Using grid inverters without solar/wind

2

Comments

  • DellyDelly Registered Users Posts: 16
    Re: Using grid inverters without solar/wind

    Just barely finished in time! Will have a meeting with the board team and supervisor in 15 mins =)
    stephendv wrote: »
    At risk of repeating my previous reply, if you want to control load shifting then your control system must be able to read data from the inverter and charge controllers in order to make it's decisions. The 2kW Sunny Island will let you read every bit of available data from it, including the battery state of charge from its own internal SoC meter- which I'd guess would be quite an important piece of data if you want to do load shifting.
    Similarly, the midnite classic (or Lite) will allow you to read and set all internal values so you can log and act on data like the Voc, the Vmp the current, you can limit the current programmatically and control diversion relays programmatically.
    The combination of the two will give you the easiest way to have a programmable setup. I don't believe there is any open way to communicate with Xantrex kit since they use a closed protocol (Xanbus AFAICR). Earlier you mentioned that a requirement is to potentially sell to the grid in the future. Can the conext do that? I know the XW can, but not sure about the conext.

    The Sunny Island costs > $4k while the Conext XW 4024 costs < $2.7k. Also From what I've seen I would need an on grid inverter to sell back too... The SMA Sunny boy 3000 costs approx $1.5k. That's why too expensive for the budget I been given.

    Right now I'm a Computer engineering/scientist and studying Master in IT. In college I studied electronics. So kind of el/IT.
    I'll come back to your post later today or tomorrow when I have time. Haven't had much sleep, and must prepare for the meeting soon :p We'll see how it goes and what they choose to do ;)

    Best regards,
    Delly
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Using grid inverters without solar/wind

    The 2kW Sunny Island goes for just over 2000 Euros. http://store.proinso.net/europe/en/stand-alone-inverters/sma-sunny-island-si-2224-p_144.html
    You have the option of either using an external charge controller like the midnite classic (around 600 Euros), or going the AC route and using a sunny boy. I had the impression that you were looking for a smaller system, the 1300W sunny boy goes for 600 Euro ish. http://store.proinso.net/europe/en/sunny-boy/sma-sunny-boy-sb-1300tl-10-p_384.html

    EDIT: Here's a chap who has the SI 2224 and uses it in grid tie mode with a sunny boy: http://www.navitron.org.uk/forum/index.php?topic=17834.0
  • DellyDelly Registered Users Posts: 16
    Updates

    So I took a little longer break than intended =)
    The meeting went well, kind of. I got several questions some of which I couldn't answer, and therefore I will be redirecting it/them here since you guys are both nice and knowledgeable :roll:

    I'm kind of in a rush to the gym, and only one question comes to my mind atm. If the charge controller is in charge of charging/discharging the battery bank, what is the purpose of having a charger in the inverter? When and how does the system know when to use cc/inverter charger?

    After I presented the order/function list or whatever it's called, they said "well, since it's going to cost so much, maybe we should merge it with a parallel project which the university administrations is in charge of. It is basically a much larger solar panel project. Therefore they said that they might opt for the SMA solution. to be honest, I wasn't really certain why. But I'll know for sure, soon =D I think it might be because it's a German (eu) company, and therefore easier to get help, They were also talking about the support for PLC, but as I said, not sure.
    stephendv wrote: »
    The 2kW Sunny Island goes for just over 2000 Euros. http://store.proinso.net/europe/en/stand-alone-inverters/sma-sunny-island-si-2224-p_144.html
    You have the option of either using an external charge controller like the midnite classic (around 600 Euros), or going the AC route and using a sunny boy. I had the impression that you were looking for a smaller system, the 1300W sunny boy goes for 600 Euro ish. http://store.proinso.net/europe/en/sunny-boy/sma-sunny-boy-sb-1300tl-10-p_384.html

    EDIT: Here's a chap who has the SI 2224 and uses it in grid tie mode with a sunny boy: http://www.navitron.org.uk/forum/index.php?topic=17834.0

    That one looks cool. I'll look into it later.

    Best regards,
    Delly
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Updates
    Delly wrote: »
    If the charge controller is in charge of charging/discharging the battery bank, what is the purpose of having a charger in the inverter?
    The charge controller charges the battery from a DC source, such as solar, wind, or hydro.
    Delly wrote: »
    When and how does the system know when to use cc/inverter charger?

    To answer that question, first consider a purely off-grid inverter/charger. It has an AC input, AC output, and a DC connection to the battery. When it sees AC on its input (usually from generator), it stops inverting, charges the battery, and the AC on the input passes through to the AC output. When there is no AC on the input, it becomes an inverter and sends its AC to the output. If you use an off-grid inverter/charger on the grid, it is essentially an uninterruptible power supply.

    Your question is much harder to answer when you have a hybrid inverter/charger, because now you can sell power back to the grid. Different manufacturers do it differently, and it can be tricky to get it to behave the way you want. If you don't get it right, you may be selling power to the grid when you should be charging your batteries, or charging your batteries from the grid when the sun is shining on your solar panels.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Updates
    Delly wrote: »
    I'm kind of in a rush to the gym, and only one question comes to my mind atm. If the charge controller is in charge of charging/discharging the battery bank, what is the purpose of having a charger in the inverter? When and how does the system know when to use cc/inverter charger?

    CC is for solar.

    Inverter/Charger is for charging from the grid (or from generator if you have one). E.g. you can charge during off-peak, then use this energy to power loads during peak.

