Solar Energy Production Estimation - How Does Solar Proof Calculate Energy Production

Solar Energy Production Estimates

Here's why Solar Proof takes energy production estimates seriously.

Recently I've been asked about the calculations in Solar Proof. Questions such as:

  • How is the energy production calculated?
  • What does the solar system efficiency mean?
  • And why are some of our "competitors'" numbers significantly higher than ours (~13%)?

So let's take a look at the answers to these questions and hopefully I can show you how our numbers reflect the most accurate available data!

How is Solar Proof Energy Production Calculated?

Solar Proof uses the National Renewable Energy Laboratory (NREL) PVWatts V8 as its primary energy calculation method.

NREL has been around since 1977 (currently 47 years) and is a widely respected laboratory whos 'activities went beyond research and development in solar energy as it tried to popularize knowledge about already existing technologies'.

Using PVWatts, we can accurately determine for any given location, the energy production (hour by hour) for a given system based (among other parameters) on its capacity, tilt and direction (azimuth).

Accounting for losses in production

You're likely well aware that energy losses occur in Photovoltaic (PV) solar systems. The question is, what are the losses in a given solar system and how can we account for them when it comes to production (and ultimately financial) estimates?

Well in PVWatts, system losses are described in the following categories and default values:

Default values for the system loss categories
Category Default Value (%) Solar Proof Value (%)
Soiling 2 2.5
Shading 3 0 (accounted for in shading)
Snow 0 0
Mismatch 2 2.5
Wiring 2 2.5
Connections 0.5 0.45
Light-Induced Degradation 1.5 1.45
Nameplate Rating 1 1
Age 0 0
Availability 3 3
Efficiency 85.92% 87.32%

This is then used to calculate losses according to the formula:
100% × [ 1- ( 1 - 0.02 ) × ( 1 - 0.03 ) × ( 1 - 0.02 ) × ( 1 - 0.02 ) × ( 1 - 0.005 ) × ( 1 - 0.015) × ( 1- 0.01 ) × ( 1 - 0.03) ]
Which gives a result of 14.076%.

From the above, we gather that the system has an overall efficiency of 100% - 14% = 86%;

In Solar Proof, by default we use an efficiency value of 87.32%, widely considered by solar industry leaders to be appropriate.

What does the solar system efficiency mean?

As you can tell, system efficiency is going to affect production. In essence, we are doing our best to account for the real-life cases where a solar system doesn't perform at its optimal peak possibly output. And by doing this, we are going to get a more realistic figure than if we base our figures on optimal performance alone (no losses).

As an example, so that it is clear... If we have a 100kW solar system in Brisbane, QLD, Australia, we might imagine that it would generate 154.5MWh in an average year. This assumes a system efficiency of 87.32%. If we assume an efficiency of 100% (no losses), we get a result of 176MWh (a 13.9% increase!).

In essence:
Higher efficiency = more production = higher savings.

EXAMPLE: 410kW Solar Power System

This example shows a system of capacity 410kW split 205kW each side on the East and West facing roofs with a small tilt of 5°

Notice that the discrepency is large - and to a business owner might very well be the difference between signing a deal and not

Of course, if your customer is signing a deal - they expect to see AT LEAST the numbers that you put in your proposal coming out in REAL LIFE!

Why are some of our "competitors'" numbers significantly higher than ours (~13%)?

If you're in the solar industry, you likely know some of the software out there. Some of our clients did comparisons and mentioned that other platforms produce a result of around 13% - 14% higher than Solar Proof.

Of course, I can't say why that is... But if you look at the above section and notice that when we set efficiency to 100% (BAD INDUSTRY PRACTISE!!!), we get a result of 13.9% higher than our default.

In Summary...

Estimating energy production is huge... In our software it is one of a few key factors which define financial returns and can make the difference between a happy customer and a very disappointed customer down the line.

If you're a solar company that hopes to stick around for more than a year or so, then you may want to consider UNDER-PROMISING and OVER-DELIVERING as an ethos.

But certainly, if you want to offer higher estimates for production (and promise higher savings to your prospects). You can do this in Solar Proof by adjusting the system efficiency.

Chris Taeni profile photo

Chris Taeni - BEngg (Power)

Solar Proof Solutions Pty Ltd


Published: June 5, 2024

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