Cost effective backup system, with future solar

PeteSPeteS Registered Users Posts: 8 ✭✭
I have reliable and relatively affordable grid energy. I'm currently using about 8kWh/day, but that includes an electric range and electric hot water heater. The house is new to me, I didn't choose what's in it, I plan on getting a gas range and could change to an on demand gas (propane) hot water heater, although there's nothing wrong with the electric hot water heater. This isn't so much about saving money as it is having immediate backup power for my sump pump, refrigerator, etc., and having longer term backup power if the grid gets knocked out for an extended period of time. Without the electric range and electric hot water heater, I would be good using 3-4kWh/day, keeping the electric hot water heater would add 2kWh/day, although hot water seems relatively non-essential.

I want to start with the backup system, then add solar later. I'm good with purchasing something like eight Surrette 6V S-550 428Ah batteries, or something similar. That provides me with 2-3 days of power at 50% discharge (roughly 10kWh of usable power). 

If I'm using the system primarily as a big UPS, is one manufacturer/product better at managing battery charge levels than another? Assuming I do my part maintaining a set of flooded lead acid batteries, whose product will be more likely to maximize the life of my batteries, which will likely be in a float state most of the time? Even if the grid doesn't go down, does it make sense for me to purposely cut grid power on a regular basis (e.g once every 2-4 weeks) so the batteries do discharge a certain amount, then recharge?

At the moment, I'm between getting:
1) an Outback VFXR3648A, plus I believe I would at a minimum need the Outback Mate3 controller
2) an SMA Sunny Island 6048-US plus the SMA Smartformer

I realize those are two completely different types of systems, with different plusses and minuses. Those two Outback products combined are half the cost of the two SMA products. A fairer comparison (power-wise) seems like it would be a pair of VFXR3648A inverters plus the supporting products, compared to the SMA SI and Smartformer. From what I've read though, at that price point, the SMA SI and Smartformer seem like the better solution than two VFXR3648A inverters with the Mate 3 and Hub10. If I understand it all correctly, the SMA solution with the Smartformer does load balancing, and is more efficient than a pair of Outback VFXR3648A inverters. I also realize that when I do install my solar array, the SMA solution will be more expensive, purchasing an SMA grid-tie inverter vs. an Outback charge controller. But the AC coupled SMA design just seems more logical to me. 

Am I okay with only 120V, or do I need split-phase 240V? If I'm going with the cheaper Outback 120V system, then I don't have hot water, unless I install a tankless propane unit, which is an additional cost. If I go with the 120V Outback system, then some of the most efficient mini-split AC units on the market won't be compatible.

Feel free to pick apart my take and offer suggestions. Thanks.

Comments

  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    I believe the Outbacks can be stacked in a 129/240v configuration, but as you noted, load balance can be an issue. I use a pair stacked in a master/slave 120v config and use an autotransformer for a 240v pump. I'm not well aquainted with the SMA product.

    There are batteries designed for primarily float service (eg. telecom applications), but any lead acid battery will eventually die of old age. In telecom applications I think they tend to replace them every 7 or so years just because. A potential problem with L16 type batteries like the Surrette you mentioned is stratification of electrolyte in float. You don't necessaily need to discharge every 2 weeks, but should do a regular bulk/absorb cycle to mix things up.
    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
  • BB.BB. Super Moderators Posts: 26,870 admin
    For purely backup power, Solar tends to be quite expensive--Even full time off grid (9+ months a year), it runs around $1-$2+ per kWH for most people. And if you are in a region with not too much sun during winter, you will usually need a good backup genset+stored fuel to get you through the winter.

    For a "near normal" off grid electrical experience, around 3.3 kWH per day is a good start for planning. LED lights, Energy Star Fridge, well pump, washing machine, LED TV, Laptop computer--And lots of conservation.

    If you can run on a genset during the day, and just need a little power at night (quiet time), then a 1 kWH per day system can be nice and very cost effective.

    It would be good to convert your stove, hot water, and (possibly) drier to propane (or natural gas) if available. A lot less expensive and does not need a genset to keep things going (although, you can size a system to support such loads, if you wish).

    My first suggestion, if your "outages" are on the order of a few weeks once a year, a genset (propane or diesel, possibly gasoline, especially if you have very cold winters) it usually cost effective.