    The system doesn't know what to do. You set it up to perform the task you need. Depending on the complexity it may be easy to do or difficult to do.
    Delly wrote: »
    After I presented the order/function list or whatever it's called, they said "well, since it's going to cost so much, maybe we should merge it with a parallel project which the university administrations is in charge of. It is basically a much larger solar panel project. Therefore they said that they might opt for the SMA solution. to be honest, I wasn't really certain why. But I'll know for sure, soon =D I think it might be because it's a German (eu) company, and therefore easier to get help, They were also talking about the support for PLC, but as I said, not sure.

    SMA uses different principle. All they devices connect to the AC line. In larger system it works better because you can combine a lot of them, you can even build your own grid. The only drawback to this approach is that they're much more expensive than traditional DC coupled devices.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Updates
    NorthGuy wrote: »
    SMA uses different principle. All they devices connect to the AC line. In larger system it works better because you can combine a lot of them, you can even build your own grid. The only drawback to this approach is that they're much more expensive than traditional DC coupled devices.

    And just to be clear, SMA offers the option of connecting everything on the AC side using their grid tie inverters and sunny island battery inverters. You also have the option of using the Sunny Island just like any other battery inverter with a DC charge controller.
  • DellyDelly Registered Users Posts: 16
    Re: Using grid inverters without solar/wind

    Thanks for all the inputs guys, I really appreciate all of the information you've given me.

    I need to ask some "academic" questions since this project is kind of, or better to say, is an academic research :P
    Is there anywhere I can get some of these facts from? I need them for referencing. I'm mainly concerned about the calculation and the efficiency rates.
    Is it possible to prove that 0.52 is what is the usual derating factor for off grid system? It's just that as it is now in my paper, it seems that I've made those things out of the blue.

    I have 4 books about smart grid system, but none of them mentions anything I'm interested in such as how to set up a system and how to calculate the needs :/ Most of what of I've found is from forums (mainly this one) and youtube >_<

    Best regards,
    Delly
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    Is it possible to prove that 0.52 is what is the usual derating factor for off grid system? It's just that as it is now in my paper, it seems that I've made those things out of the blue.

    Since it's an academic paper you'll have to go into a LOT more detail about these types of numbers. "Usual derating factor" will have to be refined as well according to what the purpose of your paper is. If you want to arrive at a value for kW installed solar vs. useable kWh coming out of the inverter then you'll need to factor in:
    - Time of year
    - Location
    - Type of panel installed
    - Type of battery
    - Efficiency losses in charge controller

    The 0.52 number probably means: average derating for anywhere on earth and for all weather on earth where people build off-grid systems for any charge controllers and for flooded lead acid batteries and poli/mono panels. i.e. it's a useful number if someone corners you in a bar and wants to know the efficiency of the system, but it's useless for a detailed academic study :)
  • BB.BB. Super Moderators, Administrators Posts: 32,925 admin
    Re: Using grid inverters without solar/wind

    I don't frequent bars (engineer :p), but the 52% off grid derating is estimated from:
    • 81% = typical "warm" solar panel Vmp/Pmp derating (standard test condition is 25C, normal operation temperature is ~45C)
    • 95% for typical MPPT charge controller
    • 80% for typical flooded cell battery operation
    • 85% for typical AC inverter

    Multiply all those together and you get ~52% end to end derating.

    For a grid tied system, we only have the 81% * 95% = 77%.

    Flooded cell batteries are much more efficient if operated between 50% to 80% state of charge, and very inefficient if operated between 90-100% state of charge. Old fork lift batteries can lose as much as 1-2% of their capacity per day.

    AGM batteries are around 90-98% efficient. A good AGM will lose only ~2% or so per month.

    A 2kW AC inverter can burn 20 watts just being turned on... For efficient homes/cabins that can be a significant hit on daily power usage.

    PV Watts does have a section on losses from their point of view:
    [CENTER] 	[CENTER][B]Derate Factors for AC Power Rating at STC[/B][/CENTER]    [TABLE="class: data, width: 100%"]
         [TR="class: gray"]
    	     	[TH]Component Derate Factors[/TH]
             [TH]PVWatts Default[/TH]
             [TH]Range[/TH]
    [/TR]
         [TR]
    				     	[TD]PV module nameplate DC rating[/TD]
             [TD]0.95[/TD]
             [TD]0.80–1.05[/TD]
    [/TR]
         [TR="class: gray"]
    	     	[TD]Inverter and transformer[/TD]
             [TD]0.92[/TD]
         	[TD]0.88–0.98[/TD]
    [/TR]
         [TR]
    				     	[TD]Mismatch[/TD]
             [TD]0.98[/TD]
             [TD]0.97–0.995[/TD]
    [/TR]
         [TR="class: gray"]
         	[TD]Diodes and connections[/TD]
             [TD]0.995[/TD]
             [TD]0.99–0.997[/TD]
    [/TR]
         [TR]
         	[TD]DC wiring[/TD]
             [TD]0.98[/TD]
             [TD]0.97–0.99[/TD]
    [/TR]
         [TR="class: gray"]
         	[TD]AC wiring
    [/TD]
             [TD]0.99[/TD]
             [TD]0.98–0.993[/TD]
    [/TR]
         [TR]
         	[TD]Soiling
    [/TD]
             [TD]0.95[/TD]
             [TD]0.30–0.995[/TD]
    [/TR]
         [TR="class: gray"]
         	[TD]System availability[/TD]
             [TD]0.98[/TD]
             [TD]0.00–0.995[/TD]
    [/TR]
         [TR]
         	[TD]Shading[/TD]
             [TD]1.00[/TD]
             [TD]0.00–1.00[/TD]
    [/TR]
         [TR="class: gray"]
         	[TD]Sun-tracking[/TD]
             [TD]1.00[/TD]
             [TD]0.95–1.00[/TD]
    [/TR]
         [TR]
         	[TD]Age[/TD]
             [TD]1.00[/TD]
             [TD]0.70–1.00[/TD]
    [/TR]
         [TR="class: gray"]
         	[TD]Overall DC-to-AC derate factor[/TD]
             [TD]0.77[/TD]
             [TD]0.09999–0.96001[/TD]
    [/TR]
       [/TABLE]
     [/CENTER]
      	The overall  DC-to-AC  derate factor is calculated by multiplying the component derate factors.
     	 	For the PVWATTS default values:
      	Overall DC to AC derate factor
     	= 0.95 x 0.92 x 0.98 x 0.995 x 0.98 x 0.99 x 0.95 x 0.98 x 1.00 x 1.00 x 1.00
     	= 0.77 
    
