Nube question, home battery back-up with future solar

Blitz128Blitz128 Registered Users Posts: 13
Hello All
New to all of this, been researching, but head is spinning so looking for advice and direction. This is what I think I want to do.

What I would like to do is start with a battery back-up system for my house, and eventually adding solar. I am thinking of 4ea 128W 24 volt flexible panels. I live in Columbus Ohio so solar is so so, but thats what I want to do. This system will be used for emergency use only for now.

I have converted my house to LED lighting, and my biggest power draw on emergency power will be a microwave, all 240V and other larger 120V items will be shut off. I have a 5KW generator presently, but plan on purchasing a 7KW which I will convert to tri-fuel, gas, propane, and natural gas and I will use this for major power usage for short periods.

I am looking at a using a 2000W(24V) inverter (does that size sound reasonable) that will be tied to my main home breaker panel(I know there are issues with that). To begin with I will use a 120V battery charger to keep batteries charged, solar later.

Questions:

What would be the best inverter to use if I wish to tie into main panel
What would be the best 120V charger to charge my 24 volt system
What type of batteries do you suggest
Is there anything I should do while setting up this system that would make sense with the idea of adding solar panels in the future.

Thanks
Keith

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,747 admin
    Re: Nube question, home battery back-up with future solar
    Blitz128 wrote: »
    Hello All
    New to all of this, been researching, but head is spinning so looking for advice and direction. This is what I think I want to do.

    Welcome to the forum Keith!

    Normally--We tell people to do two things. 1) is to work on conservation (which it sounds like you started). A Kill-a-Watt meter (for plug-in appliances) or something like a T.E.D. for larger appliances/AC/electric hot water, etc... (note: I am just giving you starting points for research--I do not sell these, and I am not in any solar/conservation business).

    2) after you have worked on conservation, using the same Kill-a-Watt/TED meters, measure/estimate your peak watts, and average Watt*Hours (or kWH) per day of power usage that you plan on using with your backup power system.

    Note, you have two critical design parameters to work with for off-grid battery backed systems. First is surge power (you need larger battery bank and inverters for heavy loads). So your 1,500 watt Microwave, a well pump, etc. are critical devices.

    The next is how many watts for how many hours per day... Your desktop computer may only use 200 watts average--but if you run it for 12 hours per day, you get (200 watts*12 hours per day =) 2,400 WH or 2.4 kWH per day--Much more "energy" than used by your typically microwave (say 20 minutes per day or 1/3 hour*1,500 watts= 500 WH per day).

    It is almost always cheaper to conserve a watt than to generate a watt.
    Once you know what your basic power needs are, then we can work on sizing the balance of system.
    What I would like to do is start with a battery back-up system for my house, and eventually adding solar. I am thinking of 4ea 128W 24 volt flexible panels. I live in Columbus Ohio so solar is so so, but thats what I want to do. This system will be used for emergency use only for now.

    Backing up a moment--Why flexible panels? In general, standard poly or mono crystalline cells mounted behind tempered glass (standard solar panels) will last longer and usually take less square footage on your roof (crystalline panels tend to be about 2x as efficient as thin film/flexible panels).

    In any case--again, size your system first. It is very difficult to "grow" a solar system. Usually, you end up having to replace major components as you go up in size (new battery bank, new inverter, possibly new solar panels+charge controller, etc.).
    I have converted my house to LED lighting, and my biggest power draw on emergency power will be a microwave, all 240V and other larger 120V items will be shut off. I have a 5KW generator presently, but plan on purchasing a 7KW which I will convert to tri-fuel, gas, propane, and natural gas and I will use this for major power usage for short periods.

    You can run a microwave from an off-grid solar power system--But it tends to be expensive. We even have a few people here that run induction "hot plates" too (more efficient than heating element type).

    Note that for most off-grid solar power systems, the average cost of power is ~$1-$2+ per kWH or about 10x what most people pay for utility power. Generator system costs are similar. Certainly can choose to run Microwave and such--Just need to plan for it (and bite the bullet for costs).
    I am looking at a using a 2000W(24V) inverter (does that size sound reasonable) that will be tied to my main home breaker panel(I know there are issues with that). To begin with I will use a 120V battery charger to keep batteries charged, solar later.

    A 2kW 24 volt inverter is certainly a very doable configuration. It is large enough to run a typical full sized Energy Star Refrigerator/Freezer plus a few lights.
    Questions:

    What would be the best inverter to use if I wish to tie into main panel

    Generally, if you hardwire a off grid / backup power system, you would put in a new circuit and run to to a transfer switch (some inverters include internal transfer switches). From there, to the Inverter/backup genset then to a protected sub panel (with a few more breakers going to your backed-up power outlets such as kitchen fridge, some ceiling lights, laptop computer, etc.).
    What would be the best 120V charger to charge my 24 volt system

    So much depends on the size of your battery bank and inverter--Nothing I could tell you now would be something may actually be able to use.
    What type of batteries do you suggest

    The little ones that go in your pacemaker after the heart attack when you see how much everything costs? :roll:

    There are "inexpensive" flooded cell batteries that will usually last around 6-8 years or so... Some good quality ones that may last 10-15 years. And "forklift" type that can last 20+ years...

    And AGM which may last 7-10 years (no electrolyte to check/add distilled water), very efficient, clean, no leaking fluid, relatively freeze resistant, etc... But 2x the cost of flooded cell.

    Many times, the best suggest is to get "cheap" batteries as a "training set"... Many people end up killing their first set (forget to check water, something fails and nobody notices, spouse or kids leave the coffee maker plugged in and run the bank dead, etc.). Also, you may need more/less batteries once you have ran the system for a few years--So you can better select the second set of batteries to match your needs.
    Is there anything I should do while setting up this system that would make sense with the idea of adding solar panels in the future

    Do paper designs and costings first based on your estimated power needs/budget. And read a bunch...

    Here are some starting points to read:

    Deep Cycle Battery FAQ
    www.batteryfaq.com

    When selecting an Inverter--There are two major types. One is the TSW (true sine wave) type that copies the utility AC power. Heavier and much more expensive. Usually needed for many electronics (wall mount transformers, small battery/cell phone chargers, induction motors, etc.). MSW inverters are much less expensive--but I would tend to avoid them, if possible, as they can be hard on some loads (old 80/20 rule... 80% of the stuff will probably work OK on MSW, and 10-20% will fail--Your guess as to which will work and which will fail).

    Some Inverter reading information:

    All About Inverters
    Choosing an inverter for water pumping

    For small/starting systems, this probably the best 12 volt 300 Watt TSW inverter (very nice for small/emergency power systems):

    Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC

    For backup power systems--Inverter/Chargers are pretty nice. They are the heart of a large UPS (uninterruptable power supply) systems. Many Inverter/Chargers have PFC (Power Factor Corrected) battery chargers. Very nice when running with smaller generators:

    Magnum Energy MS4024 4000 Watt Sine Wave inverter w/charger

    When selecting chargers, sizing for the battery bank and generator is important... Here is a nice thread on the subject:

    Question about battery charger selection with EU2000 generator.

    In the end, if you do a good job on conservation, you may not need a very large generator for emergency/backup power... I really like the Honda eu2000i (and eu1000i) family. They are small and quiet. And very fuel efficient with light loads.

    For example, if all you need to run is a fridge and few lights/laptop computer--You may average 400 watts of load. A eu2000i is rated at 1,600 watt full load (4 hours on 1.1 gallons of gas @ 1,600 watts). And for 400 watts, will run ~9+ hours on 1.1 gallons of fuel.

    A 5kW genset may run a 400 watt load on 1/2 gallon per hour of fuel--Much more difficult to store/obtain fuel in an emergency (8+ gallons of fuel per day vs ~2 gallons for a smaller genset).

    I will stop typing for the moment... Questions/Comments?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Nube question, home battery back-up with future solar

    well bill wrote a book, but didn't cover it all.

    why the whole house? most use backups on key circuits, but it is very doable if you do want the whole house. that would mean if the generator you have at 5kw you say may be replaced with a 7kw generator that it sounds like the 2kw backup will not be sufficient to run things. the kw used at any one time is different that the average power you use over the course of a day in kwh. for instance the inverter would ideally be able to supply 2kw consistently and if over a 24hr period this equates to 48kwh. you can use less and i would imagine you would use less consistently over 24hrs, but the 2kw rating will be the max on at one time power. your microwave, water pump, refrigerator, and tv on at one time may use close to that 2kw rating and depending on the actual models used and their ratings these could be much much higher than 2kw too with a definite surge way higher. one could time when some things can be used to keep the inverter size down on the inverter, but this won't change the overall kwh used over the day.

    like i said, if you find you are needing a 7kw generator over a 5kw generator, you may not only need to upscale the inverter size, but also space the usages, conserve, and finally consider newer more efficient appliances to knock your requirements down. large requirements will as said require large battery banks. roughly go with a battery bank voltage of about 12v for every 1000w on the inverter. up to about 24v is good for 2kw and up to about 4kw or more is good for 48v. current ratings will vary by the overall kwh used and one does not want to drain the batteries below 50% as this reduces cycle life considerably by doing so and that life increases with less capacity used from them.
  • peakbaggerpeakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Nube question, home battery back-up with future solar

    CHeck out this article from a few years ago in Home Power

    http://homepower.com/webextras/

    Go tot this location and scroll down for "midnight special" the article describes a battery based backup system with future solar potential. Do note, due to the age of the article some of the products may have been superceeded. Outback has a integrated system that is very similiar
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Thanks Bill you have given me a lot to digest
    Thanks for the "book"
    Keith
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Hi Neil
    Haven't figured out the quote thing, but here goes. For simplicities sake I would like to hook up to both legs of main panel so that all my outlets and lights are active(120 only). I figure with my LED lights that if I turn on every light I would be less than 200 watts, and I would not have them all on in an emergency situation, or ever for that matter. The only other draws would be perhaps a TV, DVD player(can't give up entertainment), short term microwave(have a small 750 watt I can use in this situation),and perhaps running a laptop 10W. THe big power draws, refridge, freezer, furnace, sump pump...., would be switched off and used only when generator is on.
    I have ran the whole house off 5 KW(harbor freight, no electric start need for wife), but Sam's club has a 7KW with honda engine and electric start for ~950.

    This is how I came up with 2000W inverter, however I am not sure if there is a 2000 watt inverter that could be hardwired, maybe 4000W might be better. I am planning on adding solar and ultimately being able to hold more load in future. With that in mind I would think it would be best to purchase products that lend themselves to system upgrade rather than having to change components as system expands.

    That is why I am looking for a 120V battery charger as a stop gap till I add solar. Was looking a flexible panels due to cost and ease of mounting, but I realize other panels are more efficient ad I am not stuck on flexible. I wish to set up emergency battery/generator system first and then add solar when more money is avail. Thought that a 24V system was a good middle of the road, though 48V would certainly be better.

    Batteries, aw, batteries, I like Bills idea of starting with lead acid and then expanding, but part of me wants to spend the money on better batteries and expanding storage capacity as I nail down what I need.

    Thanks
    Keith
    niel wrote: »
    well bill wrote a book, but didn't cover it all.

    why the whole house? most use backups on key circuits, but it is very doable if you do want the whole house. that would mean if the generator you have at 5kw you say may be replaced with a 7kw generator that it sounds like the 2kw backup will not be sufficient to run things. the kw used at any one time is different that the average power you use over the course of a day in kwh. for instance the inverter would ideally be able to supply 2kw consistently and if over a 24hr period this equates to 48kwh. you can use less and i would imagine you would use less consistently over 24hrs, but the 2kw rating will be the max on at one time power. your microwave, water pump, refrigerator, and tv on at one time may use close to that 2kw rating and depending on the actual models used and their ratings these could be much much higher than 2kw too with a definite surge way higher. one could time when some things can be used to keep the inverter size down on the inverter, but this won't change the overall kwh used over the day.

    like i said, if you find you are needing a 7kw generator over a 5kw generator, you may not only need to upscale the inverter size, but also space the usages, conserve, and finally consider newer more efficient appliances to knock your requirements down. large requirements will as said require large battery banks. roughly go with a battery bank voltage of about 12v for every 1000w on the inverter. up to about 24v is good for 2kw and up to about 4kw or more is good for 48v. current ratings will vary by the overall kwh used and one does not want to drain the batteries below 50% as this reduces cycle life considerably by doing so and that life increases with less capacity used from them.
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Thanks Peakbagger
    I will check this out
    Thanks
    Keith
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Nube question, home battery back-up with future solar
    Blitz128 wrote: »
    I wish to set up emergency battery/generator system first and then add solar when more money is avail.
    If you buy your batteries and inverter with your solar panels, the battery and inverter are part of a renewable energy system and will be eligible for 30% federal tax credits. The rebate on the battery and inverter may be enough to pay for the solar panels.
    Blitz128 wrote: »
    Batteries, aw, batteries, I like Bills idea of starting with lead acid and then expanding, but part of me wants to spend the money on better batteries and expanding storage capacity as I nail down what I need.
    Expanding storage capacity has its own issues. When you add new batteries to your old battery bank, the old batteries will quickly drag down the new batteries to the status of old batteries. Also, when you add batteries to your old bank you will probably add the new string of batteries in parallel to the old bank. Parallel batteries will cause you headaches, even if they are all of the same age. Better to figure out what you really need before spending money.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Thanks vtMaps

    Tax credit is interestig, a little confused by comments on parallel batteries, once you have created your voltage say 2 batteries in series for 24, then you have to add parallel pairs to up the storage capacity right? What headaches are you talking about and how do you avoid going parallel?

    Looking at a grid tie in 24 volt, 4000Watt split phase inverter with 60amp battery charger, battery bank for storage, and next question is solar cells. What do you have and what is your opinion on making your own, and flexible cells, seem relatively inexpensive 24v 128 watt, 189.00$, mount to section of steel roofing and stick down, attach to roof?

    Thanks
    Keith
  • BB.BB. Super Moderators, Administrators Posts: 32,747 admin
    Re: Nube question, home battery back-up with future solar

    Here is a thread where we discussed paralleling batteries:

    Series rule of thumb


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Nube question, home battery back-up with future solar
    Blitz128 wrote: »
    and next question is solar cells. What do you have and what is your opinion on making your own, and flexible cells, seem relatively inexpensive 24v 128 watt, 189.00$, mount to section of steel roofing and stick down, attach to roof?

    As for making your own... don't do it. Even if you could (and you can't) match the quality, safety, and reliability of manufactured panels, your home built panels would lack UL certification and would not be legal for grid tie. The lack of UL certification means that when your house burns, your insurance company may deny the claim.
    read:
    http://forum.solar-electric.com/showthread.php?t=4524
    http://forum.solar-electric.com/showthread.php?9470
    http://forum.solar-electric.com/showthread.php?11950

    As for flexible cells... I don't know enough about them to advise you, but they do not seem too popular with the more experienced members of this forum.

    As for "mount to section of steel roofing and stick down, attach to roof?" ... I'm not sure what you are getting at. Panel performance degrades at high temperatures. When you mount them there should be an air space between them and the roof. This will keep the panels and your house cooler.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • 2manytoyz2manytoyz Solar Expert Posts: 373 ✭✭✭
    Re: Nube question, home battery back-up with future solar

    Hi Keith,

    The guys are giving you great information.

