Help with small ranch house system

ChrisRChrisR Registered Users Posts: 8 ✭✭
I have a small 800 sq ft house on a piece of property in Southern Baja, just north of Cabo. It is used for a security guard that watches over the property for me.

He has lived there with no electricity of any kind for several years, and now I am in the process of upgrading the house for him.

We are keeping it very simple, and adding a small fridge, LED lighting throughout, a couple of box fans, and really that's about it. He will also have a radio, laptop computer and charge his phone and small things like this.

I would really appreciate some help designing a small solar system for the house. While I have a generator there for tools and things, I was thinking of a system that provides around 3000 watts/day.  

The house is fully wired now, so I would like to connect directly to the panel. Additionally I have a sister in law here in Mexico that owns an industrial battery operation who will make me any configuration of battery that I ask for.  

We are really trying not to break the bank on this system, but I would also like it to be reliable.

I have a guy local here in Cabo that has suggested the following, but did not give me model numbers.

4 150W solar panels
4 mounting brackets for the panels
1 Samlex 1000W inverter
1 Epsolar charge controller

He says this should provide about 3000W of electricity per day. The cost for the whole system is $975 USD if you pick it up here in San Jose.

.Please help.  I just don't trust the deals I read online.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    Welcome to the forum Chris,

    I don't know much about Baja California (not much solar data there), but I will take a guess... Always suggest that folks design a solar power system based on their energy needs. And a small cabin system at 1,000 WH per day is not bad. Add a refrigerator, and all of a sudden you are looking at a mid-size system. I suggest 3,300 WH per day (close to your 3,000 WH per day)... But if you could measure the energy usage will a Kill-a-Watt type energy meter, it would be a big help.

    And since refrigerator being the big "energy hog here", being careful to purchase one that is very efficient and "solar friendly". One of the bigger issues with refrigerators is their peak energy usage (compressor starting amps)... If this is a "standard" compressor type, typically suggest around 1,200 to 1,500 Watt PSW inverter... If you can get an "inverter refrigerator" (LG and possibly other brands seem to be common in Mexico--So that is a big help), and you might get away with a 1,000 Watt inverter (keeping inverters "small" is a big help... Small inverters waste something like 6-10 Watts when "turned on" (tare losses). Big inverters (3+ kWatt), can take 30-40+ Watts just turned on (as much energy as a "full size" north American refrigerator). Watch "bar" and smaller refrigerators--They frequently take almost as much energy as a full size fridge, and as much starting current.

    Note that "mechanical devices" such as well pumps, box fans, etc. can take lots of energy... There are "solar friendly" well pumps, or use a 12/24 volt RV water pump (if tank water), using low power ceiling fans (DC or AC), etc. can all help. Since you are not living there, non-owners that use solar systems tend to not "watch their energy budget" closely--And tend to "murder" battery banks.

    We can come back to the above later (and others who know the area can probably help more too)...

    Just going through the design process (yes, there will be math) and using our rules of thumb for a "relatively conservative" off grid home design... We start with the loads (pick 3,300 WH per day) to define the battery bank. Normally we plan for 2 days of storage (bad weather) and 50% discharge (for longer battery life).... In an area with lots of sun and no big storms, you MAY get away with 1 day of storage.. But starting conservative (note picking 24 volt battery bank--suggested for "mid-size" off grid systems--48 VDC can work too).
    • 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volt battery bank = 647 AH @ 24 volt battery bank
    That is 4x 6 volt @ 200 AH "golf cart" batteries in series (24 volts) times 3 parallel strings (~600 AH). Golf cart batteries are good first system batteries--But if you have access to good quality higher AH (2/4/6 volt batteries), they are a good choice too. Note that many people "murder" their first bank or two because of operational or maintenance mistakes.

    Next, sizing the solar array based on two calculations. One is based on 5% to 13%+ rate of charge. 5% works OK for weekend/sunny seasonal usage... 10%-13%+ works better for full time off grid.
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 3,168 Watt array "typical" cost effective maximum
    And there is sizing your array based on your daily loads and hours of sun per day by season (9+ months a year, vs winter usage, etc.)... I don't have good Baja solar data... But one source says for a fixed array tilted to 20 degrees from horizontal, facing south for Cabo:
    https://pvwatts.nrel.gov/pvwatts.php
    MonthSolar Radiation
    ( kWh / m2 / day )

    January5.84

    February6.65

    March7.35

    April7.38

    May7.22

    June6.90

    July6.47

    August6.56

    September6.25

    October6.61

    November6.13

    December5.60

    Annual6.58


    Looks like lots of sun down there and the loads (second array calculation)... Lets pick December at 5.60 hours of sun per day (20 year average), and 3,300 WH of daily usage:
    • 3,300 WH per day * 1/0.52 off grid AC system efficiency * 1/5.60 hours of sun per day (Dec) = 1,133 Watt array "Dec" break even
    Now for some more fudge factors... You should not plan on using more than 50% to 65% of a solar system's capacity for your "base loads" (loads that must always run, like a fridge and lights). Other optional loads (washing machine, TV late into the night, vacuuming, etc.) that can be put off for next sunny day (or generator backup) helps. Lets say that your "base loads" are 1,500 WH per day, then the base WH per day would be:
    • 1,500 WH * 1/0.65 base load fudge factor = 2,307 WH per day--Still well below the 3,300 WH "nominal" December
    If you decide that your base load is >>1,500 WH per day, you may need to "up size" the array.

