Abstract:
An solar energy harvester and method for controlling the solar energy harvester, in which an insolation collector is formed of one or more elements each having two opposite major sides, a first side and a second side, and being configured to collect energy from insolation incident on any of the first and second sides. A cradle enables installation of the insolation collector on a roof with the first side generally towards the sun independently of the form of the roof. One or more heliostats reflect insolation to the second side of the insolation collector. A controller controls the one or more heliostats to maintain reflected insolation incident on the collector and to decrease the reflected insolation incident on the collector when necessary to inhibit the insolation collector receiving insolation exceeding given threshold through its first and second sides.

Description:
TECHNICAL FIELD 
     The aspects of the present disclosure generally relate to solar energy harvesting. The aspects of the present disclosure relates particularly, though not exclusively, to enhancing winter time operation of domestic thermal solar energy collectors. 
     BACKGROUND ART 
     Renewable energy consumption should be increased to reduce CO 2  emissions. There are politically agreed programs to subsidize such power production with windmills. Wood pellet burners and solar energy stations are also becoming more usual. However, solar energy is poorly suited for electricity production at higher latitudes because electricity production drastically is at the lowest while the need is at its peak during winter months. Instead, thermal solar energy panels have a higher efficiency that solar photovoltaic panels do. Thermal solar panels also outperform electricity producing solar panels with economic and efficient energy storage. 
     Solar energy use is not a new invention. It is believed that Archimedes used as a weapon a “burning glass” to project a burning beam on invading Roman fleet. Modern large solar power plants concentrate sunlight from a field of heliostats that surround a solar power tower in which water or molten salt is heated. In such applications, a heat collector is elevated high up in a tower so that solar energy or insolation more accurately (heat flux from sun shine) can be reflected from a large area to the heat collector. Solar towers require very large insolation reflection field in comparison to the collector in order to gain high temperatures needed for economically sufficient efficiency. Moreover, in solar energy plants, electric surges caused by lightning may break the heliostats and pumps used for transfer of heat transfer medium, or expensive surge protection is required. Large solar power plants have transformers for connecting to a grid at high voltages (tens of kilovolts or even hundreds of kilovolts). Then, lightning surges travelling kilometers on the power lines are respectively downscaled by the transformers so that the surge voltages may remain at safe levels. However, smaller units without transformers e.g. at rooftops of commercial buildings are easily broken by surge voltages if not particularly surge protected. 
     Recently, very small scale thermal solar panels have been installed at small sites as well, even on roofs of detached houses. On the roofs, the installations are typically made along a roof surface. Such panels are yet relatively inefficient because they are not at a right angle towards the sun when the sun shines with the highest intensity. Moreover, the panels on the roof are typically exposed to accruing snow, ice and dirt which reduce their efficiency or require continuous maintenance. There are also solar panels installed on sun trackers that keep the solar panels directed towards the sun. However, in case of thermal solar panels, tracker mounted panels would require repeated flexing of heat transfer medium pipes or hoses. Thermal solar panels are also typically far heavier than photovoltaic (PV) panels that produce electricity, which sets particular mechanical requirements to use of thermal solar panels with a sun tracker mechanism. 
     The aspects of the present disclosure advantageously avoid or mitigate problems present in the existing solar energy harvesting systems, especially in small scale solar energy harvesting systems. Another aspect of the present disclosure advantageously provides a new technical alternative for solar energy harvesting. 
     SUMMARY 
     According to a first example aspect of the present disclosure there is provided an apparatus comprising:
     an insolation collector formed of one or more elements each having two opposite major sides, a first side and a second side, and being configured to collect energy from insolation incident on any of the first and second sides;   a cradle configured to enable installation of the insolation collector on a roof at an angle optimized for energy harvesting during autumn to spring, with the first side generally towards the sun independently of the form of the roof;   one or more heliostats configured to reflect insolation to the second side of the insolation collector;   cradling means for mounting the heliostats on the roof; and   a controller configured to control the one or more heliostats to maintain reflected insolation incident on the collector and to decrease the reflected insolation incident on the collector when necessary to inhibit the insolation collector receiving insolation exceeding given threshold through its first and second sides.   

