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sinthome

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Reply with quote  #1 
Hi, I am relatively new to this forum and imagine this has aleady been discussed, but I can't seem to find relevant threads and am not sure which section it should go in.. What are the pros and cons of a hybrid PV system with hydronic thermal integrated behind it and/or hot air collector? Does this maximize efficiency or actually detract from the overall energy capture? I am concerned less with the "quality" of the energy (kW vs BTU and DHW temps vs warm pool water temps, indoor heat temps, etc) than with the overall efficiency. I find the "stacking" of functions to be an appealing idea, but also the simplicity of design and diy-able projects. Thoughts?

SolarInterested

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Reply with quote  #2 
PV in front of anything is going to block/absorb most of the light, is it not? Are you thinking of trying to draw heat from the back of the PV panels by circulating air or water (in pipes) on their backside?
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Both temperature rise and airflow are integral to comparing hot air collectors
stmbtwle

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Reply with quote  #3 
If I were to try that I'd put the PV panel INSIDE a hot-air collector with airflow on both sides.  PV panels are black or nearly so and can get pretty hot.  Installing the panel inside a collector would capture that heat, and might actually COOL the PV panel.  PV panels oddly produce MORE electricity when cool.  However if you reduce your airflow in an attempt to get more heat, you'll lose power from the PV.  I'm not sure what would happen if the collector stagnated and overheated though, it might get expensive.

I think trying to heat water from the back of a PV panel would be more trouble than it's worth.  It's been tried.

With the price of PV continuing to drop, PV is now considered to be a better choice than a thermal system for domestic hot water.  
http://www.renewableenergyworld.com/articles/2013/09/solar-hot-water-which-is-better-pv-or-thermal.html

Also, once the water reaches max temperature, a thermal system has to shut down.  A PV system will continue to produce power which is available for other uses.

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Willie, Tampa Bay
Garage_Hermit

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Reply with quote  #4 
project here has PV panels integrated into roof glazing, so roofspace still gets a fair proportion of natural light...

http://www.simplysolar.supporttopics.com/post/affordable-zeroenergy-design-7506796?pid=1287963018#post1287963018

"The Bridgend house has glazed solar photo-voltaic (PV) panels fitted into the south-facing roof, allowing the space below to be naturally lit"

G_H

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sinthome

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Reply with quote  #5 
Thanks for the replies. Yeah, PV continues working after the thermal collector stagnates, but it if the DIYer can build a collector for 1/10th the cost of the pro installation, then it is still worth it. The most promising design that I have found for PV/T is thin film PV that have a PCM layer behind them with hydroni tubes integrated into it. Check this out: http://solartoday.org/2015/01/solar-electricity-and-heat-in-one-package/ and also this link suggests that thin film performs better under high heat: http://www.mtu.edu/news/stories/2012/july/more-heat-more-light-step-toward-better-solar-energy-systems.html

Not sure if these directions have shown much commercial progress or what the potential for DIY might be..
stmbtwle

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Reply with quote  #6 
It all boils down to "cost efficiency"
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stmbtwle

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Reply with quote  #7 
Then there's "space efficiency". For example:

My little ARETHA has a footprint of 8 sq ft. With the attached PV panel it takes up about 10 sq ft. 85% of the energy that strikes the PV is wasted. If the PV were inside the collector, I could (a) capture that energy and (b) build a 25% bigger collector in the same space. Total efficiency (per sq ft) should increase. Something to think about.

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Willie, Tampa Bay
SolarInterested

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Reply with quote  #8 
Quote:
Originally Posted by sinthome
... What are the pros and cons of a hybrid PV system with hydronic thermal integrated behind it and/or hot air collector? ...

sinthome this was one aspect I hadn't thought of:
"The cooler the panel the greater the PV generation, however, this means the coolant fluid is also at a lower than optimal temperature for heat generation." from;
http://www.solimpeks.com/wp-content/uploads/2012/06/pvt_presentation_en.pdf
Their solution is to offer two types of PV-T panels, one biased towards electrical generation and another biased towards thermal heat production.
http://www.solimpeks.com/pv-t-hybrid-solar-collectors/

The same PDF file mentions that "A typical PV panel on a bright sunny day will reach temperatures in excess of 110°C." Gary Reysa on the Build-It-Solar site shows that the water returning to the panel from the tank can be 57°C (134°F) so that' still a difference of 50°C for cooling.
http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/Performance.htm

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Both temperature rise and airflow are integral to comparing hot air collectors
stmbtwle

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Reply with quote  #9 
Juggling the temperature could be an issue...

The heat is there; a stagnated water collector can come to a boil, and will get even hotter if it boils dry.

However we all know that output temperature is related to flow rate.  Reduce the air/water flow and you will get higher temperatures.  Increase the flow and you'll get lower temperatures.

The problem could occur when the water storage reaches set temperature and cuts off the flow (not unusual here in Florida).  Then the collector WILL stagnate and high temperatures could be reached.  The system might need a "heat dump" to get rid of the excess heat and cool the PV.

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Willie, Tampa Bay
SolarInterested

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Reply with quote  #10 
If the PV panel is not under glazing (like the commercial options linked to above)then the lack of cooling (water flow) just returns a panel to the same state as a normal uncooled panel. You would expect a normal loss of efficiency due to operating at a higher temperature but no damage to the PV panel.
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Both temperature rise and airflow are integral to comparing hot air collectors
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