Will this work?

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tvengineer
tvengineer Solar Expert Posts: 31 ✭
in Solar Beginners Corner #1
Will this work...

So far I have some small scale solar projects at the house..

2x80w panels - morning star PWM charger - 2xgolf cart batteries running my beer cooler..

2x40w panels - to be used to run 12v attic ventilator fans in the summer..


Now I would like to step up to what I will call a medium sized system

I would like to power my refrigerator and a small deep freezer from solar.

I live in New Orleans, and having survived (barely) Katrina I never want to come home to a nasty Stinky mess of a fridge again.

Yes I know there are cheaper alternatives.. but this is my next solar project..
I am about to plunk down the money but thought I would run it past some of you experts first.

What I would like to do is build a 1kw system

my fridge (measured with a KillAwatt over a long period of time) draws 1.5kw / day at an average running current of about 160watts. Startup surge is less than 600w so I am thinking that it could comfortable run off of a Morningstar Sure Sine 300w inverter all day long.. With the morningstar auto shutdown feature saving juice when the fridge is cycled off.

so my figures for this are.

1500w/day for the refrigerator
80% efficiency on the inverter

1875 w/day for the refrigerator inverter combo


The little deep freezer draws a maximum of 48watts, and I'll assume it will run 24hrs a day worst case.
IT runs directly from 12v. so no inverter inefficiency to worry about.
48*24= 1152w/day coleman freezer

So I will need a total of 3.027kw per day of power.

I am thinking 5 panels of about 200w each (depends on what I can get the best deal on)in series feeding an outback MPPT FM-80 charge controler.


Using the a solar calculator that I found online I can figure about 4 hrs of sun per day at my location in January (worst case)

so

using the online solar calc. at Weather Underground I get..

1000w solar panels - via solar calculator 3330 w/day in January.

the way I see it.. the calculator uses an 80percent efficiency times the wattage of the panels times the number of sun hours.

so
1000w * 4.04 hrs / day sun in January.. * .8 solar = a little over 3kw per day

Does that sound about right??

Does it sound as if this 1kw system will provide the 3.027Kw/day that I think I need?

Now the worst part..

to store that energy I figure I will have a continuous 4 amp load from the little freezer..
plus a maximum of 25amp load from the inverter but not continuous.

Add a little more for inefficency on this end and it works out to a continuous load of 10amps 24hrs a day 7 days a week at 12v.

or 240 amp hrs per day from the battery

IF I want to stay above 80percent DOD I would need 1200amp hours worth of battery.
that works out in my mind to ten golf cart batteries in series/parrallel for 12v at 1100 A/h
the current draw on each set of series batteries would be 10amps / 5 .. or 2 amps per batt.

OUCH.. 10 batteries..
But I have been into electric automobiles in the past.. so keeping up with 10 batteries is not scary to me :-)


Now.. my last question.. this system is designed for the worst case.. of January..
In summer I will produce much more.. I can find uses for the extra electricity, but if I do not.. will the outback protect my batteries from overcharge.. will the outback be damaged by having too much energy from the array? Do I need a diversion load to protect the system.. or will the extra just get wasted if I don't use it?

Oh.. and would it be acceptable to use mechanical disconnects and DC rated fuses for the array and battery in lew of DC circuit breakers?

Any input or suggestions are appreciated

Louis
poche@noline.com
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
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    Re: Will this work?

    1) the Charge Controller, WILL not overcharge the batteries, when configured properly

    2) look into a 24V sure sine, and see if there is a 24V version of the Coleman deep freeze.

    3) your battery bank, at 12V w/ 10 batteries, is too big, too many connections to properly charge all the batteries. 4 strings in parallel is max, else things get un-balanced fast, and you kill batteries.
    MAybe using 6V golf cart batteries, you can keep the parallel strings down.


    Connecting on the "diagonal" will extend the life of the
    batteries by helping share the loads. Read:
    http://www.smartgauge.co.uk/batt_con.html
    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 ,

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
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    Re: Will this work?

