Grid Interconnection Cost Calculator

When Step-Up Transformer is set to No, the calculator zeroes out the transformer cost entirely rather than reducing it, since the engine only adds roughly $25,000 per MW when transformerNeeded is truthy. For a 50 MW project that's a $1.25 million swing, so this input should reflect an actual engineering determination of whether your project's voltage already matches the interconnection point — not a cost-cutting assumption.

In this version of the calculator, the Interconnection Voltage input is captured for context but isn't wired into any of the cost formulas — transmission line cost depends only on distance and your per-mile rate, and transformer, switchgear, and protection costs all scale with project MW rather than voltage class. In reality, higher-voltage interconnections often carry higher equipment costs, so treat this input as documentation of your project's voltage class rather than a cost driver here.

Cost per MW is Total Interconnection Cost divided by Project Size, and several cost components (Study & Engineering Cost, transmission line cost, protection relay's flat base, and metering) don't scale with project size at all. That means a small project spreads those fixed costs over fewer MW and shows a much higher Cost per MW than a large project with the same fixed costs, even if their totals are similar — this metric is meant for comparing relative efficiency across projects of different sizes, not as a fixed unit price.

Transmission Line cost is simply Distance to Substation multiplied by the Line Cost per mile you enter, with no cap or economy-of-scale discount — a project 10 miles from the nearest substation at $500,000/mile adds $5 million before any equipment costs are even considered. Because line construction cost per mile can vary enormously by terrain and right-of-way requirements, this single input often has more influence on the total than every other line item combined.