    

    One person has dirty panels, some minor shading from bushes/trees, used smaller diameter copper wires (more voltage losses), an "oversize AC inverter" running 24x7, and recharges the battery bank back to 100% every day--He will have more losses than the person that keeps panels clean and free of shading, cycles the battery bank 50-80% daily and fully charges 90% SOC once a week.

    I try to error a bit on the conservative side... I want the owner to be "happy" with his (or her) system 5 years down the road when the batteries are getting a bit old, dusty panels on roof, and a few winters of poor weather/sun.

    But, it is easy to "over derate" a system too. For example, I would technically add another 75% to 65% derating factor for daily loads (1/0.75 to 1/0.65 times daily loads) to account for some days of poor weather/and growing loads--You should not count on the sun providing a minimum of "average sun" every day...

    I sort of get around that "extra derating" by looking at PV Watts and dumping the lowest 3 months (poor winter production typically) and pick the next lowest month for the "break even" month--For the other 8 months, there will usually be enough sun to run their loads without firing up their generator--And that (typically February in the US) 9th month may or may not need a genset depending on weather at the time.

    It is very easy (especially in coastal areas and regions with wet/cloudy/foggy conditions) to see their average yearly sun vary by +/- 10% -- And, of course, to have a week of heavy clouds/ground fog due to local conditions (inversion layers, jet stream wandering, etc.).

    Most of us are "on the grid" and tend to forget how variable the sun is because we don't worry that we will be out of power after a couple of days of bad weather (bad weather can reduce solar power capture to 10% or even 1% of nominal capacity on a sunny day).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using grid inverters without solar/wind

    The 0.52 derating factor is based on some assumptions that may or may not be true in a real world application. First of these is that all power used is stored in batteries and then drawn from them. This is not necessarily the case as it is common to make use of energy while the sun shines using opportunity loads. That will increase the over-all efficiency dramatically, but it requires some degree of active management of the system and may not be convenient for all applications.

    It also assumes 77% panel + controller efficiency, "standard" 25% average DOD, "standard" 10% peak charge current, sufficient insolation to fully charge the batteries every day, not unusual ambient temperatures (neither to high or too low), and no location problems or help (no morning fog, no high elevation, no water reflection, et cetera).

    Curiously, information from the many users on this forum shows the 0.52 factor is accurate for basing system design. But as with all numbers involved there are no absolutes. Even if you calculate a design down to the third decimal point the real world is not going to co-operate: no one uses precisely the same amount of power every day (it isn't possible) and the conditions under which the system operates will not be identical from day to day either.

    Margins for error need to be wide to have a system that is operational year-round no matter where you put it or what you use it for. The 0.52 number is conservative enough to base an initial design on. The source of it is a lot of experience by many people with actual systems. You won't find it in a text book, because I haven't written one. Yet. :D
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    Is it possible to prove that 0.52 is what is the usual derating factor for off grid system?

    The biggest problem with off-grid solar is that the energy is produced not when needed, but when it is available. Therefore situations are common when energy would be available, but you do not need it at this very moment, so it is wasted. In a very small, badly undersized system, such losses are small (thus it is more efficent). In a healthy system designed to meet all your energy need, that is a lot. You may harvest only 60% of what you could, even less than this. I don't think you should regard this as a loss or inefficiency. You could've taken this energy, but you have chosen not to, because you didn't need it. Therefore efficiency isn't strictly related to the performance.

    For comparison. My well is rated at 20 gpm continuous, but I only use a fraction of that. Would you say that my well is badly inefficient? No, you would say it's plentiful.

    Your derating largely depends on how you design and use your system.
  • DellyDelly Registered Users Posts: 16
    Re: Using grid inverters without solar/wind

    I think you guys misunderstood wat I was trying to ask, or very possible that I'm at fault for formulating it in a stupid way.
    What I wanted (still want :P) to know was not why/how to calculate the 0.52 value, but rather as an example, why is MPPT CC rated to 95%? Is there anywhere/anyway I can prove that a typical standard derating value for MPPT CC is 95% and not 91% (or any other value)? Something like a book, academic article/paper or other "professional/trusted" sites as a reference would be the perfect solution.

    The PV Watts example by Bill was a good reference for the pv panels. That means one thing is out of the way :P
    Hope that clears things up.
    NorthGuy wrote: »
    The biggest problem with off-grid solar is that the energy is produced not when needed, but when it is available. Therefore situations are common when energy would be available, but you do not need it at this very moment, so it is wasted. In a very small, badly undersized system, such losses are small (thus it is more efficent). In a healthy system designed to meet all your energy need, that is a lot. You may harvest only 60% of what you could, even less than this. I don't think you should regard this as a loss or inefficiency. You could've taken this energy, but you have chosen not to, because you didn't need it. Therefore efficiency isn't strictly related to the performance.

    For comparison. My well is rated at 20 gpm continuous, but I only use a fraction of that. Would you say that my well is badly inefficient? No, you would say it's plentiful.

    Your derating largely depends on how you design and use your system.