    This is my usual calculation using the online PVWATTS calculator, assuming 1kW of solar panels, 0.52 derating (flooded cell batteries and 85% efficient inverter), fixed mount, default tilt (pasted this into Excel and changed the last column into kWhrs per month divided by 30 days per month):
    Month Solar Radiation (kWh/m2/day)
AC Energy (kWh)
Energy Value ($) 
           
1    3.49    52    1.73
2    4.84    66    2.20
3    5.09    75    2.50
4    5.60    77    2.57
5    5.75    80    2.67
6    5.64    74    2.47
7    5.51    75    2.50
8    5.35    74    2.47
9    5.18    69    2.30
10    5.39    78    2.60
11    4.50    64    2.13
12    3.86    57    1.90
=============================
Year      5.02 hours of sun    842 kWhr/yr    2.31 avg per day

    I folded in the charge controller, inverter, battery, panel losses into the above numbers--so you just need the kWhr per day rating of your appliances.

    Your calculations look high to me... I believe you left out the ~0.80 derating factor for the solar panels themselves (real life available output--not "factory specs."). I am down to an average of 1.7 kWhrs (1,700 Watt*Hours) per day in January.

    Also, the above program take into account weather as these are actual 20 year averages.

    You are correct to look at the size of the inverter and its idling losses... Many inverters (most/all?) run a minimum of 6-8 watts of standby/idling losses--running 24x7 gives you close to 200 watt*hours a day.

    Regarding using the little Morning Star 300 watt inverter--it may be too small for the job here. Starting surge + defrost heaters may be too much for it.

    Others have suggested a minimum of a 1kW TSW inverter for running a full size auto-defrost fridge.

    Perhaps others that are running such a combination can chime in here on their recommendations (I am Grid Tied--so I have limited direct experience to offer).

    If you are going with such a large inverter (1kW minimum), I would suggest that you look at 24 volt minimum wiring unless you really need the 12 volts DC (which could be achieved otherways too).

    1kW is pretty much a 100+ amps at full load and about the maximum I would aim for with a 12 volt system (wiring gets massive as the current goes above ~100 amps and I^2*R losses increase too).

    Just to run some "numbers" (remember more accurate numbers, like for the freezer may help--and I would look at the freezer as to if you want to "dump it" or not):

    0.200 kWhrs per day inverter standby losses
    1.5 kWhrs per day Fridge
    1.152 Whrs per day = 48 watt * 24 hours per day freezer
    ============================================
    2.85 kWhrs per day

    Battery sizing (assuming 24 VDC, 3 days of no sun, 50% maximum discharge):

    2,850 Watt*Hours * 3 days * 1/50% max discharge * 1/85% eff / 24V batt bank =838 Amp*Hours @ 24 volts
    Six volt batteries = 24V/6V * 712AH = 3,352 Amp*Hours of "6V batteries"

    In strings of 4, so 4, 8, 12 total batteries--I would avoid parallel strings larger than 3--just a personal choice for me.

    The above numbers are a bit on the conservative side--but they will give you a good base to make your decisions on.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
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    Re: Will this work?

    i agree to go with a much bigger inverter and possibly utilize a higher base battery/inverter voltage. whatever peak surge power is required for the frig and freezer would have to be able to be provided by the inverter and there's no way a 300w inverter will ever fit the bill for even for just one of them. it is conceivable that both will start at the same time at some point so the start surges for both are additive. round the wattages up from that point and it certainly does not hurt to have even more wattage capacity for future expansions if they come to be. they aren't cheap, but work when even gasoline isn't available for a generator and i'd rather store batteries in my home than gasoline.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #5
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    Re: Will this work?

    Suresine won't handle that load, I have a pair here and they are good little inverters but inductive loads use 5-10X on power-on ... the suresine can't even handle the turn on of my 42" plasma TV ...

    Something like a refrigerator is going to need an Outback class ( size ) inverter, and stay away from modsine for new refrigerators
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: Will this work?