     The first side being generally towards the sun may refer to the normal of the first side being in horizontal direction i.e. when seen from top or in horizontal plane generally towards the sun. 
     The cradle may comprise a mounting part configured to support the insolation collector in desired direction and to allow insolation incident on the second side of the insolation collector. Insolation incident on the second side of the insolation collector may be allowed to a proportion of surface area of the second side that is greater than X percent, wherein X is greater than 75, preferable 90 or 95. 
     The cradle may further comprise a fitting part comprising two or more adjustable legs for roof mounting. The adjustable legs may be extendable linearly and/or pivotally. 
     The fitting part may enable adjustment of height of the insolation collector. 
     The fitting part and/or the mounting part may enable free adjustment of horizontal angle of the insolation collector. 
     The fitting part and/or the mounting part may enable adjustment of vertical angle of the insolation collector. 
     The cradle may enable mounting of the insolation collector at a sunny location on most roofs regardless of the angle and direction of the roof. The cradle may be installed at a highest part of the roof. 
     The insolation collector may be mounted towards south. 
     The location of the cradle on the roof may be selected based on optimal energy production taking into account the track of the sun with relation to the roof. The free locations of the one or more heliostats may be also accounted for so as to select a location of the cradle enabling efficient energy harvesting. 
     The heliostats may reside in a sector between northeast and northwest with respect to the insolation collector. The heliostats may be configured to reflect solar power to the second side that otherwise would not receive substantial amounts of solar power. 
     The apparatus may also comprise a heat exchanger for a hot water reservoir. The hot water reservoir may reside below the insolation collector such that circulation of heat transfer medium through the heat exchanger occurs by natural convection. 
     The capacity of the insolation collector may be relatively low. Said capacity may be barely sufficient or insufficient in summer time at the maximum insolation. The hot water reservoir may be dimensioned according to the capacity of the insolation collector when operating alone in its mounting position and direction. 
     The insolation collector may be installed at a height over the roof such that the second side of the insolation collector is visible to the heliostats. The line of sight between the heliostats and the insolation collector may be configured high enough not to become obscured by normal winters&#39; snow layers. 
     The apparatus may further comprise one or more heliostat supports. The heliostat supports may have identical structure with the cradle. Alternatively, the heliostat supports may have a corresponding structure with the cradle but different scale. 
     The apparatus may comprise an interconnection structure between one or more of the heliostat supports and at least one another heliostat support and/or the cradle. The interconnection structure may comprise one or more beams, wires, straps, or other members capable of at least one of pushing and pulling. 
     The interconnection structure may be configured to stabilize interconnected parts with each other. 
     The insolation collector may be planar. The insolation collector may comprise a plurality of tubes arranged in a planar configuration such that as a whole, the insolation collector is planar. 
     The insolation collector may be statically installed. 
     The insolation collector may be configured to operate at maximum temperatures that are not substantially over 100° C. The maximum operating temperature of the insolation collector may be 100° C. to 130° C. 
     Said direction in which the cradle is configured to maintain the insolation collector may be such that the second side is closer to vertical than horizontal orientation. 
     The collector may be an evacuated solar tube collector configured to operate using evaporation enthalpy. 
     The collector may be configured to operate with first heat transfer medium. The apparatus may further comprise a heat exchanger configured transfer heat from said first heat transfer medium to second heat transfer medium. 
     At least most of the one or more heliostats may locate within a short range from the collector  110 , the short range being 1 to 10 times maximum diameter of reflective surface of the heliostat in question. Advantageously, the short range enables reflecting significant addition of insolation to the collector when sun light is diffuse e.g. because of clouds. 
     The one or more heliostats may have planar reflective surfaces. 
