Case Study · Energy Efficiency

One facility, three ways to finance the sun.

A photovoltaic proposal for Transflo’s Westborough facility: confirm the site can host the array, then put cash purchase, PPA, and lease side by side to find the structure that actually pencils.

Client: Transflo
Location: Westborough
Practice: Energy Efficiency
Analysis: PV Siting + Financing

The Brief

Prove the site first, then pick the structure.

This was a proposal-stage analysis, not a construction record. The value is in the method: a siting check that disqualifies weak arrays early, and a financing comparison that treats ownership structure as the real variable.

Siting came first. Photovoltaic output depends on south-facing exposure with clear, unobstructed sunlight, so the analysis mapped available roof and ground area against shading and orientation. Array capacity was estimated with the standard planning figure of 8 to 10 Watts DC per square foot of panel, and roof-mounted options were conditioned on a structural check confirming the building could carry the added weight.

With the physical envelope established, the question became financial: for the same array, which ownership structure delivers the lowest lifetime cost of electricity?

The Analysis

Cash, PPA, and lease, side by side.

Cash purchase

Buying the system outright captures every incentive directly: the 30 percent federal Investment Tax Credit, MACRS 5-year accelerated depreciation, and any state programs, together offsetting an estimated 30 to 50 percent of upfront cost. Panels carry 25-year warranties. The tradeoff is real: the owner fronts the capital and carries operations and maintenance for the life of the system.

Power Purchase Agreement

Under a PPA, the provider installs, owns, and maintains the array on the host’s roof or ground space, keeps the incentives, and sells the host power at a fixed rate per kWh, generally below utility retail, over a 15 to 20 year contract. At term end the host can buy the system at a reduced rate, sign a new contract, or have it removed. The catch is scale: providers set minimum project sizes, typically 30 to 100 kW, so the array has to clear that threshold before a PPA is even on the table.

Solar lease

A lease removes the upfront cost like a PPA does, but the host leases the equipment itself rather than buying its output. It is built for residential and very small commercial systems, and the test is simple: lease payment plus the reduced electric bill should come in under the old bill. At distribution-terminal scale it is usually the fallback, not the first choice.

The honest conclusion: no structure wins on paper alone. The right answer depends on the owner’s tax appetite, the state incentive programs actually available at the site, and how long the facility intends to hold the property.

30%

Federal Investment Tax Credit on system cost

30–50%

Upfront cost offset with incentives stacked

8–10 W

DC output per square foot used for array sizing

15–20 yrs

PPA contract term modeled in the comparison

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