grid attached PV system but w/o exporting watts

guy_c
guy_c Registered Users Posts: 7
Hello,

I want to build for my house, a PV system to work in parallel with the mains and without energy storage. During the day, the PV system would supply as much as it can and the rest will come from the mains. During the night all the energy will come from mains. I don't wont to 'export' any of the power to the electricity company nor store energy in batteries.

Do such a system has a special name?
Can someone give me links to resources for such a systems?
Local power here is 220V 50Hz

Thanks very much for your time

Guy

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: grid attached PV system but w/o exporting watts

    I don't know of any Grid Tied inverters that can do this (I am certainly no expert in the field--there maybe something out there).

    What is your application? You have a power company that will not allow GT Inverters--or just will not "pay you" if you generate "extra power"? Or is this for a generator based application where you cannot back drive it without damage?

    The question has been asked before I and don't remember anyone having a good solution that meets your description. You may be able to connect/program a Xantrex XW inverter/charger system to behave something like this--but there are still batteries required (and probably some conversion losses which could make it less cost effective).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: grid attached PV system but w/o exporting watts
    guy_c wrote: »
    Hello,

    I want to build for my house, a PV system to work in parallel with the mains and without energy storage. During the day, the PV system would supply as much as it can and the rest will come from the mains. During the night all the energy will come from mains. I don't wont to 'export' any of the power to the electricity company nor store energy in batteries.

    Do such a system has a special name?
    Can someone give me links to resources for such a systems?
    Local power here is 220V 50Hz

    Thanks very much for your time

    Guy

    what you describe is a straight gt system and exporting to the grid is necessary in such a system if you don't use it. point is that it can't export if you use it first, but stop using power and it will export power. to my knowledge none of the inverters will stop the exporting of the power as most consider this as a good feature.
    your only other alternative is to use a battery inverter system that won't export the power that will switch when utility power is lost which could be some type of sensor and relay system when pv is going strong.
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: grid attached PV system but w/o exporting watts

    The most simple solution to switch between grid and solar power is use a mains rated relay(120/240vac) connect its relay across the inverter output . so when energised it pulls in the contacts connecting the inverter output to your house wiring and when no voltage from the inverter the relay drops out connecting the grid mains to the house wiring.. but you may have a problem if the inverter size is above 3600 watts for 120v. as most double throw 120/240v relays rated at 30amps.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: grid attached PV system but w/o exporting watts

    That's called an undersized GT system. Maybe for an hour, it would export, if all appliances in the house are off (fridge, lights, fan), but overall, it would just reduce your bill a bit. Much like a guerrilla install would .
    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 ,

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: grid attached PV system but w/o exporting watts

    I'm not grid-tie guy but ... could the "sell" point be set to an "impossible" number so that this never happens?

    Not my forte. :p
  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    Re: grid attached PV system but w/o exporting watts
    I'm not grid-tie guy but ... could the "sell" point be set to an "impossible" number so that this never happens?

    Not my forte. :p

    The power has to go somewhere -- if it isn't sold, it has to be stored in batteries or it is lost forever.

    As others have pointed out, such systems don't exist because "selling" is considered the right thing to do.

    This can be done with aftermarket software, such as the product my company makes. When my PoCo decided to stop paying for exported power, I started using one of our tools to reduce exports. The result is that I went from exporting about 4KWh per day to exporting between 100 and 200Wh (more or less -- I'd have to look at the reports for exact figures. But unlike the OP, I have batteries enough that I can sometimes go off grid for 16 to 20 hours per day, with a typical suburban residential lifestyle, in the grip of a horrible, horrible heatwave.
  • guy_c
    guy_c Registered Users Posts: 7
    Re: grid attached PV system but w/o exporting watts

    First I want to thank you all for your replies

    I understand that in an ideal system I'd better either store or resell or both the excess energy.


    I don't want to sign an agreement with the power company (usually long term agreement in my place) and I don't wish the power company to be involved in what I am doing neither i.e. send me their 'experts' to control my stuff. So even in the long term I don't envisage an agreement with them. All I need is that they don't be aware of what I am doing except that I don't consume much. For instance if you export you must have your energy (KWH) counter able to count up AND down! I have a plaine counter.