     The reflective surfaces of the one or more heliostats may share a common size. 
     The reflective surfaces of the one or more heliostats and insolation collecting area of the second side of the collector may share a common size. 
     The apparatus may further comprise a photo-voltaic unit configured to produce electricity for operating the one or more heliostats and/or a pump that transfers heat transfer fluid through the insolation collector. 
     According to a second example aspect of the present disclosure there is provided a method comprising:
     mounting a collector in a cradle of the first example aspect on top of a roof of a building generally towards the sun at an angle optimized for energy harvesting during autumn to spring, the collector being a planar insolation collector formed of one or more elements each having two opposite major sides, a first side and a second side, and being configured to collect energy from insolation incident on any of the first and second sides;   mounting on the roof one or more heliostats configured to reflect insolation to the second side of the insolation collector; and   configuring a controller to control the one or more heliostats to maintain reflected insolation incident on the collector and to decrease the reflected insolation incident on the collector when necessary to inhibit the insolation collector receiving insolation exceeding given threshold through its first and second sides.   

     According to a third example aspect of the present disclosure there is provided a computer program comprising computer executable program code which when executed by at least one processor causes an apparatus at least to perform: 
     According to a fourth example aspect of the present disclosure there is provided a computer program product comprising a non-transitory computer readable medium having the computer program of the third example aspect stored thereon. 
     Any foregoing non-transitory memory medium may comprise a digital data storage such as a data disc or diskette, optical storage, magnetic storage, or opto-magnetic storage. The memory medium may be formed into a device without other substantial functions than storing memory or it may be formed as part of a device with other functions, including but not limited to a memory of a computer, a chip set, and a sub assembly of an electronic device. 
     Different non-binding example aspects and embodiments of the present disclosure have been illustrated in the foregoing. The above embodiments are used merely to explain selected aspects or steps that may be utilized in implementations of the present invention. Some embodiments may be presented only with reference to certain example aspects of the invention. It should be appreciated that corresponding embodiments may apply to other example aspects as well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some example embodiments of the invention will be described with reference to the accompanying drawings, in which: 
         FIGS. 1 to 3  show a schematic drawing of a system according to an embodiment of the invention with different directions of sunshine; 
         FIG. 4  shows a schematic perspective drawing of the system of  FIGS. 1 to 3 ; 
         FIG. 5  shows a schematic drawing of a system illustrating further details of some embodiments of the invention; 
         FIG. 6  shows a block diagram of a solar energy harvester according to an embodiment of the invention; 
         FIG. 7  shows a flow chart according to one embodiment of the invention; 
         FIG. 8  shows an exemplary horizon when seen from a typical mounting position of an insolation collector on a slope of a roof; 
         FIG. 9  shows an exemplary horizon when seen from a typical mounting position of an insolation collector when installed on a roof in a cradle as in  FIG. 5 ; 
         FIG. 10  shows a graph of typical available solar power and power demand during different months; and 
         FIG. 11  shows a flow chart exemplifying processes provided by a server according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, like reference signs denote like elements. 
       FIGS. 1 to 3  show a schematic drawing of a system  100  according to an embodiment of the invention representing different time of day and thus different directions of sunshine, while  FIG. 4  shows a schematic perspective drawing of the system. On a roof  120  of a house  410  ( FIG. 4 ), there is a ridge  122  and two faces or slopes  124 ,  126  on either side of the ridge  122 . Located in this example, on a first slope  124 , there is an insolation collector  110  mounted towards south and at a steep vertical angle of approximately 60 degrees (62 degrees is near optimal at latitude of Helsinki, Finland over winter time). Rays of sun  150  i.e. insolation is incident on a first side  112  of an insolation collector  110 . The opposite side, second side  114  ( FIG. 4 ), of the insolation collector  110  would remain in shade. However, the system  100  further comprises a plurality (e.g. two to eight) of heliostats  130 . The heliostats  130  are located near the insolation collector  110  such that preferably they do not excessively shadow each other or block each other&#39;s reflection to the insolation collector  11 . 
