need some help

Bravo1
Bravo1 Registered Users Posts: 4

I'm a newby so take it easy.  I don't wish to use a generator for a variety of reasons so.

I am looking to power my full size fridge/top freezer (upstairs) and small chest freezer in the basement in the event of a power outage with two marine batteries and a power inverter and portable solar panels.  I have been doing some reading about inverters and see that a pure sine wave is the way to go.

From a article I read, I see that the initial motor startup/surge of these two appliances can be up to 4 times the running wattage.  Figuring 700 start up wattage of each for the initial surge of the motor, I was wondering if the above is correct if a 3,000 watt inverter would be the right size noting that the two kicking on at the same time would be unlikely.

My plans are to have the portable solar panels connected to both marine batteries in series which would be connected to the inverter and then to each appliance.

If this is feasible, would there be any recommendations on inverters, solar power panels and marine batteries ?

Am I on the wrong track here ?  I'm still doing a lot of reading but my head is about to explode with the amount of info that is out there.

Thanks so much for any advice.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,617 admin
    Welcome to the forum Bravo1,

    When we size battery (and solar) powered systems, the dividing point between a "small" and a medium size system is the addition of a Refrigerator as a load.

    For starting a single refrigerator, you would usually need a 1,200 to 1,500 Watt minimum AC inverter (and run some other lights, laptop, cell phone charger, etc.). A 3 kWatt inverter may be a bit larger than you would need or want... But I am not sure--As you say, a standard AC induction motor/compressor has a lot of starting surge--In the US (and already present in many non-US countries), are "inverter compressor" (or sometimes linear compressor) refrigerators that have almost no surge current on starting.

    Getting a Kill-a-Watt type meter will help you measure/understand your daily energy needs (in Watt*Hours or kWatt*Hours--K-a-W meters do not measure surge current)--But lets start with assuming you have energy star rated refrigerator of moderate energy draw--Roughly 2 kWH per day for the fridge in hot weather, and 1 kWH per day for the freezer (these are conservative numbers, but if you have a large fridge with all of the bells and whistles, and it is getting a bit old--2 kWH per day is common).

    For the battery bank, assume 24 volt battery bank and 2-2.5 kWatt inverter, 2 days of battery storage, and 50% maximum discharge. The battery bank would be:
    • 3,000 WH per day * 2 days * 1/0.50 maximum discharge * 1/0.85 AC inverter eff * 1/24 volt batter bank = 588 AH @ 24 volt battery bank
    Do not use "marine" batteries... Use deep cycle batteries. Marine batteries will not last very many deep cycles.

    Just to give you an idea of how big of battery bank that is--4x golf cart batteries (6 volt @ 200 AH) in series x 3 parallel strings gives you a 600 AH @ 24 volt battery bank (12x G.C. Batteries total). While you can build a battery bank out of 3 parallel strings--I would suggest you get larger AH rated batteries and try to do one string or two parallel strings... It is a pain to check / water 36 cells and all of the parallel battery strings.

    Solar panels--You need around 5% to 13% rate of charge--5% is good for a weekend/seasonal system--10% or larger for a full time off grid system:
    • 600 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,130 Watt array minimum
    • 600 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,260 Watt array nominal
    • 600 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 2,938 Watt array "cost effective" maximum
    And then there is sizing the array based on your load... If you have ice storms/winter outages--Sizing the array for no genset and average weather:
    http://solarelectricityhandbook.com/solar-irradiance.html

    Pittsburgh
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 35° angle from vertical:
    (Optimal winter settings)
    Jan Feb Mar Apr May Jun
    2.98
     
    3.49
     
    3.83
     
    4.20
     
    4.07
     
    4.32
     
    Jul Aug Sep Oct Nov Dec
    4.40
     
    4.38
     
    4.45
     
    4.13
     
    2.86
     
    2.59
     
    So, if you want 3,000 WH per day for an average December (2.59 hours of sun per day):
    • 3,000 WH * 1/0.52 system eff * 1/2.59 Hours of sun (ave Dec day) = 2,228 Watt array minimum
    That is not a small solar array--That is 10 of the "large" solar panels (~225 watt, takes two people to move around safely each panel) or ~20x ~120 Watt panels (that you can move by yourself)--Plus you need to mount the panels so that they do not get blown over in a wind storm/buried by snow, etc (and they do not get hit by rocks from a lawn mower, kids, and such).