    I get your point, but this project will only be as prototype/demo/marketing for the school to show off that they are part of the "green" world... So getting the exact right derating numbers are not critcal
    but good to know. On the other hand, it is critical to prove that these numbers are correct in my paper, so they wont have the opportunity to come back to me and say "Hey, it's not working as optimal as you said!" =P

    Right now I don't know what to do. I'm waiting for a new meeting tomorrow so they can make their decision. I guess, I'll use my time on another subject in the mean time... :P

    Thanks, and wish you all a fine day,
    Delly
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    why is MPPT CC rated to 95%? Is there anywhere/anyway I can prove that a typical standard derating value for MPPT CC is 95% and not 91% (or any other value)?

    You can check the spec sheet for the particular MPPT controller you want to use. The efficiency differs based on the difference between the incoming voltage and the battery voltage. Some controllers deal with this better than others.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    I get your point, but this project will only be as prototype/demo/marketing for the school to show off that they are part of the "green" world... So getting the exact right derating numbers are not critcal
    but good to know. On the other hand, it is critical to prove that these numbers are correct in my paper, so they wont have the opportunity to come back to me and say "Hey, it's not working as optimal as you said!"

    I've not been following this thread all that closely, so please forgive me if my reply is off base, but as I see it the difference between a standard grid-tied system and the system you are trying to prove out is that in a straight GT system every bit of energy that the system can produce is produced because there is a virtually unlimited energy sink (the grid) attached to it, while with an off-grid system the amount of energy produced is entirely dependent on how much energy is used, how fast it is being used, and when (at night running off the batteries is different from during daylight hours) by whatever loads are on the system, which is a balancing act and much more difficult to quantify. In the former system the size of the PV system and the magnitude of the loads are independent variables, while in the latter system they are unavoidably entangled. You want your system's capacity to always be greater than the demand (you don't want to run out of energy), but as a result the system will never produce all it is capable of producing. That's always the problem with designing an off-grid system; you want it to be "too big", but by only a very small amount.

    EDIT: I just read the thread title again. My reply may be a non sequitur. Oh, well... :D
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using grid inverters without solar/wind

    Different deratings for different applications.

    The average derating for panels + MPPT function (whether charge controller or GTI input) is 77%. This can vary with application of course. For example my own system runs 82% at this point due to increased insolation from higher elevation.

    The average over-all derating for a battery-based system is 52% (from panel rated Wattage to AC output).
    This too will vary with the particular application. Again mine runs better due to the elevation and use of opportunity loads to increase the amount of potential power actually realized.

    Both factors are merely for getting ballpark estimates in initial system design. They tend towards the conservative for that reason. If there are known local conditions which will reduce efficiency they should be taken into account at the start.
  • BB.BB. Super Moderators, Administrators Posts: 32,925 admin
    Re: Using grid inverters without solar/wind

    Delly,

    You have to look up, understand, and model each efficiency if you want it to that detail... Here are a few references of examples (not all vendors have this level of detail):

    Solar panels output power over a wide range of light conditions and temperatures. Most equipment has fixed losses where efficiency falls as total power through the device falls. And solar panels get hotter (higher temperature rise) as the sunlight increases (more sun, hotter panels). You can use PV Watts (or other data sources) to give you, in PV Watts case, hour by hour typical solar power for 365 days a year (based on your array and losses configuration):
    1966, 1, 1, 07:00, 0
    1966, 1, 1, 08:00, 1
    1966, 1, 1, 09:00, 843
    1966, 1, 1, 10:00, 1635
    1966, 1, 1, 11:00, 2244
    1966, 1, 1, 12:00, 2559
    1966, 1, 1, 13:00, 2589
    1966, 1, 1, 14:00, 2361
    1966, 1, 1, 15:00, 1855
    1966, 1, 1, 16:00, 1214
    1966, 1, 1, 17:00, 203
    1966, 1, 1, 18:00, 0

    Solar panel have a thermal derating:

    Panel power = Pstc*Solar Irradiation%*(1+(Pderating*(Tambient+Trise-Tstc)
    • Pstc = Solar panel "marketing rating" at cell temperature of 25C and ~1,000 Watts per square meter of solar irradiation (~sea level noon-time power)
    • Solar Irradiation% = between 0=1.00 (dark to full sun), can be >>1.0 in some weather conditions/snow on ground reflections/etc.
    • Pderating = Solar panels lose power as cell temperature increases (around -0.43% per degree C or so.. Standard test condition is 25C). Vmp and wiring resistance rise with temperature and Imp falls (very slightly with increasing temperature)
    • Tambient = Ambient temperature of air around panel
    • Trise = Rise in cell temperature due to to solar irradiation (put things in sun, they get hot). Note that wind/air circulation around panel affect Trise. NOCT--Normal operating cell temperature is usually 45C (25C ambient + 20C rise). Trise can be as high as 35C (or more?). Ambient temperatures below freezing can increase solar panel operating power on MPPT type charge controllers.
    • Tstc = Standard Test temperature = 25C

    Outback MPPT Charge Controllers (page 102, graphic 103, graph of efficiency vs input array voltage on a 24 volt battery bank):

    http://www.outbackpower.com/downloads/documents/flexmax_6080/owner_manual.pdf

    If you pick a PWM (pulse width modulation controller)--They have very little operating losses, but their output current is equal to the input current--As long as Vmp-array>~1.0 volts + Vbattery charging, battery charging current is equal to Imp-array * % of solar irradiation (Imp does slightly rise with increasing temperatures). An example of basic PWM efficiency (neglecting PWM electronics draw--which is usually quite small):
    • PWM Eff = Vbatt-charging / Vmp-array-stc = ~14.5 volts / 17.5 volts = 0.83= 83% of panel STC rating

