What is the best pitch and orientation for a solar application? Generally speaking the solar application should have a southern orientation in the northern hemisphere and have a pitch close to the latitude of the location. Flush mounting is, however more aesthetically pleasing, easier to install and more durable than a precarious pole support system.
How much will it cost to have a solar application installed? This will of course depend on the size of the application, the kind of installation, the location and the installer. I suggest that you learn the basics before hiring someone to install collectors, build a sunroom or construct an entire solar home. There are many options. I measure value by the payback period. I recommend that the payback period for a contractor installation be less than 10 years and the payback period for a DIY system be less than 3 years, but you are the only one who can determine the true value of a system.
How many collectors will I need for my family? In the Long Island area where I live about 1000hrs/yr of direct sunlight @ 300 BTU/sq. ft. are available to a properly oriented collector. If the collector surface area is 100 sq. ft. and the collector is 50% efficient the energy harvest per year would be…
.5 x 300 x 100 x 1000 = 15,000,000 BTU’s per year.
If we assume that the extractable heat from a conventional oil burner is 100,000 BTUs/gallon the fuel oil equivalent of 15,000,000 BTUs would be 150 gallons. At a price of $5 per gallon this much fuel oil would have a value of $750 per year.
This crude estimate was only done for a simple DHW system. A home heating system would of course be larger and the seasonal heating requirements along with the solar heat available makes the useful heat harvest a little more difficult to calculate, but these ballpark numbers are a good start.
You may suggest more questions concerning solar heating applications. or comment on any of the posts after you subscribe…
This Differential Controller fits right inside a double wide standard outlet box so that all the wiring may be hidden inside the wall of a house.
The differential on and differential off temps may be programmed but this is only one amazing feature of this neat little unit. Freeze protection and boil protection may also be programmed. The user may also chose temperature readings to be displayed in Centigrade or Fahrenheit. Click on the illustration to find out more.
The Trickle Down Mat is the heart and soul of the Trickle Down Collector. This is where sunlight is transformed into heat and transferred to the water in a saturated film of polyester felt. No metals are used in the heat transfer process but a steel stud slot is used to frame the collector. The flanges of the steel slot are used to hold solid insulation. This solid insulation doubles as a collector backing. A Mylar waterproof film is placed on top of the insulation. Polyester felt is placed on top of the underlayment and another Mylar film is placed on top of the felt.
These three layers make up the Trickle Down Mat.
EDPN bibs are also used at the input and output edges of the mat to guide the water from a trickle down distributor into a gutter. Pressing side strips of insulation under the flange of the steel stud slot hold the mat together. Cross supports prevent side strips from migrating, hold the frame in place and support the suntuf glazing material.
A steel stud slot makes an excellent frame for for an MTD collector. The prep work for the frame only takes a few minutes but these few minutes will save hours of construction time that was once spent on wood frame construction. Steel stud slots are actually less expensive than wood and paint and they have a more professional appearance. Many people are concerned about the possibility rust, but this is not a problem since the steel stud slots are specially treated to prevent rust. Some wood is used but this is a minor part of the construction.
Home made MTD collectors are durable, fairly easy to build and cost effective. They are designed to be flush mounted on a roof and connected as an an array. Solar heat exchange takes place through a through a black polyester felt material saturated with water rather than a network of tubes and metallic absorber plates. The felt comes from recycled soda bottles made from polyethylene terephthalate commonly called PET. It has a melting point over 400* F and is well suited for solar hot water projects.. Richard Heiliger and I have have been building and testing a variety of MTD systems over the last 5 years and we believe we have a unique, cost effective solution to the solar heat extraction process. This is the first a three video set.
Solar collectors may be made with a parabolic trough that concentrates sunlight on a pipe located at the focal point of the trough. A tracking device is used to keep the sun focused on the pipe during the day. The pitch of the trough must also be adjusted from time to time to optomize heat collection on the pipe.
Concentrating collectors eliminating the need for absorber plates and a glazing materials, however sunlight must always be focused on the pipe to be effective. The heat collection pipe may get many times hotter than the boling point of water but since the surface area for heat collection is small the heat collection is small when the ambient temperature is low and heat losses are high.