    I don't want -initially- to store the power because 1) Avoid the cost. 2) Most of my consumption will be for the air condition, during the day. Summer nights are bearable and winter nights are not too cold. and 3) There is a quite constant west wind which may serve, later, for the night.

    In a switched based solution as suggested by john p will not have the flexibility to use as much as possible the sun power and only supply the delta (load-sun) from the power company.

    Even an undersized GT system per mike90045 may cause dysfunction of my counter. I know it can stop counting if load goes to zero but I don't want to try rotating it backward. I did not understand what the 'guerrilla install' is but maybe this is just what I want to do.

    A question to Cariboocoot: What does Outback means?

    Best regards,

    Guy

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: grid attached PV system but w/o exporting watts

    "guerrilla install' is an uncertified, bootleg, grid tie instalation. If you have been connected to the grid for a year, that's enought for your PoCo to "catagorize" your usage. Changes to it, will make them notice.
    If they notice, and are upset you are not buying your fair share from them, they disconnect you, for violating several safety laws.

    " Outback " is a manufactuer of inverters, charge controllers, and other such products. (Trace, Morningstar, Xantrex, SMA are the other big players)
    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 ,

  • mshen11
    mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
    Re: grid attached PV system but w/o exporting watts

    ["guerrilla install' is an uncertified, bootleg, grid tie instalation. If you have been connected to the grid for a year, that's enought for your PoCo to "catagorize" your usage. Changes to it, will make them notice.]

    i find this statement interesing. could you elaborate? i plan on creating a separate wiring system in my off grid system. sure they will notice my electricity drop (a little or significantly, depending on the size of my setup)... but im not violating anything. how would they prove i am 'messing' with their system (which i am not)?

    saying my usage dropped (even if more than 50%) is a weak argument on their part
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: grid attached PV system but w/o exporting watts

    Guy,

    The action of the utility's power meter is based on what they define it to be... In the 'old days', they were simple mechanical meters and turned forward or backwards based on the energy going through them.

    The modern meters may not count backwards--or in the electronic meter case--may actually turn forward and charge you for putting energy out on the grid (meter does not care which direction the energy goes--the utility charges for either).

    If you have a known load (say the A/C)--your most cost effective solar RE system (and legal) would be to size the battery bank to properly power the A/C and use solar panel to just keep up with the A/C during the summer months.

    I guess you are not in the US--So your laws/regulations may be quite different than ours. In our area (California)--the utility even has the right to charge a penalty for installing an alternative power generation system to power our own homes/businesses... This is based on the theory that the State allows utilities to get loans to pay for equipment based on customers that will buy energy from them in the future--basically, they took out the loans in our names. And the utility has the right to demand payment for those loans (and system expenditures) if we don't purchase the power because we generate our own. So far--there is no penalty for extreme conservation measures or "empty" buildings.

    In the end--we pay around $0.10 to $0.30 per kWhr for electricity... And if you add all the costs associated with buying a solar RE off-grid system + replacement batteries over a 20 year life--and it costs around $1.00-$2.00+ per kWhr... Very difficult to save money with an off grid system.

    However, if you want to generate power and there is no-grid (multiple power failures or too far/expensive to get grid power)--then solar RE (plus energy conservation) can be a nice way to go.

    Is your home well insulated and designed to take advantage of your location's local weather conditions (lots of insulation, double pane windows, collect sun in winter, shading in summer, ability to make use of cool summer nights, etc.)?

    Almost always, spending your money first on extreme conservation measures is a better investment than a Solar RE Electric system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: grid attached PV system but w/o exporting watts
    mshen11 wrote: »
    ["guerrilla install' is an uncertified, bootleg, grid tie installation. If you have been connected to the grid for a year, that's enough for your PoCo to "categorize" your usage. Changes to it, will make them notice.]

    i find this statement interesing. could you elaborate? .....
    saying my usage dropped (even if more than 50%) is a weak argument on their part

    They have computers that analyze the bills, in order to market themselves better. They have a VERY GOOD idea what a 1, 2, 3, 5 person household should use, and after you have been there a year, it's very odd for your pattern to change.

    You could just say you got a new energy efficient fridge !

