small system design

palausystem
palausystem Solar Expert Posts: 122 ✭✭✭
I have a few components and wonder will they fit together?

3  170 watt panels: Voc 43.2,  Rated current 4.90A
2  6v 400Ah batteries
Prostar controller PS-15  15 amp
Samplex inverter PST-60S-12A

Does the voltage of the panels mean I need 48v of battery?
Thanks...
Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    You really need an MPPT type solar charge controller...

    If your panels were Vmp~35-40 volts (not Voc voltage), then you could use those panels connected in parallel through a PWM type solar charge controller to charge a 24 volt battery bank (not your present 2x 6 volt batteries and 12 volt AC inverter).

    If you wanted to use only your PWM controller on a 12 volt battery bank, it "could" connect your panels to your 12 volt battery bank, at the cost of ~50% of your present array wattage (vs using a properly sized MPPT solar charge controller).

    For your 12 volt @ 400 Amp*Hour battery bank would "like" a MPPT controller+solar array of:
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 377 Watt array minimum (weekend/summer/emergency power usage)
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 753 Watt array nominal (full time off grid)
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 979 Watt array "typical" cost effective maximum array
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    OK, I'm back at it again.
    I'm confused... can I use the panels and the batteries I have if I get an MMPT controller? Or are you saying I still would need more batteries?
    I'm looking for the least expensive way to get 1.6 Kw per day.  400w for 4 hrs/day. Hopefully using the panels and batteries I have.. At this site I'll get maybe 5 hrs of sun/day.  Not sure, haven't checked that out yet, trees nearby.
    And lastly could recommend any partiuclar models of parts I would need?
    Thanks!
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    The first problem is that your Vmp~36 volt panels are "not a match" for PWM controller running on a 12 volt battery bank.

    Think of it like driving a car in 4th gear up a hill at 20 miles per hour... The engine is out of its optimum power range. Similar for the sola panels, the Pmp=Vmp*Imp... Imp is (relatively) fixed (based on amount of sunlight hitting the panels (100% Imp = full noontime sun).

    With a PWM controller, it will hold the Vmp-array to ~18 volts... So:
    • 170 Watt panel / 36 volt Vmp panel = 4.72 amps Imp (I am guessing at panel specifications)
    • P=V*I
    • Pmp = Vmp * Imp = 36 Volts Vmp (matching MPPT controller) * 4.72 Amps Imp = 170 Watts (excluding losses)
    • With PWM controller P=Vpwm*Imp= 18 volts PWM Vinput "clamp" * 4.72 Amps Imp = 85 Watts (excluding losses)
    You either need to run the battery bank at 24 volts with Vmp-array~36 volts (with a new 24 VDC input inverter).. Or run an MPPT controller to efficiently down convert 36 volts to the ~14.5 volts needed to charge the battery bank.

    Or, use the PWM controller and 2x more solar panels on a 12 volt battery bank (using only 50% of panel "Wattage").

    The next question. I understand that you want the least costly solution... Are your loads running during the middle of they day (only when the sun is shining, shut down/reduce loads during bad weather), or is it "charging' during the day and "discharging" at night (all load power comes from just the battery bank)?

    Also, do the loads run every day or do you have at least one day between running loads (and are loads seasonal, during summer/good sun, or 9+ months a year full time).

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    San Francisco
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 52° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    3.77
     
    4.26
     
    5.46
     
    6.07
     
    6.21
     
    6.07
     
    JulAugSepOctNovDec
    5.49
     
    5.34
     
    5.40
     
    5.05
     
    4.19
     
    3.69
     

    How "reliable" does the solar based system need to be? Suggest base loads should be no more than (roughly) 50-65% of "predicted" daily harvest.

    And sizing the battery bank... If you "nightly" use 1.6 kWH per night, I would suggest that you only plan on 25% discharge per night. In general, Lead Acid battery banks are slower to charge and need almost 2 days of sun to recharge from a 50% or deeper discharge.