    I have given you lots of numbers and choices.... Because you are in a reliably sunny region (I guess), your "break even array" is even less than your 5% rate of charge minimum array. But way more panels than your 4x150W=600 Watt array suggested.

    So, now the choices... In general, most "renters" have a habit of running "everything" (leaving lights and TV on, using hair dryers, etc.) which "kills" the battery banks. So, I suggest a "relaible" system has "extra solar" panels. This gives you a better chance of longer battery bank life (in a warm climate, "inexpensive" but good quality GC batteries may last 3-5 years. Better batteries may last 5-8 years. Heat "kills" batteries... If you can keep them cool (buried in ground, out of hot/sunny rooms/etc.--Will help (25C = normale life, 35C = 1/2 aging life).

    Flooded Cell Lead Acid batteries--Need monthly checks for electrolyte levels, adding distilled water, etc.

    AGM batteries are "cleaner" and more efficient. But also cost 2x a much... And probably would not last more than 5-7 years in your climate.

    LiFePO4 (lithium iron phosphate) batteries can be great for hot weather--But that is a whole new discussion (not cheap, no maintenance, very reliable, work better/longer in hot climates).

    You can work the math other direction too... For example, a 600 Watt array in December would produce (long term daily average) around:
    • 600 Watt array * 0.52 off grid AC system eff * 5.60 hours of sun per day (Dec) = 1,747 Watt*Hours per day
    And to back check the suggestions to you:
    • 3,000 WH per day * 1/0.52 AC sys eff * 1/600 Watt array  = 9.62 Hours of sun per day required
    9.61 Hours of sun per day--Almost nowhere in the world will you harvest that amount of energy, even in summer--Unless you are using a 2-axis tracking array (you will get around 9-10+ hours of sun per day from February thru July in Cabo--Using PV Watts link above).

    Anyway... Some thoughts and initial targets... Adding a fridge to a system is a large energy hit. You are probably not far off with your 3 kWH per day usage--But you still need to be careful (lots of box fans, inefficient fridge in a hot room, etc.).

    The suggested array is (in my humble opinion) too small. The Samlex AC inverter is a good mid-quality device (still have to pick exact model--there are differences). An EpSolar MPPT type charge controller--I have no experience but certainly a lower cost device.

    Probably some sort of simple battery monitor so that the person living there can tell at a glance if the battery bank is "happy" or not.

    Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Up_Nord_DereUp_Nord_Dere Registered Users Posts: 14 ✭✭
    I recently bought a 10 cubic foot DC fridge with a Danfoss/Secop compressor for an off grid system.  Haven't run it yet, but the company's specs say it uses 560Wh/day.  I'm sure that's an "ideal conditions" rating.  We'll see how it pans out in reality.
  • ChrisRChrisR Registered Users Posts: 8 ✭✭
    BB. said:
    Welcome to the forum Chris,

    I don't know much about Baja California (not much solar data there), but I will take a guess... Always suggest that folks design a solar power system based on their energy needs. And a small cabin system at 1,000 WH per day is not bad. Add a refrigerator, and all of a sudden you are looking at a mid-size system. I suggest 3,300 WH per day (close to your 3,000 WH per day)... But if you could measure the energy usage will a Kill-a-Watt type energy meter, it would be a big help.

    And since refrigerator being the big "energy hog here", being careful to purchase one that is very efficient and "solar friendly". One of the bigger issues with refrigerators is their peak energy usage (compressor starting amps)... If this is a "standard" compressor type, typically suggest around 1,200 to 1,500 Watt PSW inverter... If you can get an "inverter refrigerator" (LG and possibly other brands seem to be common in Mexico--So that is a big help), and you might get away with a 1,000 Watt inverter (keeping inverters "small" is a big help... Small inverters waste something like 6-10 Watts when "turned on" (tare losses). Big inverters (3+ kWatt), can take 30-40+ Watts just turned on (as much energy as a "full size" north American refrigerator). Watch "bar" and smaller refrigerators--They frequently take almost as much energy as a full size fridge, and as much starting current.

    Note that "mechanical devices" such as well pumps, box fans, etc. can take lots of energy... There are "solar friendly" well pumps, or use a 12/24 volt RV water pump (if tank water), using low power ceiling fans (DC or AC), etc. can all help. Since you are not living there, non-owners that use solar systems tend to not "watch their energy budget" closely--And tend to "murder" battery banks.

    We can come back to the above later (and others who know the area can probably help more too)...

    Just going through the design process (yes, there will be math) and using our rules of thumb for a "relatively conservative" off grid home design... We start with the loads (pick 3,300 WH per day) to define the battery bank. Normally we plan for 2 days of storage (bad weather) and 50% discharge (for longer battery life).... In an area with lots of sun and no big storms, you MAY get away with 1 day of storage.. But starting conservative (note picking 24 volt battery bank--suggested for "mid-size" off grid systems--48 VDC can work too).
    • 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volt battery bank = 647 AH @ 24 volt battery bank
    That is 4x 6 volt @ 200 AH "golf cart" batteries in series (24 volts) times 3 parallel strings (~600 AH). Golf cart batteries are good first system batteries--But if you have access to good quality higher AH (2/4/6 volt batteries), they are a good choice too. Note that many people "murder" their first bank or two because of operational or maintenance mistakes.

