This article was written together with Eng. Giovanni Ziletti (1) for the April 2009 number of the magazine “Frames”
Photovoltaic modules are increasingly common components in the design of buildings, and a new and in some ways revolutionary function has been attributed to them. Buildings no longer simply consume energy but are also able to produce it to cover their own needs, sending any excess to the public grid.
Photovoltaic technology for the production of electricity has now reached a good level of maturity and is applicable with excellent results throughout the country, with the possibility of generating electricity on a widespread scale (in technical jargon this is called “distributed production”) and with an effective contribution to sustainability.
The number of photovoltaic systems installed in Italy is increasing rapidly: 10 MWp in 2006, 50 MWp in 2007, 200 MWp in 2008 and 40 MWp in January 2009 alone, for a total of 300 MWp[2].

Since 1 kWp (peak kiloWatt) of power corresponds indicatively to a surface area of photovoltaic modules of 8 m2, the systems currently installed and working in Italy amount to an overall surface area of about 2,400,000 m2 of photovoltaic modules (240 hectares).
One of the reasons for this sharp increase is the introduction in July 2005 of the system of incentives based on a feed-in tariff and known as “Energy account”.
It was brought in later than in other countries, so that there were strong expectations on the part of users aware of the energy problem. Until that time the lack of an adequate regulatory frame work for enabling the generation of electricity by small decentralised systems and the absence of an effective mechanism of incentives meant that installing photovoltaic systems was not convenient.

The “Energy Accont” system, perfected in February 2007, was inspired by a model that had been successfully tested in other European countries already in the early nineteen-nineties.
According to this system, for a period of twenty years the owner of the system is granted a special rate for each unit of electricity generated, in addition to the possibility of either using the energy produced by his system directly (“on-site exchange” option, more convenient for systems installed on buildings) or selling the excess energy produced (”dedicated withdrawal” option).
This method has proved a winner in all those countries in which it has been implemented, with a gradual reduction of the costs of the systems, improvement of the generation efficiency and a longer life cycle of the systems.
It is important to note that the burden of the incentives paid to the owners of the systems is not charged to the state. The amounts concerned are set aside at central level thanks to a slight increase in the cost of the electricity consumed by all users.

Only three years after introduction of the new incentive system, the over 26,000 systems installed and working as of January 2009[3] are a guarantee of the practicality of this technology as well as bearing witness to the effective synergy with both new and existing buildings. It is also important to stress that the system for issuing permits and for paying the incentives is now sufficiently tried and tested, and other simpler procedures are being considered.
In view of the importance of the results achieved, many observers and operators who previously considered photovoltaic technology a niche issue capable of adding an “ecological” touch to the image of buildings but not really a useful tool for sustainable energy production, have now changed their minds and have more positive opinions.

On the basis of the data released by “Terna”[4] (the main owner of the national high-voltage transmission network) the total electricity requirements in Italy in 2007 amounted to 339,928 GWh (gigaWatt/hour or millions of kilowatt/hours), of which about 14% produced by renewable energy sources (hydroelectric, wind, geothermal and photovoltaic), but with photovoltaic accounting for a mere 0.01% of the total.
If, for simplicity’s sake, we assumed that the demand for electricity were to remain unchanged until 2020 and that the installation of photovoltaic systems continues at the rate recorded in recent months (equal to about 500 MWp/year[5]), by 2020 Italy would have an installed output of 6,250 MWp and the energy produced by photovoltaic systems would cover over 2 % of the total need for electricity.
If, on the other hand, the new output installed each year were double the current rate (a plausible hypothesis considering recent growth rates), by 2020 the electricity produced by photovoltaic systems would amount to over 4% of the total.

These would be highly respectable results, especially if we think that they could be achieved in just under a decade and that the means necessary for achieving this goal – that is to say designers, specialised installers, providers of credit and the regulatory system - are already effectively in place. It is important to note, however, that in Italy there is a lack of an industry capable of producing the materials and systems for photovoltaic plants to meet the domestic demand.