    But this is the first you've spoken of an out building being wired separately, till now, you did say you were connected to a meter.

    Heck, here in California, the PoCo shares billing info with the police, if you use a LOT, they assume you are growing pot with big lights, and raid you . Sorry, we didn't notice the pool you installed.

    Don't mess with the PoCo.
    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 ,

  • guy_c
    guy_c Registered Users Posts: 7
    Re: grid attached PV system but w/o exporting watts

    Thanks,

    My installation is legal and the consumption should not change much: Once I'll leave in it I'll add the air condition AND the PV power ;) Any idea on how do I proceed from here? I have good technical knowledge but my experience is more in electronic and less in power; especially I'd love to be pointed to a resource detailing the function of grid attached systems: synchronization, sensing, mixing, I have no idea how this is done.

    Do you know where can i find prices of these manufacturers? I entered at xantrox but no prices in their site

    Guy

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: grid attached PV system but w/o exporting watts

    Our host is a wholesaler/retailer out of Arizona USA... So you can get an idea of what the "US Internet" pricing of the products are.

    However, your IP Address appears to be out of the Middle East--You will probably want to purchase from "local" suppliers by the time shipping, import taxes, and support are taken into account.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: grid attached PV system but w/o exporting watts
    guy_c wrote: »
    ... Any idea on how do I proceed from here? I have good technical knowledge but my experience is more in electronic and less in power
    Here is an idea, hope your electronic background would help. Use AC current sensors like these, one on the wire feeding your load sub-panel, one on the wire the batteryless grid-tie inverter connects to your AC. Build a circuit to compare the inverter current, say when it exceeds 90% of the AC load current to activate a relay to partially/totally disconnect some/all of the panels to reduce grid-tie export current to be below load current. The comparison circuit should have sufficient hysteresis to keep the relay from switching back and forth.
    GP
    edit to add: if you don't want to shred the PV panels, you can use the relay to activate additional loads such has heater element to preheat water, turn on pool pump ...
  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    Re: grid attached PV system but w/o exporting watts

    As others have said, it looks like you're in the Middle East -- particularly in Israel. In which case, Happy New Year :) Outside Israel, Eid Mubarak!

    GP's suggestion that you add and subtract panels from the array based on loads is an interesting one. It would almost certainly achieve the result, but it would also waste electricity you paid a lot of money to make.

    My question is why are you trying so hard to avoid having batteries? Or did someone steer you in that direction for no particularly good reason?

    What it sounds like you want is a system that connects to the grid when it doesn't have energy from solar power for the loads, or which uses its own energy when it does. The Outback Power Systems inverters will handle that with the non-interactive ("cannot sell power to the grid") inverters they make using either "High Battery Transfer" (turn off the grid when the batteries are between two ranges of "full" and "not so full") or "Time of Day".

    Rather than doing all this switching and juggling -- what's keeping you from using batteries and something like Outback Power System's "High Battery Transfer" mode?
  • guy_c
    guy_c Registered Users Posts: 7
    Re: grid attached PV system but w/o exporting watts

    Thanks for your replies
    GreenerPower: Using separate loads supply is certainly a possibility
    tallgirl: Thanks. Thought that the Muslim holly day was Eid Al-Fitr(?) Yes I am from Israel; and you? Any how, if I refer to your "algorithm", the batteries are here as an auxiliary thing that you test and take decision according to the state. This can be done w/o batteries too:

    1) feed with mains
    2) avail solar energy?
    3) yes, take more on solar and less on main go to 2
    4) no take less on solar and more on main go to 2

    software is easy :)

    I am not sure how to implement the test 2) nor the actions 1) 3) or 4) but the concept seems to basically work (?) Furthermore, if the loop executes at, say 20ms, you shouldn't usually notice its operation, in particular all appliances should stay on and not wake up off because of a too long supply hole.