    Next, sizing the solar array based on two calculations. One is based on 5% to 13%+ rate of charge. 5% works OK for weekend/sunny seasonal usage... 10%-13%+ works better for full time off grid.
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 3,168 Watt array "typical" cost effective maximum
    And there is sizing your array based on your daily loads and hours of sun per day by season (9+ months a year, vs winter usage, etc.)... I don't have good Baja solar data... But one source says for a fixed array tilted to 20 degrees from horizontal, facing south for Cabo:
    https://pvwatts.nrel.gov/pvwatts.php
    MonthSolar Radiation
    ( kWh / m2 / day )

    January5.84

    February6.65

    March7.35

    April7.38

    May7.22

    June6.90

    July6.47

    August6.56

    September6.25

    October6.61

    November6.13

    December5.60

    Annual6.58


    Looks like lots of sun down there and the loads (second array calculation)... Lets pick December at 5.60 hours of sun per day (20 year average), and 3,300 WH of daily usage:
    • 3,300 WH per day * 1/0.52 off grid AC system efficiency * 1/5.60 hours of sun per day (Dec) = 1,133 Watt array "Dec" break even
    Now for some more fudge factors... You should not plan on using more than 50% to 65% of a solar system's capacity for your "base loads" (loads that must always run, like a fridge and lights). Other optional loads (washing machine, TV late into the night, vacuuming, etc.) that can be put off for next sunny day (or generator backup) helps. Lets say that your "base loads" are 1,500 WH per day, then the base WH per day would be:
    • 1,500 WH * 1/0.65 base load fudge factor = 2,307 WH per day--Still well below the 3,300 WH "nominal" December
    If you decide that your base load is >>1,500 WH per day, you may need to "up size" the array.

    I have given you lots of numbers and choices.... Because you are in a reliably sunny region (I guess), your "break even array" is even less than your 5% rate of charge minimum array. But way more panels than your 4x150W=600 Watt array suggested.

    So, now the choices... In general, most "renters" have a habit of running "everything" (leaving lights and TV on, using hair dryers, etc.) which "kills" the battery banks. So, I suggest a "relaible" system has "extra solar" panels. This gives you a better chance of longer battery bank life (in a warm climate, "inexpensive" but good quality GC batteries may last 3-5 years. Better batteries may last 5-8 years. Heat "kills" batteries... If you can keep them cool (buried in ground, out of hot/sunny rooms/etc.--Will help (25C = normale life, 35C = 1/2 aging life).

    Flooded Cell Lead Acid batteries--Need monthly checks for electrolyte levels, adding distilled water, etc.

    AGM batteries are "cleaner" and more efficient. But also cost 2x a much... And probably would not last more than 5-7 years in your climate.

    LiFePO4 (lithium iron phosphate) batteries can be great for hot weather--But that is a whole new discussion (not cheap, no maintenance, very reliable, work better/longer in hot climates).

    You can work the math other direction too... For example, a 600 Watt array in December would produce (long term daily average) around:
    • 600 Watt array * 0.52 off grid AC system eff * 5.60 hours of sun per day (Dec) = 1,747 Watt*Hours per day
    And to back check the suggestions to you:
    • 3,000 WH per day * 1/0.52 AC sys eff * 1/600 Watt array  = 9.62 Hours of sun per day required
    9.61 Hours of sun per day--Almost nowhere in the world will you harvest that amount of energy, even in summer--Unless you are using a 2-axis tracking array (you will get around 9-10+ hours of sun per day from February thru July in Cabo--Using PV Watts link above).

    Anyway... Some thoughts and initial targets... Adding a fridge to a system is a large energy hit. You are probably not far off with your 3 kWH per day usage--But you still need to be careful (lots of box fans, inefficient fridge in a hot room, etc.).

    The suggested array is (in my humble opinion) too small. The Samlex AC inverter is a good mid-quality device (still have to pick exact model--there are differences). An EpSolar MPPT type charge controller--I have no experience but certainly a lower cost device.

    Probably some sort of simple battery monitor so that the person living there can tell at a glance if the battery bank is "happy" or not.

    Your thoughts?

    -Bill

    Wow Bill, thanks for the thorough reply.


    Things have changed slightly, and my wife wants me to get a very simple solution that provides enough energy to allow our guard to charge his phone, have a fan, charge a bluetooth speaker, run a few 9W LED lights, maybe a modem for internet, and perhaps from time to time some other small charging needs like cordless tool batteries. NO Refrigerator.


    So my thoughts are that the following would work.

    • Would need an appropriate mounting solution for a roof that is facing perfectly south with a great angle for maximum exposure.  Important to note that we get hurricanes yearly.
    • Would need to understand the wiring diagram for this setup, and if there are connectors I could by for the panels to the charge controller.  Note - I have 10awg wire running from the roof to where the controller will be.  
    • From the controller to the battery, I understand 8 gauge wire would be preferred.
    • From battery to Inverter I read that 3 gauge would be acceptable 
    • From Inverter to house panel - ???
    I appreciate the help, this is way more complicated than I anticipated, and if it were left to me, I probably would have put a 4-5 kw system on the house.  Thank goodness for the sensibility of my wife to put me in check.

