modified sine wave for grid tie?

johnelarue
johnelarue Solar Expert Posts: 33
Can a modified sine wave dc to ac inverter be used to grid tie a few panels, ie 150watts? or does it need to be pure sine wave only?

thanks,

john

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: modified sine wave for grid tie?

    There are really two different issues here...

    First there is Grid Tied and Off-Grid type inverters.

    The off-grid inverter acts like the AC voltage source and drives your AC loads.

    The Grid Tied inverter cannot run any loads by itself--it is designed to track the AC mains. The utility sets the voltage and the current and the GT inverter tracks (or is slaved to) the AC Mains.

    The other issue is the type of AC wave form output.

    The MSW (Modified Square or Sine Wave) inverter is less expensive to produce and can operate some 80-90% of the loads just fine.

    The True Sine Wave inverter is more expensive but has less higher frequency harmonics (less than 5%) than are present in the MSW inverter.

    In theory, you can have a a GT type inverter with either a MSW or TSW output. In practice (in at least the US), TSW is a requirement for grid tie type inverters.

    You might find smaller GT inverters that are MSW (especially in other countries)--That I do not know.

    So--first you have to find a Grid Tied inverter. Then you can see if it is MSW or TSW.

    You cannot connect a standard Off-Grid type inverter (MSW or TSW) to the AC mains--it will destroy the inverter at the very least.

    By the way, there are Hybrid inverters that can do Grid Tie, then switch over to off-grid when the power fails--just to confuse the issue a bit more (those are TSW types--at least the few I know of).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • johnelarue
    johnelarue Solar Expert Posts: 33
    Re: modified sine wave for grid tie?

    Thank you BB for the information, it is getting clearer.

    I am interested in a small grid tie inverter, up to 1000watts.

    I am planning a small hybrid system of solar, wind and hydro. Starting with solar and adding on later.

    The solar and wind are less than optimal at my location. Hydro is abundant but prone to damaging a pipeline maybe.

    Does anyone have any recommendations?

    Thanks again for your patience.

    john
  • sawmill
    sawmill Solar Expert Posts: 93 ✭✭✭
    Re: modified sine wave for grid tie?

    If you have a viable hydro source, I would use it first since it operates 24 hours a day.
  • GreenPowerManiac
    GreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Re: modified sine wave for grid tie?

    Be also aware that you'll have to get in touch with your power company before the GT system is installed. In Illinois, we MUST produce the same type of sine wave power they do or better. In my case PSW only. BB's right, the power company is fussy with what power goes where and when.

    I'd start with the hydro power first since most abundant. It'll get you off the ground and produce quickly before the power company steps in. What do you mean about pipeline hydro power ? What exactly is the source ?
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: modified sine wave for grid tie?

    UL1741 specifies the quality requirement of all grid interactive inverters, I believe its 5% or lower in the harmonic distortion allowed, seeing as a square wave is close to 100% by definition little chance that would be a listed application
  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    Re: modified sine wave for grid tie?
    BB. wrote: »
    There are really two different issues here...

    First there is Grid Tied and Off-Grid type inverters.

    ...

    I thought this was an exceptionally good and consise summary. A good review for me. Thanks.

    Best regards,

    Bill
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: modified sine wave for grid tie?

    If, as you say, the wind is iffy, I strongly suggest that you read through the wind threads on this forum (and elsewhere). Few people are satisfied with small scale wind, and if it is iffy, your chances of being satisfied are between slim and none, IMHO.

    Tony

    For a small grid tie inverter, consider the enphase, also talked about on this site.
  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    Re: modified sine wave for grid tie?

    You said you have a potential micro hydro site? How much drop (head), and what kind of flow (GPM) do you have? Really dollar for dollar, a micro hydro system will typically be much cheaper than a PV system of comparable total KWH's produced. It is also a LOT more work usually, and has quite a bit more that can go wrong over the years... so it does depend how hands on you wish to be with your electrical system. As far as pipeline damage, are you worried about freezing conditions or things falling on it, or...?

    If you're looking at a hybrid system with a max output of 1KW or less, that sounds like a lot more complex and a lot more expensive than it needs to be. 1KW output continuous (as in hydro) is another story, as that would add up to 24KWH/day (720KWH a month). 1KW max output PV would add up to perhaps 8KWH/day in ideal conditions and as little as 0KWH other days, annual average outputs maybe roughly 120KWH or so. Your numbers are probably less than this for PV, but just to give some very rough numbers to think about. When designing a hybrid system, there will be some extra expenses, and a more complex balance of systems. For grid tie, I think that you would probably need separate inverters for each of they independent sources (wind, hydro, pv, etc), and separate wire runs which can get expensive for wind and hydro in particular (depending on distances).

