Rhonemas said:
x2 on PV. The cost & inefficiency is the reason I'm not a fan of them. However, sunlight converts to heat very well so solar hot water panels make a lot of sense. Since you live in MA, you can DIY but I don't know about doing it for $1000. I got this solar kit
http://www.radiantsolar.com/solar_packages_and_pricing.php but you can see the individual pricing from
http://www.radiantsolar.com/solar_component_pricing.php. There's 2 types of solar water heating, one is a drainback system the other is closed loop glycol. I prefer the latter even if slightly less efficient. Since MA does not allow you to do your own plumbing for anything tied to potable water or sewer, if you do the closed loop glycol you can do it yourself. A drainback would have to be installed by a licensed plumber since it is tied to potable. That's something to consider (and the glycol in the system has to be special glycol that's safe to drink).
Since MA incentives are based on the output of the panels and State & Federal credits must be SRCC rated to quality, it makes the most sense to buy pre-made SRCC rated solar panels. If from that company, after federal & state incentives each 4x8 panel (30+ year panels, aluminum frame, special glass, copper, special coated fins, and condensation removing device) would be $24 each panel then you'd need the mounts (which you'd get get 30% federal tax credit on). So, figure about $40-$50 a panel in the end and 30% off everything else because now you're using SRCC rated panels. I recommend the Flat panel style, not evacuated tubes.
The rest I personally prefer a kit. You have to handle overheating (which is much less a problem with FP). Have a means to fill and drain, design it so you can shut off & isolate the motor for replacement, prevent backflow, prevent thermosiphoning at night, I enjoyed the kit as all I had to do was run the pipe. My friend did a DIY system (evacuated tubes) and hasn't had as much luck as other DIY have posted (probably because he went with evacuated tubes). He's ended up three times where his system overheated and dumped steaming glycol all over his basement (twice because of a power failure), and his tank overheated and dumped steaming water all over his basement once when he left for a few days. I would stick with flat panels.
Hi,
So, the incentives in MA bring the price for a solar collector from about $800 per collector down to $40 a collector? That is one sweet deal -- or am I reading that wrong? That would certainly be a good argument for going with commercial collectors.
You made the case for closed loop glycol kit systems -- I'll make the case for A full DIY drain back system:
This is the drain back design I use:
http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm and the newer version that does space and water heating:
http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/Main.htm
These systems are full DIY (not kits), and lots of people have built them for around $1000 (before rebates) -- some of the documented here:
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Example1KSystems
- The drain backs of this type are simpler and less expensive and have fewer components than closed loop systems (no expansion tank, PRTs, or fill valves).
- If the plumbing for the drain back is installed correctly (with all lines sloping toward the storage tank), they are essentially maintenance free and provide bombproof freeze protection. The closed loop systems required yearly checks on the antifreeze and replacement if it has degraded. If you don't do the checks, and the antifreeze goes bad, it can damage the system in a couple ways.
- Drain backs are less susceptible to overheating in that the controllers allow a maximum tank temperature to be set, and once that temperature is reached, the pump is shut down and the collector drains back to the tank. The collector is subjected to high temperatures, but it should be built to take these temperatures. With glycol systems, there is always antifreeze in the collector, and when that antifreeze heats beyond a point 1) the antifreeze can degrade from the high temperatures, and 2) the pressure/temperature relief valve can vent and make big green puddles.
- Given that its inexpensive to add some additional collector area and tank capacity, its easy to oversize the systems and get a better yearly solar fraction. It only costs about $6 per sqft to add collector area and a bit over $1 per gallon to add tank capacity, it cheap to add another 30 sqft or more to get better winter performance.
- This drainback design does not need a heat exchanger between the collector loop and the heat storage tank, and that coupled with the better heat transfer capability of water vs antifreeze makes for an efficiency gain.
- Since there is no antifreeze in the system, there is no risk of someone using the wrong (toxic) antifreeze which coupled with a heat exchanger failure could put toxic antifreeze into the potable water side.
On the negative side, there are times when it does not make sense to use a drain back -- mostly when the plumbing can be run with a slope toward the tank, or when the collectors are mounted WAY above the heat storage tank. Drain backs also typically need a somewhat larger pump than closed loop systems.
I don't understand the bit about a drain back requiring a plumber and closed loop not? Both systems are connected to the potable water, else how would they heat it? Can you clarify that?
All that said for the full DIY approach, I am in the process of adding a section to Build-It-Solar that has some good kit approaches for people who just don't want to build the whole thing. If anyone has had a good experience with a kit, or has seen one they like, please let me know.
Gary
