New system planning - looking for feedback

solardadsolardad Registered Users Posts: 23 ✭✭
edited October 2018 in Solar Beginners Corner #1
Hi - Planning a new system, still waiting on the town permit right now.
A couple questions on approach related to number of MPPT controllers and / or arrays.

Some details:
Overall goal is to have a system that will supplement our house-hold use, either dedicated off-grid powering a sub-panel separating select loads and/or a grid tied inverted that will not sell back to the utility (utility has a crappy program) but instead charge a battery bank for cloudy days and night time demands.

Looking to do this in phases due to budget constraints but would like purchases to be future proof (or at least as best as they can). 

Phase 1:
Install ground mount array, 8 panels, eventually 12 (72 cell 385 watt Q-Cell rated at 48.21 VOC, 10.1 amp.)
Install MPPT .. ??
Install inverter ...??

Phase 1 questions.
Single or two MPPTs? Wire run will be 120-130' from array to house so I"ll need a decent cable to reduce voltage drop, probably a 4 or 6 gauge depending on MPPT and voltage. I like the Victron line 250/100 (at least the reviews) but they top out at 250 VOC. OUTBACK FLEXMAX 100  has a controller that handles up to 300 VOC but I have not seen many reviews on it. Related to that question would be breaking up the array into two or keep as a single?

Here are the numbers based on eventually 12 panels..

Go single array & one MPPT: either a 4s3p or 6S2P: 192VOC / 30.4amp OR  289VOC / 20amp 
Go with two arrays & two MPPT at 3S2P: 144VOC / 20amp 

The controller would need to handle at least a 48v battery bank and the incoming watts (4.6k). 
I will most likely choose a Lithium based system (no firm direction outside of I like the reuse of hybrid automotive systems aka leaf/volt) 
I don't mind running a 2nd line to the house but was not sure if there are any advantages or disadvantages with two MPPTs or trying to buy one that could handle the overall load?
I realize this will be a decent amount of power generated so I plan on converting over our electric H/W tank to support at least one element to this power so it is not wasted while i save funds for expansion. Unsure if I would go DC direct or purchase a small, 1~2k, inverter for AC?.?

Forgot to add I am in the US so inverter would have to be 110/240 single or split phase.

Phase 2 would be the purchase of the batteries and a decent sized inverter that I could use in either an off-grid or hybrid setup - no firm direction on which way at the moment.



  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    Maybe consider a 600v controller (eg  Schneider)?

    Having two controllers opens the possibility of something like one on a southeast orientation, and the other on a southwest.  This allows for a longer period of harvest instead of a stronger noon peak.

    Personally, I'd put the phase 1 money in the bank and wait until I had the loads and the hybrid vs off-grid thing firmed up better.  There are also products in development (eg Midnite) that may be of interest and available when the time comes.
    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
  • solardadsolardad Registered Users Posts: 23 ✭✭
    Thanks for the feedback. I have seen the Context line that they have, I believe the SW and XW options. Though I heard the SW has a problem determining an accurate grid demand and ends up underutilizing your solar / battery. 

    As for timing I am actually feeling pressure to get at least the mount in place since our City is looking to add restrictions on where and size of systems. 

    btw - noticed in your signature that you have a 'nighttime' system.. how does that work, based on moonlight ;-) 
  • BB.BB. Super Moderators, Administrators Posts: 30,737 admin
    What is your end goal? Save money, "go green", have a backup power system for XX days of emergency power, stuff hits the fan, or what?

    In general, the average off grid solar power system generation costs are around $1-$2+ per kWH (the sunny the location, generally the lower the costs). A hybrid system may get down towards ~$0.50 per kWH.

    For off grid power systems, batteries are a real killer. Typically 5-7 year life for medium quality flooded cell lead acid batteries. Electronics will generally last 10+ years. Lithium batteries (appropriate chemistry like LiFePO4, but not cheap) and a good Battery Monitor System (BMS) that integrates with the balance of system electronics (solar charge controller, hybrid AC inverter, monitoring, etc.).

    Grid Tied systems, you can pretty easily get under $0.20 per kWH--But as you found out, local utility rate plans/subsidies (or lack thereof), can make or break an GT power system.

    It can be difficult to "grow" a system over time... Generally you size the battery bank to your loads, and size the solar array to both the size of the battery bank, your loads, and the amount of sun you have (no shading from trees, power lines, buildings, etc. from at least 9am to 3pm).

    And you need sun. For example a fixed array in New Hampshire:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 47° angle from vertical:
    (For best year-round performance)


    So a 4.6 kWH array will generate (pick October, toss the bottom three months (use genset, less power during deep winter months) the system will "harvest" around:
    • 4,600 WH per day * 0.52 off grid system eff * 3.79 hours of sun per day (Oct average) = 9,066 WH per day
    • 9,066 WH per day * 30 days per month * 1 kWH / 1,000 WH = 272 kWH per month
    A fair amount of energy--But at say $0.25 per kWH (*272 kWH per month=) ~$68 per month (October)-- Is that an "interesting" amount of money (off grid/hybrid systems are not cheap to install).

    I am a huge believer in conservation (insulation, double pane windows, looking at HVAC using heat pumps, more insulation, Energy Star rated appliances, turning stuff off when not needed, etc.). It is generally less expensive to conserve energy than to generate it.

    I highly suggest that you get a handle on your loads (which defines the size of the battery bank) and do a bunch of paper designs first--Before you purchase any hardware. There are a lot of pieces that have to fit together to give you a "balanced" system. And for equipment that is a bit of "leading" (sometimes "bleeding") edge like Li Ion batteries, BMS, and equipment integration... This can limit your options by quite a bit.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    This may not be a bad time to buy panels.  Who knows what happens with China, a major producer, and what the affect might be on prices?

    I wish moonlight worked :smile:  The night system is a smaller 12v inverter to avoid running big 48v units with light loads overnight.  It saves roughly 1/2kwh per day, plus running some 12v loads directly with no inverter losses.
    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
  • michaelleewebbmichaelleewebb Registered Users Posts: 12 ✭✭
    whats your budget for phase 1 ??
  • solardadsolardad Registered Users Posts: 23 ✭✭
    @BB.  Goals... it is to reduce cost / go green. Ultimate goal would be 100% off grid but I do not have enough land, roof nor the ability to reduce our demand enough to get there based on critical loads we have today / near future.. Have to disagree on the battery side at least with the folks that I know who have systems, they are still rocking Rolls 2v batteries at 8 and 13 years now with no issues. Granted maintenance is required for those but that is one of the main reasons I'll be looking at lithium, no watering, better discharge range, space and weight friendly, etc.. 

    Agree. From the places that I called they are going through their current stock and will not commit to holding any future prices outside of suggesting a 20~30% bump. Moonlight.. interesting idea on the 12v system. Makes me think.. I do have one small roof that faces East/SE that I could take advantage for roughly 60% sun exposure. might be able to fit 4 panels up there for phase 3... hmmm

    5k roughly. so this is a DIY project so labor is my time but based on current list prices I am expecting to pay roughly $1k mount and 3k-3.5k for the panels, MPPT and associated disconnects, breakers, fuses, wire, etc.. 

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