    Do you know what your KWH/month or year tend to be? I'd start there, and then look at what you have for potential energy sources and price out independent systems to compare. If your consumption is higher, then it might be worth looking at a hybrid system (or if this was off grid), but at 1KW output I think I'd just go with which ever resource was most abundant or practical. My bet would be hydro *if* you have a good site for it.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: modified sine wave for grid tie?

    Bill,

    Thank you. :blush:

    John,

    What country are you looking for? Different countries have different voltage/frequency requirements (and sometimes different regulatory requirements and regions with differing voltage/frequencies AC mains).

    You have a couple requirements that make this system a bit more difficult/expensive to implement:
    1. Is this for Japan?
    2. Does your local utility allow you to legally to connect a Grid Tied inverter?
    3. Generally there are two differing types of GT solutions. One requires one GT inverter per energy source, but does not require a battery bank. The second is a GT inverter that runs from a battery bank and requires all of the energy sources to charge the battery bank.
    4. Pure GT inverters (no batteries) are the cheapest, least maintenance and most efficient (cost and energy) way to produce energy--however, if AC Mains fail (storm, etc.), the system cannot produce any power.
    5. Typically, a battery based GT inverter is a Hybrid type system--can run both GT mode and Off-Grid mode--very handy because it nearly has the efficiency advantages of GT energy production and if the power fails, can switch over to Off-Grid mode if the AC Mains fail. However, does have the expense of a battery bank+additional charge controllers (typically one per energy source).
    Here is a quick explanation of the types of Renewable Energy System setups (GT, Off-Grid, Hybrid).

    Now, if your requirements is to use Wind+Hydro -- I would guess that your optimum solution would be to install a Battery Based Grid Tied / Hybrid solution.

    First GT Inverters: Enphase is small GT inverter designed to only work with a single ~200 watt solar panel (low voltage/low power input). Most other Solar PV GT inverters are high voltage input (~200-600 VDC) for large solar arrays (~1,000-5,000+ watts). There are a few GT inverters out there that are designed to operate with generator/alternator sources (wind turbines, but probably also water turbines). SMA makes "Windy Boy" GT inverters (~700-7,000 watts). But some are hard to get (not sure anyone here has seen a 700 watt version) and I am not sure how you match one to the turbine's output power/rpm curve.

    For your needs, because of the various power sources available, you might choose to use a Hybrid based GT system with a battery bank. It might be more expensive than individual GT systems (wind, hydro, solar) and require more maintenance, but may be easier to integrate all your power sources together (in the US, a pure GT system costs around $0.15-$0.35 per kWhr; a hybrid system probably runs around $0.45-$0.75 per kWhr).

    Basically, you set up a Hybrid inverter to take excess power from a charged battery bank and convert that into GT AC Mains power. The GT Inverter Mode acts like a dump mode charge controller. A hybrid inverter will switch over (transfer switch) and power the local loads if the AC Mains fail.

    On the energy source side, you connect each to the battery bank as if this was for an off grid system. Their charge controller would be setup to "slightly" over charge the battery bank so that the GT/Hybrid inverter can dump the "excess" charging currents into the AC mains.

    Now, some of the limitations:
    • GT inverters are typically most cost effective around 3,000 watts and above
    • GT/Hybrid Inverters are typically 24 volt or 48 volt battery banks
    • Many wind turbines (and perhaps some smaller hydro turbines) operate more efficiently at 12 volts vs 48 volts
    • Wind/Water turbines typically require a constant load to prevent over-speed (no battery load, the turbine will over-speed and self destruct in heavy winds). You should have an additional dump controller to prevent battery bank overcharging in the event the AC mains fail (a dump controller takes excess battery voltage and dumps it into an electric heater of some sort).
    • In the US, there is a new Wind Charge Controller coming out in the next few months called Midnite's Classic MPPT Charge Controller (for battery bank based systems) that has a model for Wind Turbines. It is supposed to really improve a wind turbine's output (MPPT optimizes the turbine's Voltage * Current = Power equation--during testing has been shown to increase power output at various wind speeds "up to" 3x)
    • Wind only works well if you a) have trees that are "flagged" or bent in the face of prevailing winds and b) your tower is at least 60' (20 meters) tall and 30' (10m) above obstructions 300-500' away.
    • Small wind turbines rarely perform as expected. Light wind does not have much energy and small turbines just are not large enough to pull much energy from that small area with their blades.
    Before you spend much money on this system, do your research. It is easy to dump lots of money and get little return on your expenses.