    If you are out for months (after an ice storm or hurricane, and assuming the storm did not take out your solar panels, and you do not use city water or sewage), off grid solar may be helpful.

    I will do a quick design based on 3.3 kWH per day for a full time off grid home (basically a good size/conservative battery bank to run a fridge+lights+etc.). First the battery bank, 2 days of storage and 50% maximum discharge seems to be a pretty optimal setup (using our rules of thumb--for various reasons):
    • 3,300 WH per day * 1/0.85 AC inverter eff * 1/24 volt battery bank * 2 days storage * 1/0.50 maximum discharge = 647 AH @ 24 volt battery bank
    Then there is the solar array... Two calculations, one is based on a minimum rate of charge for the battery bank (larger flooded cell lead acid battery banks need more charging current for long life). 5% to 13% is typical for solar--With 5% for weekend/seasonal usage/possible emergency backup) and 10%+ for full time off grid:
    • 647 AH * 24 volt battery bank * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,008 Watt array minimum
    • 647 AH * 24 volt battery bank * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,107 Watt array nominal
    • 647 AH * 24 volt battery bank * 1/0.77 panel+controller deratings * 0.13 rate of charge = 2,622 Watt array "typical cost effective" maximum
    And then there is sizing the array based on the amount of power you use and where you will install the system. Say you are around Portland Maine, fixed array, and assume that power outages are more likely in winter (you can build an adjustable array to optimize for season):
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Portland
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 31° angle from vertical (easier to clean shown off in winter):
    (Optimal winter settings)
    Jan Feb Mar Apr May Jun
    3.42
     
    4.13
     
    4.46
     
    4.25
     
    4.14
     
    4.15
     
    Jul Aug Sep Oct Nov Dec
    4.34
     
    4.49
     
    4.47
     
    4.07
     
    3.13
     
    2.96
     
    Assuming you are going to need some genset usage in winter, pick 2.96 Hours of Sun per day (December long term average) as the "break even" month:
    • 3,300 WH per day * 1/0.52 off grid AC system eff * 1/2.96 hours of sun per day = 2,142 Watt array "break even" December
    Whether you can live with 120 VAC or need a 120/240 VAC inverter depends on what you want to power, and how long your wire runs are (well pump, longer run to pump, or to a remote power shed, etc.).

    There are other conservation measures that can help (besides lots of atic and wall insulation, double pane windows, efficient heating/air conditioning)--Heat Pumps (air source) for heating (cooling) and hot water are possible to run on grid solar.

    Heat Recovery Ventilators can be very nice for "sealed homes"--However the fan(s) for HRVs can consume a fair amount of energy too.

    Energy usage is a highly personal set of choices--My answers will not be yours. Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Registered Users Posts: 1,304 ✭✭✭✭
    edited September 4 #4
    One point not suggested is a hybrid system which has load shaving abilities, assuming peak billing periods, this configuration would allow the batteries to at least be active, rather than sitting in float for extended periods, inverter chargers which are stackable/expandable, solar could be added later and provide 120/240 V are available. The price of grid power is a determining factor, building a giant UPS for blackouts which may be very infrequent seems an expensive proposition, but that is of course just an opinion.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • PeteSPeteS Registered Users Posts: 8 ✭✭
    Say you are around Portland Maine...

    For a "near normal" off grid electrical experience, around 3.3 kWH per day is a good start for planning. LED lights, Energy Star Fridge, well pump, washing machine, LED TV, Laptop computer--And lots of conservation.

    Your thoughts?

    -Bill
    My new house is in Cape Elizabeth, three miles from Portland. That was a good guess.

    3.3 kWH per day does seem like an easily attainable target for me without the electric stove and hot water heater. Thanks for posting all that info. I was roughly thinking a 2 kW solar array would probably be appropriate when I get to that step.

    I have a 2800 W generator that I used at my previous house. Obviously using that is the cheapest option for backup, I would just need to install a transfer switch. But, if I'm planning on installing solar panels anyway, I want to be able to benefit from them when the electric grid goes down. I probably should be looking at a 120V system though.  

