Tier 1 panels, matched to your roof and your inverter.

"Tier 1" sounds like a quality grade. It isn't. It comes from BloombergNEF, a research firm that tracks which panel makers have had panels used on projects banks agreed to finance without extra security. A maker makes that list because banks trust it, not because a lab tested and ranked its panels. BloombergNEF says so itself: the list is not a recommendation, and should not be used as a measure of quality.

ZenSolar fits tier 1 panels only, from six makers: Canadian Solar, JA Solar, LONGi, Jinko, Trina and Aiko.

Did you know? Cheap panels lose 15% of output in 5 years, against under 5% for tier 1.

Almost every panel on a roof today is monocrystalline. PERC, TOPCon and back contact are different ways of building a monocrystalline cell, each a step toward less power lost to heat and higher efficiency. Polycrystalline, once the cheaper option, is old technology now, and ZenSolar does not fit it.

A monofacial panel only makes power from its front face. A bifacial panel has glass on both sides, so its rear side can pick up light too, usually reflected off whatever surface sits underneath it.

How much extra a bifacial panel gives back depends entirely on what's underneath it, never a fixed number. Jinko's own datasheet says its bifacial panel's power "increases 5 to 25% generally." Trina's own datasheet states its bifacial gain at "10 to 20%, depending on albedo" (albedo just means how much light a surface reflects). Both makers tie the figure to the ground below, not a promise for every roof.

Every panel loses some power as it heats up. This is called its temperature coefficient, stated on every maker's datasheet as a percentage of power lost per degree Celsius above 25°C, the temperature panels are tested at in the lab.

A typical tier 1 panel's temperature coefficient sits around -0.26% to -0.35% per degree C. Take a mid-range figure of -0.35% per degree C. On a hot Highveld or Free State roof, a panel's cells commonly run around 40 degrees C hotter than that 25°C lab figure. That's cell temperature, not the air temperature on a weather app, the actual heat of the cell itself, sitting close to a dark roof in full sun. Do the maths: 0.35 x 40 = 14. That panel is making about 14% less power than its rating suggests, purely from heat.

This is why temperature coefficient matters more in Gauteng and the Free State than the headline efficiency number does. A slightly less efficient panel with a better (lower) temperature coefficient can out-produce a higher-rated panel once both are baking on a real roof in January.

Example only, your numbers will differ. Here's the maths: take your home or business's average daily electricity use in kWh, divide it by your city's daily solar yield (PVOUT), and that gives you the system size, in kWp, you'd need.

Say a site uses 30 kWh a day. Using a 550 W class panel (Canadian Solar's HiKu6, 2278 x 1134 mm, about 2.58 m² per panel, weighing 27.6 kg), here's how that plays out in five cities.

These are yearly averages. Winter changes the picture in some cities: Cape Town's June yield drops to about 3.0 kWh per kWp a day, while Johannesburg's clear winter skies hold at about 5.0. ZenSolar's design checks the worst month for your city, not only the average.

Weight adds up too: about 10.7 kg per m² for the panels alone (27.6 kg over 2.58 m²), plus roughly 4 kg per m² more for mounting rails and clamps. That's exactly why every ZenSolar job gets a structural engineer's sign-off before installation, not a rule of thumb.

Real job: EFJS Printing needed 14.85 kWp: 27 panels of 550 W each, paired with a 30 kW FoxESS inverter and a 12 kWh battery. It paid for itself in about 2.5 years. "ZenSolar was excellent in all that they did. The installation at my Printing Shop and home was done to the highest standard." Bernard Synman, Director, EFJS Printing.

Example only, your numbers will differ. Say you're running a 5 kWh battery and want it refilled by the panels alone within about 4 hours of good sun. That's 5 kWh divided by 4 hours, or about 1.25 kW of panels feeding it, roughly three 550 W panels. Add in whatever else the property is using at the same time, and the real number moves. See Solar Power Backup for how ZenSolar sizes a battery from your real loads.

Panels are wired together in a string, and a string's total voltage has to sit inside the inverter's MPPT window, the voltage range it can track and use. Get it wrong and the inverter either can't use the string properly or won't accept it at all. This is a design job, done in house by ZenSolar.

One thing catches people out: a panel's voltage rises when it's cold. A string sized only for a hot afternoon can push closer to an inverter's maximum voltage limit on a cold winter morning, before the sun has warmed the panels up. ZenSolar's design accounts for that swing, not just a panel's rated voltage on a datasheet.

See Solar Power Inverters for the full sizing method and the South African rules that apply to every grid-connected system.