     The insolation collector  110  is fixed to a first cradle  420 . The heliostats are mounted on second cradles  430 . 
     The insolation collector  110  is located taking into account the horizontal shadows ( 910  in  FIG. 9 ) and the need to maintain line of sight with the heliostats  130  roughly behind the insolation collector  110 , when seen from south. When located on top of the roof  120  and directly towards the sun, rather than along a slope  124 , 126  of the roof, the capacity of the insolation collector  110  is typically far greater than if the insolation collector  110  were mounted along a slope  124 , 126  of the roof. 
     The insolation collector  110  is located in an example embodiment generally towards the sun so that, when seen in the horizontal plane i.e. in the horizontal direction, the normal of the first side  112  of the insolation collector is towards the sun for enabling the receiving of the insolation from the sun by the first side  112  of the insolation collector  110 . As described in the foregoing, in the example installation in Helsinki Finland, the insolation collector  110  is mounted towards south. 
     During winter days, the heliostats  130  track sun and multiply insolation incident on the insolation collector  110 . Hence, substantial amount of solar energy can be harvested during the winter months while the need for heating and illumination is the greatest. On the other hand, summer time maximum energy production might exceed the capacity of the insolation collector  110  so that one or more of the heliostats  130  would be directed away from the insolation collector  110 , preferably back towards the sun so as to minimize sunshine&#39;s heating of the roof. This also reduces the need for cooling interior of the house  410 . Alternatively, one or more of the heliostats  130  may be directed slightly down when not needed to reflect light to the insolation collector so as to reduce accruing of dirt on the their reflective surfaces. 
       FIG. 5  shows a schematic drawing of a system  500  illustrating further details of some embodiments of the invention. A heat exchanger  510  is located at the insolation collector  110  to transfer heat to heat transfer fluid such as mixture of water and glycol. A boiler or heat reservoir  520  is provided under the insolation collector  110 , for instance in a basement of the house  410 , with another heat exchanger  510  configured to transfer heat from the heat transfer fluid to the boiler  520 . A circulating pump  530  such (e.g. a direct current or DC pump) is provided to circulate the heat transfer fluid through the heat exchangers  510 . 
     In this example, one or more of the heliostats  130  and/or the insolation collector is further accompanied by a photo-voltaic element for producing DC voltage to a battery  550 . Alternatively, or additionally, there may be a mains-operated power supply. A controller  560  is configured to control the operation of various elements of the system  500 . The controller  560  is in this embodiment simply a DC operated microcomputer with a few analogue inputs and outputs the function of which will be described with further detail in the following. 
     A motor system  570  is drawn in connection with the heliostat  130  to demonstrate an electrically controller actuator for tracking sun with the heliostat  130  under control of the controller  560 . It is appreciated that the heliostat&#39;s  130  tracking movement may be controlled either by the controller  560  or by the heliostat  130  itself (with an internal controller), which might then receive the time and date the controller  560  or from a radio broadcast, for instance (e.g. from a CF flag of RDS transmission). Moreover, in some embodiments, the heliostat  130  may operate independently in absence of control from the controller  560 . This mode may further be dependent on the season e.g. such that between predetermined dates, the heliostat  130  does or does not operate independently, as a precaution to avoid overheating of the insolation collector  110 . 
     The boiler  520  may comprise a temperature sensor or thermostat  522  configured to output to the controller  560  temperature information or start/stop commands based on which the controller controls the operation of the circulating pump  530 . 
