The final distribution between the different forms of solar gains, and the thermal losses through the structure, are dependent on how the system is regulated between the two reflector modes. The complexity also increases due to more subjective response from the users due to thermal comfort and wish for daylight and view.

The system was initially designed for integration into a single family house, where most bright hours during weekdays are characterised by the absence of the inhabitants. A rough operating schedule is outlined: during morning hours, with low solar flux and high user activity, the reflectors can be opened to allow for daylight, view and direct passive heat gain. During solar peak hours, with family members being at work or at school, the reflectors can stand closed for maximal active performance. Late afternoons and evenings have similar characteristics like the mornings, thus the reflectors are likely to be opened. For avoiding view inside (i. e. allow for privacy) and thermal losses during dark hours, the reflectors should be mainly closed until the next morning. When integrated into larger areas, zoning of the system allows for combinations of closed and open modules during this cycle.

Another operating strategy could be automating the movement for the reflectors on response to the radiation intensity and the outdoor temperature. It could be programmed for closure at radiation levels too high for thermal or visual comfort, or at levels too low for any practical use, e. g. at night time. In combination with other “intelligent house” technologies, such as sensors indicating occupant absence, obvious opportunities for keeping the reflectors totally closed can be maximally used. For calculations on passive gains in Stockholm, Sweden (lat 59.31), the reflectors were considered closed at transmitted irradiance levels below 50 W/m2 and above 300 W/m2, and opened at intermediate levels, from March to October. Concerns have been taken to the solar shading effect of the reflectors by using the computer tool

Parasol. For November to February, the system was operated as a window with no thermal and power production and the reflectors were considered closed or opened, depending on the most beneficial thermal energy balance, for every hour. The energy balance was calculated for every hour of the year, according to Eq. (2):

W= I — U — AT

W is the net energy gain through the window, I is the transmitted irradiation, U is the heat transfer coefficient of the and AT is the temperature difference between indoors and outdoors.

The calculations indicate an annual positive net energy balance of 10 kWh/m2 for the winter season. For the warmer season, there is a loss of 14 kWh/m2 for the dark period with irradiance levels below 50 W/m2, and a passive gain of 214 kWh/m2 for the opened mode, at levels between 50 W/m2 and 300 W/m2. At levels above 300 W/m2, 245 kWh/m2 are available for the PV/T absorber.