hi everyone..need help , advise..on grid ,no batteries,two way meter , back up generator ats switch

Richie_panamaRichie_panama Registered Users, Users Awaiting Email Confirmation Posts: 8 ✭✭
i am richard,ex house contractor,living in panama central America.since 15 years.i need to install a solar system at my house ,i made a sketch of the way to do it but not to sure of my diagram .i have a consummation of 6000 kw to 10.000kw per year.
i dont want batteries, i have a generac 17kw generator with automatic transfer switch .i want to stay on grid ,with a two way meter.its possible here the power cie alows that you do it but need drawing aprouval from them.its split phase 120/240 volts.
the electricity cost here is 26 cents a kw..compare to canada were i come from at 8 cents a kw..big change..
your help would be very apreciated 


  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    You are very welcome to upload a drawing/photograph here of your plans.

    Is your question the sizing of the system, or you just need a drawing (one line drawing, or more detailed drawing) to get a permit (from local authority and/or power company?

    There are potientially other questions too... What GT inverter suppliers are approved for use in their company. Is a central inverter or micro-inverter(s) required/allowed? Newer code in USA has requirements can include rooftop solar array disconnect (or use micro-inverters instead). Do you have issues with lightning in your region?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Richie_panamaRichie_panama Registered Users, Users Awaiting Email Confirmation Posts: 8 ✭✭
    l bill , there is no lightning issue here ..never saw one in 15 years... a detail drawing to get a permit.. will take a fotos of my sketch ..tell me what you think of it.
    i did copy the foto link url.
    do not know if it did work..fist time i do it that way..let me know..
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    edited May 10 #4

    I don't see any links or uploaded fotos... You can try another post. Until you get 6+ posts, I may have to "approve" your post with links/photos (part of the spam filter configuration).

    What you might do... See if the local inspector will let you photograph a successful application drawing (just offer to cover personal information, if not a public document). That usually makes the local folks a bit more comfortable if they see "more of the same" type applications (nobody gets in trouble for accepting "something new or different").

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Richie_panamaRichie_panama Registered Users, Users Awaiting Email Confirmation Posts: 8 ✭✭
    hi bill,
    i will do that as soon as i can get out of quaranteen...in panama its total confinement,..can go out for food only twice a week at a certain hour and no more than 2 hrs..60 days now ..also no cant buy alcool... 

  • Richie_panamaRichie_panama Registered Users, Users Awaiting Email Confirmation Posts: 8 ✭✭
    hi bill.
    with my electric monthly kw consomation plus a 20% ..can i determine the size of my inverter...more or less..
    and do the grid will compensate for the hight peak of induction motor start...its a water pressure pump 1500 watt...
    its abouth 7000 kw a year..


  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    An example of how to do the calculation. Assuming a fixed a array facing south, no shading (trees/buildings/overhead wires shading the array):

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 81° angle from vertical:
    (For best year-round performance)


    Get an average of the above ~ 4.925 hours of sun per day 12 month average
    • 7,000,000 WH per year / 365 day sper year = 19,178 WH per day average
    •  19,178 WH per day ave * 1/0.77 panel+controller deratings * 1/4.925 hours of sun per day = 5,057 Watt array
    You need to look at the billing plan too... They keep changing and some utilities have changed there plans to be less than friendly towards solar energy (and some do not allow at all).


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Richie_panamaRichie_panama Registered Users, Users Awaiting Email Confirmation Posts: 8 ✭✭
    hi bill..thanks for responding..
    i want do install the panels on a car porch roof the slope is at 87 deg..
    i use 4hrs in my calculation so with the raining season it varies a lot ..
    and i think i will use a litle more air cond since i am getting older..and being more at home ..
    so i think i should install 2 - 5kw inverter..
    what do you think..
    an other thing can you give me a detail sketch about the conection of inverter with a generac transfer switch ..
    can i send fotos now...
    i just want do do it wright...
  • Richie_panamaRichie_panama Registered Users, Users Awaiting Email Confirmation Posts: 8 ✭✭
    hi bill.
    for 2 days i am checking the shade...
    i do have a litle bit..its the utility  wires ..not much one string will catch it  the 2 first hour of the day..from 6 to 7.45 am..
    thats it..one wire create a 2 inch shade..on 7 panels one complete line..
    is it very bad.....
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    A power line shadow across the array can easily kill 50% of the array output...

    You can play around with the PVWATTS program... It has a downloadable format that gives hourly harvest reports for 365 days a year. And you can see how much you would lose if you have shading until 8am--probably not a big loss for today/summer (obviously, the sun angles change over the seasons--Getting close to highest sun angle--Summer... You also need to check the rest of the year when the sun is lower in the sky (i.e., if you have shading all day for 3-6 months of the year for non-summer seasons).


    87 Degrees? Is that near vertical or near horizontal?

    Yes, you should be able to post links and photos without going into a spam review (which I check and release anyway).