    I will only add that I got into solar the exact same way you're thinking. I'm in FL, and power outages are a way of life here. Most times due to weather related storms, but other times for no obvious reason. Consequently, I wanted backup power. Solar was never a consideration.

    Generators are great, but only good for short term. Fuel becomes a precious commodity when the grid is down and the gas stations are closed. In 2004, we had an 18 day outage after two back to back hurricanes. Conventional generators can consume 1-1.5 gallons per hour, or up to 36 gallons per day. An inverter type only runs as fast as the load demands, consuming a fraction of the fuel. My Yamaha EF2400iS generator can run all my critical loads on 4.5 gallons per day. So during the 18 day event here, one generator would have used 648 gallons of fuel, the other 81 gallons. A difference of 567 gallons. Multiply that times your current price of fuel, that more than paid for my generator twice. I had this discussion with a couple of local friends that initially said inverter generators cost too much. Now they own the same model as I do. It's also VERY quiet.

    I used a Kill-A-Watt meter to measure all my critical loads. Things like refrigerators, security system, computer network, laptop, lights, TV, fan, even a small 5000 BTU A/C unit. I have found all of these items can operate from either my generator, or an 1800W inverter. Some caveats... There is a potential overload risk if both fridges are in a defrost mode, and the compressor on the A/C unit is engaged, along with the other items mentioned. Each fridge draws just under 600W in defrost mode, or 140-150W with the compressor running. The A/C unit pulls 600W with the compressor engaged and the fan on high. If both fridges are defrosting, and the A/C tries to start, it might overload the inverter due to the start up current spike. I did run this setup for a full weekend to see how it performs, and it had no issues.

    In a serious outage, I will turn off the fridge in the garage, which is only used to keep drinks cool. The indoor fridge has all the $$ food and is far more important to keep it running. FWIW, in 1995 a small hurricane knocked power out for 3 days. The replacement food cost as much as a new fridge.

    So I started with a generator, then bought a number of golf cart batteries & inverter. I used a grid powered charger to keep the batteries charged. The idea was to use the inverter/batteries at night, and the generator during the day to replenish the energy used. I've since added ~1000W worth of solar panels, and produce enough energy to run all my critical loads except the A/C unit. But by using mostly solar, and only using the generator once a day to top up the battery bank, I can greatly conserve fuel. Using maybe a gallon per day, instead of 4.5 gallons as before. Also greatly reduces the audio signature... "Hey, he has a generator!" Those who don't prepare drag extension cords to the homes of those who do. Been there...

    Some inverters have a built-in transfer switch and a charger. I pieced my setup together. Works well, but ultimately more expensive doing it this way. My next step is to have all the critical loads (not the window A/C unit) run from solar power exclusively.
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Thanks Robert
    I will check out that generator, wow all on 1800 watt inverter pretty cool. I want to do solar, but Ohio is not always the best for that, but still has value. Brother lives in Miami, only has generator, but has powered neighbors before, lol. Not sure which hurricane it was, but it was one that came up Gulf and made a hard right. He of course had no gasoline, but 5 empty cans, called me said he was done Fla...., still there though.
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Thanks
    I would have mounted the panel above roof with air space. I will keep an eye out for info on flex, otherwise ay suggestions on where to purchase panels an what kinds.

    Thanks
    Keith
  • JimMarinerJimMariner Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Hey Keith, Welcome to the Forums !

    I am doing the same process as you are at the moment. The only part I am lacking now in my system are the Solar Panels and Controllers. Living in South Florida, a Generator is a way of life. Well, during Hurricane season anyway. We also like our quiet time (Battery Power) While not running the Gen set. Candles are our very last option. When we see a Hurrincane heading in our direction we all Gas Up and Food Up, just in case.