It was necessary to use the conditional in formulating the above hypotheses, since for several years to come the economic feasibility of these systems will continue to depend on the existence of a system of incentives such as the “Energy Account”, even though according to the EPIA (European Photovoltaic Industry Association), in the sunniest parts of Italy the cost per kWh of “home-made” photovoltaic electricity could equal that purchased on the electricity market already in 2010, thanks partly to the high cost of electricity in this country[6].
Until then, it is essential for the Energy Account to be maintained, perhaps gradually lowering the incentive applied in the form of a special rate, as called for in the decree dated 19/02/2007.

Scenarios of this type would seem to support even radical theories such as that expressed by Professor Jeremy Rifkin, Chairman of the Foundation of Economic Trends[7)]and advisor to many European heads of state as well as to the European Commission itself on matters of energy and sustainable development.
To sum up their concepts, Rifkin and others maintain that in the 21st century the world will experience its third industrial revolution, with a progressive replacement of fossil fuels by a system for the production of energy from clean and renewable sources made up of a multitude of small and medium sized plants distributed on a widespread scale and interconnected with one another by means of an intelligent network capable of programming consumption on the basis of the forecasts for production of systems powered by renewable sources. Again according to Rifkin, conversion of the energy system would also require a review of the transport system and the attribution of a new and essential function to buildings, which should no longer simply be consumers of energy but also capable of producing and exchanging energy.
This perspective outlines a new possible field of action for designers, who could become leading players in this process of transformation, devising solutions calling for and promoting the inclusion of renewable energy systems in buildings, starting with solar and photovoltaic systems.

Designing of a photovoltaic system normally starts with the choice of the correct size.
The utilities present in the building are analysed, the minimum and maximum limits for adopting renewable energy sources according to the regulations are checked and the specific requests of the principals are interpreted.
Lastly, the necessary output power of the system is converted into square metres of photovoltaic surface area. The building designer will have the sometimes far from easy and sometimes stimulating task of identifying a convenient position in terms of productivity of the system, but which must be compatible with the architectural characteristics of the building. For this reason it is advisable and often important to take the “photovoltaic need” into account starting from the earliest design studies.
This type of approach, which is in any case positive in that it ensures the availability of a suitable place for installing the photovoltaic system, does however have the limit of being conditioned by a contingent assessment of how large a photovoltaic system should be installed. This limits the possibility of subsequent up-grading of the system.
The aim of this paper is to propose the possibility of a different methodological approach to sizing of the photovoltaic system, consistent with the scenarios described earlier.
This means including the possibility of installing the greatest possible photovoltaic power among the requisites of the building project, developing an “advanced compatibility” with the architectural project, regardless of the need for electricity for the activity carried on in the building.
The actual size of the system to be installed initially will only be defined at the time of erecting the building, but in any case the system will be equipped with all the provisions needed for installing simply and inexpensively new modules in future and above all in a manner already foreseen from the architectural point of view. With this in mind it is undoubtedly useful to include among the documents of the building project drawings dedicated specifically to the photovoltaic system, in which a plan of the roof, the south-facing façade and possibly other sections are shown, with the areas intended for installing the photovoltaic modules.
This drawing should be prepared in the preliminary phase, in which it is possible to make significant changes to the building, maximising the surfaces suitable for installing the photovoltaic modules.
The various designers involved will thus be able to develop the parts of the project for which they are responsible, taking the presence of the current and future photovoltaic modules into account from the very start.

