A household’s monthly electricity bill is a useful starting point when considering solar, but it does not provide enough information to determine what size system the home needs, according to John Fox, National Technical Operations Manager at Stage Zero.
Fox says households with similar monthly electricity costs can have very different usage patterns, particularly in the times of day when demand is highest and in how much power is drawn at once. These differences can materially affect the required solar and battery capacity.
“Two customers can arrive at a similar monthly electricity figure in completely different ways,” says Fox. “One may use power fairly consistently throughout the day, while another has periods where demand increases sharply. From a technical point of view, those are very different requirements even if the monthly bill looks similar.”
Stage Zero says this is why system sizing needs to account for the customer’s load profile rather than relying solely on monthly spend.
Fox points to commercial environments as an illustration. A church may use relatively little electricity during the week, but demand rises significantly over the weekend when kitchen equipment, urns, lighting, and sound systems are operating. An ice manufacturer can have a different pattern, with refrigeration equipment drawing substantial power during shorter cooling cycles but at a relatively regular cadence.
“The same principle applies at home. How much electricity you use is important, but we also need to understand when you use it and what the system will be expected to carry when demand is high,” says Fox.
According to Stage Zero, another common misunderstanding is that the rated capacity of solar panels should translate directly into constant real-world output.
“A customer may have ten panels rated at 550Wp each and expect to see that full combined figure whenever the sun is shining. When they do not, it can be assumed that something is wrong. The panel rating is a Peak value under Standard Test Conditions and should not be treated as a guarantee of consistent output. Factors such as panel placement, angle and environmental factors influence the PV yield the customer will actually see,” says Fox. For the more technically inclined reader Standard Test Conditions for a PV panel are 1000W/m3 Irradiance at a Cell Temperature of 25C at 1.5 Air Mass. These conditions won’t be met on a standard roof.
The property itself can also influence what system can be installed. Stage Zero’s technical assessment considers practical conditions such as roof construction, structure orientation and roofing materials before a recommendation is made.
Fox says customer expectations are equally important. Misconceptions can very often lead to an unsatisfied customer due to complexities surrounding Essential and Non-Essential loads within the home after installation.
“Part of our job is making sure the customer understands what can be connected to the system and where its limitations sit. That conversation is much better to have during the planning process than after installation, when the customer discovers the system does not behave as expected,” he says.
Stage Zero also cautions against assuming that a larger system automatically represents a better investment.
“Customers can just as easily be sold far more capacity than they need. I sometimes describe it as buying a Ferrari that never gets taken onto the track. You have paid for capability that your normal electricity use may never require,” says Fox.
Fox says right-sizing requires assessing how the household actually uses electricity and what the customer expects from the system. Too little capacity can leave the homeowner with a system that cannot support anticipated demand, while excessive capacity can mean paying for capability that is rarely used.
“Your electricity bill still gives us useful information, but the real design work sits behind that number. We need to understand how electricity is used in the home and what the customer expects from the system. That gives us the information needed to specify a solar and battery solution that fits the household,” concludes Fox.
