Series vs Parallel panel advantages

seems like the longer I plan my system the more I'm confusing myself. I live in a major city so all I have to work with is a 14X45ft flat roof. it currently already has 128sqft of hot water panels (4X8) for radiant floor heat and hot water preheat. now I want to put PV in. one thing that is an absolute non negotiable constraint is that we have decided to do the system "CASH" we will not finance any of the system. we can put aside about $500 a month for the system.. the final system would ideally be about 5000watt solar with a 240 volt grid tie. hope to also maybe put one ortwo small 400w wind turbines on the system with some limited battery backup..

currently I'm looking at a 24volt parallel tied panel system. with an Outback GTFX2524 inverter(s) will start with a single inverter to one side of my circuit panel, and starting with just one approx 200watt panel. adding panels until I run out of room. I know I'm going to need some serious sized wire to run about 50ft to the panel location.. I know I need some switches and stuff. and while I'm an engineer I'm not an electrical engineer. I hope to do most of the "grunt" work myself hiring a friendly electrician for the final checkout and wiring into the grid via the netmeter.

am I making any major mistakes and does this sound like a workable system... as it grows I'll add a second GTFX2524 inverter for the 240v and full 5kw of power I am not sure how many panels I'm going to be able to fit onto the roof at this point. at least 9 panels up to maybe 15-16 appear to be able to fit depending on angles etc. fortunately I can get a perfect south facing system at the ideal for my area 45degree angle.with no shawdows and 5-6 good hours of winter sun and 8-10 hours in the summertime.

I know I'm not building the ideal or most efficient system but gotta work inside my limits.

comments???

thanks
Bob

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,634 admin
    Re: Series vs Parallel panel advantages

    AccessBob,

    As I stated in the other thread--a pure "grid tied" inverter is nothing more than solar panels, the inverter, and the appropriate branch circuit connection (in an appropriately sized panel).

    One major other difference with a pure Grid Tied Inverter is that they run at a much higher voltage Solar Panel DC Voltage (typically 180-600 VDC--depending on brand/model). A standard inverter intended to connect with a battery bank will only operate at its rated input voltage (somewhere around 12-72 VDC, depending on model and input voltage options)... So, one of the nice things about a pure grid tie inverter, is that you only have 1/10 the amperage as a battery bank/charger/inverter system... So your wire gauge can be much smaller (and cheaper) and/or you can wire longer runs without going broke buying copper.

    There are solar PV chargers that can take higher voltages and switch them down to the lower battery bank voltage. Outback has a popular model--the MX 60--that can take up to around 150 VDC (if I recall correctly) and switch it, very efficiently down to your battery bank voltage (12, 24, 48, etc.)...

    The inverter from Outback that you have indicated is one that is (from what little I understand) an inverter that is intended to tie to a battery bank. So, you will also need a charge controller, like the MX 60. How you connect the panels (series, parallel, or series/parallel) depends on the brand/model of panels you purchase, the solar charge controller you use, and your battery bank voltage.

    I believe that the GTFX2524 inverter is not a Grid Tie capable inverter but, instead is Grid Interactive, meaning that you connect it to an AC source (like your utility) and it can use utility power to charge the batteries, or if the utility power fails, it switches over to inverter power (basically, a UPS). And this is a 120 VAC inverter (you would need to to operate at 240 VAC). I don't believe that this model can send power back to the utility (I may very well be wrong here--I don't know much about outback's products)...

    You did not state where you live--assuming the US, if you have a Grid Tie capable inverter (one that can send power back to the utility, you will need permits and to sign up with your utility too... If do not have a GT type inverter, then you will not need to contact your utility (and they will need to approve the final size of your system--and, in theory, you would need another city/county inspection every time you added another panel or two).

    Next, the issue of installing one, or a few, panels at a time... If you are running at battery bank voltage (say a ~32 VDC rated panel for a 24 VDC battery bank), you will be able to connect them in parallel (with additional copper to handle the higher currents).

    However, if you are going to wire for higher voltages--you will find that there are different options for connecting panels (in series/parallel)--and as you add panels, you may find that you will have to reconnect the earlier panels differently to get optimum power from your solar charger (or Grid Tied Inverter)...

    And, solar chargers (and GT Inverters) have losses that at lower power/current levels that can make them less efficient than simpler solar chargers--Especially the MPPT (Maximum Power Point Tracking) types (like the MX 60 and most Grid Tied Inverters). Near their maximum power levels, the chargers are very efficient... But at lower levels (like 200-400 watts), a large MPPT charger is not going to be as efficient because of fixed losses--and very costly.

    I will stop here--I may be restating much of what you already know and I am probably not answering the questions you were asking...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Series vs Parallel panel advantages
    BB wrote:
    AccessBob,

    > As I stated in the other thread--a pure "grid tied" inverter is nothing more than solar panels, the inverter, and the appropriate
    > branch circuit connection (in an appropriately sized panel).

    right, but I do want the ability to either hook up my generator or a battery pack, since I also have a hot water heat system the pumps MUST run when the sun shines or the system will overheat and blow my $$$$ proglycol all over the place.


    > One major other difference with a pure Grid Tied Inverter is that they run at a much higher voltage Solar Panel DC Voltage (typically > 180-600 VDC--depending on brand/model). A standard inverter intended to connect with a battery bank will only operate at its rated > input voltage (somewhere around 12-72 VDC, depending on model and input voltage options)... So, one of the nice things about a
    > pure grid tie inverter, is that you only have 1/10 the amperage as a battery bank/charger/inverter system... So your wire gauge can > be much smaller (and cheaper) and/or you can wire longer runs without going broke buying copper.

    well I plan a 24v system and have already planned in the 4(O) wire needed in the budget. my problem with the high voltage systems is the very high up front cost. as it says an absolute in this decision is that we will not finance this project (this is non negotiable) with about $500 per month avaliable for investing in the system.(a 200watt panel ever other month??) there is no way I can afford the 9-11 panels needed to just turn on a high volt low amp system.


    > There are solar PV chargers that can take higher voltages and switch them down to the lower battery bank voltage. Outback has a
    > popular model--the MX 60--that can take up to around 150 VDC (if I recall correctly) and switch it, very efficiently down to your
    > battery bank voltage (12, 24, 48, etc.)...

    opposite problem than what I have, a high voltage system is currently not practical $$$ wise unless someone is going to donate $8k to finance PV panels up front. as I said, financing is not an option. so this is the 10,000 gorrila on the bus that controls many decisions.


    > The inverter from Outback that you have indicated is one that is (from what little I understand) an inverter that is intended to tie to a > battery bank. So, you will also need a charge controller, like the MX 60. How you connect the panels (series, parallel, or
    > series/parallel) depends on the brand/model of panels you purchase, the solar charge controller you use, and your battery bank
    > voltage.

    > I believe that the GTFX2524 inverter is not a Grid Tie capable inverter but, instead is Grid Interactive, meaning that you connect it to > an AC source (like your utility) and it can use utility power to charge the batteries, or if the utility power fails, it switches over to

    correct this is a "Grid interactive" inverter. one other reason that this is useful is that I am also considering adding wind to the mix and the outback will handle the different inputs.

    > inverter power (basically, a UPS). And this is a 120 VAC inverter (you would need to to operate at 240 VAC). I don't believe that this
    > model can send power back to the utility (I may very well be wrong here--I don't know much about outback's products)...

    they claim it can send back to grid power.
    also I plan on starting with 120v but it will later be paralleled with a second identical inverter to provide 240. not sure if/how the 120 attached to one leg of the power panel would work to feed power back to the grid. information I am still gathering.

    > You did not state where you live--assuming the US, if you have a Grid Tie capable inverter (one that can send power back to the
    > utility,

    Mid Atlantic area, Maryland

    > you will need permits and to sign up with your utility too... If do not have a GT type inverter, then you will not need to contact your
    > utility (and they will need to approve the final size of your system--and, in theory, you would need another city/county inspection
    > every time you added another panel or two).

    have grid tied plans for system from Outback to use for permitting and planninng and to utility. (they limit net meters to 2/10 of 1%) will permit the entire system with it staged, will hire professional electrician to do the final hook up and inspections

    > Next, the issue of installing one, or a few, panels at a time... If you are running at battery bank voltage (say a ~32 VDC rated panel
    > for a 24 VDC battery bank), you will be able to connect them in parallel (with additional copper to handle the higher currents).


    plan a 24vdc system and have budgeted in the 4(O) copper (ouch)for the heavy run of about 50ft down the outside of the building local codes do not allow running thru roof.

    > However, if you are going to wire for higher voltages--you will find that there are different options for connecting panels (in
    > series/parallel)--and as you add panels, you may find that you will have to reconnect the earlier panels differently to get optimum
    > power from your solar charger (or Grid Tied Inverter)...

    maybe later when I need the second inverter for 240 I may just rewire for high voltagee but that will be something to consider in the future. it is at least 2-3 years out before I reach that level.


    > And, solar chargers (and GT Inverters) have losses that at lower power/current levels that can make them less efficient than simpler > solar chargers--Especially the MPPT (Maximum Power Point Tracking) types (like the MX 60 and most Grid Tied Inverters). Near their > maximum power levels, the chargers are very efficient... But at lower levels (like 200-400 watts), a large MPPT charger is not going to > be as efficient because of fixed losses--and very costly.

    not sure I understand what your getting at here

    > I will stop here--I may be restating much of what you already know and I am probably not answering the questions you were asking...

    yes no and that',s why I'm asking. only want to do this once. don't want too many mistakes if I can help it.

    thanks
    Bob
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: Series vs Parallel panel advantages

    Bob you can still wire panels in series up to 48v (maybe 60v) nominal using the MX-60 from outback.

    You need a charge controller between the solar array and the batteries, then the batteries connect to the inverter. While you could connect teh solar panels directly to the batteries this is usually bad idea unless your array is less then 2% of the battery bank.

    What parts are you starting with first?
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • BB.BB. Super Moderators, Administrators Posts: 29,634 admin
    Re: Series vs Parallel panel advantages

    Many hot water systems just use a DC pump and a single solar panel to operate (no batteries/inverters)... If you have sun, the pump runs. It is possible that an AC pump will last longer though--if you have off-grid AC, it not a bad way to go in supplying power to the circulation pump.

    I understand the issue of not having the cash up front to install a full system--I too am very "allergic" to loans and tend to pay cash even if those zero interest 12 month loans are available... However, per Wind-Sun, it appears that the price of solar PV panels is starting to come down in price--so, it may be an interesting compromise to wait until you have cash in-hand to purchase lower priced panels down the road (of course, nothing is sure in the future).

    There is also a reason why it is nice to purchase a group of solar panels at the same time... Generally, you need panels that match voltage (if operating in parallel) or current (if operating in series) and both voltage/current if running in series/parallel. Supplies of panels (again according to Wind-Sun) appear to be loosening now--but it was, at times difficult over the last few years to fill out an array with matching panels purchased at different times (difficult availability, new models, etc.).

    The price of 4(0) wire is probably not cheap--checking out how much you will be spending on that vs just getting some more panels for a high voltage system may be interesting.

    Regarding the ability to send power back to the utility--I will leave that to you and the manual--I am certainly not an expert on this inverter and its abilities. If the model you want is not grid-tie capable but is only a grid-interactive that switches to inverter output when the power fails, it will only power those downstream devices to which is connected--it will not power other branch circuits.

    Regarding the ability to send power back, whether or not you use 120 VAC or 240 VAC, the utility meter will correctly measure the power used/generated.

    Regarding efficiencies, a standard (non-MPPT) type solar controller just connects solar panels to the batteries directly and only uses a few watts or so to do the control function (either on-off or Pulse Width Modulation).

    An MPPT type controller is really a DC to DC switch mode power supply and there is a minimum amount of power it requires to operate (from ~10 to 100's of watts, depending on model). So, at low levels of power (such as with 1 solar panel), an MPPT controller will be consuming 10-20 watts or so (MX 60 If I recall correctly)... So, your 200 watt panel, may output 180 watts, and another 10-20 watts consumed by the control circuits get you down to 160-170 watts true output... And early morning/late evening power generation when the panel is only output a few ten's of watts--instead of that going into the battery, it is just being burned by the controller...

    When you have 1,000-2,000 watts of solar panels, consuming 4-5% in controller losses (50-100 watts) is not a bad deal. But using a large controller with few panels will cost you (say 10 hours per day * 20 watts fixed losses, equals 200 WattHrs of loss--or more than 20% of your panel's output--numbers are very rough here--just trying to make a point--check your unit's specifications for the details). As a note, my Grid Tie just logged around 9hr 30mins of operation today--so those fixed losses are a significant amount of time during dawn and dusk (when not full sun).

    If you want off-grid or emergency backup power, than going with a battery system with the proper charge controllers and inverters is a great way to go.... For myself, I looked at this and decided to just get a eu2000i Honda generator and a manual transfer switch--my power is down so seldom that the extra costs and battery maintenance costs (have to replace batteries every 7-15 years)--spending $1,000 for a generator and transfer switch just made more sense to me (the Honda is a pretty fuel efficient generator compared with the cheap 5kW units--and since I live in Earthquake country SF, CA, installing a natural gas generator did not make sense if the "big one" hit and damaged the natural gas delivery system.

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Series vs Parallel panel advantages
    Brock wrote:
    Bob you can still wire panels in series up to 48v (maybe 60v) nominal using the MX-60 from outback.

    You need a charge controller between the solar array and the batteries, then the batteries connect to the inverter. While you could connect teh solar panels directly to the batteries this is usually bad idea unless your array is less then 2% of the battery bank.

    What parts are you starting with first?

    starting with an inverter (leaning towards an Outback GTFX2524) charge controller, one panel (200watt 24volt) and probably two twelve volt AGM batteries wired in series. and of course the assorted switches, etc to put it together legally to start and . adding a panel and 2 batteries every third month..

    Bob
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: Series vs Parallel panel advantages

    Is the controller going to be an Outback MX-60? If so you can get away with a smaller wire run since it will take twice the voltage and down convert it to your battery bank. Basically you could put two 200w 24v panels in series and send that to the MX-60. The MX-60 will take the 48v (really about 65v) and convert it to the correct voltage for charging your battery bank. But you can start with one panel and add more as you go.

    This way you’re running twice the voltage and half the amperage, but you need a MPPT controller like the MX-60 to set be up this way.

    Mostly I am telling you thins becasue I went through 3 controllers before I finally went with the MX-60. I really wish I had started with the MX-60, it is worth the extra cost to start out right.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • BB.BB. Super Moderators, Administrators Posts: 29,634 admin
    Re: Series vs Parallel panel advantages

    Another issue is adding batteries... They will last ~1-15 years (depending on type, brand, usage, maintenance, etc.)... If you take, say three years, to build up your battery bank--it is possible that you will have to replace all of the batteries sooner--as the newest batteries will take the most load--and wear-out to the same state as the older (3 year older batteries).

    That is the reason why it is recommended to build and replace battery banks in sets...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Series vs Parallel panel advantages
    Brock wrote:
    Is the controller going to be an Outback MX-60? If so you can get away with a smaller wire run since it will take twice the voltage and down convert it to your battery bank. Basically you could put two 200w 24v panels in series and send that to the MX-60. The MX-60 will take the 48v (really about 65v) and convert it to the correct voltage for charging your battery bank. But you can start with one panel and add more as you go.

    This way you’re running twice the voltage and half the amperage, but you need a MPPT controller like the MX-60 to set be up this way.

    Mostly I am telling you thins becasue I went through 3 controllers before I finally went with the MX-60. I really wish I had started with the MX-60, it is worth the extra cost to start out right.

    Thanks this is good to know.. guess I sould put the MX-60 at the top of my list...

    Bob
  • System2System2 Posts: 6,290 admin
    Re: Series vs Parallel panel advantages
    BB wrote:
    Another issue is adding batteries... They will last ~1-15 years (depending on type, brand, usage, maintenance, etc.)... If you take, say three years, to build up your battery bank--it is possible that you will have to replace all of the batteries sooner--as the newest batteries will take the most load--and wear-out to the same state as the older (3 year older batteries).

    That is the reason why it is recommended to build and replace battery banks in sets...

    -Bill

    I have quite a bit of experience with AGM batteries in other service and can get them wholesale, I am aware of this problem. not sure there is any easy way around it.. will just have to set up strings and replace them as needed...

    thanks
    Bob
  • System2System2 Posts: 6,290 admin
    Re: Series vs Parallel panel advantages
    BB wrote:
    Many hot water systems just use a DC pump and a single solar panel to operate (no batteries/inverters)... If you have sun, the pump runs. It is possible that an AC pump will last longer though--if you have off-grid AC, it not a bad way to go in supplying power to the circulation pump.

    I understand the issue of not having the cash up front to install a full system--I too am very "allergic" to loans and tend to pay cash even if those zero interest 12 month loans are available... However, per Wind-Sun, it appears that the price of solar PV panels is starting to come down in price--so, it may be an interesting compromise to wait until you have cash in-hand to purchase lower priced panels down the road (of course, nothing is sure in the future).

    There is also a reason why it is nice to purchase a group of solar panels at the same time... Generally, you need panels that match voltage (if operating in parallel) or current (if operating in series) and both voltage/current if running in series/parallel. Supplies of panels (again according to Wind-Sun) appear to be loosening now--but it was, at times difficult over the last few years to fill out an array with matching panels purchased at different times (difficult availability, new models, etc.).

    The price of 4(0) wire is probably not cheap--checking out how much you will be spending on that vs just getting some more panels for a high voltage system may be interesting.

    Regarding the ability to send power back to the utility--I will leave that to you and the manual--I am certainly not an expert on this inverter and its abilities. If the model you want is not grid-tie capable but is only a grid-interactive that switches to inverter output when the power fails, it will only power those downstream devices to which is connected--it will not power other branch circuits.

    Regarding the ability to send power back, whether or not you use 120 VAC or 240 VAC, the utility meter will correctly measure the power used/generated.

    Regarding efficiencies, a standard (non-MPPT) type solar controller just connects solar panels to the batteries directly and only uses a few watts or so to do the control function (either on-off or Pulse Width Modulation).

    An MPPT type controller is really a DC to DC switch mode power supply and there is a minimum amount of power it requires to operate (from ~10 to 100's of watts, depending on model). So, at low levels of power (such as with 1 solar panel), an MPPT controller will be consuming 10-20 watts or so (MX 60 If I recall correctly)... So, your 200 watt panel, may output 180 watts, and another 10-20 watts consumed by the control circuits get you down to 160-170 watts true output... And early morning/late evening power generation when the panel is only output a few ten's of watts--instead of that going into the battery, it is just being burned by the controller...

    When you have 1,000-2,000 watts of solar panels, consuming 4-5% in controller losses (50-100 watts) is not a bad deal. But using a large controller with few panels will cost you (say 10 hours per day * 20 watts fixed losses, equals 200 WattHrs of loss--or more than 20% of your panel's output--numbers are very rough here--just trying to make a point--check your unit's specifications for the details). As a note, my Grid Tie just logged around 9hr 30mins of operation today--so those fixed losses are a significant amount of time during dawn and dusk (when not full sun).

    If you want off-grid or emergency backup power, than going with a battery system with the proper charge controllers and inverters is a great way to go.... For myself, I looked at this and decided to just get a eu2000i Honda generator and a manual transfer switch--my power is down so seldom that the extra costs and battery maintenance costs (have to replace batteries every 7-15 years)--spending $1,000 for a generator and transfer switch just made more sense to me (the Honda is a pretty fuel efficient generator compared with the cheap 5kW units--and since I live in Earthquake country SF, CA, installing a natural gas generator did not make sense if the "big one" hit and damaged the natural gas delivery system.

    Take care,
    -Bill

    lets see if I can answer/comment one para at a time, because of some extra controls the system doesn't always run when the sun is out and sometimes when it isn't so the direct panel to DC motor direct would not be optimal.

    as for waiting for panel prices to come down I wouldn't count on it too soon. second point is to start getting at least some payback as soon as possible even if it is minimal, and one reason for the Outback is that it will use mismatched inputs.

    yeah 4(O) wire is not cheap, but the runs aren't that long, about $2 a foot or so last I looked, heard it has come down a little. but it won't even come close to the cost of a 200w panel.

    Bob
  • RoderickRoderick Solar Expert Posts: 253 ✭✭
    Re: Series vs Parallel panel advantages

    $500 a month is a good savings rate. If your patience can stand it, and you waited a year, you could buy enough panels to hook in series to power a grid-tied, no-battery inverter. And, you would have an upgrade path by simply hooking more panels in series in the future, without worrying about increasing wire gauges (although it might be a good idea to size the wire for 2 strings, as an even later expansion path).

    And, if you put your system into operation in late 2007, you still get to take the 30% federal tax credit. The credit has a $2000 cap for homeowners, as I understand it, so it would line up well with the amount of money you could spend at that time ($6000). Note: I'm just a citizen giving an opinion, I'm not qualified to give tax advice. If there's some Maryland incentive with a time limit, then it might change the financial picture, and I retract my opinion.
Sign In or Register to comment.