    "Conservatively", a suggested battery bank size would be:
    • 1,600 WH per day * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days storage * 1/0.50 max discharge = 627 AH @ 12 volt battery bank
    And working the rest of the math... 5% rate of charge for weekend/summer usage. 10%-13% full tome off grid:
    • 627 AH * 14.5 volts charging * 1/0.77 panel+controller derating (assuming "matched" Vmp=Vbatt) * 0.05 rate of charge = 590 Watt array minimum
    • 627 AH * 14.5 volts charging * 1/0.77 panel+controller derating (assuming "matched" Vmp=Vbatt) * 0.10 rate of charge = 1,181 Watt array nominal
    • 627 AH * 14.5 volts charging * 1/0.77 panel+controller derating (assuming "matched" Vmp=Vbatt) * 0.13 rate of charge = 1,535 Watt array typical "cost effective" maximum
    And sizing based on your sun and loads (assuming 5 hours of sun per day, or ~March through October for SFO):
    • 1,600 WH per day * 1/0.52 off grid AC system eff * 1/5 hours per day = 615 Watt Array "break" even
    • 615 Watt array * 1/0.50 "base load fudge factor" = 1,231 Watt array (assuming full solar support for 1,600 WH per day base load)
    Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Thanks...
    Answers to your questions:
    This is for a greenhouse that needs lighting when the sun is not up.  So loads will be when there is no sun.  No days off between use.
     
    Still trying to work through my aversion to numbers crunching but giving it a go.  When I see you write "1,600 WH per day * 1/0.85 AC inverter eff"  I know the asterisk is multiply, but not sure of the 1/0.87 part. Is it just divide 1 by .85? and then multiply that by 1,600?


    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Yes that is a divide by... I try to write the math like an English sentence (read/perform operations left to right).

    I use 1/0.85 because 85% is a good (usually conservative) AC inverter efficiency number (i.e., typically 85%-95% efficient depending on loads, brand, MSW or PSW, etc.).

    I could use (1/0.85=) ~1.18x as a "multiplier. But that is one more "magic" number I have to remember and explain where it came from/what it represents.

    So, in this case, your "loads" are 1,600 Watts... And because of losses in the inverter you have to pull an extra 1.18x more energy from the inverter (or the 1/0.85 -- Smaller than 1.0 denominator, makes the number >1.0).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Thanks for the math.  Very helpful.  Will be running system April thru Oct. Thinking of pulling some electricity from the main system since it looks like this little sytem will get maxed out. Do you have any advice on an MPPT controller for me to buy? And it looks like my inverter is for a 24v system...
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Before recommending hardware... Really need to finish the paper design. What size battery bank, what size solar array (based on your "fudge factors/expectations". Size of AC inverter. Any special needs (remote monitoring/control, etc.).

    Once you have a cut at the details on paper (and that can include 2x designs--One MPPT, another PWM). Even battery chemistry (flooded cell, AGM, or even LiFePO4 possibly). How many years do you expect this to operate? If/when something goes wrong, expensenses to repair (and aging, etc.).

    For example, the voltage of the battery bank and size of the solar array (and what panels you can get for a good $$$/Watt price) will define what charge controller type you can use (and size).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Yeah, so I'm looking at using the three panels and the batteries I described at the start.  12v battery 400ah, daily loads of 1kw.
    1,000 x 1.18 =1180 x .083 = 98.3 x 2 days = 197 x 2 (dod) = 393ah.
    393 x 14.5 = 5698 x 1.3 =7,400 x 7% = 518w array