    If you have GT inverters and a genset (with whole house transfer switch?)... Getting a bit complicated here... There are a few "it depends" answers. For example, if you have a mechanically governed genset, it probably does not hold 60 Hz accurately enough for a GT Inverter to lock on and generate power. And if your genset is accurate enough frequency control, then a GT inverter "backfeeding" energy to the genset is a whole bundle of problems (feeding energy backwards to a genset is generally a very bad idea).

    So--The typical answer would be to have the GT solar connected on the "utility side" of a genset transfer switch. Generally do not want a GT Inverter on the genset's output (when there is a power failure).

    There are possible exceptions--But I would just avoid the GT+Genset connection. Yes, it is a neat idea to have "free solar electricity to reduce genset fuel bills.... But usually does not work that way).

    Now--There is a way you can do this--With a "hybrid inverter" -- Basically an inverter that has both Off Grid and Grid Tie modes... But you need to run a full size battery bank with this (and basically have an off grid inverter + battery bank + solar power + backup genset). And when you add a battery bank to a solar power system (vs "simple" GT solar), you have a whole bunch more costs... Batteries are not cheap, have some losses, and need to be replaced every 3-8 years or so (depending on battery quality, how hot they get, mistakes by owner, etc.).

    I guess a big question is how much do you run the genset and what are your fuel bills per year. Also, if you have an oversized genset (large genset and smallish electrical loads), you can be wasting fuel there too (gets into diesel vs gasoline/propane gensets and how the differ at low loading).

    If you can go with "simple" GT Solar and a backup genset--I would certainly start there. Note: just my personal opinion. Electrical power and self generation is a highly personal set of choices. What I guess at, vs what you need, is not the same.

    -Bill "my two cents worth" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Richie_panamaRichie_panama Registered Users, Users Awaiting Email Confirmation Posts: 8 ✭✭
    hi bill .
    i did go on the link ...its 5.16 of solar radiation... more then i was thinking..7000 kw a year for 5 kw.. with the angle of the panels wich is almost horizontal..just a small pitch 3 to 5 deg.. and 180 deg south.

    about the transfer switch its automatic  by generac  generator..
    i think logicaly ..if i connect the ac from the inverter directly to the grid ..
    iff the power goes out during the day the inverter will provide power so that means the automatic transfer switch will sense the power so it wont ask the generator to start...
    if its night wen the inverter wont produce ac ..then the switch will transfer to generator and will feed the ac to the house..
    the frequency of the generatot is good and steady ..its a 17kw generac..

    your a good help bill thanks verry much..

    i will try to send fotos.

  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    Standard GT Inverters are designed to NOT produce power if the grid is down either (a safety feature for linemen). They literally have NO way of producing AC power "on their own". That is the downside of GT Inverters--Lots of sun, lots lots of inverter power, and no electricity if the Utility Power Fails. And  if you have a generator, generally, it is NOT a good idea to connect GT inverter's to its output (either the GT inverters will not start, or they can feed energy back into the genset and destroy it).

    There are one or two that can produce some power during the day on--SMA has their Secure Power version for some of their inverters (produces up to 2,000 Watts on a separate AC output--If there is enough sun):

    https://www.solar-electric.com/lib/wind-sun/SMA-SBxx-1SP-US-41_User_Manual.pdf (page 33 for Secure Power operation)

    Other than the SMA secure power feature (which they usually suggest a separate wall switch and AC outlet, with manual plugging in your critical load(s) to the outlet, there is not really much in the way of doing what you want (powering AC loads during a utility power failure with a "pure/no battery battery bank" GT inverter (with or without backup genset). Note that the 120 VAC power can turn on and off every (minute?) if there is (for example) more AC loads than there is solar energy available--So you want loads that are not damaged by momentary energy losses (cell phone charging, laptop charging, running a fan, TV/Radio/etc.---Usually running a refrigerator on a intermittent AC power sources is not a good idea--Stopping and starting a fridge compressor can cause overheating and defrost timer issues).

    Generally, if you want to run on Solar Power during a power outage, other than the SMA secure power output, there is no cost effective way (presently) of making an emergency power system without a substantial cost of adding an Off Grid or Hybrid AC inverter and battery bank. And the downsides of having the battery bank.

    There are Li Ion batteries (LiFePO4 type for home/RV use) that are about a close to the "perfect" battery (no water, not damaged by sitting 1/2 charged, high surge power, quick charging, no messes during normal operation, and "better for warm to hot climates). But they also have their issues (generally not cheap--at least for now, should have a Battery Management System of some sort to control min/max voltage to avoid "killing" the battery bank with over/under charging, and very hazardous Hydrofluoric Acid in the case of a fire).

    My first suggestion... Look at your power usage and do as much conservation as possible (insulation of walls/ceiling, awnings over windows to block sun, energy efficient appliances, turn off stuff not in use, look at mini-split air conditioners, etc.).

    And don't buy anything until you do the research and some paper designs. It is very easy find "a good buy" for solar panels, hardware, etc... But many times what you impulse buy does not play well together or really meet your needs in the end.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Richie_panamaRichie_panama Registered Users, Users Awaiting Email Confirmation Posts: 8 ✭✭
    Tanks  for your advice..
    Will do it..
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