. An undersized transformer is replaced with a larger one, the protection is brought up to code. A technical audit calculates how much yield is lost to curtailment and shows whether the fix pays for itself through recovered generation.

What does an undersized node cost the owner?

The exact figure is calculated per site. Curtailment cuts the largest volume of kilowatt-hours during peak hours. It also removes the option of storing energy in a BESS for evening sales — creating daily losses over the entire 20–25-year life of the plant.

An independent look at your project or plant

If you are at the contractor selection stage — you can send us the design or the commercial proposal for a free preliminary technical review. If the plant is already operating and you suspect underproduction — we will perform a technical audit of the site.

The preliminary review is informational, provided at the company’s discretion, and is not an offer, a guarantee of identifying all risks, or a recommendation regarding any specific contractor. A full assessment is only possible after a site survey.

LK Energy builds turnkey solar power plants and takes over operation and maintenance of existing sites — including those their owners inherited with problems. We see these mistakes from the inside, because we are the ones who fix them afterwards.

Send your project or proposal for a free preliminary review →