Simple grid-tie system, will this work?

All,

I ordered a Solar panel and Grid Tie inverter(see below), but I'm not sure if they are compatible and if this is all I need. My concern is the Solar panel is a 24V, but the Voltage at PMax is 34.5, which is above the 28V max input of the Grid Tie inverter.

I would think the grid tie inverter is for 24v because the input minimum is 14V, (above 12V)

Do I need a Charge Controller/Regulator in front of the Grid tie inverter? Or can I run the unregulated voltage right into the Grid tie inverter?

Solar Panel: (BP)
Maximum power: 150 Watts
Voltage at Pmax: 34.5 Volts
Current at Pmax: 4.35 Amps
Warranted minimum Pmax: 142.5 Watts
Short-circuit current: 6.25 Amps
Voltage: 24 Volts

Grid Tie Inverter:
DC input voltage range 14V - 28V
Model SSI-200W
Nominal AC Output Power 200W
Maximum AC Output Power 250W
AC output voltage range (110V) 90V - 130V
Frequency (110V) 46Hz - 65Hz
Total harmonic Distortion (THD) <5%
Power Factor 0.99
Island Protection - Yes, inverter shuts down during black out
Output current waveform: True sine wave
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Simple grid-tie system, will this work?

    I looked for a link/data sheet for this grid tied inverter... But about all I could find was here.

    Don't know anything about it--and it would probably not be legal in the US for use as a grid tied inverter on utility fed mains. And if the specs. are correct, it will not meet the safety requirements of UL/NEC for use as a grid tied inverter... Plus, ideally, you should have any grid tied inverter on its own dedicated circuit for safety--although, this unit is so small it would not be the worst thing on the AC circuit... The worst thing is that, technically, this could, in theory, electrocute a lineman because it does not meet safety requirements.

    There is a youtube video of something related (maybe the same).

    The kW meter when "connected" spins about 3x faster backwards than my 3kW GT system can drive mine at home...

    The BP panel you have appears to be too high of voltage for this inverter--as you suspect... But that is just from reading the specs. that you have posted.

    I would hesitate to tell you how to connect this to your utility system--probably nothing bad would happen--but I could not tell you to do it on Wind-Sun's board. The liability and possible blow back to a fine vendor like NAWS on this (their) board would just not be worth it (IMHO--I am not a moderator here or connected with NAWS in any way).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Simple grid-tie system, will this work?

    I agree 100% with Bill, as usual!

    Consider doing a bit more homework before you dive into this. Please avoid the 'Ready, fire, aim" syndrome so many people who get trapped when they want to "go solar"!

    As for grid tie, remember that all such installations need at a minimum (in most jurisdictions) an electrical permit, (and inspection!) and most probably a permit from the utility as well as an inspection. At the very least, if you do a grid tie without going through the proper procedures you will at a minimum be buying yourself a ton of liability. Additionally, my guess is that any homeowners insurance will probably be nfg if you have a problem.

    A final note, a single 150 watt panel is not going to "turn your meter backwards" very fast. Consider that you might get somewhere in the neighborhood of ~750 watts per day, somewhere around ten cents worth. A lot of liability for ~$30 per year worth of savings.

    Read all you can, and take the advice of the more learned members here, (not really me!) because they have forgotten more about electrical engineering, solar PV than most of us will ever know.

    Icarus

    PS. For the same time, trouble and money, have you thoroughly checked out your loads? Your cheapest energy dollar is the one that is saved by not having to generate it in the first place. For example, complete Cfls throughout the house, saving ~40 watts per bulb? Reducing the the number of lights, photo cells, timers etc? Un plugging phantom loads? (A satellite receiver and TV can draw ~50 watts just sitting. An on off power strip can cut that load off all the time your not using them saving way more than your panel can produce on an average day).

    PV solar is sexy, and it shows that you want to "do the right thing". Having said that, the real right thing is to do the things that make sense first, whatever your motivation may be, either saving money, combating Co2 emissions or whatever. A way more efficient use of ones money might be, tankless hot water, up grading insulation for heating and cooling, up grading HVAC and appliances, then perhaps solar hot water, and finely PV solar.

    None of it is cheap, but it will on balance, "pay off" faster.

