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How do Solar thermal systems work?

See slideshow  Solar radiation hits an absorber surface, which converts this solar energy into heat. A heat transfer circulating fluid (water, antifreeze) transfers the heat to a hot water cylinder or heating system.

What is an evacuated tube collector?

Evacuated tube collectors consist of rows of parallel transparent glass tubes, each containing an absorber tube. Newer-technology evacuated tube collectors used to be more expensive than flat-plate collectors but costs have dropped as production increased, especially in China. Evacuated tubes have a number of significant advantages:

The collector efficiency remains high in cloudy conditions and low temperatures.
Evacuated-tubes can be added or removed as hot-water needs change.
The circular tube means that the sun is shining directly on the absorber for most of the day.
Evacuated-tube collectors have the ability to heat water to higher temperatures than flat plate collectors.

What is a flat plate collector?

Flat-plate collectors were the first generation of collectors for domestic hot water heating. They consisted of an insulated, weatherproof metal box with a glass or plastic cover and dark absorber plate with pipes to convey the heat transfer circulating fluid. The transparent cover reduces the amount of heat that can escape, but of course, a vacuum with no heat escape is better.

What is a closed-loop indirect (split) system?

A closed-loop indirect system means that a heat-transfer fluid flows through a heat exchanger in a hot water storage tank, heating the water to be used. The circulating fluid, usually glycol or water, never comes into direct contact with potable water.

How are solar water heater collectors set up?

Solar panels are usually installed on the roof. They can also be wall mounted or free standing. Solar collectors should be orientated facing the equator (south in the northern hemisphere) at a tilt angle of approximately equal to the latitude.

What size should solar collectors be?

A solar heating system used for domestic hot water heating should be sized so that no excess heat is produced in summer. A typical rule of thumb is 1 square meters of collector and 75 liters water storage per person. Up to 40% of space heating can be supplied for a well insulated 120 square meters house by using 12 square meters of collector and 750L of hot water storage. More accurate estimates can be made using the RETScreen.net program. Integrated systems are sized to match the tank and collector already, so simply purchase a integrated system with a tank of 75 liters size per person and the solar collector area will already match the tank.

What components beside collectors are needed for solar hot water?

The other main components of a solar thermal system are the hot water storage tank, regulation and safety controls. Some systems come with all components integrated, which is, the gravity-drain system with tank and collector tubes together.

How do I know the collectors I am buying are certified and tested to high quality?

Look for independent, internationally recognized third party testing from Europe (Solar Keymark) or American Solar Rating and Certification Corporation (SRCC). Our solar water panels have SRCC, Solar Keymark and CSA approval; which means that the collectors have been tested not just for efficiency, but shock tested and endurance tested as well.   

Is this a passive solar water heater, or will I need to pressurize it by connecting it to my municipal water system?

Passive or pressurized with pump are both OK with our panels...but that is a little bit of apples and oranges.  You can have passive, pressurized systems and active (pumped) non pressurized systems.  Passive means no circulation pump; hot water simply rises.  Active means forced circulation.  Pressurized systems are not vented to the atmosphere, but rather kept under pressure, which means that the water tank can be below the point of use, heat retention may be better, freeze protection is improved and no pressure reducing valve is needed connected to the pressurized municipal supply.  No-pressure, vented-to-atmosphere systems either need to gravity drain the water tank (for example, having the tank on the roof), or require a pump to deliver the hot water.   

Where is a list of USA government grants?

For USA incentives, see http://www.dsireusa.org

Why use a solar thermal water heater?

To save money, to avoid pollution, to guarantee future energy costs. To use renewable energy in a visible manner. To be seen as environmentally conscious. To satisfy laws mandating the use of renewable energy. To be independent of the electric grid and government policies, both of which may fail.

What is a solar vacuum tube?

A solar vacuum tube, or evacuated tube, is a low-iron glass tube, like an elongated thermos bottle, whose outer wall allows nearly all light to pass through, while the inner wall has a sputtered high absorption coating that absorbs 98% of the incident sunlight. The vacuum between the two walls means no heat can escape by conduction or convection.

How many kilowatts hours of energy does each heater produce a year?

No electricity is produced by a solar heater. However, the heating in kWh/ square meters is shown on test reports. For the German laboratory where testing was done, yearly gains were 600 to 800 kilowatt hours per square meter of collector.

What solar hot water system is simplest?

An integrated, or direct, system is the simplest and most economical to install, keeping high efficiency, simplicity and freeze protection by using heat pipes integrated into a storage tank. An integrated system can be assembled by anyone in a few hours.

What solar hot water system looks the best on the house?

A circulating system using panels of tubes eliminate the water tank on the roof. The tubes look like a skylight, and the hot water tank is in the house below.