    Thanks,

    Chris




  • ChrisRChrisR Registered Users Posts: 8 ✭✭
    BB. said:
    Welcome to the forum Chris,

    I don't know much about Baja California (not much solar data there), but I will take a guess... Always suggest that folks design a solar power system based on their energy needs. And a small cabin system at 1,000 WH per day is not bad. Add a refrigerator, and all of a sudden you are looking at a mid-size system. I suggest 3,300 WH per day (close to your 3,000 WH per day)... But if you could measure the energy usage will a Kill-a-Watt type energy meter, it would be a big help.

    And since refrigerator being the big "energy hog here", being careful to purchase one that is very efficient and "solar friendly". One of the bigger issues with refrigerators is their peak energy usage (compressor starting amps)... If this is a "standard" compressor type, typically suggest around 1,200 to 1,500 Watt PSW inverter... If you can get an "inverter refrigerator" (LG and possibly other brands seem to be common in Mexico--So that is a big help), and you might get away with a 1,000 Watt inverter (keeping inverters "small" is a big help... Small inverters waste something like 6-10 Watts when "turned on" (tare losses). Big inverters (3+ kWatt), can take 30-40+ Watts just turned on (as much energy as a "full size" north American refrigerator). Watch "bar" and smaller refrigerators--They frequently take almost as much energy as a full size fridge, and as much starting current.

    Note that "mechanical devices" such as well pumps, box fans, etc. can take lots of energy... There are "solar friendly" well pumps, or use a 12/24 volt RV water pump (if tank water), using low power ceiling fans (DC or AC), etc. can all help. Since you are not living there, non-owners that use solar systems tend to not "watch their energy budget" closely--And tend to "murder" battery banks.

    We can come back to the above later (and others who know the area can probably help more too)...

    Just going through the design process (yes, there will be math) and using our rules of thumb for a "relatively conservative" off grid home design... We start with the loads (pick 3,300 WH per day) to define the battery bank. Normally we plan for 2 days of storage (bad weather) and 50% discharge (for longer battery life).... In an area with lots of sun and no big storms, you MAY get away with 1 day of storage.. But starting conservative (note picking 24 volt battery bank--suggested for "mid-size" off grid systems--48 VDC can work too).
    • 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volt battery bank = 647 AH @ 24 volt battery bank
    That is 4x 6 volt @ 200 AH "golf cart" batteries in series (24 volts) times 3 parallel strings (~600 AH). Golf cart batteries are good first system batteries--But if you have access to good quality higher AH (2/4/6 volt batteries), they are a good choice too. Note that many people "murder" their first bank or two because of operational or maintenance mistakes.

    Next, sizing the solar array based on two calculations. One is based on 5% to 13%+ rate of charge. 5% works OK for weekend/sunny seasonal usage... 10%-13%+ works better for full time off grid.
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 1,218 Watt array minimum
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 2,437 Watt array nominal
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 3,168 Watt array "typical" cost effective maximum
    And there is sizing your array based on your daily loads and hours of sun per day by season (9+ months a year, vs winter usage, etc.)... I don't have good Baja solar data... But one source says for a fixed array tilted to 20 degrees from horizontal, facing south for Cabo:
    https://pvwatts.nrel.gov/pvwatts.php
    MonthSolar Radiation
    ( kWh / m2 / day )

    January5.84

    February6.65

    March7.35

    April7.38

    May7.22

    June6.90

    July6.47

    August6.56

    September6.25

    October6.61

    November6.13

    December5.60

    Annual6.58


    Looks like lots of sun down there and the loads (second array calculation)... Lets pick December at 5.60 hours of sun per day (20 year average), and 3,300 WH of daily usage:
    • 3,300 WH per day * 1/0.52 off grid AC system efficiency * 1/5.60 hours of sun per day (Dec) = 1,133 Watt array "Dec" break even
    Now for some more fudge factors... You should not plan on using more than 50% to 65% of a solar system's capacity for your "base loads" (loads that must always run, like a fridge and lights). Other optional loads (washing machine, TV late into the night, vacuuming, etc.) that can be put off for next sunny day (or generator backup) helps. Lets say that your "base loads" are 1,500 WH per day, then the base WH per day would be:
    • 1,500 WH * 1/0.65 base load fudge factor = 2,307 WH per day--Still well below the 3,300 WH "nominal" December
    If you decide that your base load is >>1,500 WH per day, you may need to "up size" the array.

    I have given you lots of numbers and choices.... Because you are in a reliably sunny region (I guess), your "break even array" is even less than your 5% rate of charge minimum array. But way more panels than your 4x150W=600 Watt array suggested.

    So, now the choices... In general, most "renters" have a habit of running "everything" (leaving lights and TV on, using hair dryers, etc.) which "kills" the battery banks. So, I suggest a "relaible" system has "extra solar" panels. This gives you a better chance of longer battery bank life (in a warm climate, "inexpensive" but good quality GC batteries may last 3-5 years. Better batteries may last 5-8 years. Heat "kills" batteries... If you can keep them cool (buried in ground, out of hot/sunny rooms/etc.--Will help (25C = normale life, 35C = 1/2 aging life).

    Flooded Cell Lead Acid batteries--Need monthly checks for electrolyte levels, adding distilled water, etc.

    AGM batteries are "cleaner" and more efficient. But also cost 2x a much... And probably would not last more than 5-7 years in your climate.