    I had an HRV in my last house and intend to put one in this house eventually. As you said, the fans in them do use a fair amount of energy, even a small unit can use close to a kWH per day, although it's really not essential in this house. My new house was built in 1958 and it needs lots of upgrades and improvements. The first improvement was to have a perimeter drain installed in the basement. In addition to the 1/3 hp and 1/2 hp sump pumps that were fairly standard, they were offering to install a third pump with battery backup for an additonal $800. I just felt that I would rather put that money toward a better battery bank and inverter that could power more essential items in the house than just a sump pump. That's what got me looking into a battery backup system first, with solar to come in the near future.
  • Raj174Raj174 Solar Expert Posts: 475 ✭✭✭✭
    You might consider an Outback Radian GS4048A. I use mine for backup power and offsetting grid power consumption, average about 9 kWh per day. For larger loads, like a water heater or kitchen range you'll need the GS8048A. The Radians are 120/240 volt.

    Rick
    12 x 300W Renogy PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 195AH HI Power LiFePO4 no BMS, 4000W gen.
  • mike95490mike95490 Solar Expert Posts: 7,307 ✭✭✭✭
    Don't forget the Conext line by Schneider, 240Vac standard split phase, grid & generator interactive (2, AC inputs)
    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 ,

  • littleharbor2littleharbor2 Solar Expert Posts: 704 ✭✭✭✭
    PeteS said:
    Say you are around Portland Maine...


    My new house is in Cape Elizabeth, three miles from Portland. That was a good guess.

    Moderators have superpowers, like x-ray vision and stuff. B)

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • BB.BB. Super Moderators Posts: 26,870 admin
    For that size battery bank, I would be suggesting that ~2,400 to 3,000 Watt AC inverter would be a nice maximum size. If you need more peak wattage, you might think about a 48 volt battery bank and larger AC inverter. And you may need a larger battery bank (and solar array)... It is a vicious circle (more power, more battery storage, more solar array, more money). If you can keep the system small and use a genset (again smallish--don't oversize) to handle extraordinary loads--That would be a nice mix.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 3,329 ✭✭✭✭
    If you do switch to propane down the road, convert to a propane generator. During a major outage the gas stations can't pump fuel and you will run out. Our town was evacuated for 7 days and 5,000 people left. Many tried to stay but they ran out of gasoline and it was hot and smokey without cooling. They came home to science projects in their refrigerators and had to take them to the dump. All of the grid tied homes had gasoline generators with 500 gallon propane tanks. Not a good plan!

     A few of my grid clients had the SMA secure power inverters with LG inverter refrigerators and they ran during the day and did well unattended. You just have to plan for it!

    Offgrid was a piece of cake as it is a normal day!  Good Luck!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • bill von novakbill von novak Solar Expert Posts: 711 ✭✭✭✭
    Raj174 said:
    You might consider an Outback Radian GS4048A. I use mine for backup power and offsetting grid power consumption, average about 9 kWh per day. For larger loads, like a water heater or kitchen range you'll need the GS8048A. The Radians are 120/240 volt
    In addition, the Radians can take a second (generator) AC input, which is pretty much a requirement for any system intended for backup.
  • PeteSPeteS Registered Users Posts: 8 ✭✭
    The battery bank that I had mentioned is 48V if run in series, which is what I would plan to do. Eight 6V 428 AH batteries. I have looked at the Conext inverters as well. Something like the XW+ 5.5kW seems to offer a lot for the price, although I've seen several negative comments about Conext inverters when used in a grid interactive mode. Have they worked out those bugs, or was that just from people not configuring them correctly? The Radian GS4048A is also a strong possibility. Thanks for all the feedback!
  • mcgivormcgivor Registered Users Posts: 1,304 ✭✭✭✭
    It's possible to find negative feedback or comments on any product, all products have their strengths and weaknesses, how an individual reacts to an issue, emotionally or pragmatically, determines the language used. Having read some negative  comments didn't dissuade me from the purchase of Schneider products, personally I'm satisfied overall with the products, support and  performance, having said that, I'm not a fan boy by any stretch of the imagination, im just not her the fan boy type. Some products enjoy a fan base and seemingly can do nothing wrong, despite numerous problems, often it comes down to support from the manufacturer. My understanding is shortly after Schneider purchased Xantrex, the support was not great, however since then they've improved, or so it would seem. 
    Reviews are to be taken at face value, they seem to be highly polarized, either the best or worst, since people don't rant when satisfied, less is heard from them. Mistakes made by end users could account for a large percentage of issues, I don't know one way or the other, but I do understand people often don't take responsibility for thier mistakes, instead directing responsibility to the manufacturer. Just some thoughts.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • Dave AngeliniDave Angelini Solar Expert Posts: 3,329 ✭✭✭✭
    Well said!  And if you search the early years of radian, there were some pretty unhappy users. A grid-tie battery based system is one of the hardest tasks for a Pro. You can imagine the amount of time for a novice to get up to speed.