I saw an integrated system that looks the same as yours, very cheap, with glass tubes with water in tube, what is the difference between that and heat pipes? They look the same on the outside.

Safety and efficiency. With water in tubes, break one tube, the water all drains out. Any calcium or other minerals in the water will eventually coat the inside of the tubes. Efficiency is higher with heat pipes, since liquid moves slower than vapour and condensation transfers more heat than conduction.

Why use drain back instead of glycol?

Elimination of the heat exchanger. Close to freezing, the water drains back to a storage tank inside a warm building.

Why use glycol instead of drain back?

Using glycol and a heat exchanger means absolute freeze protection. There is always a chance that the drain back will fail and pipes will freeze. However, a manual drain back in a basic, manual control integrated system also has 100% freeze protection.

What is the difference between glass heat pipes and copper heat pipes?

Price-glass heat pipes cost half of copper. Pressure-Copper heat pipes can stand high pressure, glass pipes are low pressure only. Glass heat pipes can stand corrosive water. Copper pipes are more efficient and faster starting in low light, since copper conducts heat better than glass.

What is the difference between U tube and heat pipe collectors?

U tube collectors have a copper pipe, attached to a heat absorbing fin, running from the top of the solar vacuum tube and making a U turn at the bottom. Heat pipe collectors have copper heat pipes inside the evacuated tubes, with water only flowing past the header of the collector. Both collectors stand high pressure and look the same externally but the U tube can be used in any orientation. Heat pipes can not work lying flat; the bottom of the pipe must be lower than the head.

Which solar collector is most efficient?

U tube collectors are almost exactly the same efficiency as copper heat pipes under standard conditions. In persistent low light, the U tubes should be better than any heat pipes, since they have no minimum start up light required. Copper heat pipes are slightly more efficient than glass heat pipes, with faster starting in low light, but yearly average performance is very similar. Any heat pipe is more efficient than water in tube. Any vacuum tube collector is more efficient than a flat plate collector if the air outside is more than a few degrees cooler than the hot water inside. Lowest cost is a different story-the all glass heat pipes win.

What are the advantage of a copper heat pipe solar collector versus u tube collectors?

Extreme high pressure-since only the manifold is pressurized, and heat pipes ends have a much smaller area than several meters of pipe, higher pressures are possible. Better drain back-draining the top manifold is easier than several meters of pipe in a u-shaped path. More resistance to corrosion and failure-less water in contact with metal and less volume pressurized mean less risk of failure. Less circulation pump load-path of water is only through the top manifold, not through several meters of pipe.

What are the advantages of u-tube solar collectors versus heat pipe collectors?

Flexibility-U tube collectors work in any orientation, including horizontally flat roofs, or on edge such as on walls or balcony mounts, while heat pipes only work tilted between 15º and 75º

How do I decide to use a heat pipe collector or a U-tube?

For horizontally flat installations or on-edge wall installations, such as balcony mounts, you must use a U-tube. For drain back systems or very high pressure systems, heat pipes are probably better. If none of the above apply, pick a certified, high-quality collector that is on special, or qualifies for a government rebate in your area.

Which solar hot water system delivers the lowest cost hot water?

An integrated (tank and collector together), gravity drain solar hot system with manual control to fill and drain the water tank. In other words, open a valve to fill the water tank in the morning, then drain the hot water in the afternoon.

Why is an integrated system cheaper than split system?

Installation costs, less parts overall and no moving parts. A tank on the roof eliminates the circulation pump, pump controller, heat exchanger and associated valves and plumbing. Setup can be done by virtually all home owners, eliminating installation costs. No moving parts on a gravity drain system with manual control mean that illiterate third-world installers can successfully set up a highly reliable hot water system.

Why use a split system if it is more expensive and complicated?

Appearance, zoning and space heating. Solar collector panels lying flat on a sloped roof blend in to the roof better than a water tank combined with collectors. Special applications, such as in floor heat or industrial processes may demand the collectors be split from the hot water storage location.

How much money can be saved using solar hot water?

100% if you live off-grid and are willing to accept a varying hot water temperature, depending on the amount of sun on a particular day. On-grid, using an electronic controller and electric backup heater to keep a constant hot water temperature, about 70% of an energy bill for water heating can be saved by using solar hot water in most of the USA. Of course, one could simply put in a larger system and use no electricity at all, but it is cheaper to use a combination of solar and backup. See the economics of an indirect (split) system using the renewable energy technology (RETScreen) program.

Why not use solar for 100% of hot water?