    From the "ask the man who owns one" department ...

    Your figure on the 'frige consumption appear accurate. However, if it has a built-in defrost this will suck up a lot more wattage. Mine runs 500 watts while defrosting, and draws 240 or less when cycling. Start-up on an efficient unit isn't so devastating as some induction motors, but it is a sudden jolt much higher than running amperage. I doubt that a 300 watt inverter will do anything but 'fault' off.

    You've got too many batteries. You just don't need that many for day-to-day operations. As others have mentioned, "too many batteries spoils the charge." You've got to have charge current of 5-10% of the amp/hr rating in order to recharge efficiently. In other words, 1000 watts of panels @12 volts will produce a maximum charge current of 83 amps which is good for up to 800 amp/hrs of batteries. In reality it will produce about 62 amps, which is still too much for an MX60 CC (60 amps max output - the FM80 handles 80). Go to 24 volt system and you can have: 24v @ 80 amps = 1920 watts of panels. (These are 'nominals' and do not reflect inefficiencies and losses.) 1200 amp/hrs of battery would want 120 amps charge current. At 12v, that would be 1440 watts of panels but would be over the limit of the CC.

    Cut to the chase: my system is entirely off-grid. It runs a 16 cu. ft. auto-defrost 'frige/freezer, satellite Internet/phone hook-up & computer (big user), lights, radio, et cetera. I've got: 750 watts of panels, MX60 CC, 360 amp/hrs batteries (not quite enough, especially as they aren't living up to their rating), and an Outback 3524 pure sine inverter.

    Since you're on the grid anyway, why not leave out the solar panels and go with a grid-tie battery back-up system? The grid will keep the batteries charged while it's on, and the batteries will keep the 'frige running when the power goes out. You could add panels later and sell back to the grid when the sun shines. This might be a better option for your situation.

    No doubt someone will tell me why I'm wrong.
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  • rplarry
    rplarry Solar Expert Posts: 203 ✭✭
    #7
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    Re: Will this work?

    tvengineer
    I think your system will probably work just fine. I am off grid with a system very similar to what you are suggesting and I run my whole house with power to spare in the winter. In the summer the system struggles a little because the refer that I have (18 cf Sears energy star) goes from 1kw a day to 3 kw a day as measured by my killawatt meter. I also run a 5 cf chest freezer, TV, satellite internet, normal home appliances and garage power tools. I have 6 evergreen 190 watt panels, an MX 60 ( which actually does 72 amps) and 2 paralell stacked 2812 Outback inverters. All powered by 6 - 2volt agm batteries totaling 1600ah. I went with agm's because they are maint free.
    Anyway good luck with your system.
    Larry
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #8
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    Re: Will this work?

    rplarry,

    Yours might work because of your location... I could not find any data for Mexico with a real quick look--but choosing Tucson Arizona as being similar weather (assuming you too have a near desert type location), using the same settings as the one I did for New Orleans (1kW of panels, 0.52 derating, fixed mount, defaults):
    Tucson AZ
Month
Solar Radiation    (kWh/m2/day)
AC Energy (kWh)
kWhrs per day
            
1    5.70    85    2.83
2    6.11    80    2.67
3    7.03    103    3.43
4    7.50    104    3.47
5    7.29    100    3.33
6    7.15    94    3.13
7    6.44    87    2.90
8    6.85    93    3.10
9    7.06    95    3.17
10    6.72    96    3.20
11    5.99    86    2.87
12    5.27    80    2.67
=============================
Year: 6.59hr.sun 1105kWh/yr 3.10kWh/day
    And if I change the derating factor from 0.52 to 0.58 (because you have ~90% efficient AGM vs ~80% flooded cell, otherwise; Tucson, 1kW of panels, 0.58 derating, fixed mount, defaults):
    Tucson AZ
Month
Solar Radiation    (kWh/m2/day)
AC Energy (kWh)
kWhrs per day

