Passive solar energy is still a big unknown for the population. We tell you everything you need to know about this type of energy and the differences that exist with active energy.
Average household energy consumption has increased by 28% after confinement in March 2020. We spend more time at home and energy consumption has shot up in many homes where teleworking has been introduced to stay. Today, we have the possibility of opting for renewable energies, which help us to move towards a more ecological energy transition such as solar energy or other sources of non-polluting origin, helping us to achieve energy and economic savings in our electricity bills.
When we refer to solar energy, we must consider the existence of two operating models; passive and active energy. Normally, we are not able to differentiate between these two terms and the fact is that passive solar energy is still a big unknown, and the benefits it can bring to household electricity consumption are not known.
What is passive solar energy?
Passive solar energy uses direct energy from the sun without transforming it. Therefore, they do not require any electrical device to carry out the transformation from one current to another and, if necessary, to accumulate energy, as is the case with active energy.
How does this type of energy work?
The elements that make up the construction of passive buildings, i.e. the walls and windows, are created in such a way that they make direct use of sunlight. This type of building is designed to fulfill two functions. One is to capture, store and distribute the sun’s energy in heat during the winter season. The other function is to reject the heat coming from the sun in summer. In this way, it is possible to optimize all the heat in the house.
If we want to make the most of the opportunities offered by passive solar energy, we must take into account factors such as the climate of the region because the temperature and solar radiation will be very influential in producing this type of energy. And not only can it be applied to new buildings, it can also be adapted to existing constructions, although the cost will be higher.
Basic considerations of passive solar design
Before carrying out any construction where a passive solar design is developed, it is necessary to know a series of basic considerations that will help us to understand the operation in a more exhaustive way. Below, we list and explain those components involved:
- Location of windows and type of glazing
- Thermal insulation
- Thermal mass
- Shadows
Location of windows and type of glazing
The location of the windows in a house that uses passive solar energy is a very important aspect, so is the orientation and inclination of solar panels where this factor plays an important role.
How is energy generated through windows? The sunlight enters through the windows thanks to the glass that allows the capture of solar radiation, keeping the interior of the house warm. However, we must also take into account the dimensions of the windows, installing the right size and orienting them towards the south in order to achieve equal heat gains and losses without overheating, as they can obtain unwanted heat in summer and generate significant heat losses in winter. It is important to consider that during the most winter seasons less heat is generated, approximately 5 hours. This balance of gains and losses can be sustained provided that the windows are correctly oriented and the perfect glazing has been chosen for maintenance.
Normally, the windows should face south at an angle of approximately 30°. If we locate the large windows to the south, we will obtain more solar energy for the interior of the house. However, houses facing north should have smaller windows since they are not capable of absorbing the same amount of solar energy as windows facing south.
Thermal insulation
Thermal insulation is an essential factor in passive solar design buildings. It intervenes as an obstacle to the flow of heat, that is, it keeps the house warm by reducing heat loss in winter and decreasing heat in summer so that our home remains cool and comfortable, thus withstanding the high temperatures reached in this season of the year. This insulation must be carried out in all the components of the construction, both in windows and walls and even ceilings.
If we select a bad thermal insulation, the heat loss in the home could reach 25%-30% in winter, thus wasting the energy we have generated.
Therefore, the better the insulation, the warmer our home will be. In more extreme climates, superior insulation should be carried out in good conditions to avoid unnecessary heat leaks.
In order to avoid this heat loss, it is advisable that most of the insulation is concentrated on the roof because this is the space where the greatest temperature control is required.
Thermal mass
Thermal mass refers to the heat that is absorbed through walls, ceilings or floors built with elements that have the capacity to absorb solar energy in large proportions, such as tiles, so that the energy is stored to be used for domestic purposes. On the other hand, to make the house cooler in summer, this heat gain is reduced through installed projections or by making use of the blinds.
A good external ventilation installed in the roofs of the house will also allow the heat to dissipate through the interior, without concentrating on a specific area since the roof surface, being the most exposed to the sun, receives more solar radiation than the rest of the construction elements.
To absorb a greater amount of energy we can use materials such as brick, concrete or stone in the construction, which will allow a higher efficiency than other types of components. On the other hand, if we build with materials that are not very robust or light, such as wood, the thermal mass will be reduced and the amount of energy generated will also be reduced.
Shadows
The shadow factor is also a component that greatly influences passive solar energy. The shadows generated by the vegetation in the geographical area affect the solar radiation received, diminishing the sunlight perceived in summer and being beneficial for the home. On the other hand, when we get closer to the most winter seasons, the shadows will cause a positive effect so that overheating does not occur.
The orientation of the house is a very important point to take into account so that the shadows that affect the building work correctly to perceive the correct passive solar energy and do not originate excesses that diminish the efficiency. Window glazing should be oriented to the south to avoid loads and overheating in the winter.
Sun loss can be significant if windows are continuously shaded without the possibility of recovering that energy. How can we avoid this problem? We only need to maintain a distance between the cornice and the top of the glazing of 50% or, if possible, 30% from the height of the window.