It is possible to use 100% solar water if one is willing to adapt usage to the sun, or spend extra for a system that would be oversized in the summer. A 100% solar system would work great in a place with little change in sun between seasons and the same amount of hot water being used every day. With occasional cloudy weeks and occasional large groups of guests, a good balance of cost and convenience is to use solar water for nearly all normal daily needs, plus an on-demand backup heater for the exceptional demand periods. On-grid, an electric controller-heater is economic with a split system, while off-grid, an integrated system with on-demand gas water heater downstream works well.

What is the difference between flat plates and evacuated tubes?

Older style flat plates with water tubes attached to a black-painted metal absorption plate were the first active systems. Newer technology evacuated tubes have higher efficiency, no heat loss across a vacuum, no corrosion of glass tubes and quasi-tracking of the sun because some part of round tube is always directly facing the sun. As cost is now almost equal, vacuum tubes are replacing the older style flat plates.

Are customs duties charged across the Canada-USA border?

No, solar water heaters should be exempt crossing from Canada to the USA. The US customs tariff number is 8419.19.00.40. Applications for refund of GST (Goods and Services Tax) paid in Canada can be made at the border post. Coming in to Canada, the Canadian import classification number is 8419.19.00.10. GST is charged in Canada.

Is there sales tax on solar products?

Tax depends on location where the solar product is sold. Goods and Services Tax must be charged in Canada. Every state in the USA is different, but many do not charge tax on renewable energy products.

How do I install a solar water heater?

Use the installation manuals and install the system yourself, or call your local dealer, who can install it for you.

How much does a solar system cost?

Nothing; it pays for itself in savings to your utility bill in a couple of years. Up-front investment is generally $500 to $5000 depending on system type and size for a house.

What is the difference between copper heat pipes and glass heat pipes?

The gravity drain system has glass heat pipes; pressure systems have copper heat pipes. In practice, this means that the gravity system has to go up on the roof or have a pump downstream to get high water pressure at the tap. The pressurized split system can put collector panels anywhere, above or below the collector panels and high flow can be achieved by increasing pressure.

Glass heat pipes are one unit, a sealed tube. Copper heat pipes are inserted into open-ended collector tubes, along with a aluminum insert to conduct heat. This means all glass heat pipes are stronger than a copper-glass tube combination, just as a whole egg is much stronger than an egg with one end of the shell cut off.

What are the advantages of the gravity drain (ie tank on roof) system?

Cost, simplicity, robustness, complete reliability. Gravity systems deliver hot water at less than half the cost per liter compared to pressure systems. All glass heat pipes never corrode even with mineral rich water, and survive shipping better because they are closed on the end like an egg rather than open like a thermos. High pressure is possible out of a gravity system-just put it up higher from the point of use, or put a pump downstream of the collector.

Which solar systems are the most popular?

Globally, the simplest and lowest cost systems are most popular. Of the several million solar water systems sold every year, over 90% are gravity drain, tank and collector integrated systems, sold mostly in China. First-world cold countries with pitched roofs (sloped to shed snow, for example) buy more higher-priced split systems because they do not like looking at a water tank on their roof. Hot countries with flat roofs buy more integrated systems since the water tank can be easily placed and hidden on the roof, and price is less.

Why are water in tube systems being replaced with glass heat pipes?

Efficiency is better, tubes are stronger with less problems, and cost is almost the same. Water in tube systems mean lower efficiency, since liquid travels slower than vapor in a heat pipe, and one broken tube will cause all the water to leak out. With heat pipes, the collector has high efficiency and keeps working with broken tubes.

How to stop the system from overheating?

The system is not going to get hurt by overheating so long as you have a water supply. That is because if the water boils, it is vented as steam and the heat is dissipated. Overheating dry eventually causes degradation of any silicon seals in the system. The glass and metal are not affected.

How can I tell how much energy the system is producing?

Three ways:

Measure it. Install temperature probes and monitor the volume of hot water used. You know how many liters of water you have used, you know the input temperature, and you know the output temperature. Multiply the temperature change by the liters of water by the specific heat of water and you have the amount of energy harvested.

Calculate it. Use www.RETScreen.net, input your panel performance and your location, which is connected to the global climate database. The program then calculates mean energy for your location with your system. Notice the solar fraction and MW-hours of energy are shown, plus cash saved. You can make the same analysis for your system.

Use standard test results. Click on the certification links for your panel to see the test results for your panel under standard conditions.

How to stop pipes from freezing?

Keep the pipe runs short outside-straight up from the roof to the tank, less than 1 meter. Insulate well and use the water regularly so pipes do not cool down. Pressurize the system.

Vent warm air from the house out the same opening the water pipes exit (also minimizes holes in roof)
Run the hot water line in the same cavity as the cold, so any heat lost does some good.
Drain the tank at night (standard system, manual control, drain-back split system)
Use a pump to circulate hot water from downstairs (split systems).
Use the controller to activate an electric heater if freezing temperatures are sensed.
Use glycol with a heat exchanger (split system)

Can I get a tank equipped with two heating element connections?