1    5.70    96    3.20
2    6.11    90    3.00
3    7.03    116    3.87
4    7.50    117    3.90
5    7.29    113    3.77
6    7.15    106    3.53
7    6.44    98    3.27
8    6.85    105    3.50
9    7.06    107    3.57
10    6.72    108    3.60
11    5.99    96    3.20
12    5.27    89    2.97
=============================
Year: 6.59hr.sun 1241kWhr/yr 3.40kWh/day
    People living in the southwest/desert areas get a lot more sun, and changing from flooded cell lead acid to AGM also helps quite a bit too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • tvengineer
    tvengineer Solar Expert Posts: 31 ✭
    #9
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    Re: Will this work?

    Thanks for all of the input.. keep it comming :-)

    I am learning a bunch from this.

    I originally wanted to only power the little freezer.. the freezer runs on 12 v.. so
    12v was what I wanted..

    When I started looking at panels / mppt chargers / battery banks..

    I could not seem to get a good "FIT" ... enough panels to power the freezer was too much for a small morningstar MPPT controller..
    and at that relatively small power level.. not using MPPT and running the panels in parallel meant that the wire size would be bigger..

    When I looked at stepping it up a bit to power the fridge.. It seemed to me that the 1000w (5 panels in series) would be a good fit with an outback MPPT FM-80 .. and by running the panels in series the wire size would be small.
    My mistake is trying to stick with 12v..

    So.. maybe I should step back a bit.. build a smaller scale system to run the freezer.. then later add the same system I just described with a bigger inverter and 24v batteryies to run the fridge and have enough left over for intermitant stuff like the TV.

    Again.. thanks for the input.. keep it comming..

    Louis
    poche@noline.com
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  • tvengineer
    tvengineer Solar Expert Posts: 31 ✭
    #10
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    Re: Will this work?

    A couple of thoughts on things you guys said in reply...


    Quote

    1kW is pretty much a 100+ amps at full load and about the maximum I would aim for with a 12 volt system (wiring gets massive as the current goes above ~100 amps and I^2*R losses increase too).

    /quote..

    Yes.. but with 5x200 w panels in series.. the current would only be 10amps or so on the panel side of the MPPT charger..
    so the only need for HUGE wire would be between the charger and the battery bank and that could be kept very short..

    point taken though.. 100Amps is HUGE even for a short run.. and well over what the 80 amp solar charge controller is capable of.. 24v batteries would eliminate that problem..


    QUOTE
    stay away from modsine for new refrigerators
    /quote...

    I have wondered weather the whole pure sine vs mod sine is really moslty hype?

    I have run my fridge and just about every thing else that I own on cheap Chinese import mod sine inverters for days at a time with absolutely no problem.

    Is the problem with long term usage? Or severe inefficiency when running on mod sign vs. grid power.? Does the mod signwave cause overheating of the motors or power supplies that cause damage in the long run?
    From my experiance I have run just about every appliance including a micro wave/ DVR / comptuers/ TVs... etc.etc.etc. from the cheap inverters with no problems.


    QUOTE
    Since you're on the grid anyway, why not leave out the solar panels and go with a grid-tie battery back-up system? The grid will keep the batteries charged while it's on, and the batteries will keep the 'frige running when the power goes out. You could add panels later and sell back to the grid when the sun shines. This might be a better option for your situation.

    /quote

    That is fine when there is a grid.. but I am talking about those times (that are sure to be more frequent in the future) when the grid is down. This past summer the grid was down at my house for 8 days straight. Don't get me started on Hurricane Katrina.. lemme think.. power came back on at my house sometime in January... so 5 months!.. that would be a BUNCH of batteries :-) :-) :-)
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
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    Re: Will this work?

    maybe i missed it, but let me kick this around a bit by asking just how far of a run is the wire going to be from the pvs to the cc? what pvs did you have in mind for this?
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  • tvengineer
    tvengineer Solar Expert Posts: 31 ✭
    #12
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    Re: Will this work?
    niel wrote: »
    maybe i missed it, but let me kick this around a bit by asking just how far of a run is the wire going to be from the pvs to the cc? what pvs did you have in mind for this?

