Simple Solar Domestic Hot Water

I'm a fan of mind maps. They help me put all the aspects of a complex project down in one place. This writing is much more intuitive and natural than trying to write a linear outline. The only problem with it is that once written, it often doesn’t fit nicely on a normal page! So, here’s what started life as a mind map, but I’ve converted it to outline form, so you can read it! The central theme of it is the title. From there, each bold heading is a category linked to the title. Likewise, there are sub-categories or thoughts related to each category. Enjoy!
Definition of Simple Solar

• Must be easy to design, install and use.
  
• Low cost. It should install quickly and use low-cost components.
• Long lived. Otherwise, what’s the point!?
• Little/no upkeep. If it’s expensive or hard to use, that doesn’t work.
• Should not require an attentive user.

What does it look like?
Passive (no, or few moving parts. No electrical usage)
1.  Large diameter piping in attic

• no separate storage tank
• 4” pipe holds .653 gallons/ft (94 feet would give 60 gallons)
• 2” pipe holds .163 gallons/ft (368 feet would give 60 gallons) 

2. Trombe wall style behind glass

•   Big Fin? This is a metal solar absorber with a pipe in the center

3.  Places where there is excess or waste heat

• equipment room
• under asphalt
• attic
• kitchen

4.  Batch heater vs active lid (Batch style is the oldest type of solar.             
      An active lid makes it far more efficient.) It could be placed on…

• roof
• ground
• sidewall

5.  Thermosyphon w/freeze resistant collector (this puts collector lower than hot water storage tank. Driven by gravity.) Collector possibilities/considerations…

• freeze expansion element inside of tubes
• plastic or rubber construction
• would need to take water pressure
• would need to expand with freezing

Active system (probably uses electricity)

• Low pressure
• unglazed collection

1. on roof
2. in attic

• attic fan-coil
• plastic tank w/pressure in coils

1. plastic collection (ie: PE or pool collectors)
2. pumped or thermosyphon

Long lived

• Plastic poly piping
• Little/no overheating
• Protected from freezing

  Climate specific

• No freeze (Hawaii)
• Freeze tolerant (everything in between)
• Freeze proof (Alaska)

Low risk

• Leakage won’t cause damage to home or contents
• Overheating can’t happen, or can only fail safe

Places for system collector to collect heat

• attic
• greenhouse
• sunspaces
• equipment room

Preheat

• don’t have to go for 100%
• even 50% is pretty good
• large inefficient collectors

Combined with other conservation measures

• drain water heat exchanger
• low volume piping
• efficient fixtures
  
• heat/water-saving shower
• efficient recirculation

As you can see, there are lots of things to consider when considering solar hot water. One thing that isn’t mentioned so far is being water efficient. If you use half as much hot water, it will be easier and less expensive to build a solar system that does the bulk of your water heating. Efficiency is always the low hanging fruit! This article may create more questions than it answers, but that’s okay. The more you consider possibilities, the more you can refine your thinking to design a system that truly meets your needs and budget.
 

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