The bigger the roof area, the bigger the system we can install, that much is obvious, but what might not be so obvious is that bigger systems are proportionally cheaper to install than smaller systems. Or in other words, they cost less per watt, and therefore pay for themselves faster and generate higher overall financial benefits. So although the initial total cost is higher, if you can fit a bigger system on the roof and can afford it, then it is definitely worth installing the biggest system.
Other than the physical size and dimensions of the roof space, there are 2 other main factors that determine the maximum size of system it's sensible to install on your roof:-
- The Feed In Tariff boundaries, which mean that it's not usually worth installing a system that's only slightly over a boundary. For domestic purposes, unless you've got a huge roof, it's usually not worth considering a system over the 4 kW Feed In Tariff boundary.
- The 16 amp per phase G83/1 connection limit, means that it's not usually recommended to install a system that will output more than 3680W AC to the grid (16amps at 230V AC), unless you have a 3 phase grid connection which is unusual in a domestic situation. It actually can be possible to go above this limit, but requires advance permission from YEDL, which takes a minimum of 45 working days to obtain, and is increasingly unlikely to be granted.
Where space is limited our Ultra Efficient systems using Sanyo HIT panels with industry leading module efficiency of up to 19% allow us to fit around 20% more generation capacity into the same roof area, so a 4kWp Ultra Efficient array will often fit into the same roof area as a 3.2kWp Value array.
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