    It is not just write a check like many of the Boaters in Florida do. Take a trip (if you are brave) up/down the Inter-coastal water way in Florida. Be a good swimmer if you do :)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • PeteSPeteS Registered Users Posts: 8 ✭✭
    I've put a bit more thought into this and gotten an estimate from NAWS. This is what I'm thinking about going with:
    Outback FLEXpower One with VFXR3524A inverter, FLEXmax 80 charge controller,...
    4 - Surrette S-550 428 Ah FLA batteries, for 24V
    8 - Canadian Solar 305 W panels, Vmp: 32.7V, Voc: 39.9V
    panels would be run as four strings of two panels, two strings on the east side of my 5/12 pitched roof, two strings on the west
    MidNite Solar MNPV4-MC4 combiner box, to run the four strings into a single FLEXmax 80
    MidNite Solar DC surge protector, assorted cables, mounting hardware, etc.

    I will install a manual transfer switch so I can use my Yamaha YG2800i generator if needed on cloudy days, during power outages. I won't be going off-grid, unless the grid goes down. 

    This system seems to do what I want it to do, which is to provide me with power during an extended grid outage without having to run a generator 24/7, and it will create more kWh than I currently use over the long term.

    My main debate now is whether to add more solar panels. I don't have a south facing roof, the ridge of my roof runs almost due N-S. I've read several articles about putting panels facing both E and W, and there are some advantages to doing that, as long as you realize that electrical production will be significantly reduced compared to S facing panels. I could run four strings of three panels each. That's 3660W STC, but far less than that in my E-W orientation. Will the FLEXmax 80 handle that, but just be capped at 80A x charging voltage? I don't want to fry an expensive charge controller. Or should I just get a second charge controller if I want more panels, one for the E side of the roof, one for the W side? I think that FLEXmax 80 will take two string inputs (but not three), so the cost of a second charge controller is partially offset by not needing a combiner box.

    Thoughts? Thanks for any input you are willing to provide.
  • Raj174Raj174 Solar Expert Posts: 475 ✭✭✭✭
    Hi Pete,
    If you're going with east/west arrays you need to base the array size on getting sufficient power production to charge the battery bank in the winter. Winter production will likely be 1/3 that of summer. If you haven't already, go to PVWatts and enter the array data for your location. That will give you an estimate of what your array configuration will produce. The system will definitely be over paneled in the summer months, but you can set the current limit in the controller to 55 amps, which is a 13% charge rate for you battery bank. No harm will come to the charge controller by being over paneled. I would definitely use a combiner box and recommend getting a box that will take 6 strings, you may need it. Two controllers might work better, but I would't go to that expense without first trying virtual tracking with one controller. 

    Rick 
    12 x 300W Renogy PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 195AH HI Power LiFePO4 no BMS, 4000W gen.
  • PeteSPeteS Registered Users Posts: 8 ✭✭
    edited November 29 #17
    Raj174 said:
    Hi Pete,
    If you're going with east/west arrays you need to base the array size on getting sufficient power production to charge the battery bank in the winter. Winter production will likely be 1/3 that of summer. If you haven't already, go to PVWatts and enter the array data for your location. That will give you an estimate of what your array configuration will produce. The system will definitely be over paneled in the summer months, but you can set the current limit in the controller to 55 amps, which is a 13% charge rate for you battery bank. No harm will come to the charge controller by being over paneled. I would definitely use a combiner box and recommend getting a box that will take 6 strings, you may need it. Two controllers might work better, but I would't go to that expense without first trying virtual tracking with one controller. 

    Rick 
    Thanks Rick. I just used the PVWatts calculator. I modeled it as two separate 1.8 kW arrays, one at 90 degrees azimuth, one at 270 degrees azimuth, and did it both with a DC to AC Size Ratio of 1.0 (winter months not controller limited) and again with a ratio of 1.8 (summer months somewhat controller limited).

    Adding the AC Energy output of the two 1.8 kW arrays in December gives me 138 kWh for the month, which seems good to me since I think 3.5 kWh/day is a reasonable usage goal for me.

