Theoretical Models of PV-EC Windows Based on the Architectural Analysis of PV-EC Technologies

both PV and EC behave like absorption glazing – a risk of heat emission to the interior arises and, as a result, overheating of the rooms is possible;

required application of the PV and the EC in glazing units with increased thermal insulation in order to reduce the “mixed-mode” effect - uneven temperature distribution in the room; regardless, the lowest achieved U parameters in single-leaf glazing units do not equal solid façades.

the EC is suitable as solar control glazing, but a slow phase transition causes it to lose its effectiveness in conditions of dynamic changes in sunlight; thus, additional support is required, e.g., the use of blinds;

PV elements as non-regulated elements are less flexible, but they can provide permanent solar control measures.

in practice, a slow phase transition in conditions of low outside temperature, makes it difficult for the TST to function as solar control glass – for this reason, the TST is the least suitable for façade applications in cool climates with a large number of sunny hours.

the lack of adequate research, but a higher and faster phase transition than that of the TST makes the TLT more suitable as solar glazing.

no possibility to apply additional external solar protection elements due to unfavorable covering of the PV layer.

considerable flexibility in adjusting the EC and the PV to the requirements related to the lighting management of the room, i.e., the regulation of the sunlight supply (lighting vs glare protection);

the EC glazing provides visual contact with the surroundings, acting as a light access regulator – suitable for use at the user’s eyesight level, however, the slow phase transition (proportional to the surface of the glazing) may require additional glare protection, e.g., blinds, roller shutters;

the PV elements interfere with the eye contact with the environment, in the case of first generation cells, they do not allow an even supply of natural light (they obstruct the inflow or cause light and shade contrasts) – the second and the third generation translucent cells are suitable for glare protection (unlike modules with first generation solar cells), while providing the room with additional lighting.

problems with obtaining transparency and color uniformity that would not cause visual discomfort, an additional negative factor may be the visible insulation elements in monolithic technology;

unsatisfactory, low Tv values, owing to which the TST glazing seriously limits the access of daylight to the room;

similarly to the SBS and the TLT, the long phase transition requiring the introduction of additional glare protection elements;

size limitations of the PV-EC glazing, due to the increase of the phase transition time with the increase of the surface area (related to monolithic technology); in the case of PEC technology, independence of the glazing size from phase transition time – potential use of façade glazing.

improved properties compared to TST in terms of the Tv value range; which enable the use of the TLT glazing in rooms requiring both natural lighting and protection against its excess (unlike the SBS);

the size of the TLT glazing surface is independent of the phase transition time (unlike TST-PEC) – possibilities of the use of large-area façade glazing;

the characteristic stipes may be a factor that distorts eye contact with the environment more than the insulation elements in the TST monolithic technology (further research required).

flexibility of the PV and the EC configurations offers optimization of protection against overheating (support for HVAC systems) with simultaneous natural lighting of rooms (reduction of electric lighting);

the simplest technologically in the discussed configurations - the lowest risk of damage (e.g., overvoltage);

the greatest possibilities to select the PV technology (impact on energy gains from insolation);

possibility of using the surplus electricity obtained (when supplying electrical devices – the application of inverters required).

protection against overheating (support for HVAC systems), but reducing the access of daylight (increased demand for electric light compared to the SBS and the TLT);

the most complex structure (referred to monolithic technology mainly) - the greatest potential risk of damage (short-circuits);

the use of the PV is practically limited to supplying the PV-EC glazing.

similar to the TST, but higher Tv values suggest a more favorable effect on reducing artificial lighting in rooms;

a less complicated structure than that of the monolithic TST carries a lower risk of electrical damage.

the possibility of matching the aesthetic features of both technologies;

practically unlimited color palette, texture and graphic effects of the PV elements;

relatively large variety of colors of the EC glazing compared to the TST and the TLT, but much poorer than the PV;

therefore, the PV should be treated as a component of the SBS, which can determine the contrast or relative aesthetic homogeneity of the SBS set - generally satisfactory possibilities of shaping the façades’ aesthetic function, mainly in scope of the color palette.

no possibility of aesthetic matching of the PV and the EC technologies (the PV should be as color-neutral as possible);

due to the fact that the TST and the TLT are still being tested, aesthetic matters, including color diversity, are not a priority at the moment;

limited color palette (mainly dark blue when darkened);

problems with obtaining a homogeneous appearance of the glass to make it look like glazing without the PV.