    AC Inverters have their performance graphs too. Here is a smaller 300 watt AC inverter, see page two:

    http://www.morningstarcorp.com/en/support/library/SureSineENG_R2_1_08.pdf

    Batteries, I have gone through that before... Lead Acid batteries are very efficient around 50-80% state of charge cycling. All batteries have internal self discharge (3% per month to 2% per day, depending on battery construction, age, temperature). The higher the rate of current flow (charging/discharging), the lower efficiency. A good website that "does much of the math". Some links from their site:

    http://www.smartgauge.co.uk/technical1.html

    Some people hate long explanations. Here are the bare facts about split charging and batteries.
    Peukert's Equation. A quick explanation of the equation.
    Peukert's Equation (Peukert's Law) properly explained (and correctly).
    A Peukert Calculator spreadhseet (extremely useful program).
    The 50% rule for deep cycle batteries.
    More on the effects of Peukert.

    Copper wire has higher I2R self heating losses as wiring temperature increases. Electric codes are based on copper wire temperatures (current flow, conduit/open air, insulation type, etc.). We typically design wiring for ~1-3% losses in our rules of thumbs.

    Designing a system using the peak efficiency of a power device (AC inverter, charge controllers, battery chargers, etc.) usually is not a good idea. You need to account for "average" power flows (not a single number at peak efficiency), aging, temperature, etc.

    Notice that many of the above discussions are around temperature--Either as a "waste heat output", but also in terms of aging. Thermal cycling kills devices mechanically (stresses of thermal cycling) and absolute temperature affects aging (for ever 10C increase, there is a factor of 2 reduction in product life). If you took calculas with an Engineering emphisis, you probably had this as a chapter:

    Activation Energy


    For AC Charge Controllers--There is a similar range of electrical efficiency and issues... Typically:
    • Power to Battery = Volts AC * Current AC * Power Factor of supply * Efficiency of Supply

    Where V*I*PF is the typical AC vector math. Power Factor usually ranges from 0.67 to 0.95 (with PF generally getting better the higher the current flow through the power supply). Efficiency ranges from ~80% to 95%. Again, poor(er) efficiency is seen at lighter loads on power supplies.

    Note that poor power factor increases current through AC wiring--Increasing waste I2R heating (and other losses) in wiring all the way through to Power Company's lines, transformers, and even their generators.

    And you can carry this through the generators... They are generally most efficient at >80% of rated output. And still pretty efficient at >50% of rated output. Fuel flow tends to plateau to a fixed minimum level as output power falls below 50% towards 0% load.

    Of course, different types of fuel based motors have different efficiency profiles. Gasoline engines tend to have very poor fuel efficiency at light loads. Diesel have much better efficiency at light loads, but should be operated at 40-60% minimum load to prevent "wet stacking", cylinder wall glazing, building up carbon in combustion/exhaust valve areas (to the point where a commercial installation will install "dump loads" to keep motor-generators properly loaded).

    When I first started posting here years ago--I used to go much deeper into the reasons and details of the various deratings and try to customize them for each poster--It took 10x longer to type up, confused readers more, and was hardly more accurate than the "rules of thumbs" we use here today.

    Until you have done the rule of thumb design to size the problem--You cannot really do the detailed calculations. You have to next pick the exact hardware/wiring/operational configuration so you can use the right models to get the detailed answers you are looking for. They are all different (scale, load and charging profiles, age, temperatures, weather, etc. all play a huge role here).

    If a poster gets within +/- 10% of their predicted output (using PV watts+rules of thumb)--They are "dead on"... There are just so many variables between the physics of the problem and the psychology of the users (some people pay attention to extreme levels of details when operating their systems--Others just flip the switch and don't pay any attention until something breaks)... It does really become an "academic" exercise to "do the math/proofs".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using grid inverters without solar/wind

    Bless you Bill, for that shining example of why we distill things down to rules-of-thumb to get peoples' systems up and running. Who'd want to do all that math every time? :D
  • DellyDelly Registered Users Posts: 16
    Re: Using grid inverters without solar/wind
    Bless you Bill, for that shining example of why we distill things down to rules-of-thumb to get peoples' systems up and running. Who'd want to do all that math every time? :D

    That's why I said that every time I read one of Bill's post my head usually starts spinning :P But nevertheless, thank you Bill!

    Now, I'm kind of finished with what I originally wanted and have therefore, during my last meeting last week, been given the task to take what I've gained (experience) and look into 2 other direction. The funny thing is that the board team and the project manager are not in complete harmony, each one of them wants me to look into a different path so I'm kind of shattered between 3 tasks :P One of them wants me to continue with what I'm doing and order the system I've described. A second one wants me to look into if a shared solution with a power size of 20-60kwh (for 20-40ish houses) and 400-1200kwh (before the voltage is transformed down from high voltage down to residential use, 230V) is more economical. lastly, the third one wants me to make a quick/short order list, just like my first one, for uncertificated system of ~600wh so we can "play" with and test out to get more knowledge before we step into the bigger one...

    My challenge here is the second one. I've looked into SMA inverters and found out that the max power they can have is 8kwh. The same thing with the Conext XW and Outback Raidan series (obviously a little lower). All of them are stackable up to a certain value.

    One thing that is really interesting is the new SMA Backup Sets that I saw. Link for the pdf: download.solarshop.net/english/uploads/SBUPSYS-DAU081312.pdf
    Is it really one inverter that is capable of 100kwh or are they stacked? Also, is it continuous power or surge?
    This one here says the L version has only 15kwh of continuous power output? Or am I ready thing wrong?

    Also, if I do get a 100kwh inverter, is it possible to achieve battery capacity of this size or higher?