    I see 12v MPPT's for $99...
    And a modified sine inverter (running LED lights) for &70...
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Sun and Loads:
    1000 x 1.93 = 1920 x 0.25 = 480w array
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Very basic - just running 250w of lights for 4 hrs/day.  No remote control, etc.  I hear that the modified sine will work fine with the LED lighting, but might cause a buzz or hum.  The batteries are lead/acid.  I've had them for awhile, they were warranty replacements from Surrette, then we bought a fresh bank and I saved these out as they were only a couple years old. If I get another few yrs I'll be happy.     
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    I see a MPPT controller that has 520w max input.  My panels will add up to 510w.  I don't suppose they could ever spike up to 520w?
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Generally, the panels only reach max power on a cold day at noon.  Most decent MPPT controllers will gracefully handle any small overpower glitches, as long as you are not crazy overpower, or running close to max input voltage on the controller
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Thanks Mike,  The inverter I have in mind is for 750w output.  I'll be running 400w max loads.  It's $50.  Is there anything I need to watch out for in these cheap inverters? 

    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    cheap inverters are nearly always mod sine, which is bad for motors and transformers, making them run hot and consume more power than normal
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Yes, I read about that. This is just for a few lights which might buzz from the mod sine. I did a search online and others say that LED lights work OK.
    I wanted to get a cheap pure sine but it was on back order, may upgrade later.
    Thanks to BB for his very helpful posts. 
    I need to build some ground mounts for the panels. Anyone point me to a simple design, preferably wood-based?

    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    For BB -
    what is "matched Vmp =Vbatt"?
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    But... Do the LED's have a transformer to get hot? Maybe they do. Maybe its a bad idea.
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    I need to build some ground mounts for the panels. Anyone point me to a simple design, preferably wood-based?
    For 3 panels you could just, mount to a couple 2x4's. us pieces of aluminum angle, and pre-drill to allow proper spacing between the panels 1/4-1/2". Use SS bolts to connect to the wood. You don't need the plastic between the aluminum and PT wood, after 8 years on some I didn't include the plastic I saw no real difference.


    Bolt to a coupe 2x4's, Most panels will provide enough cross bracing, but you could add some. If you buy long enough 2x4's to allow 2-3 feet from the bottom, you could build a free standing frame like this old set of mine, each only had a single cross/angle wood brace in the panel plane and the support plane. Survived 8-9 years before I sold the system.



    Those panels I used a wood frame base and the power center and batteries to add ballast. Another option I've used on similar quick sets to what you are talking about, is to use 'T' posts or aluminum angle screwed to the bottom of the 2x4 to slide into the ground. and again with the support. It does depend on the type of ground you have though.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    But... Do the LED's have a transformer to get hot? Maybe they do. Maybe its a bad idea.
    They have a switching transformer to reduce the voltage, arguably the weakest link, a modified sine wave may cause premature failure due to the abrupt changes in the waveform as opposed to the smooth profile of a pure sine wave. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    For BB -
    what is "matched Vmp =Vbatt"?
    Most all solar charge controllers need a "voltage drop" from the solar array to the battery bank. So, the "base minimum" voltage from the solar array starts with the question of "what is your battery bus voltage?".

    For a PWM charge controller, that means the Varray would need to be (minimum/optimum array voltage):
    • 12 volt battery bus => Vmp-array of 17.5 to 20 VDC
    • 24 volt battery bus => Vmp-array of ~35-40 VDC
    • 49 volt battery bus => Vmp-array of ~70 to 80 VDC
    For an MPPT charge controller, the specified minimum array voltage is as above (PWM)--But ideally, Vmp-array should be higher voltage... Typically around 2x Vbatt bus voltage nominal (assuming Vbatt-charging is around 15/30/60 VDC):
    • 12 volt battery bus Vmp-array ~ 30 Volts
    • 24 volt battery bus Vmp-array ~60 volts 
    • 48 volt battery bus Vmp-array ~120 volts
    To be honest, a Vmp-array maximum for a typical "higher end" MPPT solar charge controller is around 100 VDC (assuming subfreezing temperatures in winter).