Solar Farms that convert solar heat into superheated steam use thousands of hugh parabolic trough concentrators to generate electricity, but their are better options available for the residential home owner interested only in generating DHW.
Glass is a classic glazing material that has an indefinate life expectancy as long as vandles don’t throw rocks at it. Polycarbonate glazing materials have reacently become popular among DIY solar collector buildere because of high transmitance, low cost and low weight. These material also resist damage from heat and bright light and have a life expectancy of 15 years or more.
However there are still other glazing materials that should be considered. Some people find a way to recycle glass patio doors or storm windows and some people find that Kalwall Sunlite is a sufficient glazing material for their project. Polypropolene and even polyethylene may be used for temporary experimental collectors and Mylar is often used as an inner film material. The two glazing materials that are on the top of my list oar Suntuf polycarbonate and Twin Wall Lexan polycarbonate. If you have a favorite please let me know about it.
The batch heater, sometimes called the breadbox, combines the functions of collecting and storing heat inside one unit. This simple, direct connect, SHW system has been around for over 100 years and has become popular in desert areas where there’s a plentiful supply of sunlight and temperatures above freezing. The batch heater is classified as an ICS (integrated collector storage) It’s basically a tank of water, inside an insulated, foil-faced box, lined with insulation, covered with a glazing material and connected directly to a domestic hot water tank. Commercial batch heaters can weigh over 300 pounds when filled with water so they must be carefully supported when installed on a roof. Because of the weight as well as other factors the batch heater is often ground mounted and fed directly into a fossil fuel hot water tank. Above 50*F batch heaters work fine, but when Jack Frost comes a knocking batch heaters must be drained.
Solar hot water system harvest more energy per square foot and are generally more cost effective than photovoltaic system. As a matter of fact SHW systems are at least 3 times more efficient at harvesting sunlight energy even though the price of electricity is going up and the price of PV panels continues to fall. The new homes of the future will most likely come with both solar thermal and PV options. Our survival in the coming brave new world will, I’m sure, depend on our ability to become more energy independent and I expect the “green energy” revolution to carry us into a brave new world. Expect house values to increase with the addition of energy saving devices. Of course appearance will always be important but than “Beauty is in the eye of the beholder.
A well-designed SHW system could provide all, or most of a household’s hot water needs for most of the year and a well designed solar heating system could put a serious dent in a home-owners heating bill. However to transform dreams into realities we need to plan and consider all the alternatives.
Windows alow light into a dwelling while also providing some degree of insulation. Visible light that strikes a dark object is transformed into IR radiation and most of that IR radiation is reflected back into the house. BUT the main problem of heat loss through a window has to do with heat conduction through the glass.
Before thermopane became popular I helped my father install a few dozzen storm windows all around our Garden City house every year. The storm windows provided a dead air space between the exterior glazing and the interior glazing and helped reduce the heat loss. Today most people use thermopane stom windows and thermopane interior windows that are permanently installed.
Thomas Jefferson used tripple pane glass to slow down the heat loss from his Montichello home.
Unfortunately he did not use a dessicant between the glazings to remove trapped moisture.
Modern thermopane windows use a dessicant like CaO2 that absorb water vapor and create a small vacuum between the layers of glass. This vacuum greatly reduces heat loss. By increasing the vaccum the heat loss could be further reduced. Evacuated tube solar collectors have almost no heat loss… Of course they use a selective coating inside that helps trap IR.
The problem with removing too much air from standard thermopane has to do with structure. The span of a standard window is too great to support an extreem vacuum. HOWEVER… I believe this type of super insulated window could be made by imbeding glass evacuated tubes inside a clear polycarbonate material.
HEAT is defined as the product of temperature and mass. To calculate the number of BTU’s something contains, simply multiply its absolute temperature by its mass. Since ice water is 428 degrees F hotter than absolute 0 we should multiply the weight of the ice water by 428 to find the heat contained in the bathtub full of ice water. A bathtub full of ice water would weigh about 300 lbs so the product of 300 lbs times 428 would give us 128,400 BTUs. A cup of boiling hot coffee is 630 degrees F hotter than absolute zero and it weighs a half of a pound so the heat contained in a cup of coffee would be 315 BTU’s
ICE WATER is not a good heat source even though it contains more heat than a cup of hot coffee. A useful heat source should be hotter than the item being heated. Heat gain is measured from a reference temperature. The difference between the starting temperature and the ending temperature times the mass is equal to heat gain.
