Mounting a PV array

Decide where to locate the panels
 
The sun tracks from east to west during the course of the day, although is lower in the sky during the winter months by about 15 degrees.  At dawn and sunset, the angle of sun is at it’s lowest point. The energy from the sun is reduced as the solar radiation has to pass through a greater depth of atmosphere and a fixed panel will present a smaller surface area to the sun, when it is not perpendicular to it. A general rule of thumb is to angle the panel at the angle of latitude, which is 53 degrees here in the u.k., however in practice the angle of the panel is generally determined by the roof slope. The slope chosen should be the most south facing one. Tracking systems are available but not commercially viable for domestic systems.
 
To determine which face is going to be the best, you will need to study a roof plan of the property. You will want to locate the panels in a position that avoids any obstacles that will cast shade onto the panels during the course of the day.
 
So far so good, you know how many panels you need and where to place them. Next you will need to mount them on the roof. In determining whether to do it yourself, or call in the professionals, consider whether you are able to carry out the work safly. There are dangers working on a roof, particularly a steeply sloping one. Falls can be fatal. In addition, you will be working with high voltages, and if you don't have the time to invest in learning how to do it propertly, then call in a professional. In addition, grants are currently available in the u.k. of up to £2500 from the Low Carbon Buildings program. as the current system only permits registered installers to be used in order for the grant to be elligable, savings on doing the work yourself are that much less. At the same time, there is nothing so satisfying as doing a job yourself, and for some, it will be the only way to go. Even where you are planning to have the system professionally installed, understanding the technology and the equipement, with allow you to make better decisions regarding the installation, and ask the right questions of potential contractors.
  
You need to go up to the roof and survey it, noting the position of any obstructions. Then make a plan of the layout and figure the best way to position the panels across the roof. If as in most houses the support structures (rafters) are vertical, the rails will usually be placed horizontally to spread the load and for ease of mounting.
 
Safe access to the roof can only be afforded by a scaffold tower. There are a number of system scaffolds available, such as Quickstage or Cuplok, that are generally recommended over conventional scaffold for the do-it-yourself user.  However, traditional scaffolding is more flexible, and can be adapted to any configuration.
 
The PV panels will need to be securely fixed to the roof, not least to prevent wind uplift ripping it off under storm conditions. To acheive this, you will need to screw the support rail through to the rafters. and be able to locate the rafters accurately. You could try a stud finder, or look along the eaves facia for the nails that fix the facia to the end of the rafters. Draw a calk line on the roof, with the aid of a plum bob and metal rule, to position the line of the studs up the roof. It might also be useful to go into the loft space, and measure offset distances from a chimney breast or party wall, if this is visible above the roof line.
 
Mounting your solar panel
 
The first thing to remember is that a panel should be mounted at least 3 to 4 inches above the roof it is attached to, to allow air to freely circulate behind it and prevent overheating of the panel. The air gap also allow for water runoff and avoids the possiblity of ice plugs forming behind it. Panels can be fixed to corner mounting brackets or rails, typically proprietary products specifically designed for mounting PV panels, such as those by Unirac, Rails are the best option, if it is intended to mount multiple PV panels. However, propriatory systems can be expensive, so you may wish to make up your own rack system from aluminium or stainless steel U or box sections, Unistrut, amount others, sell rail sections that might be adapted for the purpose.  Depending on the rail bracket you have selcted, you may need to remove a few tiles first and install a proprietary flashing after bolting the fixing to the rafter, others systems may use a proprietary clip that loops under a replacment tile. Removing a single tile may be easier than removing a slate, as slates will generally all be nailed down, you may however be able to use a ripper to pull out the nail. An easier method, particularly with a slate roof, may be to drill through the slate and screw a 8mm roof fixing bolt down into the rafters. Installing a noggin between rafters can help with positioning, particularly with profiled tiles like clay pantiles. With all fixings avoid dissimilar metals, or use non conducting washer to avoid galvanic corrosion.
 
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Wiring a PV array