Dec, 2013

Accuracy of financial modelling for commercial solar power

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At the heart of any proposal for solar is a prediction about what solar will do for you – both in terms of electricity production and converting that into dollars.

To do these, we use a mixture of facts, some assumptions, a few predictions and almost no guesses to build a financial model for commercial solar.

It’s important to remember that models are just an approximation (or simplification) but that our goal is to make that approximation as accurate as possible. Therefore we look at as many relevant factors as we can in order to reflect reality.

We take into account:

    • Your geography and the historical output of a solar system in that area
    • The positioning of the system (angle and aspect)
    • Unavoidable environmental impact – shading
    • Output of the system
    • System losses
    • Gradual degradation of the panels over time
    • The price that you pay for power (specifically, the variable rate per kWh, not fixed charges)
    • Expected future price rises for electricity
    • Terms of your power supply agreement if you are under contract, or if you are a negotiated contract
    • Your usage patterns of electricity – days per week worked, hours per day, and  holiday periods – and the base load in ‘non work’ periods
    • A feed in tariff for exported – non used power – if relevant
    • The upfront cost of the system, including the cost of STCs
    • Ongoing maintenance costs and costs of ownership over time
    • Replacement of key components at specified times (for example we might factor in an inverter replacement at year 15 or 20, depending on when warranties expire).


In some cases, you may have complex data related to usage as part of your power bill, and we can use that in our model. If not, we can either make assumptions, or conduct some tests on load to get more detailed data.

So, what we end up with is an approximation to reality that is close enough to assist in making a decision.

This is then put together in such a way that it becomes simple to understand yet comprehensive and is the basis for the financial proposition for solar power.

We’re happy to discuss our modelling procedure, and where we get our figures from (such as the amount of power that a system will produce) so that you are comfortable. It’s an important part of  the process because we are putting forward solar power as an investment.

You’ll find  the returns are excellent (from 4 year payback to 8 year payback with the the price you pay for power  being a major factor).

If you want to explore this  further we welcome your call.