    Good luck
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    Yes I've done the CFLs, insulation, and much when it comes to conservation, however, I would like to have PV energy to charge up all my small loads, like cell phones, battery chargers, elec razor, weed wacker, etc. I would like to also get an electric Mower and just use solar to keep it charged.

    For what I'm trying to do, I guess its possible that I can be off-grid and not need to worry about batteries either because I'm using it to charge battery driven loads which don't need constant power. I will just need to have a circuit/strip dedicated for this purpose.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Simple grid-tie system, will this work?

    I don't know if your "GT Inverter" can run 120 VAC loads without being connected to a power main or not... In theory, a GT inverter only can follow an existing 120/240 VAC wave form--and would not have the ability to run (and regulate its output) just as an inverter.

    Not to say that this unit cannot run stand-alone--I just don't know.

    You are sort of between a rock and a hard spot... In theory a person can design an inverter to run on just the output of a solar panel without any batteries--but that is not a common device. Normally, the output of a solar array is so variable--that it becomes sort of wasteful to run an AC load off the panels.

    Normally, the solar panels work best with a variable load--like a DC powered well pump or a solar charger and battery--both can take 100% of the available panel power (more or less) as the sun tracks across the sky.

    Trying to do a 120 VAC battery-less inverter with solar panels just does not work well--instead of the 120 VAC output fading nicely as the sunlight dims--the voltage (and/or frequency) goes out of regulation... And the attached device (like a radio or TV) will stop working or burn out (like a fridge motor). Or--you have to way oversize the solar panels (by 2-10x) so that they can supply enough power for the expected loads).

    So--unfortunately, the optimum method is to use the solar panels to, in your case, charge a battery, and use that battery either directly to power DC loads (cigarette plug devices) or use a small AC inverter to power your loads... And yes, you will incur the costs of batteries (and replacements) and the losses of a charge controller and inverter (if used)...

    And, if you go with DC appliances/chargers--beware that a car alternator does not charge much above 14 volts--whereas a deep cycle battery charger can go as high as 15+ volts, or during discharging, down towards 10.5--and not all DC devices will respond well to that wide of voltage range... Some times, it is just better to get a good quality Pure Sine Wave inverter and go with 120 VAC devices.

    But you will have a more useful power source in the end.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Simple grid-tie system, will this work?

    You could buy, two small 12 volt batteries, a 24 volt charge controller, and a small 120vac inverter, either MSW or pure. You could wire a voltage controlled switch to the inverter (or get an inverter with a controlled input voltage) so that the loads would never exceed the battery capacity, then plug your loads into the inverter directly through a power strip.

    A much cheaper alternative would be sell the hardware you've got, get what ever 12vdc nom panel you want, 1 12 volt battery, simple 12 volt charge controller and the inverter.

    The former is much more costly, and I don't even know of a simple (cheap) 24vdc charge controller, nor a 24vdc inverter. The problem is that you have a 24vdc panel in a 12vdc world. Here is a 24vc controller:http://store.solar-electric.com/ss-20l.html Here is a 24vdc inverter: http://store.solar-electric.com/xp-125-24.html

    Neither are cheap compared to 12vdc hardware.

    Can you cancel your order and order different hardware? If not, certainly the panel should command a reasonable price to resell.

    Icarus
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    I got both the Panel and Grid inverter together for under $650 so I'm pretty sure I can sell them quickly.

    I thought the trend was going to higher voltage panels because it reduces the wire gauge sizes. I noticed many of the larger panels 150W+ were 24V. As for controllers, I know most of the new Xantrex charge controllers are both 12V and 24V. (C40, C35, etc).

    I will look at the manual of the grid converter and see if there is a bypass so I can use it as a True sine wave inverter instead. I believe that most inverters these day will either be putting out 120V or not, they shouldn't be able to burn up a device or vary in voltage. All of my rechargeable loads are 120v, so they won't be connected to any DC voltages.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Simple grid-tie system, will this work?

    Indeed higher voltages allow smaller wire sizes in wiring the arrays.

    As for controllers, you have a 150 watt panel putting out a max of 6.25 amps @ 24vdc. The need for a 35 or 40 amp controller would be overkill. Of course the advantage of an larger mppt controller would be nice, but a small ~ 10 amp controller would be much cheaper.

