Off-Grid Power Systems - Site Survey Checklist
In 17 years of supplying off-grid solar & wind power systems,
the single, most common issue we see for both solar & wind
technologies is the incorrect choice of site.
The siting of a solar pv array is simpler than that of a wind
turbine, and generally causes less planning issues. We've compiled
the following check-list of the main points to be considered when
selecting a site.
Siting Considerations - Off-Grid Solar PV
& Solar Irradiation - The closer to the equator,
the more sun we get. Ironically, the hotter the solar panel,
the less efficient it performs and so peak outputs are often
seen on a cold, clear sunny day. When designing an off-grid
system, the irradiation for the least sunny month of the year
is used, as this will be the worst case scenario. Solar
irradiation data for your location can be found here : Europe
/ Shading - A complete 'no-no' with solar pv. Beware
of long mid-winter shadows from tall trees or buildings.
Shading has a massive detrimental effect on the output from a
solar pv module and needs to be avoided wherever possible.
of Tilt - Off-grid solar pv tilt angles are normally
optimised for the worst sunlight months of the year. Generally
speaking, the lower the sun is on the horizon in mid-winter,
the steeper the optimum angle of tilt of the solar panels.
- A rough rule of thumb for sites in the northern hemisphere
(to optimise tilt angle for the winter) is to add approx 15
degrees to the latitude. For example, London is 51º and in the
winter add 15º. Thus, optimum winter tilt angle = 66º tilt
from the horizontal.
- Ideal orientation in the northern hemisphere is due south,
and due north in the southern hemisphere.
Mounting Structure - The type of solar pv mounting
structure will depend on the site and the optimum angle of
tilt. Common solutions include ; tilted roof mounting, flat
roof mounting, ground-mounting and post mounting.
- Many larger off-grid solar pv systems are ground-mounted and
smaller pv arrays are post-mounted, as these both allow ideal
orientation and provide a steeper angle of tilt than most
- Tracking mounts are also available, although it's often far
cheaper & more reliable simply to increase the size of the
pv array rather than introduce moving parts to the system.
Run Distances - The pv array ideally wants to be
sited within about 50m of the battery bank, although this all
depends on the site and the pv array voltage. Systems can be
designed to allow up to 200 to 300m of cable run, although
long cable runs can be expensive.
- If snow is to be expected regularly, a steeper tilt angle
may be selected for the pv modules. Due to the dark surface of
the solar module and the fact it's facing south on a tilt,
when the sun shines the snow thaws and slides off fairly
- In hot and sandy locations, dust may be a challenge and may
need to be manually cleaned in the case of a sand-storm or
dust-storm. Again, steeper tilt angles can help to reduce dust
- In rainy locations, most solar pv modules will do a
reasonable job of self-cleaning. However for some locations it
will be necessary to arrange occasional cleaning of the pv
glass. At the very least, we would recommend manual cleaning
once per year, and ideal timing would be at the end of the
summer, early winter.
Permission - Generally speaking, in the UK, if the
building is not in an SSSI or conservation area, and the solar
pv panels are mounted flush to the roof, planning is not
required. If you need any further information, contact your
local council's planning department. Please also see the link
Siting Considerations - Small Wind Generators / Turbines
Wind Speeds - Sites with high average wind speeds
are important for a wind turbine to work effectively.
Generally speaking you would be looking for 5m/s or more
to indicate a good wind resource.
- Turbulence -
Turbulence is the enemy of a wind turbine blade. Just like
an aeroplane 'falls' out of the sky when it hits
turbulence, the blade of a wind turbine looses lift and
produces much less power.
- Obstacles -
Obstacles cause turbulence (now public enemy #1). A good
distance is required away from buildings or trees. See
- Hills - If the
turbine can be sited on the top of a smooth hill, the wind
speeds will often be increased.
- Mast Height -
The higher the turbine, the better the wind speeds and the
less turbulence will affect the blades.
Run Distances - One of the issues with siting the
turbine in the ideal wind spot is that cable runs can work
out expensive. If the cable run needs to be a long one, it
helps if the wind turbine puts out high voltages, brought
down to the correct voltages by a control unit.
- Ice - Most small-scale
wind turbines can cope with ice, although in extremes may
stop the turbine from working until it thaws.
- Maintenance -
Annual inspections must be planned in for a wind turbine.
Every year the rotor of a wind turbine will do a massive
number of revolutions and so it's important to ensure that
everything is in tip-top shape and there has been no
unusual wear or anything has come loose.
& Planning Permission - One of the ways to
upset the neighbours is to put a wind turbine up directly
in their view. There are rules and regulations for
off-grid wind turbine installations that UK councils
publish, an example of which can be found below (link
opens in new window).
LINK TO UK COUNCIL
PLANNING DOCUMENT - SMALL WIND TURBINES