Several simple indications of a very general nature that could be helpful for the design work are provided below:

- In Italy the optimum direction and inclination for photovoltaic modules are south and 30° respectively;

- Exposure between 45° more or less from south and inclinations of between 5 and 60° can be considered acceptable;

- An inclination of less than 5° would lead to the accumulation of dust on the modules, with a negative effect on the energy yield;

- Large inclined surfaces facing in a suitable direction are the ideal supporting surfaces on which to install photovoltaic systems; the modules can be installed on the same plane as the surface, making the anchoring structures less sensitive to the action of the wind and enabling the whole available surface to be exploited;

- The photovoltaic modules must be installed in such a way as to avoid as much as possible that they will be even partly in the shade during the day, otherwise the energy yield of the whole module will be cancelled out at such times;

- On flat roofs, in the case of installation in several parallel south facing rows, the free distance between two rows should be 2 to 2.5 times the maximum height of the modules (difference between the top of the module and the base on which it rests);

- For reasons connected with operation of the inverters for converting direct current into alternating current, photovoltaic modules are installed in groups facing in the same direction and tilted at the same angle. The minimum size of each group must be not less than 10 m2 (better still 15 m2), referred to the surface area of the collector; “groups” of different sizes and exposed in different ways from one another are in any case permissible.

One aspect to be taken into consideration in the early stages of design is the fact that it will only be possible to know the exact dimensions of the photovoltaic modules at the time of purchasing them, since the dimensions can easily change also if a specific product is momentarily out of stock.
It must be added that, although greater flexibility is now possible, the minimum and maximum numbers of modules in each group depend on the electrical characteristics both of the module and of the inverters.
All this means that any arrangement of the modules on the roof may have to be changed in the working stage, with the possibility of generating a problem if the area in which it is intended to install the modules has been defined very precisely. Typical dimensions of photovoltaic modules can be: 1.0 x 1.45 or 1.0 x 1.7 or, again, 0.7 x 1.0 (measurements in metres).
Crystalline silicon modules (with no particular differences between “monocrystalline” and “polycrystalline”), the cells of which are sandwiched between tempered glass, an EVA (ethylene vinyl acetate) film and a white PET (polyethylene) film, surrounded by an aluminium frame are the standard for photovoltaic modules now available on the market.
It is also possible to find crystalline silicon glass modules – glass without a frame, or modules with the photovoltaic cells mounted between two sheets of glass, or modules created on different types of backing such as roof tiles or sun-screening components.
A designer wanting to investigate this type of product must consider that they feature a low level of industrialisation and that this means considerably higher costs, less reliability and possibly that the necessary certification will not b e available.
There are also amorphous silicon modules, also known as thin-film modules (this technology is far less widespread than crystalline silicon) which require almost twice the surface area since they are less efficient. New materials and new production technology are being studied, investigated and tested.

To conclude, the differences between the three types of architectural integration indicated in the decree dated 19/02/2007 and for which different incentive rates are envisaged in Italy should be mentioned:

- photovoltaic systems integrated into the architecture (the highest rate), in which the photovoltaic modules replace the material used to cover the roof and façades, or modules that form sheds and cantilever roofs, or systems in which the modules replace transparent or semi-transparent material, thus enabling lighting of the interiors, as well as sun screening;

- photovoltaic systems partly integrated into the architecture (for which the incentive rate is lower than for the case illustrated above), in which the photovoltaic modules are installed on top of roofs or façades on the same plane as the surface, or in case of tilted modules on flat roofs when the mean height of the modules is less than that of the parapet;

- photovoltaic systems not integrated into the architecture (for which the incentive rate is further reduced): systems not belonging to the previous two categories.

For a better illustration of the different system typologies refer to the useful guide published by the GSE (Gestore dei Servizi Elettrici) “Guida agli interventi validi ai fini del riconoscimento dell’integrazione architettonica del photovoltaic”, available via the portal www.gse.it

Notes:

[1] Giovanni Ziletti is engineer and energy certificator, he has designed the photovoltaich systems which are in the pictures. studio(at)ziletti.it
[2] Data from the “Gestore Servizi Elettrici” portal www.gse.it, up-dated to 31st Janary 2009.
[3] Data from the “Gestore Servizi Elettrici” portal www.gse.it
[4] Terna, Dati Statistici sull’energia elettrica in Italia, 2007
[5] Analysis of data published on the www.gse.it portal
[6] EPIA, European Photovoltaic Industry Association, Press release 04/09/2008
[7] www.foet.org

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