Need assistance to size solar panels for house

fm.109fm.109 Posts: 33Registered Users ✭✭
Well I am back again to ask the experts here to kindly assist me in this task of mine.

I am wanting to power my house on solar backup for 8 hours a day, considering the fact that we have power failure for around that much time in this country lol.

So for that purpose I am wanting to run the following items on solar backup which include:

1. Single 1.5 ton split air conditioning unit 220v with a operating power consumption of 2020 watts
2. 5 Ceiling fans with a rating of 100 Watts each (220V)
3. 15 Lights, 24 Watts each (220 Volt)

The area is in pakistan and the backup needed as mentioned is for 8 hours daily. There is no smart grid availability.

The area is dusty due but has adequate sunlight available.

In winters you can expect sunset to be around 5 and in summers the sunset goes to almost 8

Comments

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Need assistance to size solar panels for house

    Working from your numbers (which are calculated, not measured, and as such may not be very accurate):

    1. Air conditioner 2020 Watts * 8 hours = 16,160 Watt hours. That alone is more power than my whole in-town house uses in a day. This would require a massive amount of battery and solar to supply. Might want to consider leaving this off the list or running a generator if it becomes absolutely necessary.

    2. Five ceiling fans @ 100 Watts each is 500 Watts * 8 hours = 4,000 Watt hours. That is nearly double what my off-grid cabin uses. This can be done more easily than the A/C but is not going to be cheap either.

    3. Fifteen lights @ 24 Watts each is 360 Watts * 8 hours = 2,880 Watt hours. Even that is higher than my cabin consumption. But again it can be done.

    If you add them all up you get 23,040 Watt hours per day. This is why we always say conservation is the best investment; it pays off no matter what the power source is.

    But if you were going to do it, you'd be looking at approximately 1,000 Amp hours (minimum) @ 48 Volts for the batteries and a need for two charge controllers to handle about 6,000 Watts of solar. This would be for full solar recharging, which is not necessarily needed since the grid power is available most of the day and can do at least some of the recharging.

    I can't say exactly how big the inverter would need to be as we don't know how much that air conditioning unit pulls when it starts. Suffice to say 4kW would be minimum just from adding up the other loads, and a 6kW would be better.

    I'd suggest the first thing to do is rethink what you absolutely must keep running when the power goes down.

    Your power standard, btw, is 230 VAC 50 Hz. This means you would be looking at "European standard" inverters not "North American standard" units.
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: Need assistance to size solar panels for house

    Assuming it may be cloudy or dark during the intended 8 hour outage, you will need to get 8 x 3kWh = 24 kWh from batteries. If you discharge them to 50% SOC, you need batteries capable of storing 48kWh. This probably should be a 1000AH bank at 48V, or you can go with 2000AH bank at 24V.

    Apparently, you want your batteries charged at the begginning of the outage. When you recharge batteries, you need to return back your 24kW and then some. Counting all inefficiency, you will probably need around 1.5 x 24kW, or 36kW. You need to do that once per outage. So, if outages go every week, you need it once a week. If they happen once a month, you need it once a month.

    Unfortunately, you cannot leave discharged batteries for a long time because this dramatically shortens their live. Even if you may have a full month till next outage, you need to re-charge your batteries within few days. Assuming re-charging in 3 days, you need to produce 36/3 = 12kWh a day. If you have 5 hours of sunshine, this is 12/5 = 2.4kW. So, you will need 2.4kW of panels to do that. This will give you 50A charging rate at 48V, which is 5%, a little bit too small, so you probably will need slightly bigger array, say 3kW.

    Once your batteries are charged, you do not need solar energy, so if outages are coming once a month, your system will only use 10% of the produced energy. You can improve this by switching your loads to your system in-between outages, sort of simulating outages when you do not have them, but then if a real outage comes when your batteries are discharged, you're doomed.

