Wednesday 02/15
Some of the things that we talked about in class:
1. Types of solar collector: this a link that Alex found that seems to summarize different types of collectors and
their main uses:
http://www.canren.gc.ca/tech_appl/index.asp?CaID=5&PgID=282#Glazed_flat_plate_collectors
Short description of different types (taken directly from the web…):
a. Glazed flat-plate :
i. used for moderate temperature applications – demand
T between 30-70oC
ii. the liquid-based collectors are most commonly used for
heating of domestic and commercial hot water, buildings and indoor swimming
pools;
iii. In this type of collector a flat absorber efficiency
transforms sunlight into heat. To minimize heat escaping, the plate is located
between a glazing (glass pane or transparent material) and an insulating panel.
The glazing is chosen so that a maximum amount of sunlight will pass through and reach the absorber.
b. Unglazed flat-plate collector:
i. low temperature applications where the demand temperature is below 30C
ii. the primary market is for heating outdoor swimming pools, but other markets exist including
heating seasonal indoor swimming pools, pre-heating water for car washes and heating water used in fish
farming operations;
iii. Since these collectors have no glazing, a larger portion of the sun’s energy is
absorbed. However, because they are not insulated a large portion of the heat absorbed is lost, particularly when it is
windy and not warm outside. They transfer heat so well to air (and from air) that they can actually ‘capture’ heat during
the night when it is hot and windy outside;
c.
Batch solar collector:
i. One hundred years ago, water tanks that were painted black were used as simple solar
residential water heaters. Today their primary market is for residential water heating in warm countries. In Canada,
they can be effectively used in campgrounds and for residential water heating in temperate climates such as
Vancouver Island; during winter the tanks must be protected from freezing or they must be drained.
ii.
Modern batch collectors have a glazing that is similar to the one used on flat plate
collectors and/or a reflector to concentrate the solar energy on the tank surface. Because the storage tank and the
solar absorber act as a single unit, there is no need for other components. On an area basis, batch collector systems
are less costly than glazed flat-plate collectors but also deliver less energy per year.
d. Solar cookers:
i. Though there are many types of solar cookers, all of them have a couple of basic
components:
1. concentrator or lenses to increase the available solar energy and
2. insulation to reduce heat loss.
ii. Solar cookers are commonly able to reach cooking temperatures of 90-150 C (200-300 F)
and some can even reach 230 C (450 F)! With these temperatures, it is possible to cook virtually any food as long as
it is sunny outside.
e. Concentrating solar collectors: 4 types( parabolic trough, parabolic dish, power tower and stationary
concentrating collectors) ….all except the stationary one require sun tracking…which we don’t want to do…
i. Stationary concentrating collectors use compound parabolic reflectors and flat reflectors for
directing solar energy to an accompanying absorber or aperture through a wide acceptance angle. The wide
acceptance angle for these reflectors eliminates the need for a sun tracker.
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2. Modeling!!! We did numbers today!!! : *we decided to model mountains in Afghanistan to see approximately
how large would the collector area should be *
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January is the coldest month; however, February has the fewer hours of sun shine per day… (for the
country the range is 109-198 hours/month)….. we picked 5hours/day(=18000 sec/day) as the
average time the sun shines in February…Still need to find more accurate temperatures and sunshine times for the mountain areas only (and maybe the same thing for Tajikistan)
We picked Tin to be 0oC and T out to be 60C; therefore DT=60C
Peak Power available from the sun = 1kW/m^2…This is achieved when the collector is normal to the
sun (which usually occurs at noon). For this initial calculations we assumed that this power is
constant throughout the 5 hours of sunshine;
o Transforming this power into J/m^2/day we have 1.8*10^7 J/m^2/day available to us
We picked the average family size to be 10
After not knowing how much hot water a person needs we picked a “pseudo”-random number: 1m^3
H2O/person/day….Therefore, we need 2.5 *10^8 J/day
Dividing what we have by what we need we get the area of the collector to be ~14m^2 (which is
almost the size of a 3x5m room….) in other words: it’s HUGE!!! And this is in the ideal case of 100%
absorbance…
We believe that 1m^3 of water/person/day might be a lot more than needed…so we need to look into
HOW MUCH NEED FOR HOT WATER there is in Tajikistan !!! For this, we need to research (for the
Wednesday when we come back from long weekend) HOT WATER USAGE !! Please look into
organizations that might have that information...try to contact people who might have more information
(like the person in the Watson Institute (Stephanie and Suza)), UNDP and other organizations (Adrienne
and Amalia), Zach already contacted embassies through emails and is waiting for these replies, Alex I
believe is looking into the National Guard??? (I might have gotten this wrong)) .
If we determine that need for hot water is a lot lower, we might want to try raising Tout….
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