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Talk:Solar hot water

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Some comments[edit]

Here are some of my questions and comments on this page:

  1. The background seems to have an inappropriate amount of opinion.
  2. Should the page name be changed to Solar hot water basics, and Solar hot water just link to Category:Solar hot water.
  3. The photovoltaic references in the Energy From The Sun part seem very out of place.
  4. How is this Appropedia value added over a purely encyclopedic article that would be better placed at Wikipedia? This article should probably focus more on making it happen.

Thank you, --Lonny 19:35, 2 September 2007 (PDT)

Hey, all:

Some notes from a newbie who is not yet BOLD, and doesn't have the HTML/formatting skills to make quick improvements. First, on the technical side, "solar THERMAL energy" is incorrect since it is all sunlight of all wavelengths, and it is converted to infra red heat in the collector and transferred to the water. Collectors are black to absorb as much light as possible for this very reason. A white hose on the lawn has less energy conversion than a black one for this reason. A solar water collector works at the same conversion rate in the coldest weather as it does in hot weather for the same reason. It is not "thermal" until it is converted.

Second, functionally solar water is efficient and easy not for the reasons stated, but because the solar energy is free, i.e., NO FUEL COST. System costs can be very reasonable as well, which leads to....

Third, from a practicality standpoint, it should be stated in an appropriate place that solar domestic water heating systems are among the most cost-effective means of reducing utility and energy costs, and if fossil fuels are otherwise involved, reducing GHG is also cost-effective and direct. For this reason, a solar hot water system is the first thing people should consider purchasing or building. Single-family residences and buildings with <2-3 floors can be fitted with roof-top systems with little complexity due to pipe runs. Moer floors gets more expensive due to piping costs. Properly sized for user demand and sunlight availability, a system can supplant practically 100% of conventional water heating needs.

Fourth, I noticed a batch heater (type with the horizontal tank above the collector) photo at the top of the page and the same one at the bottom.

Fifth, to illustrate the installed extent of solar water, there is a photo of a European apartment rooftop with dozens of collectors. If I can find it, I will see about providing it.

Sorry at this point to appear to be on the sidelines kibitzing, but as I learn I will be able to act more directly to improve things.

David Messages done with sustainable energy, with Wind and Sun! 20:02 9 Aug 2008 CDT

Hi David,
Great comments. Below are responses to each of your points.
First: Good point, feel free to change the text as such. You can keep the link to the excellent, Practical Action Solar thermal energy page by placing it somewhere else more appropriate on the page. Or by using a pipe (|) to link using a different name, e.g. [[Solar thermal energy|Solar energy]] links to Solar energy.
Second: Functionally solar water is efficient for the reasons stated, i.e. it is more efficient than conversion because of the losses associate with conversion. That said, I agree that the effectiveness is even more a product of the incredibly cheap energy source of the sun (I usually differentiate between free energy and really cheap energy, solar power being really cheap because it is landing all day long but you still need to get it, whereas nothing is free... of course this is merely semantics). Please click edit on the introduction and change the text as you see fit.
Third: For any assertions, like stating what the first thing a person should consider is, citations are really useful. In addition, try to state where the statement holds true, such as "In the United States...".
Fourth: You can delete that photo by clicking edit and deleting the last image, which is written as [[Image:Solar_heater.jpg|thumb]].
Fifth: That would be great. Just make sure that you get permission (or that permission exists) to use the image under the GFDL or CC license (many photos on wikipedia and flickr use these open licenses). I took some nice photos of this in Morocco two months ago, but the camera was stolen before I could transfer them. I may have another image, that shows how extensive solar water heater installations can be, from somewhere else. Let me know if you do not find the image and I will look through my own.
Don't be sorry about kibitzing... lurking, then asking questions and starting to slowly engage is a good way to go. I hope that this feedback helps you proceed.
Please don't let your lack of formatting skills stand in your way. Most of what you need to know about formatting is at Help:Contents (and the rest under Category:Appropedia help). Please try editing and ask for assistance when you need it. All changes are stored under the history tab (click it at the top of a page to see all the changes), so we can always revert back if needed. Please do keep in mind that we are building global living library. Much more important than formatting, is truth, transparency and tone. Editorializing is great on the talk pages, but work on category pages should be referenced and scientifically valid. Thank you for helping us get closer to that.
Thank you, --Lonny 02:39, 10 August 2008 (PDT)(PS use 4 ~'s to get an automatic signature... you can set your signature in your preferences)