    It may be more economical not to use solar at all and recharge batteries from the grid. However, if you decide to go this way, you do not really need an expensive battery bank because it is much cheaper and more reliable to use a gas generator.
  • BB.BB. Posts: 27,897Super Moderators, Administrators admin
    Re: Need assistance to size solar panels for house

    FM,

    That is a lot of power, and the A/C may cycle (i.e., 15 minutes on, 15 minutes off--So, the exact power needs may differ... Also, using 500 Watts for electric fans and 360 Watts for lights is the equivalent of running an 860 Watt electric heater in your place for the A/C to manage (you are paying for the "heat" and paying to "remove the heat"--So, I would certainly look at conservation--Smaller/more efficient fans/use on low speed when running from battery, ensuring only the light needed are on when using battery (in US offices and homes, we use motion sensors--Which we all pretty much hate, but because of the cost of backup power, may be useful for you).

    Also, no computers, radio/TV, other appliances, etc. running during this time?

    Based on 100% power use for 8 hours:

    2,020 Watts * 8 hours = 16,160 WH for A/C
    5 * 100 Watts * 8 hours = 4,000 WH for fans
    15 * 24 Watts * 8 hours = 2,880 WH for lighting
    ==================================
    Total = 23,040 WH (23 kWH) per 8 hour period

    That is a huge amount of power for a backup system--However, assuming that those numbers are what you will need... For an off grid power system, we would normally suggest a 1-3 day backup and 50% maximum discharge (with 2 days 50% discharge or 4x daily load as our standard "balanced system design" for off grid). For your needs, that look a lot like an electric forklift type operation. 8 hours on , 16 hours recharging.

    You might look at electric forklift (or "traction") batteries and size the system for 1x period of storage and 50% maximum discharge (or even a smaller battery bank--your battery dealer may be able to help).
    • 23,040 WH * 1 day of storage * 1/0.50 maximum discharge * 1/0.85 inverter efficiency * 1/48 volt battery bank = 1,129 AH @ 48 volt battery bank

    You have the choice of charging the battery bank purely with solar power, or purely with utility power, or a mix (start with utility power, and add solar panels as time and money allow). But assuming your power outages are primarily during sunny days, I will guess that 4 hours a day (noon time equivalent sun) as "break even" point (you might have more or less sun, adjust to your needs--Since you have utility power, you can use it until you have a better idea of the exact solar array you would like to install).
    • 23,040 WH * 1/0.52 end to end system efficiency * 1/4 hours of sun per day = 11,077 Watt Solar array based on power usage

    The above is based on charging during the day and using power at night--I would guess that yours will be different. Part of the power will be used when the sun is up, your solar array will be supplying part of the operating power and you will be 20% or so more efficient as the power is not going through the battery charge/discharge cycle). Also, you will need to monitor the battery bank state of charge (electrolyte specific gravity). You want to keep the battery in the 50% to 90% range (get >90% SOC at least once or twice per week, and keep it over 50% SOC during normal usage). So, you may find that you want to use utility power once or twice a week to get the battery >90% SOC if the solar array cannot.

    And, from the battery bank point of view, you want around 5% to 13% rate of charge (can go as high as 25% rate of charge if thermal management of the battery bank is done). A larger battery bank can "force" a larger solar array. Your numbers (based on my rough guesses) for array size based on battery bank would be:
    • 1,129 H * 58 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 4,252 watt array minimum
    • 1,129 H * 58 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 8,504 watt array nominal
    • 1,129 H * 58 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 11,055 watt array "maximum cost effective"

    So, with a "smaller" battery bank, your minimum solar array based on energy usage, and maximum recommended solar array based on battery size is pretty much the same---11, 0xx watt array

    If you use an AC battery charger for charging your bank, the battery/charger dealer may be able to help with their recommendations--But at this point, I would suggest around:
    • 1,129 AH * 0.13 rate of charge = 147 Amp @ 48 volt minimum/nominal battery charger

    If you where going to run that from utility power/backup generator using a "standard" battery charger, your circuit would need to be around:
    • 147 Amps * 58 volts charging * 1/0.80 charger efficiency * 1/0.67 Power Factor = 15,906 VA

    Note that VA is always at least equal to or higher than Watts. VA is used for sizing the wiring/transformers/generators.

    Power = Volts * Amps * Power Factor

    Your AC battery charger supplier should be able to give you more information on their chargers (note: more expensive chargers will have efficiency near 0.90 and PF > 0.95). An "efficient and power factor corrected" battery charger can save you on wiring and backup generator capacity.

