When a Good Photovoltaic Location Is Not Enough: Spatial–Economic Vulnerability of a 1 MW Solar Farm to Non-Market Curtailment—A Case Study from Poland

The rapid expansion of photovoltaic capacity in Poland has exposed distribution-grid constraints and increased the incidence of non-market curtailment. This paper examines a 1 MW ground-mounted photovoltaic plant in Zalesie, north-eastern Poland, using complete documentation. The study combines a spatial multi-criteria site-suitability assessment based on the Weighted Sum Model, a sensitivity analysis of criteria weights, an analysis of 28 curtailment compensation applications, and a transparently parameterised LCOE/NPV/IRR model under four curtailment-severity scenarios. The results indicate a high and weight-robust site-suitability score (S = 4.45/5.00; sensitivity range 4.35–4.55), with curtailment concentrated in spring: 68% in April and May. Economic modelling shows that, under merchant market conditions and without support schemes, profitability is already constrained in the baseline case (IRR 4.2–6.4%), while increasing the share of unsold energy from 0% to 10% raises LCOE by approximately 3–11% and deepens the already negative NPV by a further PLN 0.09–0.36 million. A Monte Carlo simulation confirms that the NPV stays negative across the whole plausible parameter range. This case study demonstrates that classical spatial suitability may be a necessary but insufficient condition for the economic security of PV investments unless grid-related and regulatory risks are incorporated into the planning stage.