The sun is everywhere and the building’s skin is exposed to it. And this is where Solar energy can be converted into useful energy.
The sun can be used to produce electricity or heat. In general, there are 3 few types of devices that are suitable for buildings to actively produce energy. Photo voltaic, or PV-cells and modules can be applied to make electricity
Solar collectors or solar thermal modules produce heat, transferred to a liquid. And PV-thermal or PVT modules produce electricity and heat at the same time. Yet, solar collectors produce higher temperatures than the PVT modules.
The application of solar energy products on buildings is often done by simply mounting solar modules or collectors on roofs. But well-integrated solutions contribute both to the sustainability as to the attractive appearance of buildings.
as we will see. The efficiency of solar cells has doubled last decennium and the production costs have dropped rapidly. Therefor pay-back times have dropped by a factor of 10 in the last 10 years.
And since the solar industry has grown rapidly into a maternal industry, very affordable PV-modules and many different solar products are on the market of which many can attractively be integrated in buildings. We see here 2 examples: different types of fully integrated Photo voltaic roof tiles and coloured PV modules, integrated in the façade. Solar systems can not only be integrated in buildings in roofs, and facades, but also in sun shade systems, in balconies and in windows. There are 3 main types of PV-cells and modules that are used in the building industry to produce solar electricity, all have their specific advantages.
Multi-crystalline: These are typically blue and you can recognize the crystals and the silver electricity conductors on top of the cells. But also other colours are available. They have good performances, around 17%, for a relative low price. For smooth integration in buildings this typical appearance may be a draw-back.
Mono-crystalline: These are typically black and the cells have a uniform appearance. The modules have a high efficiency, around 20% and are also slightly more expensive. In full black modules, they can easily be integrated in buildings in an attractive way.
Thin film: these modules exist of large homogeneous cells that are often black and flexible. They are much cheaper but also their efficiency is lower, around 12%. But with their homogeneous appearance they may be the best option for optimal integration in buildings.
Multi-crystaline
Mono-crystaline
Thin-film
PV-systems consist of an array of PV- modules; they convert solar radiation into low-voltage direct-current-electricity that is transformed in an inverter into Alternating Current, as we use it in our homes, often on 110 or 220 volts. We can now use our solar electricity or put the excess production on the electricity grid. Today, PV systems have typical efficiencies of 12 to 20%. But they don’t produce everywhere the same amount of electricity.
The amount of solar radiation differs for each location in the world, closer to the equator there is more solar radiation. The orientation of the modules also influences the amount of solar radiation. The highest annual production of solar energy can be reached when solar products are maximally oriented towards the sun. This is often on pitched roofs facing the equator, so south facing in the northern hemisphere and north facing in the southern hemisphere. Or on tilted solar modules on flat roofs. The further from the equator, the larger the tilt should be for a maximized production. In mid Europe, the optimal orientation is somewhere around 40 degrees facing south.
But we can easily deviate from the optimum to still have good yields, also if the modules are more East or West facing, as we can see in this last diagram.
We can make a quick estimation now, of how much 1 PV module on a 45 degrees pitched South East facing roof would annually produce in Amsterdam. We see on the solar radiation map that Amsterdam gets 3600 Megajoule of solar radiation per horizontal square meter in 1 year, which equals a 1000kWh. We assume a system efficiency of 20% and 5% less production for South East facing compared to South facing. But we have a 100% optimal inclination and orientation compared to 90% horizontally. In total this 1,6 square meter module will produce 338 kWh of electricity in 1 year.
Solar thermal collectors applied on buildings are generally flat plate collectors or evacuated tube collectors. The last one is able to produce higher temperatures, even above 100 degrees Celsius would be possible. Efficiencies very much depend on the desired temperatures; the higher the temperature, the lower the efficiency. Solar collectors for domestic use have system efficiencies of around 25-35%. The heat must be used locally and has to be stored; as we can see on the below picture, for example, on top of the collector. They are often used to provide domestic hot water for which there is a demand all year round
Flat plate collector
Evacuated tube collector
Heat from solar collectors can also be used for space heating. In this scheme, the solar heat is used as a source for a heat pump system. In colder days, the heat pump increases the heat to provide heat for the floor heating system. And for domestic hot water.But since most heat will be produced in summer, when the demand for heating is the lowest, a seasonal storage system could increase the use of solar heat. For example, by storing it in in the underground, in a Borehole thermal energy system in this case. If you want to learn more about borehole thermal energy system please follow link below:
Finally, we opt PV-Thermal modules, they are winners in efficiency, they produce electricity with around 20% efficiency, and low temperature heat with up to 50% efficiency.
Maximized roof production
Coloured PV facade
Evacuated tube collectors in the facade
