
              TECHNICAL INFORMATION ABOUT SOLAR HEATING

 Hi friends

 This page is intended to give some technical information about solar energi,
 and the reason it has'nt been used more extensively.

 The sun is radiating the earth at an effect equal to 130,000 TW (TerraWatt),
 some claims 200,000 TW, perheps depending of the calculate method.
 Anyway,
 1 TW = 1,000,000 MW (MegaWatt), 1 MW = 1,000,000 W (Watt), making the total
 effect a fairly strong.....

 Having the sun at a medium elevation, we are receiveing 1000 W/m2 (Watts per
 squaremeter) a sunny day. 1100 W has been measured at Mount Everest heights.
 A pequliar thing is that snow or buildings are able to increase the radiation
 significantly.
 On a snowcovered lawn, I measured 1300 W, a sunny winterday.
 On a dual split solar collector, we metered far better effect on the side
 that was least covered by the sun. We found out that a opposite mounted roof
 acted as a reflector.

 Sun radiation is composed of electromagnetic waves within a spectre of
 3,000 to 24,000 A (Angstrom = wavelength)  1 A =  0,0000001 millimeter. 
 Instant radiation has the strongest wavelength at 4000 A, whilest indirect
 radiation (cloudy weather), has strongest wavelength at 5000 - 6000 A.
 Ultraviolet 3000 - 4000 A are also significant at instant radiation.
 Black object radiation (heat radiation) is the spectre between
 20,000 - 200,000 A. This is what is radiating from your solar collector
 when it is beginning to heat up.
 X-rays 0.1 - 3000 A are defined electromagnetic waves as well as radar,
 radio or common alternate current (AC).
 The scientist world has not yet decided whether to define light as waves or
 particles (fotons), but state it could be both. As a matter of fact, it has
 been proven both.

 This rises new questions about what is beyond light emissions.
 News from Chandra X-ray laboratory implicate X-rays to be a form of light,
 as they can use x-rays to look at far distant dark objects in the space.

 When we shall choose matter for the solar collector, we want it to be able
 to receive all sun radiating spectre.
 About thermal solar collectors.
 MAXORB adhesive sheet has absorbing rate of 97 - 99 %, and black chrome on
 cupper the same. In fact, we have come almost all the way.

 Now, when radiation has turned into heat inside the absorber, we want the
 heat to stay put, therefore the absorber shall have the quality of low heat
 emission (black object radiation). We have developed good material for this
 purpose also, and a common value is 10 %, ie. the matter radiates 10 % of
 the heat.
 I think even better values are on the way.
 The heat, now landed on the absorber must be prevented from leaking out to
 surrounding air, and this is where insulation comes in handy.
 Insulation is mainly used for plane thermal collectors.
 Reflector collectors has tiny absorber area, so insulation has little
 significance.

 Lambda, (specific heat loss), or U-value lately named, is the ability of
 a matter to hold different temperatures apart.
 Also named specific heat conductance.
 Insulation is very important to do when we accumulate or transfer
 heat or cold.
 Most common matter is spinned glass (Gullfiber) or spinned rock (Rockwool).
 The values are 0.04 - 0.05 W/m3*C (Watts per squaremeter and degree).

 The heat leakage from one cubicmeter of Rockwool is 0.05 Watt whith one
 degree temperaure difference between the sides.
 1 W leakage with 20 degree difference.
 Common air specific heat conductance is 0.0242 W/m3*C, better performance
 is difficult to acheve as long as air act as medium.

 Cellular plastic has better values due to small cavities filled with a low
 conductive gas, such as Diclordiflourmetan (freon).
 But the cavities has a small leakage, so the gas is eventually replaced with
 air, and the freon is loose in the atmosphere.

 This is the reason our frigdes are blamed to be pollutive to the jonosphere.
 Development of new insulation materials (AEROGEL) has eliminated these
 disadvantages.
 AEROGEL is a highly hygroscopic glass material compsed of millions of
 microcavities filled with a gas. The freon is replaced with different
 mixtures, most common hydrocarbon and ethanol. AEROGEL is leakproof but
 fragile against impact damages or breakage.
 It has also better performance due to thinner cavity walls.
 If you are to replace your fridge, be sure to buy this kind of equippment.

 AEROGEL is not yet used to solar collectors, maybe due to the fragility of
 the material. Solar collectors are faced to extreme conditions such as gails
 and heavy snow.

 All solar collectors has to be light transprent at the front.
 Plane thermal collectors are insulated at rear and sides.
 Transparency is a look thru capability and is measured in percent.
 Common window glass value is 87 %. Specially composed lowironglass has 91 %.
 Glass has also a highly reflective surface, making the transparence
 angledependent. Efforts to solve this problem has lead to structured surfaces,
 but to me it has resulted in severe cleaning difficulties.

 Recently a Swede has developed a process to add a thin film of silicon to
 the surface, improving transparency from 87 % to 92 % for common window glass.
 The long term reliability is to be proven.

 There is a small space between glass and absorber (glass distance), and this
 distance is very important, as it determine both insulating and thermal air
 movement (convection). Troublesome is that they go opposite ways. When you
 increase the distance, insulation increases, but faster air movement makes
 greater heat loss anyway.
 Merging the two diagrams gives a dip (best distance) at different
 mounting angles,
 upright mounting (90 degree) says 25mm distance,
 and ground level mounting (0 degree) says 50mm distance.
 As your collector will be mounted somewhere in between, your best distance
 will also be somewhere in between.

 Increasing the front insulation (konvection obstacle) has been made using a
 thin plastic film (TEFLON) beween absorber and glass,  no doubt increasing
 net collected energy.
 Difficulties to secure the film between absorber and glass makes the long term
 benefit uncertain. As a result, price rises also.

 Efficiency is a major aim, when you shall choose material, but you must take
 into account both strength and corrosion stability.
 The collector shall whithstand gails, heavy snow, sulfur air, air humidity,
 ultraviolet radiation, extreme temperature differences and variations inside
 the collector, waterpressure, exhaustion and freezing damages.
 Among a few things.....

 To mix everything to the best isn't as easy as that, or ?
 Now, the collector shall be cheap also, as the last and most significant
 parameter.
 Be happy

 Stig Larsson
 