One extra note about licenses[edit]

It's important to only use images with free licenses - which in CC terms means CC-BY-SA or CC-BY, and not anything with an NC or ND clause (i.e. "non-commercial" or "no derivatives").

Non-commercial license specifications make Richard Stallman sad ;). --Chriswaterguy 03:22, 10 August 2008 (PDT)

System types and circulation options[edit]

  • Batch Solar Heaters: A batch heater is basically a metal tank inside a box that is glazed on the sun facing side and insulated on the other sides.

There are a bunch of designs for them here: They are pretty efficient and widely used. The tanks are somewhat resistant to freezing, but the plumbing between tank an house can freeze. People in cold climates often shut them down for the deep winter. In a climate like the one mentioned in the article you sent, they would probably be fine year round. Probably the biggest challenge is finding the tanks, but they are nice simple, low maintenance systems that don't require any power or control system.

  • Thermosyphon Collectors: This is the type of collector shown in the article you sent. Basically a solar collector that is mounted below a storage tank. When its sunny, the collector heated water rises up into the tank as its density decreases. At night the circulation automatically shuts down as the water in the collector cools and becomes more dense. They are nice simple systems in warm climates, as no heat exchanger is required. They do get more complicated in freezing climates and require a heat exchanger as in the one in your link. Some thermosyphon designs here: One thing I noted in the article is that they don't appear to specify what kind of antifreeze is used. There should be a warning against using ethylene glycol as it is poisonous. Propylene glycol is not poisonous and should always be used.
  • Drain Back Systems: Drain back system have the storage tank located below the collector and when the sun is not on the collector and the controller shuts the pump down, all of the water in the collector drains back into the tank -- this provides freeze protection in that there is no water in the collector when its cold. Normally these systems use a controller and a pump that work off line power, and this adds to the complexity, cost and maintenance. But, they are good reliable and simple systems. If the vertical distance between the tank and the top of the collector is relatively small, then it is possible to use a small DC pump directly powered by a small PV panel. This eliminates the need for a controller, as the PV panel only generates electricity when the sun is on it. PV panels and small DC pumps are available at pretty low prices these days.

Of all the systems mentioned above, the drain back and the thermosyphon with heat exchanger are the only ones that will work in a climate with hard freezes.

Mention in article, info from Gary from BuildItSolar KVDP 00:30, 12 July 2013 (PDT)


Images: solar water heating system.JPG and may be added to the solar hot water article; however they include "self-closing valves"; aldough I think this is possible to implement, not sure whether it allows the systems to be used as "appropriate technology" alternatives

Tank placement[edit]

I think the placement (height) of the tank is important aswell. For example, The Zaragoza system placed the tank above the collector. This seems to be inefficient (pump needs to work harder, more energy loss). I think the basic concept/design can be kept, yet needs to changed a bit. Ie, by placing the tank lower -same height and size of collector-, see this image. Another main design flaw is that there is no metal between the pipes guiding additional heat to the pipes. This metal can be either a bend flat plate or fins; see and

Other improvements may be painting the box of the device black, correct tilt of the collector to the sun, depending on location (latitude) and time of the year, facing true south or north (depending on hemisphere), possibly more insulation on part, pipes, making the pipes to the boiler as short as possible, ... KVDP 00:54, 31 May 2013 (PDT)