Solar Energy for architects
General aspects
The first requirement when optimising a photovoltaic system
integrated into a building is that it must receive a substantial input
of solar energy. The unit of measurement for this quantity is radiation,
and normally we measure the energy received in one place over a period,
which is usually a year.
Radiation varies throughout the year, increasing in the summer months
due to longer days. Radiation also allows for weather and cloud cover,
and this is why, for example, October has less radiation than March,
despite the fact that the length of the day is similar in both.
There are radiation maps for each geographical area, which indicate the
approximate radiation levels in each place in kWh/m².
The more radiation there is, the greater the yield obtained by the PV
module.
- Orientation. Inclination:
With the exception of urban planning and design, normally the
designer does not decide the building location, but can decide the
orientation of the façades and the inclination of the roofs.
The quantity of radiation received over a year is at its maximum when
the photovoltaic field is perfectly oriented towards the south (provided
that the location is in the northern hemisphere) and has an inclination
similar to the latitude of the location.
If it is not possible to establish the orientation and inclination of
the photovoltaic field perfectly to the south, this will lead to energy
loss. The figure below is used to calculate these losses with Madrid as
an example:
All photovoltaic fields must be completely free of shadows throughout
the entire day and the four seasons of the year. However, there are a
multitude of elements on a building that can create barriers or
obstacles to the photovoltaic field being integrated. Pre-design
strategies to prevent problems with shadows may be:
- Placing potential obstacles to the north (chimneys, ventilation
shunts, etc).
- Locating technical plants to the north (machine rooms, lift
cabins, tanks, etc.).
- Ensuring that stairways do not cast shadows.
- Removing trees or any other urban element of a certain height
from the façades as much as possible.
- Temperature and ventilation:
One aspect to take into account is that the efficiency of a photovoltaic
module drops as the temperature increases. The photovoltaic module therefore
needs to be ventilated; a moderate wind system is therefore useful for
maximum efficiency, especially in summer, which is when the photovoltaic
modules are at their hottest.
Other aspects to consider are the site topography and its winds.
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