    Anyway--Those are the rough rule of thumb numbers I would start with.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: Need assistance to size solar panels for house
    NorthGuy wrote: »

    It may be more economical not to use solar at all and recharge batteries from the grid. However, if you decide to go this way, you do not really need an expensive battery bank because it is much cheaper and more reliable to use a gas generator.

    Totally, completely agree. To build such a relatively massive and expensive solar system that will only be used once in a while - - - - - - - definitely not the way to go.
    You did right by coming here and asking questions before you started dishing out your money. Solar definitely has it's place, but this use is not one of them.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Need assistance to size solar panels for house

    Need to mention that if there is a predictable pattern to the power outages that will help. If you never know when it will go off or for how long a time, you're stuck.
  • fm.109fm.109 Posts: 33Registered Users ✭✭
    Re: Need assistance to size solar panels for house

    Okay firstly I would like to thank you all for the awesome advice and yes I completely agree to using energy efficient items to save on a bulk load of solar cost.

    However let me explain to you what happens here in this country.

    The area where this solar power is needed has no set pattern of load shedding. The area experiences 3 hours of load shedding and then one hour of electricity and then again 3 hours of load shedding and so on. This is a continuous pattern and not something that is temporary. So you are looking at only 6 hours of electricity a day and that too not confirmed because authority here changes their mind every day.

    The gas problem is that the area has no gas line available and even if it did have gas line available then from our experience with nearby surroundings, that too would experience load shedding of at least 12 hours. (lol it sounds like i live in hell)

    So the purpose of this entire solar power activity is that the family there just wants to have electricity for fans and bulbs during day and night hours but would like to use the air conditioner only at night so that the elders of the house can sleep comfortably as the area during summer times experiences a lot of humidity and temperatures of above 40 degrees Celsius.

    So it is either a huge diesel/petrol generator (which honestly has a lot of running cost and the problem of breakdowns too) or a solar array system.

    We can replace the items with more energy efficient fans and air conditioners so just so that you all can have an idea of what an energy efficient air conditioner is available in pakistan, then you can have a look at this link here:

    http://www.haier.com/pk/products/air_conditioner/wall_mounted/hsu-18lk03e8b.shtml
    http://www.haier.com/pk/products/air_conditioner/wall_mounted/hsu-18lk03e8a.shtml
    http://www.haier.com/pk/products/air_conditioner/wall_mounted/hsu-12rk03-r2-sdb-.shtml
    http://www.haier.com/pk/products/air_conditioner/wall_mounted/hsu-12lko310g.shtml

    The city is Faisalabad and our voltage here is 220V and now I would ask the respected experts to help me here decide what to use though I am thankful for the input and knowledge received but if you all require more information then do tell me all the questions and I will try to help out with the designing.
  • fm.109fm.109 Posts: 33Registered Users ✭✭
    Re: Need assistance to size solar panels for house

    And BB once again thank you for helping me out, I remember last time even you helped me out with deciding a good course to learn solar and all too
    BB. wrote: »
    FM,

    That is a lot of power, and the A/C may cycle (i.e., 15 minutes on, 15 minutes off--So, the exact power needs may differ... Also, using 500 Watts for electric fans and 360 Watts for lights is the equivalent of running an 860 Watt electric heater in your place for the A/C to manage (you are paying for the "heat" and paying to "remove the heat"--So, I would certainly look at conservation--Smaller/more efficient fans/use on low speed when running from battery, ensuring only the light needed are on when using battery (in US offices and homes, we use motion sensors--Which we all pretty much hate, but because of the cost of backup power, may be useful for you).

    Also, no computers, radio/TV, other appliances, etc. running during this time?

    Based on 100% power use for 8 hours:

    2,020 Watts * 8 hours = 16,160 WH for A/C
    5 * 100 Watts * 8 hours = 4,000 WH for fans
    15 * 24 Watts * 8 hours = 2,880 WH for lighting
    ==================================
    Total = 23,040 WH (23 kWH) per 8 hour period

    That is a huge amount of power for a backup system--However, assuming that those numbers are what you will need... For an off grid power system, we would normally suggest a 1-3 day backup and 50% maximum discharge (with 2 days 50% discharge or 4x daily load as our standard "balanced system design" for off grid). For your needs, that look a lot like an electric forklift type operation. 8 hours on , 16 hours recharging.