    LiFePO4 (lithium iron phosphate) batteries can be great for hot weather--But that is a whole new discussion (not cheap, no maintenance, very reliable, work better/longer in hot climates).

    You can work the math other direction too... For example, a 600 Watt array in December would produce (long term daily average) around:
    • 600 Watt array * 0.52 off grid AC system eff * 5.60 hours of sun per day (Dec) = 1,747 Watt*Hours per day
    And to back check the suggestions to you:
    • 3,000 WH per day * 1/0.52 AC sys eff * 1/600 Watt array  = 9.62 Hours of sun per day required
    9.61 Hours of sun per day--Almost nowhere in the world will you harvest that amount of energy, even in summer--Unless you are using a 2-axis tracking array (you will get around 9-10+ hours of sun per day from February thru July in Cabo--Using PV Watts link above).

    Anyway... Some thoughts and initial targets... Adding a fridge to a system is a large energy hit. You are probably not far off with your 3 kWH per day usage--But you still need to be careful (lots of box fans, inefficient fridge in a hot room, etc.).

    The suggested array is (in my humble opinion) too small. The Samlex AC inverter is a good mid-quality device (still have to pick exact model--there are differences). An EpSolar MPPT type charge controller--I have no experience but certainly a lower cost device.

    Probably some sort of simple battery monitor so that the person living there can tell at a glance if the battery bank is "happy" or not.

    Your thoughts?

    -Bill

    Wow Bill, thanks for the thorough reply.

    Things have changed slightly, and my wife wants me to get a very simple solution that provides enough energy to allow our guard to charge his phone, have a fan, charge a bluetooth speaker, run a few 9W LED lights, maybe a modem for internet, and perhaps from time to time some other small charging needs like cordless tool batteries. NO Refrigerator.

    So my thoughts are that the following would work.


    • Would need an appropriate mounting solution for a roof that is facing perfectly south with a great angle for maximum exposure.  Important to note that we get hurricanes yearly.
    • Would need to understand the wiring diagram for this setup, and if there are connectors I could by for the panels to the charge controller.  Note - I have 10awg wire running from the roof to where the controller will be.  
    • From the controller to the battery, I understand 8 gauge wire would be preferred.
    • From battery to Inverter I read that 3 gauge would be acceptable 
    • From Inverter to house panel - ???
    Thanks for your help

    Chris
  • ChrisRChrisR Registered Users Posts: 8 ✭✭
    Another thing that can be considered is that we have 350 days of sun/year here, so no need for more than 1 maybe 2 day of battery storage.
  • ChrisRChrisR Registered Users Posts: 8 ✭✭
    This is what I assume the wiring would look like.  However, Not clear if there are two batteries.



  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    For a cabin with no AC/DC fridge, 500-1,000 WH per day is probably enough (remember, my guesses, but your needs).

    If need fan(s), I would tend towards the 1,000 WH per day system... How that would divide would be something like (all guesses here--Picking very efficient fans/devices, measuring actual draws, etc. all help):
    • 500 WH per day fans / 12 hours per day (afternoon/evenings?) = 42 Watts for fans
    • 500 WH for LED lighting, cell phone charging, tablet computer, 12 volt RV water pump, etc.
    Don't know your guy... But using the phone as a WiFi hotspot can work well (assuming cell phone is a "smart phone" and good cell service in area). Saves another bill (data) and power usage (probably not much for a dedicated hotspot).

    So, just to size the battery bank... 2 days of storage, 50% max discharge, 12 volt bank:
    • 1,000 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/12 volt bank = 392 AH @ 12 volts
    That would be 2x 6 volt batteries in series (12 vols) * 2 parallel strings (200 AH per string) for 12 volts @ 400 AH battery bank... Note, for a 500 WH per day system, everything is 1/2 (12 volts @ 200 AH battery bank, etc.).

    Charging battery bank at 10% rate of charge (happy batteries). 5% to 13% is typical for solar, 10%+ for full time off grid "better".:
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 753 Watt array nominal
    And based on hours of sun per day (round down to 5 hours of sun per day--Still a lot for most people):
    • 1,000 WH per day * 1/0.52 off grid AC system eff * 1/5.0 hours of sun per day minimum (average) = 384 Watt array
    So, the choices... A 1,000 WH per day system is pretty nice for a cabin (no fridge). 500 WH per day can work--But the person living there needs to be very careful about energy usage. The big issue is that "renters" and non-technical people tend to run systems until the battery "goes dead". Let it recharge some the next day, then go dead again.

    You have lots of sun, so a 384 Watt array can supply the 1,000 WH per day loads pretty nicel. Using a 753 Watt array, keep the batteries "happy", and hopefully have a long/uneventful life, and you don't have to hover over the system (to keep from running dead).

    If you decide on 500 WattHour per day system, just everything above divided by 1/2.

    Next--Do you really need an AC inverter? 12 VDC LED lighting and getting a couple 12 volt USB chargers would work pretty nicely:

    https://www.amazon.com/s?k=12+volt+usb+charger+multi+port

    If you decide to use an inverter--Keep it small. Large inverters tend to waste more power--And frankly can draw more current than the battery bank is capable of... A suggested AC inverter would be:
    • 400 AH * 12 volts * C/8 discharge ratge = 600 Watts would be a maximum (for the 1,000 WH per day system).
    And even a 300 Watt AC inverter should be more than good enough unless need to use power tools or something bigger than you have listed so far.