    As always, Thanks
    Delly
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    I've looked into SMA inverters and found out that the max power they can have is 8kwh.

    I'm not sure what you mean. If it's 8kW (not kwh), then SMA makes larger string inverters than that. Their TL line goes up to 11kW.
    Delly wrote: »
    Also, if I do get a 100kwh inverter, is it possible to achieve battery capacity of this size or higher?

    You are mixing terms here; you cannot equate kWh to kW, and at any rate, the SMA line of PV inverters cannot invert from battery voltage.
  • BB.BB. Super Moderators, Administrators Posts: 32,925 admin
    Re: Using grid inverters without solar/wind

    Delly,

    Your problem is that most battery systems are designed to provide output power / performance of roughly equal capacity (watts/kWatts) when running from utility power or from a battery bank. Very few are capable of running 10 kWatt through them from the utility and 0.8 kWatt to "help" reduce power usage during parts of the day.

    Your choices probably come down to:
    • wire a 800 watt heater directly to its own hybrid/offgrid type inverter
    • get a full grid tied/utility interactive inverter (i.e., one designed for solar panels=>GT inverter=>AC mains) and has an input that is compatible with a battery bank. Just "inject" support power into the main panel. Power is carried through main power panel as normal. Injected power is "just another circuit". You can find smaller GT inverters that may work OK for the inverter part of the experiment. I would look at micro inverters (enphase and others now). How you setup control circuitry--Your part of the problem (I don't know how remote control friendly Enphase inverters are--Certainly not part of the normal customer interface). M215 looks like it would work OK with a 24 volt battery bank.

    Nice power point from Enphase for background information:

    http://ewh.ieee.org/r6/scv/pels/archive/enphase_pierquet_PELS-SCV.pdf

    Regarding a large system for multiple homes--In English/Economics we have a term--"Tragedy of the Commons".

    Tragedy of the commons
    - Wikipedia

    In economics, the tragedy of the commons is the depletion of a shared resource by individuals, acting independently and rationally according to each one's self-interest, despite their understanding that depleting the common resource is contrary to the group's long-term best interests. The concept is often cited in connection with sustainable development, meshing economic growth and environmental protection, as well as in the debate over global warming. "Commons" can include the atmosphere, oceans, rivers, fish stocks, national parks, advertising, and even parking meters. The tragedy of the commons has particular relevance in analyzing behavior in the fields of economics, evolutionary psychology, anthropology, game theory, politics, taxation, and sociology. Some also see the "tragedy" as an example of emergent behavior, the outcome of individual interactions in a complex system.

    Your whole project is for the "common good"--And may quickly become a (another) study in human behavior.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DellyDelly Registered Users Posts: 16
    Re: Using grid inverters without solar/wind
    ggunn wrote: »
    I'm not sure what you mean. If it's 8kW (not kwh), then SMA makes larger string inverters than that. Their TL line goes up to 11kW.

    You are mixing terms here; you cannot equate kWh to kW, and at any rate, the SMA line of PV inverters cannot invert from battery voltage.

    You are right. That's what happens to me when I'm stressed and in a hurry :P And yes, I'm aware of the fact that SMA's grid inverters can't be used for battery systems. That's the reason I'm looking for hybrid inverters or setting up a combined system of on and off grid inverters. When I looked at SMA's homepage, I found only the XT and MV versions which were rated for >500kw. I could not find the TL nor the backup set versions that I posted in my previous reply.


    Bill, it is true that very few (normal)systems are capable of running watts of 10k+, but surely there are some inverters meant to do that. Otherwise they (ie. SMA) wouldn't have made inverters supporting >110kw?

    Just wondering here, do the inverters in the link below support batteries? If so, what size of the batteries do they support? Is it the same size as the "rated DC input"?
    http://www.sma.de/en/products/central-inverters/sunny-central-500mv-630mv-800mv.html#Technical-Data-8803
    http://www.sma.de/en/products/central-inverters/sunny-central-500cp-xt-630cp-xt-720cp-xt-760cp-xt.html#Technical-Data-14560

    Is there anyone or any project here that have a large on/off grid system with a size of >60kw? Also, I'm sure that no common solar stores sells inverters of this size and I'm guessing I'll have to look for industry companies (not sure of the right term here) instead. Anyone here knows of such a large company that sells large sized inverters rated for >100kw?

    About the tragedy of the commons, I must admit that problem never occurred to me. But I think that if the utility company are the one in charge of the system, we can avoid this problem? (Just me thinking here). After all, they are connected to the grid, and it is the utility company that needs the extra power to reduce the load peaks. Wiring a 800 watt heater directly to its own inverter would not solve my problem since heating is a small part of the complete picture.

    About the enphase m-inverters; I've looked into to them a while ago, but people where saying that they did not support battery backups and therefore I just skipped over them. But now I'm thinking; why can't i just plug the inverters into the ac input of a hybrid inverter (maybe even off grid inverters)? Wouldn't that work just like having an off and on grid inverter combined together?


    Best regards,
    Delly
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    Bill, it is true that very few (normal)systems are capable of running watts of 10k+, but surely there are some inverters meant to do that. Otherwise they (ie. SMA) wouldn't have made inverters supporting >110kw?