    The actual Vmp-array min/max (standard temperature/marketing number) is solar charge controller, PWM/MPPT type, location's min/max outdoor temperature range, and specific brand and model. It does get a bit complicated and, here, details matter (no generic "optimum" answer).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    Yes my lap top uses a switch mode power brick .
    Chew through 2  before going to pure sine . 
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    FWIW, I run most of my LED lighting directly on DC.  They normally use a 120vac power supply in a regular household installation, which outputs ~13vdc.  Running off DC directly eliminates inverter and transformer costs/losses and avoids the MSW issue (albeit at a cost of heavier wiring for higher current at low voltage).  If lights are close to batteries, this might be worth considering.

    The lights do need to be able to take the range of battery operating voltages (~10.5-16v for 12v nominal).  You'd need to confirm for your particular lights.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Having to redesign a bit after finding I had only 2 170 panels available. Now I need one more 170 w panel and am trying to understand how much of a match the new needs to be.  So I have 170w 24v panels.  I need to add 170w, there are a lot of 12v 170's out there, if I have MPPT can I mix these two voltages? Are there other numbers that have to match?
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    The general rule of thumb for parallel connecting solar panels... Match Vmp of each panel/series string voltage of 2x 12 volt panels to within 10% (i.e., 35 Volts Vmp for one, 38 Volts Vmp for the other). i.e., if your "24 volt panels" are Vmp~35 volts, then two "12 volt panels" with 2x17.5Vmp=35 volts Vmp.

    Same for series connecting panels... The Imp of each series component should be within 10% (or less)...

    Where you need to be careful... "24 Volt" panels can have Vmp range from 24 to 30 to 36 volts Vmp. If you have 30 volt Vmp panels (60 Cell 170 Watt panels), then you should not parallel with 2x "12 volt" panels which are typically Vmp~18 volts (36 cell panels). You put 2x in series for 36 volt Vmp... More than 10% away from 30 Volts for the other panels (if 60 Cell panels).

    So, what is the Vmp+Imp of your 170 Watt "24 volt" panels... And what is the Vmp+Imp of your "12 volt" panels.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    my 2 panels are 34.8 Vmp. The 12v I'm looking at is 17 Vmp. So two of the 12's in a string = 34. The Imp of mine are 4.9 A. Imp of the proposed 12v is 10.3.
    Based on what you're saying,  I would need two of the new 12v. On a separate string. But now with the Imp being so different...can I connect these two strings and have it work?
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    In parallel is fine... A+B+(C-D).

    C+D are the "12 volt panels" in series. Then connect A, B, and (CD) in parallel.

    Check the series fuse requirement in the spec. sheets... Each parallel connection should have it own series fuse/breaker (typically around 10-15 amps or so)... The 35 volt panels may need 10 amp, and the CD string need 15 amps.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Thanks, Bill,
    so I see an mppt controller spec as "fit 900w (12v), 1700w (24v), max input 150v".
    If I understand correctly, the max wattage it will accept is 900w for my setup? And the voltage I will be inputting is max 70?

    The one I already ordered when I felt the urgency was "Max. PV input power:520W(12V Battery) & 1040W(24V battery)" which sounds like it will not work with this many panels, am I right?

    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    What is the planned Wattage of your array?

    For an example, the 900 Watt (MPPT) controller would output (average maximum/peak power on cool clear day near solar noon):
    • 900 Watts * 0.77 panel+controller deratings * 1/14.5 nominal charging voltage = 48 Amps "peak" charging current on rare cool/clear days
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    4x170w total 680w array.
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    680 Watt array on a MPPT controller, the "minimum" suggested rated output (on a 12 volt battery bank):
    • 680 Watt * 0.77 panel++controller derating * 1/14.5 volts charging = 36 Amp (rough) minimum suggested
    And as long as the MPPT controller Vinput (Voc-array-cold) rating is respected, ~35 volts is a good Vmp-array for a "12 volt" (~15 volt max) charging battery bank (~2x Vbatt for Vmp-array is a good starting point).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset