24v or 48v?

SolarSailor
SolarSailor Solar Expert Posts: 49
What are the criteria best used to determine whether one would prefer a 24-volt or 48-volt system?
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Comments

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: 24v or 48v?

    Greater then 2kw becomes tougher at 24 vdc. The large current requires larger cable gauge and there will be additional losses in connectors and inverter efficiency is less.
  • peterako
    peterako Solar Expert Posts: 144 ✭✭
    Re: 24v or 48v?

    as stated before 2000 W by 24 V is around 100A. the same 2000W by 48 V is 50 A.

    But at the same time if you are not using this delay and only as backup the extra cost for the higher class inverter charger and more Battery's is also a problem.

    Tell as what type of system and use your are planning and there will be a lot of responses helping you.

    Greetings from Greece8)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: 24v or 48v?

    1. Do you need 12/24/48 volts DC for anything else?
    2. What is the voltage of your power source (12 volts DC, 24/48 VDC, 120 VAC, etc.)
    3. How much power do you need (200 watts, 2,000 watts, etc.).
    4. Any special needs (motors, lights, A/C, special voltages, etc.)...

    I tend to recommend higher voltages to keep current down and allow you to but batteries together in series rather than in parallel. I tend to believe that there are less costs and battery management issues when there are fewer parallel strings.

    However, for the "average system"--you will probably see that there are several solutions to pick from and either would work fine for you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?

    Well, I'm thinking of this as a ground-up design.
    Nothing is currently in use, and nothing is being collected.

    Just want a nice, tidy, easy to maintain and, of course, the least costly system which will do the job.

    So, what is the job?

    I'm currently thinking in terms of basic replacement of my existing energy
    system (on-grid) for typical household use.

    I suppose it'd take something on the order of 3-5kW of available power,
    with an average background of 2kw winter load and probably 3.5kW cooling
    load in the summer. The rest would be for heavy use or motor startup, etc.

    Though, I think I'd like to consider capacitor type motor startups if possible.

    To start off, it seems I must consider the devices themselves, too.
    If I use a 48-volt system, is it best to also have everything driven also
    be 48-volts? That is, refrigerator, dishwasher, lighting circuits. Or,
    is it normally expected to convert 48-VDC to 120VAC to drive normal
    appliances?

    I'm guessing (definitely NOT an electrical guru of any kind), but seems the
    less conversions going on, the more efficient the system as a whole would be.

    Do appliances even come in 24/48-VDC versions, and if so, are their costs
    comparable to 120VAC types?

    ...as you can see, there's lots of questions, which is why I joined up here.:p

    Simple, transparent, efficient would be goals, then at the least cost.
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?

    btw, in a 'replacement' system, that 3-5kW would be divided into, say, 1500-2400 watt circuits, with dedicated circuits to appliances likely. If everything were ON at the same time, perhaps it could get out of hand.

    But, I currently don't ever exceed 5kW at one time afaik.

    For design sake, let's just say two 2400-watt lighting circuits and two 2400-watt recept circuits, then dedicated appliance circuits, one for dishwasher & disposal, one for refrig, one for microwave, one for toaster oven. HVAC would need two circuits (it's 120/240-volt now).

    That's ten circuits total.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: 24v or 48v?

    To beat the dead horse once again,,,you do realize of course, that a battery based system will cost ~twice as much per KWH compared to a grid tie system. If your goal is to "save money on your power, you are not likely to with a battery based system. If you are looking for security by having a battery based system, please consider the idea of a stand by generator instead. Unless your grid is quite unreliable, a grid tied PV system with a simple generator back up will (IMHO) be the cheapest system per KWH as well as the most reliable.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: 24v or 48v?

    I am a bit confused about your requirements:
    Well, I'm thinking of this as a ground-up design.

    Nothing is currently in use, and nothing is being collected.

    Just want a nice, tidy, easy to maintain and, of course, the least costly system which will do the job.

    So, what is the job?

    I'm currently thinking in terms of basic replacement of my existing energy system (on-grid) for typical household use.
    Is this a house boat on shore power (or similar). Or is this a true cruiser of some sort that spends a lot of time on shore power? Or is this your "home on land"?

    Note: Running solar+batteries+charge controller+inverters is expensive, a fair amount of losses, and batteries that will need replacement every 4-8 years or so.

    Also, I am confused about your need for DC Power... Typically people use batteries for portable power, remote installations (no power lines nearby), or for emergency power (utility power goes down for long periods of times due to ice storms, hurricanes, etc.).