    Regarding the charge controller, that is a PWM controller and will not "be optimum" for a 12 volt battery bank. And a 75 AH @ 12 -- That is pretty small. It will supply (1 day storage/50% max discharge):
    • 12v * 75 ah * 0.50 max discharge = 450 WH
    And you have to have enough panel+sun to recharge fully the next day... Lead Acid batteries generally take more than 1 day to recharge from solar to 50% discharge.

    And the maximum suggested inverter wattage for that battery:
    • 12 volts * 75 AH * C/8 hour discharge rate = 113 Watts average load for 4 hours
    A 1,000 Watt inverter is 10x as large and would suck the battery to 50% in less than a 1/2 hour at full load (if the battery was even capable of that high of current output).

    You are kind of "pushing" the edges of what the hardware is capable of... And it will probably not be an install and forget type system....

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,403 ✭✭✭✭✭
    This is past experience with providing power for a caretaker, at first I provided just enough for light and cell phone charging using DC only, using LED strip lights and automotive cigarette lighter USB adapters. That worked perfectly for several  years, then I decided to increase the capacity including an inverter, primarily for myself during my annual 2 month visit, things didn't work out well after i left. Long story short, the available AC power allowed the use of a fan overnight, then a refrigerator, the battery simply wasn't up to the task it wasn't built for. Moral of the story keep it simple because simplicity has a quality all of its own.

    We're I to do it again today, I would  use a LiFePo4 battery with built-in BMS for two reasons, the BMS would protect the battery with its protections, over charge, over  discharge, temperature , short circuit  etcetera and they tolerate the heat better. Downside is it would initially  cost more. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • mike95490mike95490 Solar Expert Posts: 8,761 ✭✭✭✭✭
    I'd suggest the following

    single ~300w PV panel
    25A MPPT controller (maybe you can find one with USB outlets too)
    an efficient 300w pure sine wave inverter, not a automotive plug in inverter
    a pair of 6V 200ah golf cart batteries wired for 12V
    some 12V brushless, silent computer case fans
    12V LED strip lighting
    Fuses to match your wires.
    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 ,

  • ChrisRChrisR Registered Users Posts: 8 ✭✭
    I appreciate all the advise guys.  As I have never done this before, I was looking at AC, because it is all I am familiar with, but it seems after reading all your posts, for the job at hand (security guard), it would probably be easiest, cheaper, and less likely to tempt add-on's to run a DC setup.

    AS I have already finished running the wiring in the house for AC to the panels, I am curious if this can still be used to power outlets and light fixtures for LED bulbs and USB outlets.  It is all run with 12 gauge wire, and the furthest distance is probably 35 feet.

    We are really trying to just give a couple of lights and ability to charge phone, bluetooth speaker.  A small personal fan would be nice, but certainly not imperative.  Any time we need power tools or something more hungry, I have a generator on property for this.  It however is not for comforts, more for when I am there, and we are working on a project, and we use it to pump water to the pile for the house.

    It would be really great if I could just take the wires to the 9W LED lights we have installed, as well as all the outlets.  If the outlets don't work, so what, we can have a usb charging station near the Battery, and that is it.

    So given this as the case, Any suggestions what equipment to do this?

    Chris
  • just startingjust starting Registered Users Posts: 235 ✭✭✭
    BB
    LiFePO4 (lithium iron phosphate) batteries can be great for hot weather--But that is a whole new discussion (not cheap, no maintenance, very reliable, work better/longer in hot climates). , I was under the assumption that lifepo4 get the best cycle life at 75°f or lower..
    200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    Don't disagree that LiFePO4 may be a good option here...

    But, really need to define the loads first. 500 WH per day may be "good enough". Days of storage... You really need 2 days of storage for a Lead Acid battery bank (4x daily use). With LiFePO4, they recharge much quickly/more effectively than lead acid, so you can use 70% or a bit more of capacity in one day, and recharge the next... But if you have a few days of bad weather (heavy clouds, hurricane, etc.), then you do have the question of what happens to power needs during that time...

    Just to try:
    • 500 WH per day * 1/0.70 (90% to 20% cycle) * 1/12 volts = 60 AH Lithium battery
    So--A 60-100 AH Li Ion battery does not look bad (with 1 day of storage)... How much?

    Vs 2x 6 volt @ 200 AH golf cart batteries for equivalent 500 WH per day system (with 2-3 days of storage).

    If you get a Battle Born (or other Li Ion with BMS) with battery management system integrated, it should last a long time and no maintenance... Battle Born (from our host, list price), around $600 for 50 AH @ 12 volt and ~$1,000 for 100 @ 12 volts (Battle Born are not cheap batteries)... I am sure that people who know more than me, can do better.

    Golf Cart Lead acid batteries are around $100 USD or so--So 2x of those would be ~$200 for a set.

    Once you figure out the paper requirements, then start looking for hardware. One thing to look for is the local price of solar panels. In the USA, "12 volt panels" (typically around 140 Watts @ Vmp~18 volts) are ~$1.00 to $2.00 per Watt, and "GT Solar panels" (200+ Watts and Vmp>=30 volts are around $0.50 to $1.00 per Watt).

