Solar machine is a work machine, in which the driving force is taken from the sun's rays. Even ancient men, such as Euclid (born 325 BC), Archimedes (born 287 BC) and Heron of Alexandria (born 10 AD), mentioned the possibility of using solar heat as a driving force. Of course, they did not design any real work machine, based on solar heat.
Den förste, som synes ha sökt en verklig lösning av detta problem, är fransmannen A. Mouchot (f. 1825). Hans maskin består av en trattformad spegel (se fig. 1), vars vinkel i spetsen är 90°. Ställs denna tratt så, att dess axel pekar mot solen, så faller de från dess sidor återkastade solstrålarna tillbaka mot trattens axel, längs vilken en cylinderformad (i fig. genom streckning betecknad) ångpanna är förlagd. Ångpannan är svärtad och omgiven av ett skyddande glashölje, som i hög grad förhindrar värmeförlust genom luftströmmar och värmestrålning från pannan, utan att i synnerlig grad ta bort de infallande solstrålarnas värme. Den speglande tratten utgörs av en kraftig järnstomme, vilken bär upp kopparplåtar, som är starkt försilvrade på den speglande insidan. Genom en enkel anordning med motvikt (svart i fig.) kan tratten vridas så att dess öppning hålls inriktad mot solstrålarna. Från pannan leds ångan till en liten ångmaskin. Med denna solmaskin gjordes försök i Algeriet 1860. Trattens diameter var 2,2 m. Arbetsförmågan befanns utgöra en niondels hästkraft, motsvarande 3 % av det infallande solvärmet. Effekten ansågs vara alltför liten, vilket i huvudsak berodde på den ringa verkningsgraden hos dåtidens ångmaskiner, och maskinen var dyrbar och fördärvades snart, varför försöken gavs upp.
Several new constructions were tested, among which the most famous is John Ericsson's. His most important improvement was that Mouchot's funnel was replaced by narrow, silver-plated and later varnished long glass ribs, laid on a stand (black drawn in Fig. 2) bent like a parabolic cylinder, along the focal line of which a steam boiler (dashed in Fig. 2) was inserted. Experiments, in which the mirror's opening was directed towards the sun, were made in New York and were described in 1888 in the English magazine "Nature". An effect of 10.5% of the incident solar heat was stated to have been obtained. This figure is probably far too high.
John Ericsson's solar machine
Large-scale experiments with an improved Ericsson machine have been performed by the American Shuman at Meadi near Cairo. The mirrors in his machine lie horizontally and rotate automatically, so that their openings face the sun, around axes running in the north-south line. The mirrors were 5 pieces, each with an opening 4 meters wide and 60 meters long. The boiler in the axis of each mirror was made of cast iron, 62.5 meters long, 37.5 cm high and 9 cm wide and laid out on rollers to be able to expand freely when heated. It was covered with window glass on top. The steam was led from the boilers to a low-pressure machine of 100 horsepower (74 kW). The experiments were checked for 3 weeks by engineer Ackermann, who found that with a few simple improvements an effect of 38.6 W / m² mirror aperture should be achieved (with the somewhat imperfect devices only two thirds of this effect was obtained, with a steam turbine engine it should be possible to achieve significantly more favorable results).
The working capacity, 1.5 hp / m², was only about half of that stated by J. Ericsson, but was undoubtedly more correctly calculated than by him. According to the cost calculations provided by Shuman, the machine with the specified efficiency should have left one kilowatt hour at the workplace for 5.5 öre. Transformed into electrical energy and transported from Meadi to Cairo, the ability to work should have required a cost of about 13 öre / kWh. The machine was of about the same price and power as a wind engine of the same power at the time. In front of this, it had significant advantages in countries where the sun shines almost constantly, such as in Egypt. However, it was inferior to the steam engine, as it could not work in cloudy weather or at night.
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