     One or more sensors  580  may be located on the roof  120 , for instance by fixing to the insolation collector  110 , one or more of heliostats  130  or a cradle thereof. These sensors may involve, for instance, one or more of: a temperature sensor, wind speed sensor, light sensor, vibration sensor, and force sensor (indicative of force created by wind or snow, for instance). For instance, a light sensor may be used to produce an instant indication of variation of the insolation power that is received by the insolation collector  110 . With faster detection of excess power, the reaction time can be substantially reduced e.g. in comparison to reacting to changes in heat transfer fluid temperature. This in turn can help to avoid overloading and breaking of parts in the system  500 . It is especially noteworthy that the system  500  may have an entirely closed heat transfer fluid system in which pressure increases drastically when the temperature increases. Therefore, efficient heat control may be particularly important. In this sense, the use of a photo-voltaic element adds a further layer of security. A malfunction in electricity distribution network or simply a service break could deprive the system  500  of operating power. With the circulating pump  530  stopped and the heliostats  130  reflecting insolation on the insolation collector  110 , the system  500  may break in a matter of minutes in July if configured for sufficient heat production in January. 
     The controller  560  controls the operation of the circulating pump  530  and also the operation of the heliostats  130  according to its programming as described with further detail with reference to  FIG. 7 . The controller  560  may also be capable of communicating, either directly or via a third party (e.g. mobile phone, computer or personal digital assistant device), with a remotely located server  590 . Operations related to the server will be discussed with further detail with reference to  FIG. 11 . 
     The installation of the system  100  is next described with some further detail with reference to  FIGS. 1 and 5 . First, the system  100  is installed on the roof  120  so that a sunny location ( FIG. 9 ) is selected for the insolation collector  110  (fixed to the first cradle  420 ) such that the heliostats  130  can be mounted (with second cradles  430 ) preferably adjacent to the insolation collector  110  and generally in a sector of north-west to north-east (over north) i.e. behind the insolation collector  110  when seen from south. In one embodiment, the heliostats  130  are mounted on two or three common interconnecting members such as rails that rest against the roof  120 . The interconnecting members may further be fixed to the first cradle  420  of the insolation collector  110  so as to reduce necessary fixing points to the roof. 
     The fixing of the insolation collector  110  and of the heliostats  130  is made using normal roof-specific or generic technologies. In one embodiment, no holes are made to the roof at all, but the insolation collector and heliostats  130  are assembled to form one or more structures that are anchored in place using cables connected to walls of the house  410  or over gutters of the roof  120 . In some embodiments, the structure is dimensioned and formed such that it form locks itself to other structures of the roof  120  (such as chimney, ridge  122 , ladders etc.). In such a case, the insolation collector  110  and the heliostats  130  can be installed with very little effort. 
     The insolation collector  110  and the heliostats may be relatively small. For instance, the insolation collector  110  may be a square or rectangle of e.g. 0.5 m2  to 5 m 2  size. The heliostats can be of similar size, larger or smaller. For instance, the heliostats may have surface area (of reflecting surface) that ranges between 20% to 150% of the surface area of the second side  114  of the insolation collector  110 . 
     The insolation collector  110  is installed on a first cradle  420  that has two major parts, i.e. a fixing part and a fitting part. These two major parts may be made of discrete or common elements.  FIG. 5  shows a structure in which the first cradle  420  has two cross-bars interconnecting legs of the cradle and in which some legs are longer than the other. This effect is created e.g. by use of telescopic structure that is locked e.g. with clamps when the cradle is at desired height and orientation (see  FIG. 9 ). Typically, the first cradle  420  has three or four legs. In the aforementioned embodiment in the insolation collector  110  or one or the heliostats  130  is interconnected to one or more heliostats, some legs may be substituted by diagonal supports to the foot of the other element that is installed on the roof  120 . Thanks to the adjustability of the first cradles  420  and of the second cradles  430  (which may be identical in structure with the first cradles  420 ), the insolation collector  110  and the heliostats can be installed on the roof  120  in an optimal direction (see  FIG. 9 ) regardless of the orientation of the roof  120  itself. For instance, looking at  FIG. 9 , the optimal direction may be slightly below 180 degrees for best operation by the first side  112  of the insolation collector  110 . Moreover, the insolation collector is preferably mounted in a vertical orientation that is best suited for the winter months, with the objective of increasing winter time efficiency (see  FIG. 10 ). Summer time insolation power is typically that high that non-optimal angle has little adverse effect, especially as the more steep angle increases the projection of the insolation collector  110  towards the heliostats  130  located behind or about the insolation collector  110 . This further increases the capacity of the system  100  to harvest solar power in the winter time. 
