SOLAR ELECTRICITY GENERATION SYSTEM REFERENCE TO RELATED APPLICATIONS Reference is made to U.S. Patent Application Serial No. 11/852,595, filed September 10, 2007 and entitled SOLAR ELECTRICITY GENERATION SYSTEM, the disclosure of which is hereby incorporated by reference and priority of which is hereby claimed pursuant to 37 CFR 1.78(a) (1) and (2)(i). FIELD OF THE INVENTION The present invention relates to solar electricity generation systems generally. BACKGROUND OF THE INVENTION The following U.S. Patents and published patent applications are believed to represent the current state of the art: (Table Removed) SUMMARY OF THE INVENTION The present invention seeks to provide improved solar electricity generation systems. There is thus provided in accordance with a preferred embodiment of the present invention a solar electricity generation system including a solar energy-to-electricity converter having a solar energy receiving surface including at least an electricity-generating solar energy receiving surface and a plurality of reflectors arranged to reflect solar energy directly onto the solar energy receiving surface, each of the plurality of reflectors having a reflecting surface which is configured and located and aligned with respect to the solar energy receiving surface to reflect specular solar radiation with a high degree of uniformity onto the solar energy receiving surface, the configuration, location and alignment of each of the reflectors being such that the geometrical projection of each reflecting surface is substantially coextensive with the electricity-generating solar energy receiving surface. Preferably, at least 90% of the specular solar radiation reflected by the reflectors is reflected onto the electricity-generating solar energy receiving surface. Preferably, the solar energy receiving surface also includes a heat-generating solar energy receiving surface. Additionally, nearly 100% of the specular solar radiation reflected by the reflectors is reflected onto the solar energy receiving surface. Preferably, no intermediate optics are interposed between the reflecting surfaces and the solar energy receiving surface. Preferably, the solar electricity generation system also includes an automatic transverse positioner operative to automatically position the electricity-generating solar energy receiving surface and the heat-generating solar energy receiving surface relative to the plurality of reflectors, thereby to enable precise focusing of solar energy thereon, notwithstanding misalignments of the reflector assembly. Additionally, the automatic transverse positioner receives inputs relating to voltage and current produced by the solar energy-to-electricity converter and is operative to fine tune the location of the plurality of reflectors to optimize the power production of the system based on the inputs. Preferably, the solar electricity generation system also includes a dual-axis sun tracking mechanism for positioning the solar electricity generation system such that the plurality of reflectors optimally face the sun. Additionally, the dual-axis sun tracking mechanism includes a rotational tracker and a positional tracker. Preferably, the dual-axis sun tracking mechanism receives inputs relating to voltage and current produced by the solar energy-to-electricity converter and is operative to fine tune the location of the plurality of reflectors to optimize the power production of the system based on these inputs. Preferably, the electricity-generating solar energy receiving surface includes a plurality of photovoltaic cells. Additionally, the photovoltaic cells are individually encapsulated by a protective layer. Alternatively, the electricity-generating solar energy receiving surface is encapsulated by a protective layer. Preferably, the solar electricity generation system also includes a reflector support surface and the plurality of reflectors are attached to the reflector support surface using clips. Additionally, the reflector support surface includes a plurality of slots for inserting the clips to assure proper placement of the plurality of reflectors. There is also provided in accordance with another preferred embodiment of the present invention a solar electricity and heat generation system including a solar energy-to-electricity converter having an electricity-generating solar energy receiving surface, a heat exchanger coupled to the solar energy-to-electricity converter and having a heat-generating solar energy receiving surface, a plurality of reflectors arranged to reflect solar energy directly onto the electricity-generating solar energy receiving surface and onto the heat-generating solar energy receiving surface and a selectable positioner providing variable positioning between the plurality of reflectors and the electricity-generating solar energy receiving surface and the heat-generating solar energy receiving surface, thereby to enable selection of a proportion of solar energy devoted to electricity generation and solar energy devoted to heat generation. Preferably, no intermediate optics are interposed between the reflecting surfaces and the solar energy receiving surface. Preferably, the solar electricity and heat generation system also includes an automatic transverse positioner operative to automatically position the electricity-generating solar energy receiving surface and the heat-generating solar energy receiving surface relative to the plurality of reflectors, thereby to enable precise focusing of solar energy thereon, notwithstanding misalignments of the reflector assembly. Additionally, the automatic transverse positioner receives inputs relating to voltage and current produced by the solar energy-to-electricity converter and is operative to fine tune the location of the plurality of reflectors to optimize the power production of the system based on the inputs. Preferably, the solar electricity and heat generation system also includes a dual-axis sun tracking mechanism for positioning the solar electricity and heat generation system such that the plurality of reflectors optimally face the sun. Additionally, the dual-axis sun tracking mechanism includes a rotational tracker and a positional tracker. Preferably, the dual-axis sun tracking mechanism receives inputs relating to voltage and current produced by the solar energy-to-electricity converter and is operative to fine tune the location of the plurality of reflectors to optimize the power production of the system based on the inputs. Preferably, the electricity-generating solar energy receiving surface includes a plurality of photovoltaic cells. Additionally, the photovoltaic cells are individually encapsulated by a protective layer. Additionally or alternatively, the electricity-generating solar energy receiving surface is encapsulated by a protective layer. Preferably, the solar electricity and heat generation system also includes a reflector support surface and the plurality of reflectors are attached to the reflector support surface using clips. Additionally, the reflector support surface includes a plurality of slots for inserting the clips to assure proper placement of the plurality of reflectors. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: Figs. 1A, IB and 1C are simplified illustrations of solar electricity generation systems constructed and operative in accordance with a preferred embodiment of the present invention in three alternative operative environments; Figs. 2A & 2B are simplified exploded view illustrations from two different perspectives of a preferred embodiment of a reflector portion particularly suitable for use in the solar electricity generation systems constructed and operative in accordance with a preferred embodiment of the present invention; Figs. 3A & 3B are simplified assembled view illustrations corresponding to Figs. 2A & 2B respectively; Fig. 4 is a simplified pictorial and sectional illustration showing a preferred method of attachment of reflectors to the reflector portion of Figs. 2A-3B in accordance with another preferred embodiment of the present invention; Fig. 5 is a simplified pictorial illustration of a preferred arrangement of mirrors in the solar electricity generation systems of the present invention; Fig. 6 is a simplified pictorial illustration of a solar energy converter assembly constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 7 is a simplified pictorial illustration of beam paths from some of the mirrors of the reflector portion to the receiver portion of the solar energy converter assembly of Fig. 6; Fig. 8 is a simplified exploded view illustration of a solar energy converter assembly constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 9 is a simplified assembled view illustration of the solar energy converter assembly of Fig. 8; Figs. 10A, 10B and IOC illustrate impingement of solar energy on the solar energy converter assembly of Figs. 8 and 9 for three different positions of the solar energy converter assembly relative to the reflector portion of the solar electricity generation system; and Figs. 11 A, 11B and 11C illustrate impingement of solar energy on the solar energy converter assembly of Figs. 8 and 9 for three different positions of the solar energy converter assembly relative to the reflector portion of the solar electricity generation system. DETAILED DESCRIPTION OFPREFERRED EMBODIMENTS Reference is now made to Figs. 1A, IB & 1C, which are simplified illustrations of solar electricity generation systems constructed and operative in accordance with a preferred embodiment of the present invention in two alternative operative environments. Turning to Fig. 1A, there is seen a solar electricity generation system, generally designated by reference numeral 100. Solar electricity generation system 100 preferably includes a solar energy converter assembly 102, a preferred embodiment of which is illustrated in Fig. 6, to which specific reference is made. As seen with clarity in Fig. 6, solar energy converter assembly 102 includes a solar energy receiving assembly 104 and a reflector assembly 105, including a plurality of reflectors 106 arranged to reflect solar energy directly onto a solar energy receiving surface 107 of the solar energy receiving assembly 104. Each of the plurality of reflectors 106 has a reflecting surface which is configured and located and aligned with respect to the solar energy receiving surface 107 to reflect specular solar radiation with a high degree of uniformity onto the solar energy receiving surface 107. The configuration, location and alignment of each of the reflectors 106 is such that the geometrical projection of each reflecting surface is substantially coextensive with the solar energy receiving surface 107. It is a particular feature of the present invention that no intermediate optics are interposed between the reflecting surfaces of reflectors 106 and the solar energy receiving surface 107. This is shown clearly in Fig. 7. Turning now additionally to Fig. 8, it is an additional feature of a preferred embodiment of the present invention that the solar energy receiving assembly 104 includes a solar energy-to-electricity converter 108 having an electricity-generating solar energy receiving surface 110 and a heat exchanger 112, which may be active or passive, thermally coupled to the solar energy-to-electricity converter 108 and having a heat-generating solar energy receiving surface 114. Both solar energy receiving surfaces 110 and 114 are arranged to lie in a collective focal plane of the plurality of reflectors 106. Returning to Fig. 6, it is seen that preferably there is provided a selectable Z-axis positioner 116 providing variable Z-axis positioning along a Z-axis 118 between the plurality of reflectors 106 and the solar energy receiving surface 107, thereby to enable selection of a proportion of solar energy devoted to electricity generation and solar energy devoted to heat generation. Figs. 10A - IOC show the impingement of solar energy from reflector assembly 105 for three different relative Z-axis positions: Fig. 10A shows impingement on both electricity-generating solar energy receiving surface 110 and nearly all of heat-generating solar energy receiving surface 114 when solar energy receiving surface 107 is at a distance of Zl from the center of the reflector assembly 105; Fig. 10B shows impingement on both electricity-generating solar energy receiving surface 110 and part of heat-generating solar energy receiving surface 114 when solar energy receiving surface 107 is at a distance of Z2