Assessing existing assets – what really matters for operational solar parks

Why existing assets follow their own logic

Existing assets initially seem simpler to many investors than new projects. The plant is built, it produces electricity, and the revenues are visible. Compared with project rights or construction projects, the risk appears lower.

In practice, however, only the type of question changes. While for new projects the uncertainty lies in the future, for existing assets it often lies in the details of the past.

A solar park that has been operating for years comes with data. And it is precisely this data that must be put into context.

Yield data – between reality and interpretation

The greatest advantage of an existing asset lies in its actual yields. They show what was truly produced – not what would be theoretically possible.

At the same time, experience shows that there are regular deviations between simulated and actual yields. In analysed projects, these are often in the range of around −3 to −10% compared with the original simulations. In individual cases, however, the deviations can be significantly larger – with observed outliers of more than −20%.

These differences rarely arise from a single factor, but from the interaction of several influences. Weather deviations, soiling, system losses that are not fully captured, or operational downtime often have a greater impact in reality than models reflect.

The key question, therefore, is not whether a simulation is “correct”, but how it is interpreted.
Yield models provide guidance – the actual performance of a plant only becomes apparent in operation.

For the assessment, this means:
Actual yield data is the most reliable benchmark, but should always be viewed in context. A single year can distort the picture just as much as an overly optimistic simulation. Only over several years does a robust picture emerge that allows conclusions to be drawn about a plant’s actual performance.

Assessment methodology – how existing assets can be structured and classified

In practice, it has proven that the assessment of existing assets is only robust if it is carried out systematically. Individual metrics or isolated views are not sufficient to obtain a complete picture.

A well-founded classification is generally based on three central dimensions.

First, the technical history is central. What matters is not only which components were installed, but how they have developed over the years. Modules, inverters and monitoring systems provide valuable indications here – especially when maintenance, failures and deviations are documented in a traceable manner. Technical assessments often follow standardised expert-report procedures that place the as-is condition in a long-term context.

The second dimension is the contractual structure. Lease agreements, grid connection agreements, easements and, where applicable, existing marketing agreements form the legal foundation of the plant. Their quality determines how stably the project can be operated in the long term. In practice, this includes reviewing and classifying, among other things, site plans, lease and right-of-way constellations, and existing direct marketing agreements.

The third level is the financial assessment. It goes beyond simple return considerations and is based on conservative assumptions. Models built on NPV and IRR logic make it possible to assess economic viability under different scenarios. The key is not optimising an individual case, but the question of how robust a project remains under realistic conditions.

Only the interplay of these three perspectives produces a picture that is robust enough to base investment decisions on.

Conclusion – you understand existing assets through structure and track record

An existing asset cannot be assessed on numbers alone. It must be read like a track record.

Yields, technical development, contractual structure and operating history together create a picture that is far more meaningful than any single metric.

For this very reason, a sound assessment is not carried out in isolation, but along clear review logics – technical, contractual and economic. Only when these levels are brought together does a realistic understanding of opportunities and risks emerge.

For investors, this means the quality of an existing asset is not reflected in its current condition, but in the traceability of its development and the stability of its structure.

Those who understand how a solar park is structured and how it has been operated can also assess how it will behave in the future. And that is precisely the difference between an investment based on data – and one based on understanding.

More articles

• How Solar Parks Generate Revenue: Income, Marketing Models, and Economic Relationships
• Purchase Price, Lease, and Ancillary Costs: How the True Total Investment of a Solar Park Is Determined
• Profitability of a Solar Farm – How to Arrive at a Realistic Valuation