     In one embodiment, the pump  530  operates with solar power obtained by a solar panel in connection with one or more of the heliostats  130  and the insolation collector  110 . Moreover, the heliostats may be driven by solar power. In this embodiment, the system  100  can be installed without need for an electrician. Moreover, the system  100  is also entirely separated from the mains and from the grid around with the advantage that surge voltages from thunder strikes kilometers away from the system  100  do not break surge sensitive parts such as pumps and controllers. Further still, electricity is spared as the pump  530  becomes automatically stopped when insolation  150  is not available and pumping is not needed. This also extends the life time of the pump and ensures that the pump will start anytime insolation is available (and the temperatures of the insolation collector  110  and the boiler  520  make pumping feasible so that the controller  560  would control the pump  530  to operate). 
     Communication channels between the controller  560  and the heliostats  130  and sensors  540  may be implemented using any wired or wireless connections. The pump  530  may also be located on the roof, e.g. integrated with the insolation collector  110  so that the pump gets its electricity from a solar panel and the sensors and the pump&#39;s control interface are electrified by solar power. In this case, the controller  560  can be operated by mains power or a power line (e.g. 12 Volts DC line) can be arranged from a solar panel to the controller  560 . The power line and/or control line can also be combined with a fluid pipe that connects the insolation collector  110  and the boiler  520 . 
     The controller  560 , pump  530  and the heliostats may be configured to operate with a total power of some 5 W to 30 W. The controller&#39;s own power consumption may be that low that a battery of 1000 mAh can maintain the controller operable for one or more days. The heliostats may be adjusted e.g. once a minute or few minutes, depending on the availability of insolation, need of insolation, and geometry of the system  500  (e.g. mutual angle and distance of between a given heliostat  130  and the insolation collector  110 ). The frequency of adjustment may vary from one heliostat  130  to another such that most proximate heliostats  130  and the heliostats that are least tangential to the sun are adjusted most frequently. Each heliostat adjustment may take a matter of seconds. Hence, the system  500  may be extremely power efficient, whether operated by photovoltaic electricity or mains electricity. 
       FIG. 6  shows a block diagram of an apparatus  600  according to an embodiment of the invention. The apparatus  600  has functionalities that make it suited to operate as the controller  560  or as the server  590 . In practice, the controller  560  is implemented as a low-power device that has rather modest capabilities in comparison to the server  590 , but either entity can be understood based on apparatus  600 . 
     The apparatus  600  comprises an input/output (I/O) block  610  for exchanging information with other entities, a processor  620  for general control of the operations of the apparatus  600 , a user interface (U/I)  630 , a memory  640  that can be a typical random access memory, computer executable software (S/W)  650  or instructions for the processor  620 , a non-volatile memory such as a mass memory  660  that stores the software  650  when the apparatus is not powered. The controller  560  may be battery operated with power supply to the battery from a charger and/or photovoltaic elements. In some embodiments, the controller  560  may operate solely with photovoltaic power and then power breakages are frequent. 
     It is appreciated that one or more of the blocks of the apparatus  600  may be integrally formed. On the other hand, any block of the apparatus  600  may be distributed or shared between two or more elements. For instance, the processor  620  may comprise one or more cores or even separate processor units operating together as one functional unit. Likewise, the memory and the processor may be formed on a single integrated circuitry, e.g. on one application specific integrated circuit (ASIC). 