Yes, but it may take a while to arrive! Many tanks already have top and bottom electric backup elements. Hot water is taken from the top of the tank, where temperature is highest. The top element heats a small amount of water quickly for instant use. The bottom element is to warm the whole tank. Electronic control is used to set the optimum heating cycle.

I would like to add a DC voltage water heater element to the tank. We have a low cost DC wind power system with battery back up that is cheaper and more efficient if we don't invert it to AC. Is this a good idea?

Probably too expensive. An analysis with RETscreen will show that it is vastly cheaper to store the energy as thermal instead of chemical. Put another way, keep energy as hot water, not chemical storage in a battery. Solar thermal absorbs 98% of incoming solar; commercial grade solar PV is good at 5%; and putting the in and out of a battery loses 80% of the energy. Much cheaper to make hot water directly, then store it. With well insulated tanks as we have, the heat lasts for days. If you are spilling excess DC power to a resistance heater after your battery bank is charged, by all means, do it. For backup heat if the solar hot water runs out at night, a on-demand gas heater is a simple and economical solution.

Is it practical to keep the lines and tank from freezing or should I plan on using only drain down split systems here in the north?

It is possible to use the integrated system in cold places, yes. The tank is not a problem; it is well insulated, and any sun will add energy only one way. The problem is the supply and return water lines; they must be insulated and the runs outside kept to a minimum, straight up out of the roof to the unit if possible. Ultimate freeze protection is glycol inside a split system, or an integrated system with the lines drained after use. The glycol split system can never freeze since water never goes out into the cold, even if every moving part in the system fails and every pipe clogs up. Manual control no pressure system, also has 100% freeze protection. Manual control means you fill the tank in the morning and use the water at night by draining the same water line used to fill the tank. There is no way to freeze because there is no water in the line after use.

Are the evacuated tubes (1.8 m, used with copper heat pipes) more brittle than the all glass type?

The glass is about the same strength, but the design with an open end (to insert the copper heat pipe) means that the open-ended tubes break much more easily. Compare crushing a whole, hard-boiled egg (the all glass heat pipe tubes) with crushing a hard boiled egg cut in half (the open-ended solar tubes) to visualize the difference. Even if the half-eggshell was twice as thick, it would still crush more easily than the sealed, whole egg.

What is the maximum temperature the copper heat pipe tube can reach?

Failure temperature is the melting point of copper. Testing at no water flow, full solar irradiance produced a stagnation temperature of 200 degrees Celcius with no degradation (see high temperature resistance test in European test report, page 17). Water boils at 100 degrees Celcius, so a constant supply of water with a steam vent would keep temperature at 100 degrees.

What is the difference between a gravity drain and pressurized solar water heater?

A gravity drain solar heater drains the water by gravity, with the water tank being vented. A pressurized system is not vented to the atmosphere, but rather has pressure in the water tank. A pressurized tank can be below the point of use. A gravity drain tank must be up above the point of use.

What kind of systems are best for DIY (do-it-yourself)? Small systems?  Large systems?

Do-it-yourself (DIY), with two basic kinds of solar water heater systems: simple modular kits that have the solar thermal tank and vacuum tube solar collector integrated together, and systems with solar collector panel split from the hot water tank. Both integrated and split systems can be scaled for larger installations via the addition of solar panels, or additional integrated systems in series. 

Simple modular solar water heater kits allow anyone to assemble and being using solar hot water within a few hours. All parts are supplied in the kit, including high efficiency glass heat pipe vacuum tubes, insulated solar hot water storage tank, seals, assembly hardware and corrosion proof extruded Aluminum frame. Accessories such as auto fillers, pumps, electronic controllers and back up heaters are sold to make the operation more convenient, but the basic, manual control model is the best value for the environmentally conscious do-it-yourself person.

Split system solar thermal panels should be used for installations that require large, central water storage tanks, pool heaters and space heating. Fully certified and tested, these high pressure heat pipe solar panels can be joined in series to heat any size solar water tank, from 300 liters for a house, to thousands of liters for a hotel. Installation of solar panels split from the hot water tank is more complex than putting the tank and collector together, but the solar collector blends in to the building better, which is important for city zoning and customers who value appearance. A split solar water system can be made independent of the electric grid by using a photovoltaic (PV) solar powered circulation pump.

Can I pay by check (cashier's); if yes, please let me know to whom I should write the check?

FreeFuelForever Ltd., 2872 Chowat Road, Agassiz, BC, Canada, V0M 1A2. Telephone +1 604 796 2649 or +1 323 366 8777