    Which leads us into what we always suggest before installing a Renewable Energy system... Spend your time and money first on extreme conservation measures. It is almost always cheaper to spend your money on insulation, double pane windows, energy efficient appliances (heat pump based heating/hot water, gas/propane cooking, solar thermal), down sizing (laptop vs desktop computer) and turning things off (entertainment center, DVR's, Computers, Printers, Lights, etc.) than to generate the power in the first place.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: modified sine wave for grid tie?

    I shouldn't think any utility would be keen on having MSW inverters attached to their system; the wave form on the grid is usually 'dirty' enough without adding square wave pulses to it.

    (I will now be told I'm wrong - my first prediction for the New Year. :p )
  • johnelarue
    johnelarue Solar Expert Posts: 33
    Re: modified sine wave for grid tie?
    Be also aware that you'll have to get in touch with your power company before the GT system is installed. In Illinois, we MUST produce the same type of sine wave power they do or better. In my case PSW only. BB's right, the power company is fussy with what power goes where and when.

    I'd start with the hydro power first since most abundant. It'll get you off the ground and produce quickly before the power company steps in. What do you mean about pipeline hydro power ? What exactly is the source ?

    Thanks GPM, oh I know the power company will be fussy for sure. About the hydro it is a year round creek, but needs to be tapped with a pipeline to bring to my property.
    icarus wrote:
    For a small grid tie inverter, consider the enphase, also talked about on this site.
    Yes, I am looking into it thanks.
    hillbilly wrote:
    You said you have a potential micro hydro site? How much drop (head), and what kind of flow (GPM) do you have? Really dollar for dollar, a micro hydro system will typically be much cheaper than a PV system of comparable total KWH's produced. It is also a LOT more work usually, and has quite a bit more that can go wrong over the years... so it does depend how hands on you wish to be with your electrical system. As far as pipeline damage, are you worried about freezing conditions or things falling on it, or...?

    unlimited head and flow, but the pipeline needs to cross other properties, need permisssion. also we have typhoons, need to take out the inlet a few times per year. I'm looking at 4inch flexible hose, maybe 2 inch. I know hydro is the best but like you say it is not maintenance free like solar.
    wrote:
    If you're looking at a hybrid system with a max output of 1KW or less, that sounds like a lot more complex and a lot more expensive than it needs to be. 1KW output continuous (as in hydro) is another story, as that would add up to 24KWH/day (720KWH a month). 1KW max output PV would add up to perhaps 8KWH/day in ideal conditions and as little as 0KWH other days, annual average outputs maybe roughly 120KWH or so. Your numbers are probably less than this for PV, but just to give some very rough numbers to think about. When designing a hybrid system, there will be some extra expenses, and a more complex balance of systems. For grid tie, I think that you would probably need separate inverters for each of they independent sources (wind, hydro, pv, etc), and separate wire runs which can get expensive for wind and hydro in particular (depending on distances).

    yikes, starting to get expensive here, wasn't planning on seperate inverters, thanks
    wrote:
    Do you know what your KWH/month or year tend to be? I'd start there, and then look at what you have for potential energy sources and price out independent systems to compare. If your consumption is higher, then it might be worth looking at a hybrid system (or if this was off grid), but at 1KW output I think I'd just go with which ever resource was most abundant or practical. My bet would be hydro *if* you have a good site for it.

    we use avg.500 KWH/month hydro is sounding better, the negotiations with landowners and town will be difficult, don't think anyone round here has ever done grid tie hydro, solar is very common though.
    BB wrote:
    John,

    What country are you looking for? Different countries have different voltage/frequency requirements (and sometimes different regulatory requirements and regions with differing voltage/frequencies AC mains).

    You have a couple requirements that make this system a bit more difficult/expensive to implement:

    Is this for Japan?
    yes
    wrote:
    Does your local utility allow you to legally to connect a Grid Tied inverter?
    yes
    wrote:
    Generally there are two differing types of GT solutions. One requires one GT inverter per energy source, but does not require a battery bank. The second is a GT inverter that runs from a battery bank and requires all of the energy sources to charge the battery bank.
    Pure GT inverters (no batteries) are the cheapest, least maintenance and most efficient (cost and energy) way to produce energy--however, if AC Mains fail (storm, etc.), the system cannot produce any power.
    Typically, a battery based GT inverter is a Hybrid type system--can run both GT mode and Off-Grid mode--very handy because it nearly has the efficiency advantages of GT energy production and if the power fails, can switch over to Off-Grid mode if the AC Mains fail. However, does have the expense of a battery bank+additional charge controllers (typically one per energy source).

    our grid is very reliable however it may not be forever, and I like the idea of a hybrid system. Peak KWH is now 30cents, average though is 20cents and rising. Of course I don not like the price of hybrid system haha.