    The array would be on the roof.. controller just below in an elcosure with the batteries just outside the house... maybe 15 to 20 feet at most.

    Either the Evergreen ES-A-205-B 205 Watt, 11.15 Imp, 18.4 Vp

    or the non UL rated SUN panels

    Sun-A-205 205 Watt, 11.15 Imp, 18.4 Vp

    looking at Sun Electronics in Miami as they seem to have the best price right now.

    Louis
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  • homerramirez
    homerramirez Solar Expert Posts: 102 ✭✭
    #13
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    Re: Will this work?

    Yeap, MSW iverters ( the cheap ones) will work for a little while but I have enough comon sense and did the math...Samlex model S-2024 A InverCharger 24v/2000w cont./3000w peak Pure Sine wave (3 stage charging profiles 4-40 amps) for $749.00 new shipping included....I was not going to smoke my wifes new full size Kenmore fridge that we paid $650.00, besides, I just tried the kenmore washer machine not energy efficient, (1200w cont.) with this inverter with no problem ....so far my wife finally pleased:D......the MSW will be waiting just in case....good luck.

    H.R.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #14
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    Re: Will this work?

    Just a quick comment... The 100amps was referring to a 1,000 watt inverter's input current at 10.5 volts (low voltage cutout, and 85% efficiency).

    Regarding the Outback FM/MX xx family (and others too)... The input current is reduced when the string voltage goes up (P=I*V)... Double the voltage 1/2 the current... So when you run a 48 volt bank, the same FM/80 will control 4x the amount of power (~P=IV=80a*60v=4,800 watts vs P=80a*15v=1,200 watts).

    Similar for the inverters... 4x the voltage, 1/4 the amount of current (and wiring) you have to pay for and install.

    The reason a hybrid system may look good for you... It has the efficiency of a Grid Tied system (don't have the 20% losses of charging/discharging a battery bank, plus the batteries are not being cycled for the 360 days of the year you have grid power), and the batteries could be sized much smaller to handle, for example, perhaps you want only 1 day of back and 50% max discharge (2x instead of 6x for normal off-grid rule of thumb)...

    And, since you are already in an emergency--perhaps you run the batteries down to 20% state of charge (instead of 50% max)... You will still have 2 days or so of backup power (no sun)--and perhaps the batteries down last as long--but you only have 1/3rd of the amount of batteries to replace a couple years early.

    The reduced battery size is one of the things that Jim/Crewzer has been "selling" to his customers. A pretty good decrease in cost, whole house UPS. Plus, if it looks like a long power failure, you cut back on your home power usage (essentials only)--and you can run for weeks or longer with minimum power (enough for fridge, freezer, a few lights, central heat, radio/small TV). And no/small generator fuel bills/long hunts for a station that has power and fuel to sell (at any price) because the solar is powering 90%+ of your needs.

    -Bill

    PS: The MSW inverters run ~20% or so more power into motors/inductive devices (and sharp peak currents into capacitive coupled electronic power supplies). For stuff that is now made Energy Star efficient, this extra heat and fast edge rates can do cumulative damage to your equipment... How much and how fast, and what is affected... Difficuilt to say. Perhaps 90% of your stuff will run fine, and the other 10% will be damaged. Also, the 20% motor losses require you to have 20% larger panels, batteries, and inverters.

    In the end, an MSW is fine to run corded electric drills and trouble lights. I even ran my 1972 color TV on one just fine.

    However, if you are going to run drill chargers, cell phone chargers, modern energystar fridges, etc. and you cannot afford to have them fail a week into an emergency... Please spend the money on a TSW inverter.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #15
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    Re: Will this work?

    Why the seperate freezer ? What about a big energy star fridge with a good freezer, or a 120V chest freezer ? Trying to use the 12V freezer is holding you back.
    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 ,

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