    The output in May, June and July is 450+ kWh per month with DC to AC Size Ratio of 1.8. Using the ratio of 1.8 as compared to 1.0 only results in a loss of about 100 kWh of potential output (per year) due to the over-paneled array going into a single charge controller.

    So I think my answer is to go with six panels on each face of the roof, instead of just four. I can do that as four strings of three panels each and still be well under the 150V max for the FLEXmax 80. For much more balanced output throughout the year, perhaps it would make more sense to put four panels on each roof face and another four panels vertically on the south facing side of my garage. That would bring my December output up to 186 kWh, but cut my May, June and July production down to about 400 kWh per month.

  • Raj174Raj174 Solar Expert Posts: 475 ✭✭✭✭
    I would try to avoid using 3 panel strings with a 24 volt battery bank. Down converting the higher voltage will cause increased heat production in the controller and will be less efficient. What about just adding another 2 panel string to each side. I like the idea of the south facing panels, although they would likely need their own controller. 

    Rick 
    12 x 300W Renogy PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 195AH HI Power LiFePO4 no BMS, 4000W gen.
  • westbranchwestbranch Solar Expert Posts: 4,873 ✭✭✭✭
    Pete, did you adjust/calculate the output, based on the angle the PVs  are set at, for each of the months? ie if aligned for winter, the actual summer output will be less than the optimal summer output.
     
    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, Hughes1100 Sat Modem
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • PeteSPeteS Registered Users Posts: 8 ✭✭
    edited November 29 #20
    Pete, did you adjust/calculate the output, based on the angle the PVs  are set at, for each of the months? ie if aligned for winter, the actual summer output will be less than the optimal summer output.
    I did try different tilt angles, but it has almost no effect on the output from the east and west facing arrays in winter vs. matching the 5/12 pitch of the roof (22.5 degrees). Increasing the angle would help snow slide off, but it negatively impacts performance in the spring, summer and fall. For south facing panels it would be a different story.

    Raj174 said:
    I would try to avoid using 3 panel strings with a 24 volt battery bank. Down converting the higher voltage will cause increased heat production in the controller and will be less efficient. What about just adding another 2 panel string to each side. I like the idea of the south facing panels, although they would likely need their own controller. 
    Using six strings of two panels each, two strings facing east, two west, and the other two vertical on the south facing wall of my garage, provides much smoother output throughout the year:
    Jan: 7.4 kWh/day
    Feb through Sept: 10+ kWh/day
    Oct: 9.0 kWh/day
    Nov: 6.4 kWh/day
    Dec: 6.0 kWh/day

    That's better than I was hoping for. I just need to figure out if the wall mounted panels are feasible. My neighbor's house may partially shade them near the winter solstice. 
  • Raj174Raj174 Solar Expert Posts: 475 ✭✭✭✭
    That sounds great, hopefully there is not too much shading. If so, better in the morning or evening. Keep an eye on the charging current, you don't want to cook those batteries.

    Rick
    12 x 300W Renogy PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 195AH HI Power LiFePO4 no BMS, 4000W gen.
  • Dave AngeliniDave Angelini Solar Expert Posts: 3,329 ✭✭✭✭
    If the system will ever grow 48V should be used and hi voltage charge controllers make this so very easy. Outback is suppose to have them out next year. A schneider CSW 4048 and its 600v mppt could be looked at. Are you sure you can't build a pergola in the yard to stay off your roof?
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • PeteSPeteS Registered Users Posts: 8 ✭✭
    If the system will ever grow 48V should be used and hi voltage charge controllers make this so very easy. Outback is suppose to have them out next year. A schneider CSW 4048 and its 600v mppt could be looked at. Are you sure you can't build a pergola in the yard to stay off your roof?
    Dave, that's very nice. I timber framed my last house, barn and woodshed. I could make one of those.
    Raj174 said:
    Keep an eye on the charging current, you don't want to cook those batteries.
    Rick, what did you mean by this this? Cook them by undercharging, or overcharging?