    Anyway--As you can see, if I was to "guess" your power needs and design a nominally worst case system that can keep your fridige+freezer running 24 per day without a genset (deep dark winter storm, you will need a genset or shed loads--Solar panels do not generate a useful amount of power in dark weather).

    If your outages are short/few times a year--A genset (natural gas/propane available?) is usually a better backup system (unless you are in an apartment/condo or other place you cannot use a genset). Solar Power + Battery Bank is usually better where there is no utility power and the power needs are not that great (lots of conservation).

    The system above is enough to run a full time off grid home (LED lighting, fridge, washer, well pump, TV, laptop, cell charger--A very conservation minded home) and the system I have suggested above, is probably way over kill for your needs (or at least your expectations).

    Some of your needs may be different--For example, if it is winter power outages, a freezer in a cold space will use much less power than in a sunny kitchen during summer.

    Anyway--An initial stab at your problem statement. Questions and comments?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Bravo1
    Bravo1 Registered Users Posts: 4

    Bill,

    Thank you so much for all the info.  I didn't know about the deep cycle battery so I learned thanks to you about that.

    I got to thinking as my wife and I were discussing in the event we would loose power in the spring, summer or fall here in the Pittsburgh region that all the meat and vegetables in the freezer and fridge would be lost if it lasted more then a day.  

    I wanted something to run only those two appliances believing we are able to go about our daily routine not needing to much more.  I don't need lights having oil lamps, wood for heat in the winter, propane for the grill for cooking all year. 

    We live out in the country and don't have access to natural gas and propane is very expensive here. We eat out of our garden, can what we don't and I hunt as a way to cut down on the food bill.

    Having taken steps to use wood as a source of heat for the winter months in the event of a power outage (which we have had), I thought we would really loose a lot of food if we lost power which now a day's with the world situation is a real possibility.

    Thus the only thing that I can think of is what would we need  to keep both of these appliances going in the summer time and hopefully it didn't exceed more then a week.  In winter I would just unload the food onto the deck being it's plenty cold here in PA so that does not present a problem,

    I was simply going to run a extension cord from the inverter to those two appliances unless you don't think that is wise.

    Could you be so kind as to send me a email with a link and or the manufacture of inverter and solar panels I would need  or which manufactures to stay away from ?

    Thank again for your response and a great site.  Hope to hear from others here to.





  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,167 ✭✭✭✭
    edited July 2016 #4
    Bill just gave you a very complete and excellent breakdown with all of the details. I cannot improve on what he said, but I would like to add:

    Are you trying to design for the occasional 2-5 day outage, or are you thinking long term grid down? Your comment about "today's world" made me think longer term goals. If so, you will find that the cost goes up very fast for a full standalone system that doesn't ever require generator operation. Yes, it is done all of the time - but it is very expensive.

    I see many systems that are designed to handle refrigerator/freezer loads with solar during decently clear weather, then a small generator is used for short runs to provide a boost directly to the battery bank when needed.

    In very round numbers, my little Honda EU2000i driving a battery charger can put your estimated daily load of 3,000 watts of energy back into a battery bank using about 2/3  gallon of gas. This is far different than running a generator full time.

    Again, if you are designing for long term grid down without gas, you will need to build a bigger system using the advice provided by BB above. Remember that batteries are the "short life" part of your system so you should design accordingly.
    I always have more questions than answers. That's the nature of life.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Bravo,

    Don't forget that Bill's numbers give you only 2 days of battery power.  You may need more than 2 days.  A decent 600 ah, 24 volt battery will set you back at least $2500.

    If you spent a couple thousand dollars on an ultra efficient DC freezer and fridge, you would save more that that on the solar power system you need to run them.   You wouldn't even need an inverter.   My inverter has a self consumption of 20 watts (very low for a 3500 watt inverter).  Over the course of a day it consumes about as much power as my fridge or freezer.

    If you have more brains than money, take Marc Kurth's advice and get yourself a honda eu2000 generator.  My honda is 13 years old with untold thousands of hours on it.  They are remarkably quiet and efficient. 

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Bravo1
    Bravo1 Registered Users Posts: 4

    Thanks for all the comments.  I cannot tell you guy's how much I appreciate it. 

    Yes I am thinking for short term Marc,  2-5 day's but to answer your other comment that I made about this world, It did cross my mind if I needed it longer I could just use the same set up.

    It seems that isn't the case and appears by all accounts that it's much more complicated and expensive then I first thought.

    At 61 years of age, I simply wanted to provide for my wife and I in the event we had a short term outage but then thought what If the electrical grid went down what my options would be.

