As a rule of thumb, with the decline in Feed-in Tariffs and the advent of battery storage, a grid-connected commercial solar system is best sized with an annual output (kWh) approximately equal to the annual load of the business / property.
So if your load is 36,000kWh a year, and a kWp outputs 900kWh a year, size the system at 40 kWp.
What if your roof is too small to achieve this with standard panels? Which panel do you turn to?
Our answer is SunPower or BenQ high efficiency panels. SunPower solar panels also happen to be the best panels on the market; BenQ panels are our favourite 'second best'. In fact we have just completed an install in London using 100 BenQ 335W panels where space was limited (see picture).
Both SunPower and BenQ's 327W panels have an efficiency of 20.4%, thus allowing the installation of a 30% bigger system and generating 30% more power than a standard 15-16% efficiency panel would with the same roof space.
Further, SunPower claims that their panels will generate an extra 20% over the life of a system compared to the same sized standard panel system through reduced panel degradation, better performance at high temperatures, better performance at low light, high quality anti-reflective glass. SunPower warrants that their panels will still offer 92% of their original output after 25 years, compared to BenQ's 87% and the industry standard of 80%:
SunPower offers the very best overall warranty - superior output warranty (as above), 25 year workmanship and product warranty, with any defective panel removed and replaced at their cost. Now that's confidence. BenQ offers a 25 year warranty, but won't cover the removal and re-installation costs.
Finally, while BenQ only offers blue panels as above, SunPower offers panels as above but also offers a sleek black panel which looks great where looks matter:
Of course nothing is free in this world.
SunPower panels typically add £350-£400 per kWp to the cost of the installation using standard panels - around a 20% to 25% uplift on a typical installation cost. BenQ adds around £200, or 12%.
But if space is at a premium, 12% to 25% is generally worth the extra, particularly given the superior warranties, and with SunPower, the additional 20% extra power generation expected in comparison with a standard system of the same rated size.
We have a page on our website dedicated to SunPower and BenQ panels. You can read all about these high performance solar panels and download the latest specifications and warranty details.