    If you have reliable Utility power for a fixed installation... Normally, the most cost effective system is to setup a Grid Tied Inverter + a large solar array and no batteries. No batteries, no replacement costs, no watering/cleaning, etc.

    Grid Tied systems produce power that is near the price of utility power (or sometimes even cheaper for places like California where we can have very high power charges >$0.30 per kWhr compared to the $0.10 per kWhr that many other states have).

    You do need to live where Grid Tied Net Metering is supported by the local utility (many smaller utilities and co-ops do now allow Grid Tied solar as they probably lose money on the deal).
    I suppose it'd take something on the order of 3-5kW of available power, with an average background of 2kw winter load and probably 3.5kW cooling load in the summer. The rest would be for heavy use or motor startup, etc.

    Though, I think I'd like to consider capacitor type motor startups if possible.
    Trying to be clear here... There is a 100 watt light bulb running for 10 hours is 1 kWhour:

    100 watts * 10 hours = 1,000 Watt*hours = 1 kWatt*Hours

    So--I am unsure about the 3-5kW of available power. Are you talking about 3 kWatts (motor, heating, etc.) running for hours a day--or are you talking about 500 watts loads running for 5-10 hours per day?

    Watts and KWatts is a "rate" (like miles per gallon). Watt*Hours and kWHrs is an actual unit of energy (like Gallons used). It is confusing at first--but it does work out (and sometimes I still make the typo/mistake :blush:).

    Note that running 500 watts for 10 hours is a big difference running 5,000 watts for 10 hours (that is a lot of solar panels).

    I am not sure what you mean by Capacitor Type Motor Start-up. It sounds like you are asking about Induction Motors (AC). And there are starting capacitors for some of those types. There are also DC PM motors for use on DC systems--and even sometimes used in AC systems too (more efficient, variable speed, etc.).
    To start off, it seems I must consider the devices themselves, too.

    If I use a 48-volt system, is it best to also have everything driven also be 48-volts? That is, refrigerator, dishwasher, lighting circuits.

    Or,is it normally expected to convert 48-VDC to 120VAC to drive normal appliances?

    I'm guessing (definitely NOT an electrical guru of any kind), but seems the less conversions going on, the more efficient the system as a whole would be.

    Do appliances even come in 24/48-VDC versions, and if so, are their costs comparable to 120VAC types?
    You will find a fare amount of appliances that run on 12 VDC (microwave ovens, crock pots, computers, refrigerators, TV's, etc.). These devices are typically for the RV market.

    Some 24 VDC devices are available for trucks/boating/military market (and they tend to be more expensive--if available).

    48 VDC items are probably few and far between.

    The typical, good quality True Sine Wave, inverters are available in 12/24/48 volt devices from various vendors--and not much difference in price based on voltage (obviously, inverters with higher wattage are more expensive). The smaller inverters tend to be lower voltage (such as 12 volts).

    A good truse sine wave inverter is around 80-85% efficient or so. So, you do have to deal with the 20% of losses (more solar panels, more batteries, etc.). However, depending on what you purchase you can actually come out ahead with 120 VAC appliances + Inverter instead of the DC version of those devices.

    For example, you can get some pretty nice Energy Star Refrigerators for <$1,000 vs similar DC versions (usually without frost free/through the door water/etc.) at 2-4x more expensive. Also, many of the DC appliances have ongoing quality issues (poor door seals, leaking water, poor reliability).

    You can take the money you save with a normal Energy Star Fridge/Freezer and apply it towards more solar panels, batteries, inverters to make up for the extra losses (by the way, the current Energy Star Fridges are about as efficient at the very expensive off-grid models).

    So--Depending on your needs--You may decide on 24 VDC power to power some 24 VDC loads (water pumps, sump pumps, etc.) and use a 2,000 watt inverter for the 120 VAC loads. Or you may choose 48 VDC to run a 120/240 VAC Inverter for heavy loads.

    To look at the basic components (batteries, panels, inverters, charge controllers)--visit our host's store Northern Arizona Wind & Sun (this is a forum funded and maintained by a commercial business). You are welcome use their services or not... (Neither of us moderators have any business relationship with NAWS).

    In general. Define your needs, measure your loads, spend your money on conservation, then design a power system to support your loads.

    Sorry for the random nature of my reply... You have asked many good questions that each probably require detailed posts of their own.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?
    icarus wrote: »
    To beat the dead horse once again,,,you do realize of course, that a battery based system will cost ~twice as much per KWH compared to a grid tie system. If your goal is to "save money on your power, you are not likely to with a battery based system. If you are looking for security by having a battery based system, please consider the idea of a stand by generator instead. Unless your grid is quite unreliable, a grid tied PV system with a simple generator back up will (IMHO) be the cheapest system per KWH as well as the most reliable.

    Tony

    Well, the goal wasn't necessarily to save money. Wondered how close to parity I might be able to get at this point, though. So, your info does help in that respect.

    The grid is reliable here, and relatively inexpensive compared to east/west coast prices. I do currently have an emergency generator capable of 5700-watts (about 4 circuits) and keeps the frig/freezer, a light circuit and a recept circuit going. NOISY, though! Came in handy during that 9-day outage 2 yrs ago, though.

    Maybe I should mention that I'm not in AZ. The 9-day deal was from a "100-yr ice storm" ( that seems to come about every 4-5 years here). I'm in Oklahoma.

    I've been hoping prices for full systems might be getting cheaper today, but seems they're going up in price soz we can be 'green', capture tax credit.

    Right now, I was mostly concentrating on the battery array possibilities, assuming a generator of proper capacity on the other side, and trying to get a feel of the needs, especially as it relates to spec (24vdc vs 48vdc, or even 12vdc which my cars/motorcycles/trucks run).

    Actually, truth be known, I'm designing a shipping container house. Wanted to design a low-voltage DC system for it rather than using any 120vac at all. But, not sure it's considered practical. LED lighting for sure. Just now starting to see what the deal is with appliances.
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?

    Thanks BB for your considerable reply.

    Yeah, I was talking of 3-5kW peak demand. Not kWH's.
    Guess typical might be 3kW during evening hours (no sun, 100% battery).

    That's a model of my current use, which I suppose will be lightened, tightened and conserved in my container house design.

    Just trying to get a feel. See if LED lighting is practical and info on appliances.

    Thus, the 12v/24v/48v decision and criteria.
  • jeffkruse
    jeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: 24v or 48v?

    I am sorry but I still havent figured out what you want to accomplish and what your loads would be. :confused:
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?
    jeffkruse wrote: »
    I am sorry but I still havent figured out what you want to accomplish and what your loads would be. :confused:

    Sorry, don't know what's not clear here.

    Certainly, approaching from a conceptual level, though.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: 24v or 48v?

    SS, A full 12vdc (or 24vcd) house is quite do-able. Between the RV/Trucking industries all manner of 12vdc stuff is out there. On the other hand, many things (if not most) run more efficiently on 120vac, probably because there has been a push for energy efficiency.

    We lived for years with no 120vac, 12 vdc lights, radio, etc. We used 12vdc to charge the computers as well. I have to say, having 24/7 120 vac is pretty nice, and with a small inverter (like the suresine 300) it is pretty reasonably priced.

    Tony
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?
    icarus wrote: »
    SS, A full 12vdc (or 24vcd) house is quite do-able. Between the RV/Trucking industries all manner of 12vdc stuff is out there. On the other hand, many things (if not most) run more efficiently on 120vac, probably because there has been a push for energy efficiency.

    We lived for years with no 120vac, 12 vdc lights, radio, etc. We used 12vdc to charge the computers as well. I have to say, having 24/7 120 vac is pretty nice, and with a small inverter (like the suresine 300) it is pretty reasonably priced.

    Tony

    Ya know, since I started this thread, I'm starting to lean to a 12V system for the Container House.

    There are lots of 12v appliances (that is, lights, radios, heaters, etc as accessories for vehicles), as well as the Mobile Home and Travel Trailer market items. AND, in a bad situation, I could jump the car/truck to it to run off the alternator and/or charge batteries. Converting up to 120v from 12v isn't a problem when necessary either.

    Got me to think more in a functional mode rather than traditional comfort mode.

    I know most of you probably think the Container House is a long steel box, but it's not really that. First, in full configuration it would be composed of as many as ten 40' High Cube containers with large tented common spaces in between. As currently designed, it would be approx 3,500 square feet on three levels.

    But, it also will most likely start configured in substantially less number of containers, probably two or three to start. And, one of those will likely be off by itself as a shop/storage for construction.

    So, maybe I can do 12v for the initial configuration during construction and as the thing expands, it'd be easy to combine two descrete 12v panels/systems into a single 24v or 36v system.

    That's starting to make some sense, especially from a practical standpoint.
    Don't want to try to install a 24v/48v system big enough for the whole thing until
    it actually expands to that.

    Let's see, then. In order for me to get enough amps to power a 120v window type A/C unit or a 120v clothes washer motor, for example, what would I need?

    120v at 15 Amps coverts down to 12v how? Actually UP from 12v.

    W = Volts x Amps

    or W = 120 x 15 = 1,800 Watts

    then, 1,800 = 12 x A = 150 Amps at 12v

    150 Amps would take something like a 4/0 wire, right?

    Is there any battery able to put out 150 Amps like that?

    Best stop here until I get some feedback. I may be off track here altogether.


    But, the biggest question on my mind right now is what it takes to 'plug in' my car to the system? Something more than jumper cables, I presume.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: 24v or 48v?

    A couple of thoughts (I wrote a whole response and it got eaten so I'll make this shorter)

    You are going to have hard time building a big enough battery bank to run a A/C system

    Additionally, "deep cycle" batteries don't like to be cycled beyond 50% or you will significantly shorten their life. (some of us prefer to only cycle to ~20% DOD)

    I suggest that you read the following links:
    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries
    http://www.batteryfaq.org/

    Second, Using your car to charge your battery bank is a bad idea for a variety of reason, not the least of which is that it is very inefficient. Additionally, auto charging systems are not well suited to charging deep cycle battery systems for a variety of reasons.

    I suggest that you do some more reading on this site and off, so that you get a more thorough understanding of battery based systems.

    Good luck,

    Tony
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?
    I am not sure what you mean by Capacitor Type Motor Start-up. It sounds like you are asking about Induction Motors (AC). And there are starting capacitors for some of those types. There are also DC PM motors for use on DC systems--and even sometimes used in AC systems too (more efficient, variable speed, etc.).

    BB,

    I'm not sure, and I'm definitely not an electrical wiz, but I've read/heard somewhere that large capacitors could be used to 'absorb' the load of
    a large motor starting up, until it gets up to speed when its' draw becomes more 'regular'. IOW, provides the amperage to get it going, thus saving big draws all at once on a battery array. Suppose a couple of capacitors could even be used for different cycles of a washer motor if configured so.

    The capacitors are slow-charged over time between uses/cycles and released all at once when the motor starts. Like pulling back a sling-shot.

    Anyway, if that's describing an induction motor, o.k. I don't know about different motors other than AC/DC and PWM controllers on DC motors (robotics).

    Seems to make some sense to me, though.
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?
    icarus wrote: »
    A couple of thoughts (I wrote a whole response and it got eaten so I'll make this shorter)

    You are going to have hard time building a big enough battery bank to run a A/C system

    Additionally, "deep cycle" batteries don't like to be cycled beyond 50% or you will significantly shorten their life. (some of us prefer to only cycle to ~20% DOD)

    I suggest that you read the following links:
    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries
    http://www.batteryfaq.org/

    Second, Using your car to charge your battery bank is a bad idea for a variety of reason, not the least of which is that it is very inefficient. Additionally, auto charging systems are not well suited to charging deep cycle battery systems for a variety of reasons.

    I suggest that you do some more reading on this site and off, so that you get a more thorough understanding of battery based systems.

    Good luck,

    Tony

    Would've enjoyed the long version. But, thanks.

    Guess I've something to learn yet about batteries and charging.
    Seems simple on the surface. Not so in reality, I suppose.

    But, even if I can break away from the array and run directly off the auto alternator for short terms (emergency) for some lighting and minimal stuff, like the invertor that swaps out grid to non-grid, it could be helpful.

    As things develop this would be less important/needed as the frugle initial implementation expands into the as-designed system.

    Just thinking out loud at this point.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: 24v or 48v?
    I'm not sure, and I'm definitely not an electrical wiz, but I've read/heard somewhere that large capacitors could be used to 'absorb' the load of a large motor starting up, until it gets up to speed when its' draw becomes more 'regular'. IOW, provides the amperage to get it going, thus saving big draws all at once on a battery array. Suppose a couple of capacitors could even be used for different cycles of a washer motor if configured so.

    The capacitors are slow-charged over time between uses/cycles and released all at once when the motor starts. Like pulling back a sling-shot.

    Anyway, if that's describing an induction motor, o.k. I don't know about different motors other than AC/DC and PWM controllers on DC motors (robotics).

    A capacitor does store energy--and can be used to supply short bursts of power, especially if the power source/battery is some distance away (in electronics, we use little caps near the IC's to help keep the local voltage stable for the few tens of nano-seconds the chip takes a lot of current to switch states). However, for various reasons this is not needed or usually a good idea to put caps on the DC input side of the inverter. You are better off with short+heavy leads back to the battery bank.

    Capacitors with AC motors have a very specific reason they are used. Caps are used to change the current flow into a set of windings in an AC Induction Motor to create a "rotating field" to turn the motor. Sizing the caps does change the characteristics of the motor (starting torque, average current, etc.)... But it is not because the cap is storing energy to help the motor start and reduce starting loads on the inverter AC output (i.e., a bigger cap makes things better).

    The math behind AC Motors, caps, inductors/field coils is surprisingly complex (at least it really surprised me when I took motor theory in college :roll: ).

    Regarding your 2nd post--running off of the auto alternator and such... I am not really understanding where you are trying to head with this.

    For anything you need, there is a solution. However, as your power usage goes up... The solutions get "bigger" and more expensive.

    I have 3.5 kWatts of solar panels on the roof of my 3 bedroom home with 4 people living there (two adults and two kids). The array is "Grid Tied" (no batteries) and supplies over 100% of my loads (I have an unused credit of ~$300 per year from my power company). And we use natural gas for heating/cooking/hot water.

    However, I do not have A/C, and we are pretty conservation minded (OK--we are cheap). The same home with another family (before we moved in) had an electric bill almost 10x ours (before the GT System was installed). It was a combination of a different lifestyle and some conservation measures that we put in (insulation, energy star appliances, double pane windows, etc.).

    Going "Green" (solar, wind, etc.) requires a lot of effort to minimize and characterize your loads/needs/etc... Picking 12/24/etc. volts without looking at the entire "system" is putting the cart before the horse.

    Practically, 12 volts is a bare minimum of acceptable voltage/power for a small home. For a large installation, you will probably end up with a 48 volt battery bank and using 120/240 VAC to wire around the home.

    12 volts with a 1.5 drop is a "dead" battery for most devices. 48 volt or 120 Volts with a 1.5 volt drop is more of a "don't care" situation. And because the current at 120 volts is 1/10th that of a 12 volt system, all of the wiring can be 1/10th the cost too. 12 volt systems require very heavy (expensive) copper cables to send power any appreciable distances.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?
    BB. wrote: »
    A capacitor does store energy--and can be used to supply short bursts of power, especially if the power source/battery is some distance away (in electronics, we use little caps near the IC's to help keep the local voltage stable for the few tens of nano-seconds the chip takes a lot of current to switch states). However, for various reasons this is not needed or usually a good idea to put caps on the DC input side of the inverter. You are better off with short+heavy leads back to the battery bank.

    Capacitors with AC motors have a very specific reason they are used. Caps are used to change the current flow into a set of windings in an AC Induction Motor to create a "rotating field" to turn the motor. Sizing the caps does change the characteristics of the motor (starting torque, average current, etc.)... But it is not because the cap is storing energy to help the motor start and reduce starting loads on the inverter AC output (i.e., a bigger cap makes things better).

    The math behind AC Motors, caps, inductors/field coils is surprisingly complex (at least it really surprised me when I took motor theory in college :roll: ).

    Regarding your 2nd post--running off of the auto alternator and such... I am not really understanding where you are trying to head with this.

    For anything you need, there is a solution. However, as your power usage goes up... The solutions get "bigger" and more expensive.

    I have 3.5 kWatts of solar panels on the roof of my 3 bedroom home with 4 people living there (two adults and two kids). The array is "Grid Tied" (no batteries) and supplies over 100% of my loads (I have an unused credit of ~$300 per year from my power company). And we use natural gas for heating/cooking/hot water.

    However, I do not have A/C, and we are pretty conservation minded (OK--we are cheap). The same home with another family (before we moved in) had an electric bill almost 10x ours (before the GT System was installed). It was a combination of a different lifestyle and some conservation measures that we put in (insulation, energy star appliances, double pane windows, etc.).

    Going "Green" (solar, wind, etc.) requires a lot of effort to minimize and characterize your loads/needs/etc... Picking 12/24/etc. volts without looking at the entire "system" is putting the cart before the horse.

    Practically, 12 volts is a bare minimum of acceptable voltage/power for a small home. For a large installation, you will probably end up with a 48 volt battery bank and using 120/240 VAC to wire around the home.

    12 volts with a 1.5 drop is a "dead" battery for most devices. 48 volt or 120 Volts with a 1.5 volt drop is more of a "don't care" situation. And because the current at 120 volts is 1/10th that of a 12 volt system, all of the wiring can be 1/10th the cost too. 12 volt systems require very heavy (expensive) copper cables to send power any appreciable distances.

    -Bill

    O.K., that's very interesting. Perhaps I am entering at the wrong point in trying to decide the system voltage first. The original intent was to mirror a traditional home environment, only do it with [mostly] locally generated power. As we progressed, a 12v solution as an interim solution seemed practical and could easily be upgraded to 24v or 48v over time.

    Now, no longer as sure about anything as I was when I started :blush:

    Suppose there's going to be more starts/stops in this process. But, I did start, and that's the important part. I'm already learning a lot.

    Thanks for your, and all the others, help, btw.

    Sometimes jumping one hurdle answers a whole array of cloudy issues. That's the kind of stuff which could take years to stumble onto if one where to just read.

    Wanted to ask if your gas heating system was driven by solar powered fan motors.
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?

    btw, you said 100% of your power (actually, more with the credit) and no battery array. I guess this means you're producing more than you use during the day (sunlight hours), enough to more than offset grid use at night.

    And, all that with only 3.5kW of panel. What voltage do you use?

    Then, I suppose, the question is if the entire place runs 120/240v, what can one expect in the way of costs for the different input voltages of 12, 24 & 48 for the invertor? Suspect this to be significant, but offset by smaller wire sizes, too.

    And, as far as LED lighting goes, there's almost no reasonable configuration for 120vac LED circuits, so those would seem to tend to run at lower voltages. Then, would one re-convert locally, probably back to 12v, for those, like the PC power cords do? What would that do to efficiency? Again, wire sizing figures in, too.

    Still lots of things banging around in my head.
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?

    A little more info on the Container House.

    It WILL be a GeoThermal + Solar water heating system of some sort, not necessarily the Ground Source Heat Pump type, but may be, too. Haven't got that far yet.

    I've actually wondered about ground source AIR system for cooling and heating and have been investigating that. For any such system, for the most part, I'd need energy for only fans to move air, not heat or cool it.

    BB, I'm surprised you haven't integrated solar water heating since that's usually the first place one could start.
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?

    I've been looking at invertors.

    For 12vdc-115vac and around 400W
    the cost differences between "Pure Sine Wave" and "Modified Sine Wave" invertors is significant.

    Obviously, by cost, Pure is better. I'd guess much better. But, don't know how or in what way.

    Are the Modified types useful at all for anything?
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: 24v or 48v?
    ....
    Obviously, by cost, Pure is better. I'd guess much better. But, don't know how or in what way.

    Are the Modified types useful at all for anything?

    mod-sine are good for incandescent lighting, heating appliances (toaster, coffee pot) where power quality is not a factor.

    here's an article about inverters: http://www.solar-electric.com/solar_inverters/inverters_for_solar_electric.htm
    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 ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: 24v or 48v?

    Solar Sailor,

    Lets see if I can make a coherent answer for your three posts or so:

    If you make major changes in your system (off grid to grid tied, 12 volt to 24/48 VDC, etc.)--a good portion of the original system components will not survive the transfer to a larger/higher voltage system (inverters, some charge controllers, perhaps the solar panels, fuses/breakers/much of the wiring).

    The reason we use some rules of thumb for sizing a system (based on the owner's needs) is that the RoT's have taken into account many of the other details that will be "addressed" by following RoT's. You can stretch and work around the other issues--but then you need to get into the details of what they are--and frequently it is not worth working around them anyway).

    My home is a standard two store 70 year old wood sided (no insulation originally) 3 bedroom (sort of) home. We have all the normal urban appliances (dishwasher--we actually choose not to use to save energy, extra full size freezer out back, hand full of computers, network, printers, cable, etc.). Gas cooking, drier, hot water, central heat (using 120 VAC for fan). We set the heat to 58-65 degrees and generally use the heater for 6 months of the year (insulation, double pane windows keep the heating use fairly low--perhaps $40 worth of gas for heating in the winter months in our mild climate).

    My system is Grid Tied (solar panels -> GT Inverter -> AC mains). the 3.5 kW of panels generate around 13+ kWhrs per day (1 year average). Some months are >500 kWHrs, and other are down to near 100 kWhrs (i.e., winter).

    My system both generates more kWhrs per year than I use. I am also on a Time of Use (summer afternoons power is $0.30-0.60 kWhrs per hour on Peak, others periods are $0.09-$0.12 per kWhr).

    I am on a 1 year net metering plan with my utility. Basically, the read my meter every month and figure out how much power I used (I pay) or how much I generated (they credit my account based on my retail power rates). And I pay a minimum charge of $5.80 per month connection fee / minimum XX kWhrs of power. I end up at the end of the year with ~$300 credits with the utility--and I currently lose it (I don't get a check). Overall, a very good deal for the customer (me).

    Yes, the meter turns backwards during the day and forward when the sun is down.

    The Vmp of my panels (solar input to my GT Inverter) is around 310 volts at 9+ amps when full sun. The output of the inverter is 240 VAC 60 Hz and just connects to a pair of breakers in my AC Mains panel (20 amp pair of breakers).

    Generally, wiring/fuses/switches get big, expensive, and difficult to deal with when your current is over 100 amps or so... So, 12 vs 48 volts. The DC battery bus current is cut to 1/4 at 48 volts (you can get 4x the Wattage with the same current). Battery bank voltage does not change the number of batteries you need for your installation (if you need 4 batteries, they can be 4x in parallel for 12 volts, or 4x in series for 48 volts--the energy storage/delivery is still the same).

    One of the problems with 12 VDC devices is they are frequently designed for car use. In your car, the voltage goes between 12 and 14.4 volts or so. An off-grid battery bank may run from 11 to 15.5 volts... Some devices will not operate or even self destruct when running over the wide battery voltage range.

    You need to look at what appliances / devices you need and see what voltages are available. Right now, many of the energy star 120 VAC appliances are the same or more efficient than their DC versions. So the 15% power loss of the inverter is more than made up by the fact that the AC appliances are 1/2 the price (or less) of their off-grid battery based brothers (put the some of the extra $$ in more solar panels).

    Regarding LED's--they actually don't run at 12 volts either. They run from ~3-6 volts and need some sort of ballast (current based power limiting) to operate correctly. There are so many options out there--you would pretty much have to get samples and measure their DC and AC characteristics compared against their light output. The variations are just too large to assume that DC LED's are more efficient than an AC setup. And even then, sending 12 volts 40' to the fixture still may end up with voltage drop issues (need heavy wire to send current with less than 1 volt drop, for example).

    I am not convinced that solar hot water will be cost effective for our home--we don't use that much and a cheap water heater replacement every 12 years vs the costs of a solar thermal install + ongoing maintenance. And, I don't have a good place for solar collectors (my good space is already taken by 3.5 kW of solar pv panels).

    I did grid tied first because I did not trust California Electric Regulations/politicians (remember, back around 2000--we had rolling blackouts and utilities going bankrupts). There were a set of good rebates and pro-consumer Net Metering regulations that seem too good to pass up. Some of those options are no longer available to new Solar GT customers (I am grandfathered in for now).

    If you have utility power available--use it. Your power usage is 3x or more that of my home (I am around 200-250 kWhrs per month)

    Cost wise, Grid Tied solar is going to cost you almost 1/5th to 1/10th that of an off grid system (over twenty years).

    Regarding TSW vs MSW--for a "home", use the TSW inverter. The MSW has "issues" with about 10-20% of the devices out there. Read the FAQ that Mike gave. Another FAQ:

    Choosing an inverter for water pumping

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?

    O.K., BB, I've been soaked with a bucket now. I'm going to spend a little time absorbing and drying out. Thanks for your considerable information.

    Mike, interesting link on invertors. Everything I read now is teaching me something I didn't know. But, had to get past the vocabulary hurdle before much of it started to make sense.

    Appears I've now made it past the starting point. Now if I can get it all to jell a bit.
    Have no fear, though, I'll certainly be back with a new set of questions directly.
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?

    Oh, one more, if you don't mind.

    You're using a 240V invertor which I understand are rare. Is it a true 240V or a pair of 120Vs stacked? If 240V, would you mind stating the mfgr/model info?

    UPDATE: Never mind, if I had read your sig, I wouldn't have asked.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: 24v or 48v?

    120 VS 240 VAC inverters...

    For the most part, the GT inverters (in the US) tend to be 240 VAC designed to work on typical home type 120/240 VAC circuits. Basically, the higher the wattage (basically over 1,500 watts--although, some inverters down to <200 watts are also 240 VAC too). Running at 240 VAC cuts the current by 1/2 (vs 120 VAC)... Smaller wires, less voltage drop, more efficient.

    For Off Grid inverters, many are 120 VAC and there are ways around it... One is the "stacked" inverters. Two 120 VAC inverters with a special circuit that lets them to be synced so that it looks like a 120/240 Split Phase utility circuit from the utility. I believe both Outback and Xantrex (and I am sure others) offer stacked operation (you will have to check their specs. closely--product lines change and not all options survive the upgrades).

    Another is to get a transformer. The primary winding is 120 VAC, the output winding is a center tapped 240 VAC. I believe both Outback and Xantrex offer transformers for this function (there are other reasons to use a transformer too--such as balancing loads across 120/240 VAC circuits with inverters or gensets).

    Another is some inverters have native 120/240 VAC output with no additional hardware (the Xantrex XW Hybrid Inverter).

    All have their advantages and disadvantages. The details of which will work better for you depends on your loads (transformers add losses, two inverters have higher idle losses--although you can configure your load to run 120 VAC on one inverter and 240 VAC on two).

    By the way, if you need AC, the Split AC systems can be very nice for on-grid or off-grid use. Soft start, efficient, and very reasonable wattage when set on low (on the order of 300 watts or so):

    Sanyo mini split AC (inverter/variable speed)

    Another thought for your home--if it will be near air-tight, you will probably want to look at a heat recovery ventilator.

    In the end, define your loads, then try and figure out the optimum solution.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?
    Another thought for your home--if it will be near air-tight, you will probably want to look at a heat recovery ventilator.

    This wasn't quite what I was expecting.
    My current house system could use heat recovery, but not this kind.
    First, I'm nowhere near air-tight (built 1921, no wall insul, original windows w/storms).

    But, the HVAC system is an exterior package with both heat and A/C.
    It was installed around 1992 and has been maintained to a large degree,
    so runs at about as designed for that time. BUT, I swear it blows enough of the burner exhaust out the top to heat the whole house.

    Since it's outside, I often wonder if I couldn't restrict it more than it is. But, there's a dedicated 6" blower fan down there pumping it out. And, air pressure sensors have to detect this air motion before allowing burners to ignite.

    Thought about putting a copper water coil in it's path just to collect heat.

    I keep thinking I'm going to find some homeless person living out there. :D

    Anyway, a 'fresh air intake' isn't really needed here, but can see where it could be useful on an air-tight box.
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?

    I can see why a transformer for an isolated instance of 240vac would be the way to go. Besides, transformers would be fairly cheap compared to invertors.

    I think of them as big ignition coils from my car/motorcycles.
    And, I've come to understand those pretty well (i.e., burned a finger or two).
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: 24v or 48v?

    Transformers can be surprisingly expensive... Look for Auto Wound type transformers for a simple voltage change. The are not "isolated" transformers (there can be a DC current flow from primary to secondary windings).

    Adding Wall insulation and Double Pane windows can really reduce your power needs and make the home much more comfortable. I am very happy I did this with my current home.

    Check out your A/C options... The new stuff is much better--and heat pumps can be pretty efficient down to near freezing.

    Also, if you use a lot of AC for much of the year, a desuperheater (high side of A/C) can be used to heat your hot water FOR FREE!

    Solar Guppy, in Florida (I assume a lot of A/C to remove humidity), thinks a desuperheater may even be a better investment than solar thermal hot water (SG: forgive me if I am misrepresenting your thoughts/posts).

    -Bill

    PS: And Ceiling insulation >R40 too.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolarSailor
    SolarSailor Solar Expert Posts: 49
    Re: 24v or 48v?
    Also, if you use a lot of AC for much of the year, a desuperheater (high side of A/C) can be used to heat your hot water FOR FREE!

    This is basically what a heat pump does. I presume you mean as an accessory add-on for the basic HVAC system.

    Oklahoma has a diverse climate, subject to wide variances in short terms. So, a heat pump, while efficient, would be slow to react here. Right now, we're seeing 30-deg daily temp swings as a normal seasonal weather. But, spring and fall also bring very wide swings in even a couple of hours.

    I'd guess our average winter temp is around freezing, but it has gotten down to -15F, and regularly below zero, just not for more than a few days at time.

    Same for the 100+F days, though they can run 10-14 days sometimes.
    I know AZ is hot, but 100+ with 80%-90% humidity is something even you guys could get cranky over.