    As for trying to run your inverter as a stand alone, I can't comment.

    Icarus
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Simple grid-tie system, will this work?

    Your inverter is probably a variant of the OK4U brand, which is really a newer trace micro-sine.

    Its a 200 watt Non-UL listed gridtie inverter that puts out nothing if its not connected to an AC power source. Its made in the netherlands, is illegal for use in the US and has been sold on and off on eBay for years.

    It will not work as your hoping for, to have 120vac backup, the lowest price unit around is the MorningStar SureSine ( 300 watts ) and its a stand alone unit, not Gridtie. You will also need a battery bank, all inverters that are stand-alone require batterys, the solar has no storage and hence can't handle variable loads or surges.
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    All of my loads are 120V power packs that charge batteries in devices. So I don't think I need a battery bank. This is no different than powering a solar water pump or attic fan, just a little larger scale. I believe that if you de-rate the loads, it will work. I have a 150W panel, and would hook up no more than 100W of loads.

    The inverter is full on or off, so it will shut off if I put too much load, otherwise it will continue to put out 120V and charge the loads.

    Batteries are needed for loads that need power at night, or have surges that exceed the Solar panel output. In my case, I am charging stuff up in the daytime. The devices all have batteries so they will work at night.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Simple grid-tie system, will this work?

    The difference is that the water pump or the attic fan will simply slow down if they receive less than full power--and still do useful work. An inverter will choke and reset if it does not receive enough power for the loads--so once you have exceeded 100% available DC power--probably no useful work will be done with an inverter+panel system.

    Power wise--If I had to pick a ratio of panel to load--my GT system has 3.5 kWatts of panels and I would probably pick ~2kW for my "average" maximum load. And even then, that would would only account for maybe 1/2 the power that is gathered in the day (when sun does not support 2kW minimum load, and the "wasted" available power for when the panels can support 2.5-1.7 kWatts during the mid-day).

    So, your 150 watt panel--perhaps 75 watts of load on an inverter (assuming the inverter is stable with just a solar panel--plus probably a few big electrolytic caps to manage peak current).

    You may be able to, with battery bank, harvest about 4x the solar panel output vs a solar panel and inverter+caps only. If you add a solar panel tracker--you may get more "average" power--but with added costs.

    Just a guess--

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Simple grid-tie system, will this work?

    Not to mention, how to defeat the anti-island function.

    It would be an interesting exercise if you could design a UL/NEC rated inverter that would allow you to do just what you are wanting to do, but wouldn't be a true grid tie inverter. Something for those that want to do a simple pv harvest for some load(s) but not reverse the meter.

    For some people the headaches of doing the redtape and permitting required for a simple installation. I could envision such a system to say reduce the grid load for a hot tub, or to charge battery devices as the OP suggests.

    An inverter like this could draw contain switching to feed a dedicated outlet(s)from the inverter when the PV supply was right, then switch to feeding it from the grid when there was not enough sun, and finally, switch off in the event of a grid power failure to prevent any safety hazard.

    If such a device was available as a stand alone, "plug and play" device, then any issue with codes and installation would be addressed by UL/CE rather than NEC and the utility.

    Just an idea for the EE genus' out there who want to make their millions.

    Icarus
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    BB - I agree I would be giving up a lot of energy by not storing the excess.

    Great ideas Icarus. I think I've seen a "Transfer switch" relay that is AC powered. It is used for Sump pumps. If it loses 120VAC from the main source(grid), the relay will de-latch and connect a secondary source (battery powered AC inverter)

    So in my case, I would do the Opposite - I would use the 120V from my sine wave inverter as the main source, and if it loses power, it would go to the Grid.

    This might be an idea for a product since its an alternative to dealing with grid-tie regulations.

    I'm trying to think of a down-side. In my case, its not a big deal if the power switches, or even in a sump pump, but if someone has critical equipment, they would need a UPS (adding to cost)

    Also, if sunlight is fluctuating, would the relay 'chatter'? I'm not familiar enough with panels/inverters to know the behavior in transition states/cloudy days.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Simple grid-tie system, will this work?
    Also, if sunlight is fluctuating, would the relay 'chatter'? I'm not familiar enough with panels/inverters to know the behavior in transition states/cloudy days.

    Yep--you would probably want to put some delay and/or historisis in to try an reduce the switching... Remember that relays also draw power too--and on a small system they can become significant loads in themselves too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Simple grid-tie system, will this work?
    BB - I agree I would be giving up a lot of energy by not storing the excess.

    Great ideas Icarus. I think I've seen a "Transfer switch" relay that is AC powered. It is used for Sump pumps. If it loses 120VAC from the main source(grid), the relay will de-latch and connect a secondary source (battery powered AC inverter)

    So in my case, I would do the Opposite - I would use the 120V from my sine wave inverter as the main source, and if it loses power, it would go to the Grid.

    This might be an idea for a product since its an alternative to dealing with grid-tie regulations.

    I'm trying to think of a down-side. In my case, its not a big deal if the power switches, or even in a sump pump, but if someone has critical equipment, they would need a UPS (adding to cost)

    Also, if sunlight is fluctuating, would the relay 'chatter'? I'm not familiar enough with panels/inverters to know the behavior in transition states/cloudy days.



    The relay could be energized only when grid powered so that the losses would be insignificant. I have an Iota transfer switch that is normally closed to send power from the inverter. When I connect the generator, it energizes the relay to open the contacts from the inverter and closes them from the genny.

    I'll have to think about this a bit more. I'm sure that Bill and others will give good advice.

    T

    PS With a bit more looking, it looks at though Iota makes just such a product, used as combination inverter/transfer switch for emergency lighting. I haven't read enough to to see how you could use this type item in this context. http://www.iotaengineering.com/iisguide.htm

    T
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    Here is the transfer switch I saw:
    http://tekrispower.com/inverters/product_info.php/products_id/124

    They want $196

    I think I can buy a $25 relay with socket than can handle 10A (more than I'll ever need) and put it in an enclosure for much cheaper. I might need a fuse to protect the relay in case someone plugged in a large load or there was a short.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Simple grid-tie system, will this work?

    Since you don't have a battery in the system, you will still need to address the issue of low voltage/low amperage. You can't simply have a voltage controlled relay turn your system on when there is sun. You have to account for a voltage drop when you put the system under load. Sharper minds than mine will have to solve this.

    Icarus
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    Well the low voltage situation could be handled by the Inverter if it has a Low Voltage disconnect, but I agree, the low current situation would need to be addressed.

    I would need to research this. You could detect a voltage threshold that would be too low for your loads, however, isn't the PV voltage affected by the load size? In that case it becomes really difficult. You would have to disconnect the load to measure.
  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    Re: Simple grid-tie system, will this work?
    icarus wrote: »

    It would be an interesting exercise if you could design a UL/NEC rated inverter that would allow you to do just what you are wanting to do, but wouldn't be a true grid tie inverter. Something for those that want to do a simple pv harvest for some load(s) but not reverse the meter.

    If such a device was available as a stand alone, "plug and play" device, then any issue with codes and installation would be addressed by UL/CE rather than NEC and the utility.

    Just an idea for the EE genus' out there who want to make their millions.

    Icarus

    Then you may want this:
    http://www.xantrex.com/xw/00_prod-page_inv.html

    If they made a 12V version, I would have one right now sitting in the basement.

    Hunter44102-Using a panel to power an inverter direct will not work the problem lies in you have too much panel wattage, this will raise the voltage above the the inverter upper cutoff. If you go battery or batteryless you will still need a charge regulator to keep the voltage in check.
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    N3, that thing looks sweet but I'm sure its out of my price range. If I built a house in Arizona though, that would be a good buy!
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Simple grid-tie system, will this work?

    Hunter, it won't work.

    The inverter you puchases isn't stand-alone and even if you had one that was, no stand alone inverter will work without a battery.

    A solar panel is a unregulated output, its voltage changes with the load, a 12V panel, no load is 21V, no inverter will handle this. When an inverter is connected, the charging of internal caps will cause the panel to go into array collapse. Thats when the IV curve turns neagitve ( voltage goes below the vmp point and any increase in load yeilds LESS power )

    Charge controllers don't regulate fast enough to supply an inverter without a battery as a buffer, so just adding a charge controller won't help and only Mppt units down convert, pwm types are just on/off

    You will find this out all soon enough .. were just telling it like it is
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    Guppy, in a grid tie inverter there are no batteries and the load varies.