    At this point I'm not sure.

    I have looked at the exact generator you two mentioned for longer term but simply didn't want to have the noise of a generator because it would attract attention, deal with fumes and have a supply of gasoline on hand.

    I'm not a prepper and don't fault those who are but simply believe that one should have a backup planin either situation.

    Back to the drawing board as they say.

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    edited July 2016 #7
    Bravo1 said:
    I have looked at the exact generator you two mentioned for longer term but simply didn't want to have the noise of a generator because it would attract attention, deal with fumes and have a supply of gasoline on hand.
    When my generator is running, it sounds like a car idling in the driveway.  I prefer the sound of the generator to the sound of thawing food :)
    The fumes are less than what a idling car produces.
    As for gasoline, keeping a can of fresh gasoline around is much much less hassle than maintaining batteries. 

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,617 admin
    edited August 2016 #8
    With 10-20 gallons of stored gasoline (and fuel stabilizer, change 1-2 times per year) for a small/quiet Honda eu2000i--Run during the day, and get 2-4 golf cart batteries and a small AC inverter (300 Watt 12 volt TSW inverter) to run LED lighting, cell phone charger, laptop) at night (when the genset is not running).

    The fuel should last you 5-10 days. And the inverter gives you power 24x7 for the small loads. 2 or 4 golf cart batteries:
    • 2 * 6 volt * 220 AH golf cart batteries * 0.85 * 1/2 days storage * 0.50 max discharge = 561 WH per day
    • 4 * 6 volt * 220 AH golf cart batteries * 0.85 * 1/2 days storage * 0.50 max discharge = 1,122 WH per day
    5% to 13% rate of charge--Choose 10% as a good full time off grid power system:
    • 2 * 7.25 volt charging * 220 AH golf cart batteries * 1/0.77 panel+controller derating * 0.10 rate of charge = 414 Watt array
    • 4 * 7.25 volt charging * 220 AH golf cart batteries * 1/0.77 panel+controller derating * 0.10 rate of charge = 829 Watt array
    Assume February at 3.49 hours of sun per day, 9+ months of the year as the break even month (generator for darker days when needed):
    • 414 Watt array * 0.52 system eff * 3.49 hours of sun per day = 751 WH per day
    • 829 Watt array * 0.52 system eff * 3.49 hours of sun per day =1,504 WH per day
    Replace the batteries every 3-5 years. Get yourself a Hydrometer (to monitor battery health) and a DC Current Clamp DMM (Digital Multi Meter) for maintenance/debugging.

    Get an ~20-40 amp Iota Battery charger with optional smart charger module (for bad weather AC line/Genset charging).

    You can use 4-8x ~140 Watt (Vmp~18 volt) solar panels (not cheap, but smaller panels, easier to move around and ship) plus inexpensive PWM solar charge controller. Or get 2-4 ~220 Watt (Vmp~30 volts) panels (cheaper) plus not cheap MPPT type solar charge controller.

    Solar panels should last you ~20+ years easily. Electronics (charge controllers, AC inverter) should last around 10+ years. Honda should last 2,000 to ~6,000 hours with recommended oil changes.

    Do you have a well pump? Many AC well pumps will take a 4 kW minimum inverter (or genset) to run (unless you go with a "solar friendly well pump)... Run a genset and pump to cistern/tank (elevated tank ~40 feet or more above point of use--Or an RV type 12 volt water pump to pressurize home).

    I would suggest avoiding oil lamps. LED lighting + AC inverter (or even LED flashlights) are much safer (fire)--And avoid the heat/fumes of oil lamps.

    That would be my suggestions as a starting point.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Bravo1
    Bravo1 Registered Users Posts: 4
    edited August 2016 #9

    Bill,

    I looked over your figures and your recommendations and will immediately start purchasing the things yiu mentioned. No well pump.

    Is there a certain dealer whom I should look at for the solar panels you mentioned ?  I figured the guy's that hang out here are partial to a few and on the recommended list.

    Thanks so much again to everyone who chimed in.

    I learned a lot and still have much to learn.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,617 admin

    Sorry, I got a few sentences mixed up and missing information in my previous post (Fixed).

    Basically, assumed 3.49 hours of sun, not 4.0 hours minimum (Pittsburgh is not that sunny).