The mother load of evacuated tubes are now manufactured in China. They have become popular because of the high temperatures they produce made possible by vacuum that separates the outer shell of the tube from the inner shell where sunlight is transformed into heat. Although the heat gain associated with evacuated tubes is less than the heat gain of flat-plate collectors the heat loss is minimized by the vacuum. Heat transfer takes place through a selective coating on the glass that’s attached to a conductive material that’s attached to a copper heat pipe. A low boiling point liquid such as acetone boils when heated. As the vapor from this low boiling point liquid travels up the heat pipe heat is lost through the bulb and transferred into the domestic hot water heat exchange system through a water/glycol heat transfer liquid that’s circulated over the heat exchange bulb. The cooled Acetone then drops to the bottom of the heat pipe where the cycle begins again.
Trickle Down Solar Thermal Roof
In the 1950’s, Harry E. Tomason, a North Carolina engineer, had a dream about a low cost solar heating system that used of the entire surface area of a south facing roof. His invention became known as the ‘Trickle Down Solar Thermal Roof”. It involved a corrugated metal roof covered with glass. Cold water from a large insulated tank in the basement was pumped to the top of a specially prepared roof where it was allowed to “trickle down”. Solar heated water from the roof was than collected in a gutter and returned to the basement storage tank. This innovative solar heating system is still functioning in numerous households along the US/Canadian border, but there is now a new improved, more cost effective, more efficient, more DIY friendly modification of Tomason’s invention called: Modified Trickle Down Solar Heating or MTD solar. Upon close examination of the Tomason thermal roof we notice that water flows over the steel corrugations. The underside of the corrugated steel is insulated to prevent heat loss, but a lot of heat is still lost through the cold outer glazing surface. This is why the MTD design makes use of a Mylar inner film
Parallel-flow, flat-plate-collectors are common. They were developed by Hottel and Whillier in the 1950′s and they consist of a dark absorber plate to change light into heat, a transparent cover that traps IR radiation, a heat-transport fluid like water, and an insulated backing. Commercial flat-plate collectors use copper absorber plates soldered to copper flow tubes. A selective coating such as CrO2 is applied to absorber to convert incoming radiation into heat. Commercial collectors are often built with a stainless steel or aluminum frames. Glazings materials made from low iron content plate glass materials BUT some manufacturers are starting to use Twin Wall Polycarbonate for glazing. Heat is normally transferred to flow tubes bonded to the absorber plate but today stainless steel plates with flow channels are made directly into heat exchangers to improve collector efficiency and lower manufacturing costs. An alternative to metal absorber plates is the non-metallic heat exchanger with freeze-tolerant water channels are made of silicone rubber. Since polymers are flexible they will not have a freeze problem with plain water, so that they may be plumbed directly into existing water tanks.
All animals from the microscopic ameba to the to the macroscopic sperm wale have have some kind of circulatory system that makes life possible by transporting food energy, nutrients and oxygen. Most multicultural organisms are equipped with a heart that circulates oxygenated blood through a parallel network of capillaries. If the surface area of a person 1′x1′x6′ could be spread out with a thickness of .1″ their surface area would be 720 sq ft. The surface area of a solar collector this large, operating at an efficiency of 50% could harvest the heat energy equivalent of 108,000,000 BTUs per year… with a street value in excess of $2000.
4x8 serpentine collectors with side and center supports
A serpentine flow tube is easy to fabricate for DIYers once the temporary jig is screwed into the back of the collector frame. The wood used to make the bending jig may also be used to make the pounding jig. Although jigs may at first seem unnecessary you will soon understand how they greatly simplify the construction process and aligb the flow tubes with the absorber plate. Think for a moment about the time and expense of hammering out sixteen 8″x 40″ aluminum fins. Now devide this time by 10. This is about the time it takes to hammer out the two 20″ x 96″ aluminum absorber plates for this collector. These absorber plates are made from inexpensive sheets of aluminum flashing. Both serpentine collectors were fabricated and assembled in about a day. Your first serpentine collectors will of course take longer than 4 hours to assemble but you should be able to open your own serpentine collector factory in less than a week. .