    The panel is going directly to the inverter and to the loads. Only when the inverter is fully loaded does the grid take over the excess loads.

    So essentially it -is- possible, but I'm not arguing that existing charge controllers can do it.

    And in another scenario, how about those portable Solar chargers for Cell phones? This is what I'm trying to do, but at a larger scale. They don't use battery banks, they just transfer solar energy to a load.

    http://www.buy.com/prod/powermonkey-explorer-solar-charger-for-cell-phones-mp3-players-ipods/q/loc/111/206229850.html
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Simple grid-tie system, will this work?
    Guppy, in a grid tie inverter there are no batteries and the load varies.

    The panel is going directly to the inverter and to the loads. Only when the inverter is fully loaded does the grid take over the excess loads.

    So essentially it -is- possible, but I'm not arguing that existing charge controllers can do it.

    And in another scenario, how about those portable Solar chargers for Cell phones? This is what I'm trying to do, but at a larger scale. They don't use battery banks, they just transfer solar energy to a load.

    http://www.buy.com/prod/powermonkey-explorer-solar-charger-for-cell-phones-mp3-players-ipods/q/loc/111/206229850.html

    I've been down this road before, The way a grid tie inverter works, it trys to put 140VAC onto the "grid". It's always fully loaded It requires the "grid" to regulate (load) it's output, and if it's output rises above 135V or so, it's supposed to shut down.

    Same with the solar phone chargers - they charge the phones internal battery, and they are designed with a specific purpose and load in mind. When 30% losses occur, you only have a watt or so to deal with, not 30W (30% loss from a 100W system).
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Simple grid-tie system, will this work?

    Hunter,

    There is a fundamental difference between Grid Tied and a "standard" inverter...

    The GT inverter regulates its energy output (i.e., energy pumped into the home's wiring) based on available energy from the solar panels. The "grid" is being treated almost exactly like a giant "AC" Battery.

    There is no interaction between the inverter and home loads or where the "grid" takes over loads once the GT inverter is fully loaded... The energy flowing into or out of the home through the electric meter is simply the sum of the energy used by the home added with the energy supplied by the GT inverter. Since all wiring in the home is in parallel, when the load+GT is negative, power is used from the grid. When the load+GT is positive, energy flows out back to the grid.

    A GT inverter does not regulate its or the grid voltage or frequency--it simply follows what is already there and pumps current out based on the solar panel's power output at that point in time.

    It may sound like a subtle difference--a standard inverter regulates the output based on the load without regard to input energy available--and a GT inverter regulates the output energy based on the available solar panel input. But it is a huge difference. The standard GT inverter's main feedback loop is based on its input. The standard inverter's main feedback loop is based on its output.

    The only reason a GT inverter works is because of the utility grid behaves like a battery--able to supply virtually any amount of energy to the loads as needed and in the GT inverter's case, able to accept any amount of energy from the GT inverter and share it across the rest of the network. More or less the same thing a DC battery does.

    For charging cell phone batteries--all of those devices are pretty much just charging a DC battery based on available power from the solar panel--if the panel is only able to supply a little current--the battery still charges... If the solar panel can output a lot of current, the battery accepts it too. They are not going through an 120 VAC 60 Hz adapter.

    But, for an AC device--if it demands more power than available from the AC source--either the frequency, voltage, and/or current will collapse and the AC load will fail to run correctly (motors will burn up, chargers will begin to oscillate in and out of reset, etc.).

    Now, that is not to say you cannot design electronics to run between the solar panels and the cell phone load. There are various things that make sense--boost circuits to raise solar panel voltage, or buck regulators to limit voltage. And obviously charge controllers to monitor battery charge state and energy being fed in to ensure save operation.

    However, these functions are very much defined based on the Input and Output characteristics. Could an inverter be designed to operate without a battery--yes... But it would end up not being very useful for standard AC devices which are designed to expect a stable, utility like, AC source. Since most AC devices would not like variable frequency or variable voltage inverters (trying to adjust input power available to output power voltage/frequency/current--for example higher frequency when more solar power is available, lower frequency when less solar is available--or the same thing with voltage) it is not possible to make a generic solution.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    Re: Simple grid-tie system, will this work?