    And I intended to have a link for a Hydrometer and a, "good enough" DC current Clamp DMM (Sears):

    http://www.solar-electric.com/midnite-solar-battery-hydrometer.html
    http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P

    Don't buy any equipment just yet... We first try to back of the envelope design for the system (rough battery bank capacity, solar array, AC inverter, etc.)... Once you have a system that meets your estimated needs, then start selecting equipment (or at least "classes" of equipment)--And when you have the list of compatible hardware--Then finalize pricing to ensure that you are not spending beyond your comfort zone (solar power is not cheap).

    I would suggest that you look around our host's store (Northern Arizona Wind & Sun). They have good pricing and service.  Note, I do not work there and I am purely volunteering my time here. NAWS founded this forum and is funding and maintaining it. You are under no obligations to purchase your hardware from them--And we will still work with you no matter where you buy from (virtually everyone here are volunteering their time. We have a few folks from NAWS from time to time, and some mfg. that have answered questions here

    You may find that batteries are cheaper/easier to get locally (batteries can be hazardous), and solar panels can be expensive to pack and ship in less than full pallet quantities---So make sure you get shipping and insurance costs too.

    So--Have you decided on a Battery Bank and AC inverter capacity (i.e. 2-4 golf cart batteries, 300 Watt AC inverter, etc.)? Once you have the overall system sizing penciled in, we can talk about details for hardware.

    For Solar panels, there are two "classes"--The ~120-140 Watt that are relatively small and have Vmp~18 volts (~$2.00 Watt, easier to ship and a single person to move around/install)--But they tend to be more expensive. And then there is the >200 Watt panels that tend to be Vmp~30 volt panels (~$1.00 per Watt, large, usually need two people to move around safely, can only ship by truck, etc.).

    https://www.solar-electric.com/residential/solar-panels.html

    But you need to pick a charge controller to support these panels. PWM (Plus Wave Modulation--Basically a simple "on/off" switch) are inexpensive and work well with Vmp~18 volt panels.

    The other choice are MPPT (Maximum Power Point Tracking) type charge controllers which are ~3-6x more expensive than PWM--But can take the higher voltage from the large solar panels and efficiently down convert to the low voltage/high current needed to charge the battery bank (think like the DC version of a variable AC transformer).

    One place that MPPT controllers do well at is to allow you to run high voltage solar array (~100 VDC Vmp-array for many controllers and upwards of 400 VDC Vmp-array for a few)--This allows you to install the solar array a 100 feet or more away, while the PWM controllers (especially for 12 volt battery banks) should have very short cable runs (10's of feet).

    Also, if you like to "computerize" your stuff... Some of the newer/high end MPPT controllers have Ethernet connectivity and others may have other computer interfaces to let you download the daily/monthly data (and remote monitoring). Some people love this, others do not.

    Battery banks--There are flooded cell batteries which are cheaper, typically more forgiving, and easier to monitor/understand (measuring specific gravity of each cell). AGMs are an option, but tend to be much more expensive and a bit less forgiving.

    And there are LiFePO4 batteries--Not cheap, but have some advantages over lead acid--And some complexities...

    Basically, most people end up "murdering" their first (and sometimes second) battery bank--And getting a cheap "training bank" for the first time or two (i.e., golf cart batteries or similar) is a good way to save some money. Here are some battery FAQs:

    http://www.windsun.com/Batteries/Battery_FAQ.htm
    http://www.batteryfaq.org/
    http://batteryuniversity.com/

    And there is thread with lots of basic information and links to other projects, etc.:

    http://forum.solar-electric.com/discussion/4426/working-thread-for-solar-beginner-post-faq

    -Bill


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    A conventional Fridge and Freezer will require up to 10x running power, to start, and the inverter will have to supply it,  The smallest inverter I've heard of being able to reliably start a fridge is about 1,000 watts pure sine wave.   It will NOT be able to start both, you will have to let them run alternately,  Having good batteries and ample cable size is mandatory.  A 48V system would be preferred over a 12 or 24V system, to run 2 fridges/freezers (one of each)
    Sadly, a drawback with many of the frost-free units, after power is restored, they inexplicably initiate a defrost cycle.
     A 3Kw inverter seems overkill, I think a 2Kw would generally be able to do this, as long as you prevent both from starting at the same time when you switch to inverter power, allow at least 5 minutes before plugging in the 2nd one.
     And using a generator to recharge would be better than a large PV array being idle for months at a time,

    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 ,

  • Johann
    Johann Solar Expert Posts: 245 ✭✭✭
    While the grid power is still available, charge your batteries with an electric charger and/or your solar panels to keep the charge up.  Test your equipment on a regular basis and do maintenance on it.
    In an emergency, use your generator and/or solar panels.