    I look forward to reading of your progress in setting up your system. Good Luck !!
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Thanks Jim
    Still playing around, trying to figure out the battery situation, and aways comes down to money. A series set up of 4 or 6 volt reds would be the best, all series no parallel and the problems with that, or I go "cheap", here is an idea I had. Buy Optima 2 strings of 48 volt, but don't series them. Use an charge them separately. If I have a longer power outage, I can switch banks when nearing 50%. Probably a stupid idea, but those big batteries are expensive, Optimas are no joke either.
    "where is the earth shattering kaboom"
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Nube question, home battery back-up with future solar

    NO problem with the idea of 2 switched banks as long as the wire lengths to the switch/bus bars are the same.
    You can use a Blue Sea marine battery switch to choose which bank or both will provide power.
    hth
     
    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
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Nube question, home battery back-up with future solar

    you could lessen the costs by going golf cart batteries. we do recommend them as starter batteries just in case you mess up and many of us have first time around. also note that the solar really isn't necessary at this point and can be added later and can be made expandable if you lay things out right. the controller and wiring would need to be capable of the planned max of the system and with each pv added you increase the ability of the system as closer to being independent.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Nube question, home battery back-up with future solar

    Something to keep in mind for long outages - you do not need to power fridges and freezers 24/7. This can mean buying less PV, using a smaller battery bank, and/or using less fuel. Due to thermal carryover they will maintain a safe internal temperature for hours w/o power, as long as you keep them closed. In the summer this is easiest overnight when it is coolest. Just understand that they will then run longer during the times they are powered to catch up, but on something like a genset this can mean getting more watts-per-gallon since you are loading it up closer to its limit while it is running.

    You should keep gallon jugs of water in a freezer to take up empty space (leave expansion room in the jug), and gallon jugs of water in a fridge. This gives you additional thermal mass and also an additional source of drinking water if you need it.

    Also be sure to "bag-n-tag" everything in fridges and freezers if it is likely you'll have to "bug out" before or after a hurricane passes. Put everything inside heavy-duty trash bags, duct tape them shut and put them back inside the fridge or freezer. Then put a small bowl in the freezer with a single ice cube. After you come back if the ice cube is unmelted or mostly unmelted you know the power stayed on - or stayed on enough - and the food is safe. If it is melted, throw it all out in your conveniently pre-wrapped packages. And the duct tape? If you are gone for days or weeks and the food rots you won't have to buy a new fridge when you get back. You always read about people that have to buy a new fridge after an evacuation because of the odor and mess, even though it is functionally fine, this solves that problem.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Thanks Techntrek
    I had thought of this, when power is out many of the big power draws such as stove, freezer, dryer, A/C, are not needed or can be used when gen is going. I am also in the market for new kitchen appliances, so I should end up with more efficent refridge, and am thinking of going gas on stove. My desire to use a split phase inverter is about being able to use all outlets, lights in house with existing wiring. Switch off high power items. Lights are all LED so basic power needs should be rather small.
    I am sure this has been covered many times, but I am going to ask for another explanation. What amount of power comes from a battery bank? I was looking at Trojan 6V deep cycle. 425 AH, If I use a 48 volts system through a 4,000 W split Phase, how do I figure out how much AC power I can use before battery charge is too low? Solar is something I am looking to add down the road.
  • offgrid meoffgrid me Solar Expert Posts: 119 ✭✭
    Re: Nube question, home battery back-up with future solar

    The basic rule is to not run a battery down below 50%. So you would take the Ah rating and divide it by two. Take this # and multiply it by the system voltage to get usable watt hours. In your proposed battery bank you would use 212ah*48v which gives roughly 10200watt hours of usable energy before the battery must be recharged. There are many other variables which can effect usable energy such as temp and rate of draw, but as a start this should give you a good idea.
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Thanks Offgrid
    So if I have 10200 watt hours of usable energy, and say I am using 1000watts(120v), then I could run this load for ~10 hours?
    Thanks
    Keith
  • BB.BB. Super Moderators, Administrators Posts: 32,747 admin
    Re: Nube question, home battery back-up with future solar

    The math is "correct"--but as always, the devil is in the details. There are inverter losses (~85% efficient), there are battery losses (the more current you draw, the higher the battery losses), etc...