    (darn while I composed my post Bill beat me to it)

    In a grid tied inverter they use the grid as the battery to stabilize the system. It has to be stable either coming in to the inverter or out of it. In a stand alone setting you have the solar panel, (usually a charge controller) battery, inverter and then loads. In this situation the battery stabilizes the system. With a grid tie inverter you have solar panels, inverter and the grid; in this case the grid stabilizes the system. If you take the grid out even with the safeties bypassed the inverter won't stay steady.

    Another way to think of a grid tie inverter is a small car (gird tie inverter) behind a semi (grid). The small car can floor it and push as hard as it can, but the semi won't go faster (voltage), just consume less fuel. Then when the sun is shaded by a cloud the small car pushes with less force causing the semi to burn more fuel, still maintaining the same speed (voltage). Now take away the semi and the small car is going to speed up and slow down as the sun changes.

    The simplest thing to do would be to add one or in this case two small 12v batteries, even UPS or lawn mower sized to even out the load. Then somehow shut the system off if there is no sun as to not run the batteries dead. This would also help out a lot as larger loads started. Say you plugged in a 150w light bulb, even without the voltages issues the inverter would ramp up dropping the input voltage to almost nothing as it started the lamp in turn shutting off the inverter, full sun or not, then once off the inverter would see full voltage and turn on again then pulling the input to nothing and shutting off again. Again there is nothing to stabilize the system.

    Could an inverter be designed to do this probably, but right now they are not.

    I do really like the idea of having a true grid tie inverter with two outputs and no battery, one output to the grid which could have all the safeties of islanding and all that to meet grid tie and then a second output that only powered loads on the down stream side, even if it were one half or even one quarter the array size wattage, maybe just plug your fridge in to it. I am sure they would have done this but stabilizing the system without batteries is the trick.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    Ok, this is making more sense, however, I think I have one last main question.

    IF I put in a couple small batteries 12+12V to stabilize the system, what happens when my loads are connected in the daytime while the battery is charging? They will drop the voltage that is meant to charge the battery, right?

    Or is this all taken care of by the charge controller? Some charge controllers have a Load connection, but I know you usually need to connect an AC inverter to the battery itself.

    I know I was told in the past that you cannot Charge AND use a battery at the same time. (or it might damage the battery - something about the loads fooling the 3 stage charging circuit, and they might get 'stuck' in the wrong mode?).
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Simple grid-tie system, will this work?

    You can charge your battery and power loads at the same time. Works fine.

    The details are that it is sort of difficult to tell when a battery is not fully charged if you have varying loads on the system. That is why different charge controller manufacturers have tried different algorithms to tell a battery's state of charge.

    In the end--accurately measuring the battery's voltage and temperature--and controlling the voltage over time to determine when to switch to float seems to be a pretty good method (like the Outback MX 60).

    As long as the battery is above 75% charge (avoiding undercharging) and is not boiling away water (from excessive overcharging), then you have a working system.

    And the proof is the number of people here running off-grid systems have having very respectable battery life (equal or in excess of mfg. lifetime ratings) when following some basic guidelines (good controllers with accurate battery voltage & accurate temperature measurements, keeping batteries clean and watered, and monitoring of battery bank's state of charge to ensure that all is well--recommend via a battery monitor which makes it easy).

    But, as of yet, the system is not fool-proof. We have more than enough threads here with system problems and unrealistic usage patterns that can, and do, kill battery life. More knowledge and care is needed for a solar off-grid system than many people are initially prepared to take on (and I will include myself in that boat--I have an RV that 8 years ago I let the batteries go to pot just because I did a plug and forget thing on them).

    You can find specialized solar charge controller that have a LVD (low voltage disconnect) of some sort--usually only small controllers have this and it is intended for light automatic loads (such as solar lighting). And larger controllers (such as the MX 60) also have programmable outputs that can control a LVD relay... But the problem with virtually all of these are simply based on battery voltage--and battery voltage is not a good indicator of battery State Of Charge... So, usually it just ends up protecting the load from "dead" batteries--but does not do a very good job of keeping a battery from getting a damaging deep cycle discharge.

