Environmental Engineering Reference
needed. Many roofs have enough space for large photovoltaic systems that are
capable of supplying more electricity than required and can, therefore, be optimal
in protecting the climate. But even small systems can make a contribution.
From Thinking about Having a PV System on the Roof to
Getting a Quote
Determine orientation and tilt angle of roof.
Is the roof suitable from the point of view of orientation and tilt angle?
Recommendation: min. 100% according to Figure 5.16.
Establish shading conditions on the roof.
Does my roof have little shade?
Recommendation: Take shaded areas into account during planning; also pay
attention to chimneys, aerials and lightning conductors.
Identify available roof area with little shade.
Calculate installable MPP power for the photovoltaic system.
Recommendation: Effi ciency min. 12% in formula above.
Calculate possible annual electric energy yield.
Use formula above or online tools.
5.4.2 Planned Islands
The design of photovoltaic island systems is fundamentally different from grid-
connected systems. Island systems cannot rely on the public electricity grid if there
is no sun. Instead these systems use suffi ciently large batteries to avoid any power
failures. However, in principle a battery is only used to bridge the days that are
less than optimal. Therefore, photovoltaic modules also have to deliver as high a
yield as possible during the months with the least sunshine. The recommendation
for reliable operation in winter is to place photovoltaic modules at a steeper angle
than is necessary with grid-connected systems, which are angled optimally for
operation all year round. In Europe and North America a tilt of around 60° to 70°
towards the south provides optimal solar yield in the month of December. The closer
one gets to the equator, the less marked are the differences between summer and
winter. In these parts of the world a fl atter installation is also suffi cient for winter
The objective of island systems is not to achieve as high an output yield as possible
but to provide reliable electricity supply to certain consumers. Consequently, the
main criterion for the design of such a system is the estimated consumption level
for the worst month of the year. In Europe and North America this is December.
Furthermore, solar systems are equipped with a certain safety margin. In a normal
case this should amount to an extra 50%. As with grid-coupled systems, the perform-
ance ratio PR takes into account the losses.