Doing your own shade check, from the ground

1. Find the bottom of the panels

Every measurement is taken from the point where the lowest row of panels would sit, usually a little above the gutter. That is the point that sees obstacles at their highest. Estimate its height above the ground: on a two-storey house the gutter is often around 5 m up, but measure yours by counting brick courses from the ground to the gutter (each about 75 mm).

2. Direction

Stand in the garden or street in line with the roof and point your phone's compass at each obstacle. Note the direction as one of the 16 compass points the checker uses (S, SSW, SW and so on). A map is a useful check: online maps show which way a street runs, and therefore which way the house faces.

3. Distance

Measure horizontally, from the wall below the panels to the obstacle: across the garden with a tape, or across the street on a map's measuring tool. For a neighbour's chimney on the same terrace, the distance is along the roofline, roughly the width of the houses in between plus half a stack.

4. How much higher the top is

This is the obstacle's height minus the height of the bottom of the panels. Two ways to get it:

• Brick courses. For a chimney or wall, count courses from a known level, such as the gutter, to the top, and multiply by 75 mm.
• Angle and distance. From a point level with the bottom of the panels (an upstairs window, roughly), sight the top with a phone angle app. The rise is the distance multiplied by the tangent of the angle.

Rise = distance × tan(angle).

5. Width

For a stack, measure across it at the top; most are around 0.6 to 1.5 m. For a house or a row, use the width of the part that stands to the south of your panels. For a tree, use the width of the crown.

6. Run each one

Put each obstacle into the shade checker separately and note the share of direct sun it takes. Obstacles in different directions add up roughly; obstacles in the same direction overlap, so count only the bigger one. Anything taking more than a few per cent is worth raising with an installer.

Recording what you find

Write each obstacle down as you go: what it is, its direction from the bottom of the panels, its distance, how much higher than that point its top is, and its width. A photograph taken from an upstairs window at around midday, and another in the late afternoon, helps you and the installer see the same thing. Take the list and the checker's results to the survey and ask the installer to show how the shade factor on the quote compares.

Safety

Do all of this from the ground, the garden, an upstairs window or the loft. Do not climb onto a roof or lean a ladder on a gutter to measure a stack; an installer will check the roof properly at the survey.

Related pages

• Shade checker
• Chimneys
• Trees and hedges
• All guides

References

1. NOAA Global Monitoring Laboratory: general solar position calculations
2. MCS MIS 3002 version 6.0: the solar PV installation standard
3. GOV.UK: high hedges, complaining to the council