    Problem is that with PWM controllers, you need Vmp~18 volt panels to charge a 12 volt bank. For MPPT controllers, they can take a wider range of solar panel Vmp... So, spend more on MPPT controller, less on panels. Spend less on PWM controllers, spend more on panels.

    Also note, 140 Watt and smaller panels can usually ship on any major carrier. Typically >200 Watt panels need to ship truck.

    See what you have available locally. Shipping can double the cost of panels when shipped a couple at a time (especially the large format panels). Lots of shopping to do.

    Also--Is theft an issue? Cheap system, less losses if stolen and replaced... For any battery, 25C/75F is "room temperature" specifications. For every 10C/18F increase in temperature, aging life is cut by 1/2.

    Li Ion batteries have much better charging characteristics (no "absorb" charge--Pretty much charge at full current to set point, then stop). Lead Acid batteries, as they approach full charge, start to "self heat" (at EQ voltage, something like 50% of charging current goes into heat). So--Li Ion tend to stay cooler in hot temperatures--Which is better for everyone.

    In the end, after the first pass or two at a pure paper design... Then a second design pass where you pick hardware (and probably different hardware--Like PWM+12 volt panels; and MPPT+GT type panels), and see what works best.

    A 500 WH per day system is on the smaller/lower cost side--So you can afford to do some "learning" on the system and how it will be used.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ChrisRChrisR Registered Users Posts: 8 ✭✭
    BB. said:

    500 WH per day may be "good enough".  
    This seems like a good option to start, but hopefully could add a bit more if needed.

    You really need 2 days of storage for a Lead Acid battery bank (4x daily use).
    This seems like the best option for this project.

    But if you have a few days of bad weather (heavy clouds, hurricane, etc.), then you do have the question of what happens to power needs during that time...
    He goes without for a couple of days, or uses the generator if emergency.

    Golf Cart Lead acid batteries are around $100 USD or so--So 2x of those would be ~$200 for a set.
    I like this best, and understand they will not last as long.  In two to three years, the property will be under development, and we will have all the power we need at that time.

    So, spend more on MPPT controller, less on panels. 
    Sounds like the best option.

    See what you have available locally. Shipping can double the cost of panels when shipped a couple at a time (especially the large format panels). Lots of shopping to do.
    I have options for 36 cell panels or 72 cell panels locally.  335W panels are right at 200 locally.

    Also--Is theft an issue? Cheap system, less losses if stolen and replaced... 
    Theft is always an issue, but if my security guard has a theft problem, I have a bigger one.

    In the end, after the first pass or two at a pure paper design... Then a second design pass where you pick hardware (and probably different hardware.

    I think I like the idea of eliminating the Inverter, and using a 12V DC setup.  I would still like to keep it as inexpensive as possible, as it really only needs to function for 3 years max.  This house will eventually become a home for someone on my administrative team, at which point we will make the necessary upgrades and spend the money to make it appropriate for this person.

    I think I would only allow a few of the possible lights to be wired, and eliminate the idea of using the electrical outlets for now, and just purchase a USB charging station.  This seems like the easiest and best way to ensure that abuse of the system is minimized.

    I would really appreciate hardware advise to accomplish this setup.  Wether it is using a 335W 72 cell panel and a reasonable priced MPPT controller, or buying a couple of 150W Newpowa panels and the Appropriate charger for them.

    I would say if I can get a decent MPPT controller for around 200, this would be a great option.  As far as batteries are concerned, I want to just go buy a couple of $100 Deep Cycle 115-120Ah batteries if this will work.  Again, they only need to last a couple of years.

    I also really appreciate all of the detailed advise.  I think it has been enlightening, and certainly helped me enormously.

    Chris


  • ChrisRChrisR Registered Users Posts: 8 ✭✭
    This was part of Renewable Resources Coalition - Top 6 Solar Charge Controllers

    EPEVER MPPT 20A Solar Charge Controller 20A Tracer A 2210AN + Remote Meter MT-50 Solar Charge with LCD Display for Solar Battery Charging

    At only $120, sounds great to me.


  • Wheelman55Wheelman55 Registered Users Posts: 98 ✭✭✭
    Building Off-Grid in Terlingua, TX
    14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048, Mini PDP, MPPT 80-600, SCP. 1 Discover AES 48 volt LiFePO4 battery 130 ah
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    Depending on your AC fixtures--If they are Medium Base Edison Bulbs, these 12 volt RV bulbs may work (technically, you could even use them in standard lamps (and just run 12 VDC to the AC light and outlet wiring--For now).:

    https://www.amazon.com/12-volt-medium-base-light-bulbs/s?k=12+volt+medium+base+light+bulbs

    Or, get a few 12 volt LED fixtures and install them where needed...

    The 14 AWG wiring will not carry a lot of current without excessive voltage drop. Say 0.5 volts drop, 14 AWG wire:
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=12&phase=dc&noofconductor=1&distance=50&distanceunit=feet&amperes=2&x=0&y=0

    50 Feet (one way run), 2 amps (2*12=24 watts), on 14 AWG wire 
    Voltage drop: 0.51
    Voltage drop percentage: 4.21%
    Voltage at the end: 11.49

    Should run a few LED lights for a "reasonable" distance on the AC house wiring... Obviously, this needs to be documented and protected against somebody hooking up 120/240 VAC and frying the existing 12 VDC devices.