    Maybe I should consider a 48V battery bank. Since the batteries are primarily for grid outages, I was trying to keep costs down, but another $1400 for four more batteries and cables isn't a huge amount compared to the overall cost. The problem is that I may then consider a more expensive inverter, more panels, etc.
  • Raj174Raj174 Solar Expert Posts: 475 ✭✭✭✭
    PeteS said:
    If the system will ever grow 48V should be used and hi voltage charge controllers make this so very easy. Outback is suppose to have them out next year. A schneider CSW 4048 and its 600v mppt could be looked at. Are you sure you can't build a pergola in the yard to stay off your roof?
    Dave, that's very nice. I timber framed my last house, barn and woodshed. I could make one of those.
    Raj174 said:
    Keep an eye on the charging current, you don't want to cook those batteries.
    Rick, what did you mean by this this? Cook them by undercharging, or overcharging?

    Maybe I should consider a 48V battery bank. Since the batteries are primarily for grid outages, I was trying to keep costs down, but another $1400 for four more batteries and cables isn't a huge amount compared to the overall cost. The problem is that I may then consider a more expensive inverter, more panels, etc.

    Pete,
    Spring to Fall the arrays have the potential to produce more charging amps than is recommended for your 428 amp hour battery bank. Even with an east/west configuration, they may produce as much as 70 amps depending on your location. Max recommended for your bank is about 55 amps, so you might have to set the current limit in the controller. Just recommend keeping an eye on the charging once up and running.

    Rick 
    12 x 300W Renogy PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 195AH HI Power LiFePO4 no BMS, 4000W gen.
  • PeteSPeteS Registered Users Posts: 8 ✭✭
    I think I previously misunderstood something about the Schneider Conext SW inverters, as far as their abilities in grid-interactive mode. Especially since the Schneider gear is on sale right now from NAWS, I took another look at them, and I think that's what I'm going to go with. What I've primarily been interested in is having a system that can meet my basic electrical needs in an extended outage, secondary is reducing my current electric bill.

    I lost power around Halloween for a day and a half, due to 60 MPH winds. I was actually lucky, most people in my town lost power for 3 or 4 days. I was running my old (~2000 hours) Yamaha inverter generator around the clock, but it's loud and stinky now. It would be great to just use it to supplement solar/battery backup when needed. 

    I'm now thinking about going with an SW 2524 Inverter, MidNite Solar E-panel, Conext XW MPPT 60 CC, Conext SCP, Conext Combox, a MidNite Solar array combiner, four Surrette S-550 6V 428 Ah batteries, six 305 W Canadian Solar panels, plus assorted surge protection, cables and panel mounting hardware. I could go with eight 305 W panels, but I don't think that makes economic sense. It may be current limited by the CC during the good solar months, and I'll still need to rely on the generator during bad winter weather.

    So, I think I'm happy with all of that. I'm wondering about the Conext battery monitor. I don't think I need it, it's surprisingly expensive, and Schneider doesn't even show it in many of their system diagrams. I'm guessing that between a multimeter and a hydrometer, I can do a better job understanding the state of my batteries than the battery monitor can? 

    I need to find out what edition of the NEC my state/town follows and figure out what my town's building/electrical inspector expects. I was reading an article the other day that described how some NEC sections related to solar power were not clearly defined, or required the use of equipment that may not have even existed, but much of that was fixed in the 2017 NEC. Many places still are on the 2011 NEC though, for better or worse. I guess my biggest concern related to that is related to the combiner box, shutdown switches and AFCI breakers in the DC side of things.

    Also, thanks for all of your input. You have all been very helpful.
  • Dave AngeliniDave Angelini Solar Expert Posts: 3,329 ✭✭✭✭
    Good choice and yes skip the battery monitor. It really is not needed in this application. Often the locals do not care about back-up but you should follow all the requirements to keep your fire insurance legal. Have a disconnect for the solar outside and if you mount solar on the roof do exactly what is required. The internal GFI to the cc is fine for a ground mount.  I would use all of the Schneider AC & DC boxes as they are designed for your inverter and less problems with both the locals for docs and schneider themselves if warranty issues arise.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    In thinking about number of panels, a couple of things to keep in mind.
    1. In most climates, the panels will rarely put out rated (STC) power. Normal operating cell temperature (NOCT) rating, ~75% of STC is likely closer to real life output in most places. Cold, high altitude locations may get close to or even better than STC, but most of us see more like NOCT. In this case, 8x305x.75=1830w. At 25ish volt bulk charging ~73a. The controller won't draw that much, but not as overpanelled as it might appear at first using STC numbers.

    2. Where having more panels is helpful is on lightly overcast days, and in low winter sun. The panels still produce, but at a reduced rate. This can be important off-grid, but maybe less so in your application.
    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
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