    As for the rest of the information BB thank you so much! I need the alt. eng. education badly.

    Grid tie solar is very popular here. Our home location is however not suitable, hence I was thinking hybrid. The biggest problem is, the ream factor here is incredible! Panels made here in Japan cost 3X the price as in the US wtf? same goes for inverters etc...

    The only way to go is to approach a very large solar grid tie installation company, and swallow whatever they offer you. Subsidies do apply for approved installations by approved installers, however.

    One of the companies around here has a few micro wind turbines at bus stops around town, mostly PR stuff. They're always spinning like mad so they dont seem to be loaded. I inquired about them, and they talked ME out of it, wtf? It is very hard to buck the system here.

    Hydro would probably freak them bigtime. I'm sure it can be done, but the price of course would be unbearable, subsidies for hydro, don't think so but will check.

    Perhaps a major commitment of about 20K$ towards hydro, using the company is the only way to go. Can't afford that though. Putting together a hybrid system peacemeal is looking difficult. But I really appreciate your and everyone's input and time.

    Firstly, I will be looking at the recommended small inverters and contact the utility to see how to legally hook one up even if the ROI is not favorable now.

    If I've missed anything- everyone, please feel free to point it out, I'm happy to learn.

    john
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: modified sine wave for grid tie?

    Of course, if you have a good hydro stream -- you can directly connect your hydro generator (AC Alternator) to the utility grid with the correct alternator and controller(s). You don't need the GT Inverter setup that "we" solar PV people use (we only get DC out of our panels).

    You might have problems finding a hydro company that can setup a "small" hydro (less than 1 kW?) for generating power.

    Heck, you can even take an appropriately sized AC induction motor -- get it spinning with AC main power, then start driving it with water flow. A standard induction motor, when driven by an external power source will generate electricity just fine (it will basically be synchronize to the AC mains power.

    Obviously, such a simple system would not be legal--but I would bet you can find some hydro vendors that would talk to you about small hydro direct connected systems.

    Using a GT inverter + battery bank is a "hack" that lets you, more or less, meet the legal requirements for grid tied (via the electronic GT inverter) and you can do anything on the DC side (build your own for example) without having to explain anything to the utility.

    There are other variations for off-grid power... It turns out that if you back drive an Off-Grid inverter, it will very nicely charge your battery bank (you can back drive with a GT inverter, for example). The issue is that a off-grid inverter is not tested/listed for this kind of use and there is no battery charger/controller. A back driven Off-Grid inverter will over charge a battery bank unless there is a dump controller and/or some other charge limiting setup involved.

    If you can get approvals for the water run (and justify the costs)--I am sure you can the balance of the system (turbine+generator+electronics) running for your setup.

    In the end though, you probably would be better off spending the money on conservation for your home--much better return on investment in the end unless you can get some solar RE subsidies from the government (I am not a fan of subsides myself).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • johnelarue
    johnelarue Solar Expert Posts: 33
    Re: modified sine wave for grid tie?
    BB. wrote: »
    Heck, you can even take an appropriately sized AC induction motor -- get it spinning with AC main power, then start driving it with water flow. A standard induction motor, when driven by an external power source will generate electricity just fine (it will basically be synchronize to the AC mains power.

    I've heard of this before. So you apply some AC to "excite" the field, then stop the input of AC. And as the turbine spins it then makes AC. Something like this?
    This is using a 3phase AC induction motor?
    BB. wrote: »
    Obviously, such a simple system would not be legal--but I would bet you can find some hydro vendors that would talk to you about small hydro direct connected systems.

    That would be great if it were legal to hook to mains.
    BB. wrote: »
    Using a GT inverter + battery bank is a "hack" that lets you, more or less, meet the legal requirements for grid tied (via the electronic GT inverter) and you can do anything on the DC side (build your own for example) without having to explain anything to the utility.