    Most GT systems are limited by the rules of back-feeding service panels and utility wiring. For example your typical household service is 200 Amps, meaning a maximum 40 Amp back-feed breaker and a total of 9600 Watts (10kW basically). Beyond that a larger service or line-side tap is limited by the capacity of the wiring to the utility grid. For most places 110kW would be beyond that wiring's ability (typical service is about half that).
    Just wondering here, do the inverters in the link below support batteries? If so, what size of the batteries do they support? Is it the same size as the "rated DC input"?
    http://www.sma.de/en/products/central-inverters/sunny-central-500mv-630mv-800mv.html#Technical-Data-8803
    http://www.sma.de/en/products/central-inverters/sunny-central-500cp-xt-630cp-xt-720cp-xt-760cp-xt.html#Technical-Data-14560

    These are PV powered GTI's. The term "support batteries" is confusing as some standard GTI's can be used to AC couple to battery-based inverters. If it is not a battery-based inverter it can not be powered by batteries.
    Is there anyone or any project here that have a large on/off grid system with a size of >60kw? Also, I'm sure that no common solar stores sells inverters of this size and I'm guessing I'll have to look for industry companies (not sure of the right term here) instead. Anyone here knows of such a large company that sells large sized inverters rated for >100kw?

    Around here we deal with standard household installs for the most part. Again it is unlikely any would be that large. For straight-forward GTI's, however, stacking smaller units together is not an issue as they all synch to the grid's waveform.
    About the enphase m-inverters; I've looked into to them a while ago, but people where saying that they did not support battery backups and therefore I just skipped over them. But now I'm thinking; why can't i just plug the inverters into the ac input of a hybrid inverter (maybe even off grid inverters)? Wouldn't that work just like having an off and on grid inverter combined together?

    With the right battery-based inverter micro inverters can be AC coupled to provide additional power to the system when the sun is shining. Not all battery-based inverters can support this. Some that do include SMA's Sunny Island, Xantrex XW series, and Outback Radian. For a standard GTI the AC signal has to be present on their output first before they will work, so they can't be connected to the AC IN but rather would be connected to the AC OUT. Most off-grid inverters would have no way of regulating the power supplied by the GTI's and so will not work in this manner.
  • BB.BB. Super Moderators, Administrators Posts: 32,925 admin
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    Bill, it is true that very few (normal)systems are capable of running watts of 10k+, but surely there are some inverters meant to do that. Otherwise they (ie. SMA) wouldn't have made inverters supporting >110kw?

    I think we are talking about different systems/solutions. Are you looking at using stored energy to reduce peak loads by 10-20% or are you looking for UPS (uninterruptable power supply) type of AC/battery backup?

    I was speaking of the issue of trying to use a "typical" hybrid inverter that is designed for UPS type function. Where you would pass ~10 kW through the inverter but feed back only 1-2 kW of power (Schneider XW or SMA Sunny Island type systems) and basically not using the "UPS" function of the hybrid inverter--Only the ability to feed power back to the grid from a battery bank for a few hours at a time.
    Just wondering here, do the inverters in the link below support batteries? If so, what size of the batteries do they support? Is it the same size as the "rated DC input"?
    http://www.sma.de/en/products/central-inverters/sunny-central-500mv-630mv-800mv.html#Technical-Data-8803
    http://www.sma.de/en/products/central-inverters/sunny-central-500cp-xt-630cp-xt-720cp-xt-760cp-xt.html#Technical-Data-14560

    I am not sure--But these appear to be just larger GT type inverters... Take the DC power from a large solar array and feed it into the utility grid at ~1,000 VAC.

    Remember that solar panels also are DC output devices--Just like batteries are (in that sense). Many MPPT type controllers (GT Inverters and solar MPPT charge controllers for battery banks) can connect to batteries instead of solar panels on their solar array input. Some companies do this for product development and testing. A few companies will actually rate their controllers for both battery and solar array inputs (mostly done with Solar MPPT Battery Charging controllers--Not usually rated for Battery input on the GT solar input).
    Is there anyone or any project here that have a large on/off grid system with a size of >60kw? Also, I'm sure that no common solar stores sells inverters of this size and I'm guessing I'll have to look for industry companies (not sure of the right term here) instead. Anyone here knows of such a large company that sells large sized inverters rated for >100kw?

    There is this place--But it is pure off grid. There is no utility power in the area (private land completely surrounded by a national park):

    Extreme Off-Grid


    There are major projects looking for utility scale battery systems. There is a small town in the US southwest somewhere that has a substation with batteries in it to event out loads and as short term backup (single long distant power line to town) (I think we had a thread here--But could not find the link).

    And there are other battery technologies that companies are looking at for utility scale systems. Might be of interest to a utility/battery developer for your type of system.
    About the tragedy of the commons, I must admit that problem never occurred to me. But I think that if the utility company are the one in charge of the system, we can avoid this problem? (Just me thinking here). After all, they are connected to the grid, and it is the utility company that needs the extra power to reduce the load peaks. Wiring a 800 watt heater directly to its own inverter would not solve my problem since heating is a small part of the complete picture.

    You are talking about a completely different level/scale of power here... Utility Scale Solutions have different requirements.
    About the enphase m-inverters; I've looked into to them a while ago, but people where saying that they did not support battery backups and therefore I just skipped over them. But now I'm thinking; why can't i just plug the inverters into the ac input of a hybrid inverter (maybe even off grid inverters)? Wouldn't that work just like having an off and on grid inverter combined together?

    I was suggesting using the Enphase with 24 volt batteries instead of solar panels on the Enphase solar input. This would allow you to start out small (200 watts per inverter) to GT power back into the grid. I believe it could work--especially in a "laboratory" type environment.

    Your other idea, yes, you can connect a GT Inverter system to the output of a standard off grid inverter and share AC loads between the GT inverter and the Off Grid inverter.

    In fact, many TSW inverters can actually transfer power "backwards". From GT inverter backwards through off grid inverter and actually recharge the battery bank.

    There are now hybrid inverters that are designed for this task (a standard OG inverter would overcharge the battery bank as they were never designed to have power back fed through their AC output). The SMA Sunny Island is the best of this sort of system configuration. Schneider XW line can, and perhaps some Magnum inverters too.