    Note: While 2x 6 volt @ 200 AH batteries (connected in series) stores as much energy at 2x 12 volt @ ~100 AH batteries in parallel--I do recommend the 2x 6 volt series batteries if possible. 1/2 the number of cells to check water level on (6 cells vs 12 cells), and easier to do a quick sanity check on your battery bank health (you can measure 6 volts across each battery--Whereas 2x 12 volt batteries in parallel--If you have a "weak battery" you only see the "combined" voltage of both batteries--A bit more work to debug.

    Just to confirm the math choices:
    • 500 WH * 1/12 volts * 2 days storage * 1/0.50 max discharge = 167 AH @ 12 volts -- Round up to ~200 AH @ 12 volt batteries
    Using 2x 6 volt @ 200 AH Batteries in series, the 10% charging array would be:
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 377 Watt panel nominal
    • 200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 470 Watt panel "typical" cost effective maximum
    And based on 5 hours of sun per day, south facing array, 500 WH per day:
    • 500 WH * 1/0.61 off grid DC output system eff * 1/5.0 hours of sun per day = 167 Watt array "break even" winter
    More or less, the above array numbers are "approximate"... In solar energy +/- 10% for solar panels/battery capacity/etc. are pretty much "identical". Just using 3 digits to avoid round off error build up, and so you can follow the numbers (rather than using variables Like Cbatt, etc.).

    You are looking at a 167 to 377+ Watt array... Personally, if you can justify the larger array (377-470 Watts), you should have much less "issues" with over discharging / under charging the battery bank (especially winter/during bad weather).

    Now--You should look at your XXX Watt array in both "12 volt" (Vmp~18 volt) panels with a PWM controller, and in XXX Watt in higher Vmp panels + MPPT controller.

    If the array is close to the charge controller+Battery bank, the "12 volt" panels can work OK (need to look at current and voltage drop--Typically 1-3% suggested). If the array wiring run is "too long", the 12 volt array cables can be much heavier... An example of the math. Say 3x 140 Watt panels (Vmp~18 volts, Imp~7.78 amps) and 30 foot wire run. Using the voltage drop calculator looking for 3% or less drop. 3x7.78a=23.4 Amps (need ~30 amp+ PWM controller):
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=1.296&voltage=18&phase=dc&noofconductor=1&distance=30&distanceunit=feet&amperes=23.4&x=56&y=27

    6 AWG cable gives:
    Voltage drop: 0.55
    Voltage drop percentage: 3.08%
    Voltage at the end: 17.45

    And do the same for MPPT controller. Say you take the same 3x140 Watt panels:
    • 3*140w= 420 Watts
    • 420 Watt array * 0.77 panel+controller derating * 1/14.5 volts charging = 22.3 Amp minimum MPPT controller rating
    • Vmp-array= 3 * 18.0 volts Vmp series = 54 volts Vmp-array @ 22.3 amps @ 30 foot run @ ~100 volt rated input MPPT controller
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=5.211&voltage=54&phase=dc&noofconductor=1&distance=30&distanceunit=feet&amperes=22.3&x=74&y=29

    12 AWG wiring:
    Voltage drop: 2.13
    Voltage drop percentage: 3.94%
    Voltage at the end: 51.87

    So, much lighter Array Wiring and/or longer distance from Array to charge controller--With much lighter wiring. (as always, use conduit or exterior rated wiring (wet, UV).

    And could do other Vmp~30-36 volt panels (60 to 72 cell panels) too.... In 2 series or 3 series to get your XXX Watt array. Price of controller+panels onsite. Wiring, panel racking, etc. pricing too.

    As you can see, there are lots of variables to juggle, and once you narrow things down, you have to double check the panels, configuration, and controller requirements.

    I am not in the business, and I do not have experience with the 1,000's of controllers out there... I will give you a few links from our host's store (higher end, typically more features available, more option$)--You are welcome to talk with them, or buy elsewhere. If you have specific controllers (of any brand, you can ask for feedback here):

    https://www.solar-electric.com/residential/charge-controllers.html?manufacturer=79&nav_ctrl_voltage=417 (general search)
    https://www.solar-electric.com/midnite-solar-brat-pwm-solar-charge-controller.html (simple PWM)
    https://www.solar-electric.com/morningstar-prostar-ps-30m-solar-charge-controller-display.html (more features PWM)
    https://www.solar-electric.com/midnite-solar-kid-mppt-solar-charge-controller-black.html (MPPT)

    A remote Battery Temperature Sensor is nice (especially if controller is not in same space as battery bank).

    Hydrometer (if flooded cell lead acid battery bank):
    https://www.solar-electric.com/search/?q=hydrometer

    If you decide you want a small AC inverter (I would suggest that 300 Watts is about maximum "useful" for 2x 6 volt @ 200 AH golf cart batteries):

    https://www.solar-electric.com/morningstar-si-300-115v-ul-inverter.html (with low power standby/search mode)
    https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?nav_inv_frequency=434&nav_inv_input_voltage=436&sine_wave_type=549 (other PSW 12 volt AC inverters)

    Look at the available options (remote panel, remote on/off, standby/search mode, etc.).

    If you are interested in remote monitoring--Victron has module that interfaces with some of their inverters and charge controllers--Looks cool (and adds $$ to project):

    https://www.solar-electric.com/victron-energy-ve-direct-lorawan-us902-928.html

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