       FIG. 7  shows a flow chart according to one embodiment of the invention. The flow chart starts from step  710  in which operating parameters of the controller  560  are initialized. For instance, the mutual locations of the insolation collector  110  and the heliostats  130  and their relation to compass directions may be stored. Other initial parameters may involve desired temperature, sizes of the heliostats and of the insolation collector, size of the boiler  520 , identity of the installation, and co-ordinates of the system for calculation of the sun&#39;s track  920 ,  930 . 
     The controller  560  continually monitors  720  energy input of the insolation collector  110  e.g. based on combined light sensor&#39;s output and/or temperature difference over the insolation collector  110  when the pump  530  is running. If excessive energy input on the insolation collector  110  is detected, the controller  560  commands  730  one or more of the heliostats  130  to direct their reflections away from the insolation collector  110  so as to avoid overloading hazards. Otherwise, the controller  560  may control  740  that the heliostats  130  remain directed to reflect insolation upon the second side  114  of the insolation collector while the sun is shining  150  and need for energy accumulation exists. The controller  560  also controls  750  the circulating pump  530  to run when energy is being collected from the insolation collector  110 . 
     The controller  560  may be implemented without user interface  630  such that the controller  560  uses a user device for user interfacing. The user device can be, for instance, a Bluetooth or wireless LAN enabled mobile phone, computer, personal digital assistant, or gaming device. In such a case, the controller  560  can exchange information  760  with the user device e.g. whenever the controller  560  can establish a connection with the user device or according to a schedule such as once a week or once a year. 
     The controller  560  may also monitor the state of the operation of the system  100  and issue an alarm (e.g. by a sound through a speaker) if an alarm condition is met,  770 . The alarm condition may be, for instance, that the temperature of the boiler  520  declines to a given low limit value, meets a high limit, that erroneous signals are received from the sensors  540  or from the motor system  570 . 
       FIG. 8  shows an exemplary horizon or  810  skyline when seen from a typical mounting position of an insolation collector on a slope of a roof.  FIG. 8  also shows the track of the sun at its extremes of June  920  and December  930 .  FIG. 9  shows a corresponding drawing with an exemplary horizon  910  when seen from a typical mounting position of an insolation collector as in  FIG. 8  when installed on the roof in a cradle as in  FIG. 5 . In comparison to  FIG. 8 , the skyline  910  appears at far lower vertical angles and the sun shines directly from south (180°) at the insolation collector even when the sun is at its lowest track. 
       FIG. 10  shows a first graph  1010  of typical available solar energy and energy demand  1030  during different months in a system with four basic insolation collector panels mounted on a slope of a roof, see  FIG. 8 . A second graph  1020  shows the available solar energy in the system  500  that has only one basic insolation collector panel  110  and six heliostats  130 , see  FIG. 9 . The basic insolation collectors  110  each have surface area of 2.25 m2 and efficiency of 60%. The roof angle is rather steep, 45° and it is towards south-east, see  FIG. 8 . The heliostats  130  have planar mirrors with 85% efficiency to account for some dirt on the reflective surface and some shadows that may be cast at some time of a day by trees or other elements of the system  500 . The heliostats and the insolation collector are mounted (see  FIG. 9 ) on or about the ridge  122  i.e. higher up than in the traditional slope installation. The demand of heating energy for warming of the house  410  and for heating hot water is calculated for the needs of a five person family. 
     The second graph  1020  shows significantly higher energy production capabilities that the first graph  1010 . In particular, the period when solar energy suffices alone for the demands of this example for the entire period of April to September i.e. 6 months. The prior art system ( FIG. 8 ) would only suffice during the highest insolation in June and July. Moreover, the system  500  produces a substantial share of the energy consumption even outside this self-energizing period. For instance, it can be seen from  FIG. 10  that in January, 15% of the heat demand can be satisfied with solar power, nearly 50% in February and more than 70% in October and March. The top power in the summer months is not exploited, but during this time, the mirrors can be used to shadow the roof and reduce heating of the house  410 . It is between August and May that the system  500  particularly outperforms the prior art insolation collector systems. 
