There are many issues to consider when deciding whether your roof, wall or other location is suitable for a solar PV installation, and many tricks that we will use when designing your system to make the best possible use of the area available based on our range of over 150 different system combinations.

We can design your perfect system for you for free and with no obligation.  Simply use our 'request a quote' section to provide us with some basic information, and we aim to post or email you a detailed personalised system design, quote and performance estimate within 3-5 working days, without us needing to set foot in your house.

These are some of the issues that we take into account when designing your system, and assessing the long term performance of the various options.

System Size

The bigger the roof area, the bigger the system we can install, this 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:-

1. 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.
2. 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 upto 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.

Roof Orientation

The direction the roof faces affects how much sunlight it will receive through the year, and how much electricity any solar PV system will generate.

South facing roofs are best, but anywhere between South East and South West facing roofs will produce almost the same amount of electricity over the year.

East and West facing roofs will produce in the region of 15-20% less electricity per year than a South facing roof, but if a larger system can be fitted on your roof then economies of scale often compensate for this and the payback times can still be good. 

More Northerly facing roofs are generally not recommended for use, although if they're at a shallow enough slope then it may be possible to generate a reasonable return from them

Roof Slope

The perfect slope angle for the panels to generate the maximum amount of electricity is around 38^o for south facing roofs, but anywhere between 30-50^o will generate almost as much over the year.

Steeper angled roofs reduce the overall performance up to a vertical wall mounted system which would perform around 30% worse than a perfectly sloped south facing roof.

Shallower sloped roofs perform less well on South facing roofs, but on East and West facing roofs, can actually improve the system's performance.

Shading

Shading is perhaps the biggest problem for solar PV systems, and a poorly designed system can lose a huge amount of performance due to a relatively small amount of shading.

A basic solar PV system, run in series, will operate at roughly the same power output as the most shaded PV cell or string of PV cells in the entire array. Essentially this is because a shaded cell will act as  an electric radiator, absorbing excess electricity from the other panels and emitting it as heat, so not only will a poorly designed system lose a huge amount of performance from a small amount of shading, but it's also likely to reduce the life of the shaded panels.

To get around this problem all Leeds Solar's PV panels organise their PV cells into strings of cells, and have bypass diodes between the strings of cells that automatically bypass a shaded string of cells. When bypassed, a shaded cell will only take one string of cells out of production, and not affect the rest of the panel or arrays output.

The more strings of cells that are affected by shading, the greater the impact on the overall systems output. 

Some SMA inverters have a special function to allow them to cope much better in shaded situations, known as Optitrack Global Peak. This function is available on the 4000TL and 36000TL inverters as standard, and we can now add this function to the HF inverters and Sunny Tri-power inverters if required. This function needs to be specifically set up by the installer during the commisioning process.

Ventilation / Panel Temperature

The performance of all Solar PV panels drops the hotter the panel gets, with most panels (including our value and standard system panels) losing around 0.45% power output per degree C they rise above 25^oC. In peak sunlight the panels can reach temperatures of 50-60^oC or higher, resulting in a performance loss of 10-15%, or higher, if there's little wind to cool the panels.

Sanyo's HIT panels in our Ultra Efficient systems also have much better high temperature performance than most panels, as their performance only reduces by 0.3% per degree C, meaning their high temperature performance is roughly 33% better than standard panels.

The performance loss at higher operating temperatures in peak sunlight is the main reason that Leeds Solar's XL systems make sense, as a standard 4kWp will rarely actually produce an output of more than 3.3-3.4kW for longer than a few minutes, whereas a 4.5kWp system would naturally run at an output of around 3.7-3.8kW AC in peak sunlight levels. It will also obviously produce around 12% more energy all day, every day when the sunlight levels are lower.

The need for ventilation to reduce the panel operating temperatures is the reason that solar PV panels are almost always mounted on rails above the roof surface, instead of being integrated into the roof as solar water heating systems often are.