    Some of the battery monitors have a programmable output that can indicate low state of charge based on actual battery capacity (the new Xantrex battery monitors coming out soon can do this--I think) and automatically shut down loads (or start a generator)--if desired.

    In the end, to do what you want (stable 120 VAC inverter output), you will have to add batteries to the system. And once you do that--you have choices to make--add a small battery and only run during the day (and probably have poor battery life and low surge capabilities)--or design it correctly and size the batteries, inverter, and solar panels to your load, location, weather, and needs.

    And you will have to monitor it... The first few times you let the batteries deep cycle to near 0% state of charge--will be the next time you have to buy replacements.

    And, unfortunately, the small systems are not easy to monitor well. The hardware is expensive relative to the overall cost of the system. And the labor of monitoring (switching loads, checking SOC, connecting a back-up charger/generator for cloudy weather) etc. is not cheap either relative to the small amount of power being generated...

    In the end, define the problem first (charging batteries or running AC loads on an inverter, how much load, how long, location, optional loads vs mandatory loads requiring a generator backup, how much to spend, alt. fuel source availability, etc.). Then define the solution(s).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Simple grid-tie system, will this work?

    You can charge and draw loads at the same time. This is what off grid systems do everyday! It is true that it makes it more important to use good battery monitoring equipment if you intend to maximize the life of your batteries however. This is also why using a good charge controller makes sense as well.

    For your system, a simple battery bank, a simple charge controller and a simple inverter would do it all well. Having said that however, I go back to my much earlier comment(s) that it seems as if you are continuing to put a square peg in a round hole. All this investment just to charge the items you suggest may be a bit silly. You might think about selling your hardware and start from scratch to achieve your desired result. IMHO

    Icarus

    Bill, you are way to fast!
  • System2
    System2 Posts: 6,290 admin
    Re: Simple grid-tie system, will this work?

    may be im wrong or right the it hash voltage sensor it adjust on the voltage input and output ... like the new TV you if look at the back 100~240 meaning you can put 100 volt to 240 volt with no problem.
  • hunter44102
    hunter44102 Registered Users Posts: 24
    Re: Simple grid-tie system, will this work?

    It has a physical -Switch- for 110V or 220V operation
  • Tm PV1
    Tm PV1 Registered Users Posts: 3
    Re: Simple grid-tie system, will this work?
    The ssi-200w inverter is designed to work on 12 volt panels. It plugs straight into a wall outlet. If external AC power is removed (grid goes down, inverter gets unplugged, etc.) The inverter shuts down, no output at all. It synchronizes to the grid and follows its sine wave. The island protection prevents the inverter from energizing a dead line. If the voltage drops below a certain point, it shuts off.

    As for having a 24 volt panel, you may have problems keeping the inverter feeding power. The inverter tries to keep an input voltage of 15.5-17 volts. I don't have a 24 volt panel to try this with, but as long as the voltage is ramped up to give the inverter time to start up, it probably will feed out power, but as soon as the high voltage is reached, the inverter will shut off. You could sell the 24 volt panel and buy 12 volt panels or buy a capacitor to buffer voltage spikes. These inverters are designed specifically for 12 volt panels. And as for charging your battery-powered stuff, just plug it into the wall like normal, plug your grid-tie inverter into the wall like normal, and the energy produced will offset energy consumed by the equipment. The ssi-200w was made so small solar is seamless and automatic. Also, a kill a watt meter put between the inverter and the wall will make things easier in tracking your power production. I have one of these inverters with three 85 watt panels, works beautifully. Power goes "panels"--> "inverter"--> "grid". I make between .5 kwh to 1.2 kwh per day.

    I've tested the island protection myself. I'll unplug the inverter with the kill a watt meter still attached to the cord. As soon as the prongs lose connection, the red fault light comes on and the meter goes dark, zero voltage, zero current. Also, if you do have a battery between this inverter and the solar panel, the inverter will only pull a small amount of power from it at night, just what it takes to power the tracker and led. It won't feed out current below 14 volts, and a 12 volt battery sits between 12 and 13 volts.