Roof Material vs Panel Temp?

I'm fixing to start building my Garage with one bedroom and game room above, I'm trying to get my oldest daughter out of the house! I want all the power to come from solar for the second floor so it will be off-grid. I hope to accomplish a couple of things, first get my feet wet in solar. Second teach my daughter about conservation, she wants to be an engineer and is eager to help me. And third In the event of another hurricane we will not be without the bear essentials for almost three weeks. Sorry, to my question….. I know heat is an issue with solar as temps rise the efficiency decreases. What would be the best roof material to try to reduce the heat in and around the panels? I can use just about anything I want metal, composition and the color is not an issue? I plain to have 6 200w evergreen up there as soon as I can, they will be facing full south with no obstructions.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,611 admin
    Re: Roof Material vs Panel Temp?

    As I understand--the solution to keeping the panels cool is to have the panels raised at least 6 inches off of the roof to allow natural air flow (more than 6" does not improve cooling, less than 6" and the panels start getting warmer from the lesser air flow).

    Doing raising the panels is probably a 5% improvement in output vs placing them flat against the roof. So--if you want to keep the panels against the roof (for example, aesthetics)--the panels still work work fine.

    Regarding off-grid vs grid tied systems--when all is said and done, a grid tied system will provide power at ~$0.10-$0.30 per kWhr, and an off grid system will cost you around $1.00 to $2.00+ per kWhr (less efficient, only has ability to store power for 3 days vs "up to a year" for net metered utility connections). Note the kWhr pricing is a very rough estimate assuming ~20 year system life and no interest/unusual maintenance costs.

    Also, some rebates/tax credits are only for grid tied systems.

    A 1,200 watt system is not that large--but if you plan on going larger and still want the advantages of a off-grid system and grid tied too (battery backup, with longer battery life and the ability to use the grid as a "giant battery")--take a look at the Hybrid systems.

    Xantrex's XW system has a 48 (or 24) volt inverter that will automatically run as a grid tied inverter when the utility power is up--and fall back to off-grid when the utility power fails. Not cheap, but a very nice system with a 120/240 volt split phase inverter (no two inverters required or external transformer--plus has support for external genset for backup power). You may be able to use a smaller battery bank for emergency power (vs off-grid living). Keeps some of your costs lower (initial purchase, and replacement every ~7-15 years).

    Even if you decide not to install a hybrid system--it would still be a nice excessive to compare the three setups (GT, off-gird, and hybrid) costs and different capabilities.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Roof Material vs Panel Temp?

    Thank for the information. I will have to look more into that inverter but I do like the idea of having the option for both on and off grid. I wish the unit could be mounted outside, I think NEMA4 instead of NEMA1.

    I don't think we have the 30% rebate here in Houston I think it's only Austin here in Texas

    Thanks
  • BB.BB. Super Moderators, Administrators Posts: 32,611 admin
    Re: Roof Material vs Panel Temp?

    You can use the Xantrex hybrid inverter as an emergency power circuit for your home (a line to your kitchen fridge, a couple lines to interior lighting, the garage room, TV/Radio area, etc.). It is a 4-6kW system--so it does have the ability to run a well pump and other large loads--if needed.

    There is (or should be) a 30% Federal Tax credit... You can look at this site for a set of links to your location (US Tax Credits and various state + local rebates).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Roof Material vs Panel Temp?

    For the roof, look at metal in white or gray in color.
    Testczar wrote: »
    I'm trying to get my oldest daughter out of the house!

    Hum, maybe cheaper just to marry her off.:D
  • ehornehorn Registered Users Posts: 6
    Re: Roof Material vs Panel Temp?
    Testczar wrote: »
    ...I plain to have 6 200w evergreen up there as soon as I can, they will be facing full south with no obstructions...

    Have you considered BIPV's (Building Integrated PV Array)?

    I have not performed any analysis (cost/performance/reliability) but thought I might mention it as you appear to be in the analysis/planning phase.

    Best wishes
  • theLongHairedGuytheLongHairedGuy Registered Users Posts: 6
    Re: Roof Material vs Panel Temp?

    If you live in Houston, I would definitely go with a white metal roof. I did. You can see the picture of solar panels on my garage with a white metal roof in the Solar Beginners Corner under the Pics. sticky.

    For more information, try a Google search for "Cool Roofs".
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