     Notice that the comparison of ( FIG. 8 ) four insolation collectors  110  versus ( FIG. 9 ) one insolation collector  110  and six heliostats  130  is fair in two ways: 
     the insolation collectors when mounted on slopes of the roof occupy their own surface area of roof area. A heliostat of system  500  is nearly upright (above 45° N latitude or below 45° S latitude, for example) and occupies only a fraction of its surface area in roof area. 
     the insolation collectors are expensive parts that require heat transfer fluid circulation. The total costs of the four insolation collector system are close to those of the system of  FIG. 5 . 
       FIG. 11  shows a flow chart exemplifying processes provided by a server according to an embodiment of the invention. The controller  560  collects and stores data from the sensors  522 ,  580  in a local memory such as its own memory  660 . The controller connects  1120  periodically or when opportunities arise to the server  590 . To this end, the controller  560  may employ a direct connection e.g. using a wireless LAN or mobile data connection. Alternatively, the controller  560  may first establish a connection with a user device and use that as a data carrier, either simultaneously or in a batch transfer mode. When in connection with the server  590 , the controller  560  reports  1130  to the server the stored measurement data together with its location and or identity. Armed with the measurement data of the controller  560 , the server  590  stores these data in its database and compares  1140  them with other measurement data received from other systems, preferably within proximate installations. If no proximate installations are available, the server  590  may interpolate or extrapolate comparison values. The server  590  then provides feedback  1150  to the controller  560 . The feedback may comprise average values for comparison of the efficiency of the system with those of other users. The feedback may also comprise alarms regarding forecast weather conditions such as storms or heavy snow fall. Based on the feedback, the controller  560  may take responsively action such as issue an alarm, schedule turning of the heliostats to a storm-safe position (e.g. towards wind or against the roof or other fixed structure). The controller  560  may also update its estimates for energy consumption and for energy production, based on the feedback (such as weather forecast or statistical information obtained from other systems with similar installation and/or age, for instance). The feedback may also comprise updates to the software  650  of the controller  560 . 
     The server  590  may also adaptively adjust service intervals for the system based on reports sent by the controller  560 . In the absence of the reports, the interval may be set based on a fail-safe mode to short period such as two or three months. When the reporting is frequent, the service interval may be extended dynamically depending on the capacity and operation of the system. For instance, the controller  560  may set the maintenance just before the system&#39;s heat production capacity is expected to fall below the heat consumption  1030 . The regular service can be a pre-requisite condition for the warranty and the warranty period may be extended if or dependent on that the controller  560  has a regular connection with the server  590  and the controller  560  can verify to the server  590  that the system has been appropriately services. Hence, the server  590  can monitor  1160  that the system has been properly serviced. The server  590  can also issue user reports  1170  by various media such as short messages, email, multimedia messages or synthesized phone calls to the user. These user reports may involve e.g. warnings  770  related to the system, information about available upgrades to the system  650  and information on optimizing the operation of the system  500 . 
     In the foregoing description, the examples have related to collecting of heat by the insolation collector  110 . The insolation collector  110  may alternatively or additionally be configured to produce electricity using received insolation. In case of sole photovoltaic operation, circulating pumps  530  and boilers  520  are not connected to the insolation collector  110 . The embodiments relating to the control of heliostats  130  and to the co-operation with the server  590  are yet directly applicable in that case as well. 
     Various embodiments have been presented. It should be appreciated that in this document, words comprise, include and contain are each used as open-ended expressions with no intended exclusivity 
     The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments of the invention a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented above, but that it can be implemented in other embodiments using equivalent means or in different combinations of embodiments without deviating from the characteristics of the invention. 
     Furthermore, some of the features of the above-disclosed embodiments of this present disclosure may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present disclosure, and not in limitation thereof. Hence, the scope of the present disclosure is only restricted by the appended patent claims.