    I've got three, 50 watt panels. If I get them grid tied (forgetting about ROI) using a Sunny Boy 700 or similar domestic GT inverter for example.
    I wonder if I could then add on hydro ( within the limits of the inverter of course) by myself. Or would this require another inverter as Hillbilly mentioned earlier?

    BB wrote:
    There are other variations for off-grid power... It turns out that if you back drive an Off-Grid inverter, it will very nicely charge your battery bank (you can back drive with a GT inverter, for example). The issue is that a off-grid inverter is not tested/listed for this kind of use and there is no battery charger/controller. A back driven Off-Grid inverter will over charge a battery bank unless there is a dump controller and/or some other charge limiting setup involved.
    working on understanding this :cry:

    BB wrote:
    If you can get approvals for the water run (and justify the costs)--I am sure you can the balance of the system (turbine+generator+electronics) running for your setup.



    In the end though, you probably would be better off spending the money on conservation for your home--much better return on investment in the end unless you can get some solar RE subsidies from the government (I am not a fan of subsides myself).

    -Bill

    I can't get much more efficient- wood heat, double windows, CFLs, air-source heatpump hot water on night mode, IH electric cooking . No gas, propane, kero, dryer, dishwasher. So we're using 500KWH/month on mostly hot water, fridge tv computer, cooking and lighting. Does this seem high?

    Right now I'm on the hobby-side of all of this. I'll check with the solar dealer and my electrician on pricing all options.

    The hybrid system of course sounds best, but I'm dreading the price .

    thanks again for your time, sorry if I'm repeating myself or misinterpreting your information,

    john
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: modified sine wave for grid tie?

    John,

    You are doing fine.

    Using a single or 3 phase induction motor at alternator--Basically, the motor is started with AC mains and "left to run". If you now start turning the motor faster than its synchronous RPM (i.e., 1,800 RPM for 60 Hz line to a 4 pole motor)--then it starts outputting current. You just increase torque and the motor now outputs current into the AC mains (spinning your meter backwards--if bi-directional meter).

    Regarding back driving an inverter--First, setup a normal "off-grid" system. Battery + Off-Grid inverter. Turn OG inverter on and now you have your normal off-grid battery based system.

    Now, connect a Grid Tied inverter that is the same size or smaller than the Off-Grid inverter. The GT inverter will see the AC power from the OG inverter and sync up to the AC power. The GT inverter will now start output current/power in proportion to the PV array available power.

    The GT + OG inverter will support loads up to the OG+GT output--Or, if the load is less than the GT output power, the energy will flow back into the OG inverter and start charging the battery bank.

    Since there is no charge controller in the GT+OG system, the batteries can be overcharged unless a charge controller is added (dump controller or turns of the GT inverter when the batteries are full).

    Regarding small hydro + small solar... I cannot see being able to connect hydro alternator + solar panels with off-the-shelf components and getting a successful result.

    The Enphase inverters (if available in Japan) are small enough to work with ~200 watt solar panels. There may be an issue with regulatory approvals--They may require exact brand/model of solar panels (tested/approved) and it may not be legal to connect 2-4 50 watt panels to one Enphase (more than likely such a setup would work fine). Not cheap, but not adding $1,000 of USD either.

    Run the 700 watt SMA Windy-Boy GT inverter with your hydro (assuming it is designed to connect with your turbine/alternator--I don't know the details).

    500 kWhrs per month for ALL Energy Costs (all electric, no natural gas/propane/etc.) is very impressive. With natural gas for cooking/hot water/heating/drying clothes--I can get down to ~200 kWhrs per month +/- for my family of four (just south of San Francisco CA--a moderate climate-no A/C). Roughly $20-$30 worth of electricity and $20-$60 per month for natural gas (depending on season).

    You can play with the PV Watts program... It has 3 Japanese cities--perhaps one is close enough to your location to help estimate the amount of sun/solar energy you can get from a setup.

    Note, use Array size as 1 kW (minimum value accepted) and a Derating=0.77 for Grid Tied and =0.52 for off grid system.

    It is possible that solar hot water would be an interesting hobby/investment. Typically you can do a lot yourself (build collectors, etc.). And the parts are not that expensive.

    If you don't have them yet--you might look for the local equivalent of Kill-A-Watt meters and a T.E.D. (The Energy Detective). You can log the kWHrs of your major (and minor) appliances and see what your major energy hogs are and if there are cost effective alternatives.

    Some random links from this thread (working to be come a detailed FAQ):

    Solar Shed and other Solar Thermal Links
    Chest freezer as a chest refrigerator
    Home Power Mag

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset