|
1.
Vist our list of solar thermal rebates and incentives here:solar thermal rebates.htm
Top of Page
2. How do Solar thermal systems work?
All types of solar thermal systems function similarly. Solar radiation hits an absorber surface, which converts this solar energy into heat. A heat transfer circulating fluid (refrigerant, water, antifreeze or air) cools the absorber and transfers the heat to a hot water cylinder or heating system. Top of Page
3. 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 are fragile, but they have a number of significant advantages:
4. 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 allowed light to strike the absorber plate whilst reducing the amount of heat that can escape. Top of Page
5. 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. Top of Page
6. 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. Top of Page
7. 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 m2 of collector and 75 1itres water storage per person. Up to 40% of space heating can be supplied for a well insulated 120m2 house by using 12m2 of collector and 750L of hot water storage. More accurate estimates can be made using the RETScreen program. Top of Page
8. 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, such as the gravity drain system. Top of Page
9.
FreeFuelForever heat pipe collectors (TZ58-1800/20R) and u-tube collectors (SLU1500/12) are both certified in Canada and Europe and the USA. See certification on the top menu. Top of Page
For USA incentives, see http://www.dsireusa.org
http://www.builditsolar.com/References/energyincentivesrs.htm
11. 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. Top of Page
12 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. Top of Page
13 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/m2 is shown on test reports, at HUwww.freefuelforever.com-see downloads. For the German laboratory where testing was done, yearly gains were 600 to 800 kilowatt hours per meter squared of collector. Top of Page
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. Top of Page
15. 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. Top of Page
16. All glass tubes with water in tube are very cheap, why use anything else?
No pressure is possible. 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 lower than heat pipes, since liquid moves slower than vapour and condensation transfers more heat than conduction. Top of Page
17. 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. Top of Page
18. 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. Top of Page
19. 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. Top of Page
20. 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. Top of Page
21. Which solar collector is most efficient?
U tube collectors are about a half a percent more efficient than copper heat pipes; almost the same, in other words (see www.freefuelforever.com downloads, test reports and certification for numbers). Copper heat pipes are more 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. Top of Page
22. What are the advantage of a 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. Top of Page
23 What are the advantages of u-tube solar collectors versus heat pipe collectors?
Very slightly higher efficiency- about 0.5% higher. 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 Top of Page
24. 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. Top of Page
25. Which solar collector system is cheapest to buy?
Gravity drain integrated systems are cheapest, followed by pressurized integrated systems, followed by split systems. Manual control is cheaper than automatic control, no pumps are cheaper than using pumps, mechanical controls are cheaper than electronic controls, and drainback is cheaper than glycol. Top of Page
26. Why use a pressure system when a no-pressure system is cheaper?
Pressure systems can be installed at any level. High flow rates are possible on a pressure system by increasing the pressure. On a gravity system, the higher the collector is placed, the more pressure is possible. If the roof is low, a gravity system will need a pressure boost from a pump downstream of the collector. Top of Page
27. Which collector delivers the lowest cost hot water?
An integrated, gravity system is best, then the premium pressure system, then the split system. Top of Page
28. Why is an integrated system cheaper than split system?
A tank on the roof eliminates the circulator pump, pump controller, heat exchanger and associated valves and plumbing. Setup can be done by virtually all home owners, eliminating installation costs. Top of Page
29. Why use a split system if it is more expensive and complicated?
Appearance-the collectors alone blend in to the roof better than a tank. Special applications-in floor heat, or water tanks that must be inside a building.Top of Page
30. How much money can be saved using solar hot water?
About 70% of an energy bill for water heating can be saved in most of the USA. See the economics of an indirect (split) system using the renewable energy technology (RETScreen) program here: http://www.freefuelforever.com/House%20example%20split%20system.pdf and a direct (integrated) system here: http://www.freefuelforever.com/House%20example%20integrated%20system.pdf Top of Page
31. Why not use 100% solar?
The system would be oversized in the summer and cost too much. A 100% solar system would work in a place with no summer and winter seasons and the same amount of hot water being used every day. With occasional cloudy weeks and occasional large groups of guests, a backup heater is needed. Top of Page
32 What is the difference between flat plates and evacuated tubes?
Older style flat plates with water tubes attached to the metal were the first active systems. Newer technology evacuated tubes have higher efficiency, no heat loss across a vacuum 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 supplementing the older style flat plates. Top of Page
33 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. Top of Page
34 Is there sales tax on solar products?
Tax depends on location where the solar product is sold. In most Canadian provinces, such as BC, no Provincial Sales Tax (PST) is applicable, but Goods and Services Tax must be charged. Every state in the USA is different, but many do not charge tax on renewable energy products. Top of Page
35 How do I install a solar water heater?
Use the installation manuals on www.freefuelforever.com and install the system yourself, or call your local dealer for a suggestion on who can install it for you. Top of Page
36 How much does a solar system cost?
Price lists for complete systems are on www.freefuelforever.com under “home”. Top of Page
37 What is the difference between a premium pressure system and a gravity system?
The gravity system has glass heat pipes; the pressure (premium) system has copper heat pipes. This means the gravity system drains by gravity, while the pressure system can be put under high pressure. In practice, this means that the gravity system has to go up on the roof, or somewhere high, to get high water pressure. The pressure system can be put anywhere, even below the point of use and high flow can be achieved simply by increasing the input pressure. Both systems have collector areas sized to heat up their tanks of water in the same time-about 3 or 4 hours in full sun. The difference in price comes about because the pressure system has to have everything made stronger and has extra components (pressure relief valves, copper pipe, aluminum fins, brass collars). Top of Page
38 What are the advantages of the premium, pressure system?
The premium system can be pressurized for high water flow even if the collector is lower than the water outlet. Construction materials are more robust than the gravity drain. Use the premium, pressure system if you have no elevated place for the collector or you simply like heavy-duty stainless steel components. The pressure system comes with a reflector as standard, adding some rigidity to the frame. Both the inner tank and the outer shell of the pressure system are stainless steel, making them very heavy, but very tough. Top of Page
39 What are the advantages of the gravity drain system?
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, probably because they are closed on the end like an egg rather than open like a thermos-see the installation manual, all glass heat pipe end photo: http://www.freefuelforever.com/Gravity%20System%20Installation%20Manual.pdf High pressure is possible out of a gravity system-just put it up higher from the point of use. There are other tricks as well, such as a pump downstream of the collector, or a standpipe on the air vent to increase pressure. Top of Page
40 Which systems are the most popular?
Of the several million solar water systems sold in China every year, over 90% are gravity drain and the rest are split systems. Pressure systems with copper heat pipes are not for general sale in China; these are special order for the export market. Copper heat pipes are too expensive for the Chinese market. Moreover, over 90% of Chinese gravity systems are water in tube. Glass heat pipes, with their higher efficiency, yet moderate cost, are a recent innovation. The Chinese top of the line domestic system is our gravity system. Top of Page
41 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. For these reasons, heat pipe gravity drain systems are the top of Chinese domestic line.
Top of Page
42 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, but with a water supply, you are fine. Top of Page
43 How can I tell how much energy the system is producing?
The temperature probes on the controller can show how much energy the system has produced. You know how many liters of water you have used, you know the input temperature, and you know the output temperature from solar. Multiply the temperature change by the liters of water by the specific heat of water and you have the amount of energy harvested. There are different controllers, different functions, a few of them can display the total solar gain directly; with our standard one, we would need to program it to display directly. To show people a good visual indication, see the RETScreen.net government program, see here: http://www.freefuelforever.com/House%20example%20integrated%20system.pdf for an example. Notice the solar fraction and MW-hours of energy are shown, plus cash saved. You can make the same analysis for your system.
44. 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 regularily so pipes do not cool down
- Pressurize the system (pressure, premium 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 (gravity system, drainback 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)
Top of Page
|