    So, you sometimes need to add correction factors (inverter usage, battery losses, charging losses, solar panel deratings, etc.) to ensure you don't overestimate your system's capabilities to support your needs... Overall, from solar panel rating to actual AC power output at night, the overall end to end efficiency of a typical off grid solar power system is about 50%.

    A typical small home power system would provide around 1-3.3 kWH per day (1 kWH per day is not much power; 3.3 kWH per day or 100 kWH per month can be done, but you have to be very careful on overall power usage). So, a typical solar array for a 3.3 kWH per day / 4 hours of sun per day system would need:

    3,300 kWH per day * 1/0.52 system efficiency * 1/4 hours of sun for nine months of year = 1,587 Watt Array minimum

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Thanks BB
    I get the fact that you can not really know, 1000W was just a number since this would be for emergency use, I am looking at a number more like 200w, led lighting, computer, maybe TV, have small one or this. Have a 5 KW for big items, but am really interested in honda 2000 most of you seem to have. Enough power, quite, and efficient
    Thnks
    Blitz
  • offgrid meoffgrid me Solar Expert Posts: 119 ✭✭
    Re: Nube question, home battery back-up with future solar

    Blitz
    Besides what BB said you also need to factor in the power the inverter uses to give you power. I dont know which inverter you have but I can tell you that mine uses roughly 30watts all the time no matter what I draw from it. Over a 24hr period the standby losses can really add up. In my case it is 720 watt hrs per day. So all of a sudden you get yourself down to 9480wh of available power. Small loads over long periods really add up. A cable box if plugged in will draw roughly the same amount of power as the inverter so subtract another 720wh. Same with some wireless routers. Best advice figure out all your loads even the small ones. They really add up.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Nube question, home battery back-up with future solar

    There's one more factor - the Peukert Effect. You'll get 10200 watts out of the battery only if you are pulling amps out of the battery at its 20 hour rating. If you pull it out faster you'll get less than 10200 watts. Pull it out slower and you'll get more.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Understood Techntrek
    I am learning a lot about battery life, draw, losses, power usage. I have to decide what I want my system to do, and how much to spend.
    Thaks
    Blitz
  • JimMarinerJimMariner Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Something else to consider, we in Florida don't worry about our Electric Ranges, which most of us have. We Usually all buy BBQ's with the Extra Side burner. Then we fill all our propane tanks prior to the hurricane hitting. I have 3 myself. I also fill all my 5 gallon gas cans for the Gen Set. If the Hurricane blows past, the gas goes into the cars, after we drain the full tanks they got prior to the storm too.

    In Past hurricane outages, we did the 6 hour on, 6 hour off on the Generators. And of course, kept the Fridge and Freezer doors opening to a minimum on the Off hours.
  • Blitz128Blitz128 Registered Users Posts: 13
    Re: Nube question, home battery back-up with future solar

    Good point JIm

    I have agrill with side burner, as well as coleman stove, former Boy Scout Leader, coleman oven, coleman coffee pot, colema lantern, both propane and white gas, vent free NG fireplace,and 4 propane tanks at the ready. Being prepared is key
    Thaks
    Keith
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Nube question, home battery back-up with future solar

    And the other "gotcha" is the power factor on motors. 1.0 is perfect. .3 is lousy. Many appliances with motors vary between .5 and .8 Newer modern stuff has better power factor, which results in less losses in the inverter and device.
    Example - screw in florescent bulbs : some are .95, some are .5
    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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