Getting a 6.36KW system installed soon!

After using a VERY small solar setup at a remote farm (I'm upgrading that this fall), and setting up solar thermal (evacuated tubes that have worked amazingly well) we're moving forward for solar for the house (upstate NY...hour north of Albany). Current costs have come down, incentives still pretty good. I am curious to see how much of our future bill this covers - we sized it for pre-solar hot water (as we haven't had that a year yet), but want some room to "grow" as we have young kids and I don't see our power consumption decreasing.... Interesting to see this June we used 378 KWh for the month, last June (pre hot water) 498. Our hope is to try and cover 100%. Annual usage previously was about 8000 KWh. Post solar thermal I'm hoping around 6000, but we'll see how this winter goes (system wasn't operational until Jan., and then had a few leaks we had to work through anyway). Less than 500kwh every month from March on so far. It appears 4.2 to 4.3 hours of sun per day is an appropriate guess for our location. With a bit of tree work I've already started I'm hoping to go from 90% full sun to 100% year round (no shading).

Anyway, here is the setup to be installed this fall:
24 SolarWorld 265w panels
SMA SunnyBoy 6000 grid-tie inverter

Half the panels will be fixed installation on a roof; the other half will be pole mount where I can adjust the angle. I found an interesting site, not sure how valid their figures are, but it was interesting to run through the calculations: http://www.macslab.com/optsolar.html

I've been trying to learn more about the systems, and I have a question about what figure to use to "de-rate" them - most calculators seem to use .75. I know (in theory) the SMA SunnyBoy claims 96%+ efficiency... but there are likely other losses (at least the inverter will be mounted very, very closely to the panels, so a little less loss there). What other factors are considered, and what IS a good de-rating figure to use?

Any other words of wisdom?

Thank you in advance - so far this forum has been tremendously helpful, and void of a lot of the egos and politics you find on other boards sometimes.

Comments

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Getting a 6.36KW system installed soon!

    that .75 derate will apply to ALL systems as it is ~ the losses of sun> pv> CC> Batt >inverter.
    It is the approximation of all system losses.. ball park but a good figure to plan with.

    enjoy
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Getting a 6.36KW system installed soon!
    westbranch wrote: »
    that .75 derate will apply to ALL systems as it is ~ the losses of sun> pv> CC> Batt >inverter.
    It is the approximation of all system losses.. ball park but a good figure to plan with.

    I think the derate is about .75 for grid tie, and much lower for a battery system. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • couchsachragacouchsachraga Solar Expert Posts: 84 ✭✭
    Re: Getting a 6.36KW system installed soon!

    Searching around a bit more I found this site: http://rredc.nrel.gov/solar/calculators/pvwatts/version1/derate.cgi part of the PVWatts site / program.

    Using the info I have from the Inverter and Panels, and leaving the rest the defaults same I get .85 or so, at least when new.

    I'm not sure how realistic that is. It will be fun to see.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Getting a 6.36KW system installed soon!

    do your panels have NOTC ratings? or just STC?.
    the first one is more representative of their 'real' performance IIRC
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • BB.BB. Super Moderators, Administrators Posts: 32,925 admin
    Re: Getting a 6.36KW system installed soon!

    More or less, to allow for aging, dust on panels, batteries towards end of life/not operated in the most efficient manner possible:
    • 0.77 for solar panel+charge controller deratings (summer time)
    • 0.52 for full off grid+flooded cell batteries+AC inverter (summer, assuming "average" system operation)

    • 1,000 Watt panels * 0.77 derating * 4 hours of sun per day = 3,080 WH per day = 3.1 kWH per day (GT)
    • 1,000 Watt panels * 0.52 derating * 4 hours of sun per day = 2,080 WH per day = 2.1 kWH per day (OG)

    Could "you" do 10% better, yes. Pretty easily and in cooler weather with an MPPT controller (near/sub freezing weather).

    Batteries tend to have a wider derating--based on how people operate them (and the age/condition of the battery).

    ~0.90 to 0.98 range for AGM/Sealed type batteries. ~0.80 to 0.90 (or even better) for flooded cell.

    Charging batteries at less than 80% state of charge, higher efficiencies. Lots of >90% SOC and Equalization, can approach much less than 50% average efficiency. Run batteries in the 20-80% SOC, much higher efficiencies.

    Very large batteries vs usage, or very lightly used batteries, less efficiency.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • couchsachragacouchsachraga Solar Expert Posts: 84 ✭✭
    Re: Getting a 6.36KW system installed soon!

    Both ratings... STC (and guaranteed to be at or above panel rating), as well as NOTC (95% +-3%). I used STC numbers to start with.

    As it is grid-tie I don't have to worry about batteries (at the other installation, which will be the 1 kw you describe) I do... but I've been able to make that work with about 150w of panels... going to 1kw (and a mppt controller) (and doubling battery capacity) should bring me to a balanced system with more reserve (there's another thread on that already here).

    We're lucky to be in NY - between the NYSERDA incentive (1.40 a watt directly to the installer), then Federal (30%) and state (25%) tax credits the break-even looks like just a few years... so even if the system doesn't offset everything, our break-even still isn't too bad.

    Thank you all for your thoughts-I learn more with each post.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Getting a 6.36KW system installed soon!

    I like that I have batteries. Makes me appreciate the system more. And I enjoy it more tweaking at it and all that (mainly for the batteries, also for the generator - exercising it under load - requires non-standard settings to exercise under productive load), and the batteries need watering, etc..
  • Lee DodgeLee Dodge Solar Expert Posts: 112 ✭✭
    Re: Getting a 6.36KW system installed soon!

    I would recommend the use of PVWatts Version 2 (http://gisatnrel.nrel.gov/PVWatts_Viewer/index.html), and their default derating factor is 0.77, before accouting for aging factors that will further degrade performance over time. For three PV systems that I am monitoring in a high altitude (7100') part of Colorado, the 0.77 factor causes PVWatts to underpredict the actual performance meaasured over about 3 years by about 15% or 20%, as shown at http://www.residentialenergylaboratory.com/comparison_of_pv_systems.html in Figures 6-11. There is also some discussion of derating factors in the same link.
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