    You might look at electric forklift (or "traction") batteries and size the system for 1x period of storage and 50% maximum discharge (or even a smaller battery bank--your battery dealer may be able to help).
    • 23,040 WH * 1 day of storage * 1/0.50 maximum discharge * 1/0.85 inverter efficiency * 1/48 volt battery bank = 1,129 AH @ 48 volt battery bank

    You have the choice of charging the battery bank purely with solar power, or purely with utility power, or a mix (start with utility power, and add solar panels as time and money allow). But assuming your power outages are primarily during sunny days, I will guess that 4 hours a day (noon time equivalent sun) as "break even" point (you might have more or less sun, adjust to your needs--Since you have utility power, you can use it until you have a better idea of the exact solar array you would like to install).
    • 23,040 WH * 1/0.52 end to end system efficiency * 1/4 hours of sun per day = 11,077 Watt Solar array based on power usage

    The above is based on charging during the day and using power at night--I would guess that yours will be different. Part of the power will be used when the sun is up, your solar array will be supplying part of the operating power and you will be 20% or so more efficient as the power is not going through the battery charge/discharge cycle). Also, you will need to monitor the battery bank state of charge (electrolyte specific gravity). You want to keep the battery in the 50% to 90% range (get >90% SOC at least once or twice per week, and keep it over 50% SOC during normal usage). So, you may find that you want to use utility power once or twice a week to get the battery >90% SOC if the solar array cannot.

    And, from the battery bank point of view, you want around 5% to 13% rate of charge (can go as high as 25% rate of charge if thermal management of the battery bank is done). A larger battery bank can "force" a larger solar array. Your numbers (based on my rough guesses) for array size based on battery bank would be:
    • 1,129 H * 58 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 4,252 watt array minimum
    • 1,129 H * 58 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 8,504 watt array nominal
    • 1,129 H * 58 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 11,055 watt array "maximum cost effective"

    So, with a "smaller" battery bank, your minimum solar array based on energy usage, and maximum recommended solar array based on battery size is pretty much the same---11, 0xx watt array

    If you use an AC battery charger for charging your bank, the battery/charger dealer may be able to help with their recommendations--But at this point, I would suggest around:
    • 1,129 AH * 0.13 rate of charge = 147 Amp @ 48 volt minimum/nominal battery charger

    If you where going to run that from utility power/backup generator using a "standard" battery charger, your circuit would need to be around:
    • 147 Amps * 58 volts charging * 1/0.80 charger efficiency * 1/0.67 Power Factor = 15,906 VA

    Note that VA is always at least equal to or higher than Watts. VA is used for sizing the wiring/transformers/generators.

    Power = Volts * Amps * Power Factor

    Your AC battery charger supplier should be able to give you more information on their chargers (note: more expensive chargers will have efficiency near 0.90 and PF > 0.95). An "efficient and power factor corrected" battery charger can save you on wiring and backup generator capacity.

    Anyway--Those are the rough rule of thumb numbers I would start with.

    -Bill
  • fm.109fm.109 Posts: 33Registered Users ✭✭
    Re: Need assistance to size solar panels for house

    Lol you are absolutely right, the power consumption is huge and this is mainly because the construction there is old (50 plus years old) and also appliances have not been upgraded in a while there, hence the less efficiency and more power hogs.
  • westbranchwestbranch Posts: 5,089Solar Expert ✭✭✭✭
    Re: Need assistance to size solar panels for house

    interesting read http://en.wikipedia.org/wiki/Haier

    In June 2005, Haier made a bid to acquire Maytag Corporation, backed by private equity funds Blackstone Group and Bain Capital. The bid was for USD $1.28 billion, or $16 per share, topping a previous offer of $14.26 per share made by Ripplewood Holdings.[9] In the end however, Maytag was bought by Michigan based Whirlpool Corporation which offered $1.7 billion in cash and stock, or $21 per share, plus assumed debt.[10]
     
    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,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • fm.109fm.109 Posts: 33Registered Users ✭✭
    Re: Need assistance to size solar panels for house

    Yup haier is pretty famous in this region and quite a business maker
    westbranch wrote: »
    interesting read http://en.wikipedia.org/wiki/Haier

    In June 2005, Haier made a bid to acquire Maytag Corporation, backed by private equity funds Blackstone Group and Bain Capital. The bid was for USD $1.28 billion, or $16 per share, topping a previous offer of $14.26 per share made by Ripplewood Holdings.[9] In the end however, Maytag was bought by Michigan based Whirlpool Corporation which offered $1.7 billion in cash and stock, or $21 per share, plus assumed debt.[10]
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: Need assistance to size solar panels for house
    fm.109 wrote: »
    So it is either a huge diesel/petrol generator (which honestly has a lot of running cost and the problem of breakdowns too) or a solar array system.

    Solar array per se cannot be used for a backup power, let alone at night. With the solar array to do backup, you will need batteries. These batteries will provide backup power. Solar array will simply charge the batteries. Batteries can provide the backup function even without solar array.
    fm.109 wrote: »
    The area where this solar power is needed has no set pattern of load shedding. The area experiences 3 hours of load shedding and then one hour of electricity and then again 3 hours of load shedding and so on. This is a continuous pattern and not something that is temporary. So you are looking at only 6 hours of electricity a day and that too not confirmed because authority here changes their mind every day.

    If there's no limit on how much electricity you can use when it's on then such pattern may be Ok to charge the battery bank from the grid.

    If I were you, I would first start from a simple battery system - battery bank and hybrid/off-grid inverter. It would charge batteries when power is available and then you could use the stored power when the grid is off. If that didn't work well and I felt I need more power, I would add a solar array, which is very easy to do when you already have batteries and inverter.
  • westbranchwestbranch Posts: 5,089Solar Expert ✭✭✭✭
    Re: Need assistance to size solar panels for house

    NG I agree if the power is on longer than it is off, but the OP said it is off 3 hrs and on 1 hr so would need a pretty beefy charger to bulk up the batteries in that short a time.
     
    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,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: Need assistance to size solar panels for house
    westbranch wrote: »
    NG I agree if the power is on longer than it is off, but the OP said it is off 3 hrs and on 1 hr so would need a pretty beefy charger to bulk up the batteries in that short a time.

    It would be good to know more about power on/off pattern. That is certainly a very unusual situation, but it may be possible to figure out the charging regiment that would work. And if not, a moderate amount of solar should be able to supplement it.
  • BB.BB. Posts: 27,897Super Moderators, Administrators admin
    Re: Need assistance to size solar panels for house

    You might think about doing some "extreme" conservation... For example, insulate just a couple rooms (main room, sleeping spaces, etc.)--Double pane windows (or heavy drapes, some even use foam boards during hot times of the years), overhangs/shrubbery/trees to block sun... False wall on outside, add insulated/wall inside... Etc.

    You have to be careful with some of this--Humidity can be a big issue in some climates. Adding "mass" (concrete, water filled tanks, etc.) and creating a cold space on one side with hot/humid other side can condense water at the mid point (mold, rot, smells, etc.).

    I don't know your construction and weather for your home/region--but insulation can be a big help. In our older wood frame home, we had zero insulation (except for some added insulation in the ceiling). We added 4" of fiberglass insulation and made the home much nicer. Used to bake in the summer (during our short hot season) and use a lot of heat in the winter... Now, we tend to use a bit more heat in the summer--because the house is so cool (on average), but use much less heating overall.

    You might take a look at this magazine (they have some free articles). Many of these ideas for home building are doen by people that are building their own homes and trying to use natural/local materials:

    www.homepower.com

    In your region, many times you use concrete+stone construction--So you have a lot of thermal mass. Adding some insulation or shading to keep heat off the walls (plus ventilating the roof/attic area) can really reduce heat gain.

    In the US, there are a fair amount of homes that are built using mud or stucco (cement type material) over straw bails (for insulation, use timber frame construction for support).

    Search for "straw home construction" and see if anything can apply for your area (using natural/local materials for insulation vs fiberglass/foam boards/etc. which may not be available or cost effective locally).

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