    But this is all getting confusing (to me) as to your actual requirements.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bill von novakbill von novak Solar Expert Posts: 891 ✭✭✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    About the enphase m-inverters; I've looked into to them a while ago, but people where saying that they did not support battery backups and therefore I just skipped over them. But now I'm thinking; why can't i just plug the inverters into the ac input of a hybrid inverter

    Because the AC input of a hybrid inverter is designed to sense that condition and shut down. A very few inverters will work if you connect the Enphase inverters to the OUTPUT side of the inverter, but then you also need an AC disconnect relay to disconnect the source when the batteries are full. It's called AC coupling. If you do a Google search for the Outback white paper titled "AC Coupling in Renewable Energy Systems" it contains a few examples.
  • BB.BB. Super Moderators, Administrators Posts: 32,925 admin
    Re: Using grid inverters without solar/wind

    Here is the paper that Bill von Novak was referring to:

    AC Coupling in Renewable Energy Systems
    (PDF download)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    Bill, it is true that very few (normal)systems are capable of running watts of 10k+, but surely there are some inverters meant to do that. Otherwise they (ie. SMA) wouldn't have made inverters supporting >110kw?

    The Sunny Island Multicluster boxes are the big ones that support >100kW. They are just paralleled 5kW Sunny Islands prewired and preprogrammed into a cabinet.
    The other brand that springs to mind for large off grid systems is Ingeteam: http://www.ingeteam.com/en-us/energy/photovoltaic-energy/p15_24_44/ingecon-ems-home.aspx
  • solar_davesolar_dave Solar Expert Posts: 2,395 ✭✭✭✭
    Re: Using grid inverters without solar/wind

    Here are some commercial size inverters
    http://pvpowered.com.phtemp.com/inverter-commercial.php
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Using grid inverters without solar/wind
    solar_dave wrote: »
    Here are some commercial size inverters
    http://pvpowered.com.phtemp.com/inverter-commercial.php

    Wow! 260V minimum battery bank voltage. But even at this voltage, the 260kW inverter will need 1000A from batteries. That's a serious cabling. Would need 2000 golf batteries or so. Or 500 batteries like mine - some $600,000 worth of batteries.

    They don't mention that they can work as chargers, so probably an equally sized charger will be required.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »

    Just wondering here, do the inverters in the link below support batteries? If so, what size of the batteries do they support? Is it the same size as the "rated DC input"?
    http://www.sma.de/en/products/central-inverters/sunny-central-500mv-630mv-800mv.html#Technical-Data-8803
    http://www.sma.de/en/products/central-inverters/sunny-central-500cp-xt-630cp-xt-720cp-xt-760cp-xt.html#Technical-Data-14560


    No, they are grid tied, high (DC) voltage inverters. The only product that SMA makes that inverts from batteries is the Sunny Island, and it cannot be connected directly to a PV array.
  • DellyDelly Registered Users Posts: 16
    Re: Using grid inverters without solar/wind
    BB. wrote: »
    Are you looking at using stored energy to reduce peak loads by 10-20%
    ^This
    BB. wrote: »
    You are talking about a competely different level/scale of power here... Utility Scale Solutions have different requirements.
    When I suggested this idea, I was thinking that the utility company would only have the switch to regulate or turn on/off system when they were in need of extra power to reduce load peaks. More like the president having the switch button to launch a nuke missile on someone without necessary having to get involved in how the launch system works :P
    BB. wrote: »
    I was suggesting using the Enphase with 24 volt batteries instead of solar panels on the Enphase solar input. This would allow you to start out small (200 watts per inverter) to GT power back into the grid. I believe it could work--especially in a "laboratory" type environment.

    Your other idea, yes, you can connect a GT Inverter system to the output of a standard off grid inverter and share AC loads between the GT inverter and the Off Grid inverter.

    In fact, many TSW inverters can actually transfer power "backwards". From GT inverter backwards through off grid inverter and actually recharge the battery bank.
    I've drafted this idea, but then I couldn't understand why it wouldn't be wiser to use the enphase directly on pv array and share the load with the off grid inverter from there, so I drafted yet another idea. See the included image =) Isn't draft 2 a more "correct" solution? Another thing I'm uncertain of is if the direction from off g. inverter to battery is bi directional or only single in draft 1. I mean, the enphase is there after all...

    Also about the AC coupling document you linked, all the inverters were directly connected to the batteries. The very first thing I learn from this solar project was to not connect the inverter directly to the batteries! So why aren't they using CC in between?

    BB. wrote: »
    But this is all getting confusing (to me) as to your actual requirements.l
    Trust me, I was confused too at start every time they were making changes to the plan. The focus is the same, but they went from cheap chinese system for testing, to medium range system, to (now) shared large scaled system. Basically, they want me to research what's the most cost effective solution is (disregarding the deratings).
    stephendv wrote: »
    The Sunny Island Multicluster boxes are the big ones that support >100kW. They are just paralleled 5kW Sunny Islands prewired and preprogrammed into a cabinet.
    The other brand that springs to mind for large off grid systems is Ingeteam: http://www.ingeteam.com/en-us/energy/photovoltaic-energy/p15_24_44/ingecon-ems-home.aspx
    The ingeteam products looks very interesting. Especially the INGECON EMS Plants and SUN Power! The down side is that I can't find any dealer or distributor so I can't find any price information on these type of large scaled inverters!! :grr The only dealer I managed to find was affordable-solar.com, but they had only a few ones of the GTI types, not the battery based ones.

    Edit: How do I make my image attachments show only thumbnail unless it is clicked instead of the full image?

    As Always, Thanks
    Delly

    Attachment not found.
Sign In or Register to comment.