    Can someone point me to the block diagram of GA and not GA systems? Do the inverter need be phase or at least frequency locked to the mains?
  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: grid attached PV system but w/o exporting watts

    Guy, your #1 through #4 are done automatically by the grid-tie inverters. Look at those here. You would want 220V/50Hz models. Download the installation mannual to see details. You only need to take care of the case "#5" : solar is available and more than what you use -> #6 more loads or cut solar to less. By "grid-tie", they already meet UL1741 or European Gxx standard i.e. automatically sync/locked to grid frequency (and more). The AC current exported would net with the current used. The net is what the electric meter would see.
    GP
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: grid attached PV system but w/o exporting watts

    Grid Tied inverters are frequency synchronized to the utility power. They do not have any voltage regulation either--they need the grid to set the operating voltage. The GT inverter simply outputs as much current/power to the grid as it can (based on solar panel array and internal power limits).

    GT Inverters do have "emergency shutdown" if the voltage for frequency get out of specifications (to prevent the inverter from operating if the grid goes down, or if the grid exceeds safe operating conditions).

    The utility looks to the GT Inverter like a giant AC battery. The GT inverter and utility simply share the home's loads, and any excess power is sent out to the utility for use by neighbors (does look like charging the AC Battery--just like a car generator and car battery in parallel. The loads do not care where the energy comes from, the generator does not care if the power goes to the battery or to the loads, and the battery is what sets the 12 volts for the car's electrical system--too little power from the generator, the battery makes up the difference; too much power from the generator, the battery takes the excess current and charges itself).

    Even if you could setup a feedback loop "at the utility meter" with a GT Inverter--you still have issues.
    1. In the US, you still would need to meet the laws/regulations required to connect a GT type inverter to our home.
    2. GT Inverters generate power based on how much sun is available. They have no energy storage capabilities--if you stop the inverter from collecting all of the power avialable (stop meter from turning backwards)--that power is lost forever.
    3. Grid Tied systems use the AC Mains/Utility like a battery for "energy storage" (i.e., meter spins backwards, you are storing $$$ in your account for use later when the sun is down). Off-Grid systems store the excess energy in the battery bank for use later (up to limit of battery bank).
    4. Batteries are not cheap, have losses (80-90% efficient when cycling), and wear out. GT systems don't have battery costs and wear out issues.
    5. Usually GT systems are designed to "spin the meter backwards" when the sun is up, and the meter spins forward when the sun is down. At the end of the day, the amount of power generated roughly equals the amount of power used (and you end up with a near zero power bill). The whole billing issue/utility approval stuff is highly political and depends on local laws and regulations (typically at the "state" level in the US).
    6. A GT system can be smaller than needed (just reduce peak charges during the day to run AC if you have Time Of Use metering/billing and/or penalty pricing for high power usage). Or, your system can generate more than you use (say more in summer, less in winter; zero power use after 1 year)--in the US, typically any excess power generated ($$$ in account) is lost at the end of 1 year (state/utility does not want people to become net electricity generators--a few places do pay for excess energy generated--but the economics of such a system is highly dependent on local regulations).
    In general, a solar PV electric system only makes sense if there is some sort of "energy storage" element. It cost a lot to generate the power (panels, inverters, batteries, etc. are expensive). When you start limiting power collected -- is is power that is lost forever if there is no storage element. And reduces the systems overall power generation (and makes the $$$/kWH costs higher).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • guy_c
    guy_c Registered Users Posts: 7
    Re: grid attached PV system but w/o exporting watts

    GreenerPower,

    Can you please send a link to the installation manual you were refering to? Thanks

    Guy
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: grid attached PV system but w/o exporting watts

    Guy_C,

    Each major vendor usually has their product manuals online at their website. In no particular order, here are some of the major GT players (in the US):

    www.outbackpower.com
    www.xantrex.com
    www.sma-america.com
    www.fronius.com

    There are many models and functional types of systems... You kind of have to narrow down your needs/choices and perhaps we can point to a system or two that might meet your needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: grid attached PV system but w/o exporting watts
    guy_c wrote: »
    GreenerPower,

    Can you please send a link to the installation manual you were refering to? Thanks

    Guy
    These vendors I believe have 220V/50 Hz models. Look at the installation section in these
    http://www.xantrex.com/web/id/1746/docserve.aspx
    http://www.renewableintegrator.com/images/Fronius/Fronius%203000%20man.pdf
    http://download.sma.de/smaprosa/dateien/4776/SB30-40US-IUS092024.pdf

    These give you ideas what's available, search for one with wattage suitable to your needs in a retail store near your place.
    GP
    PS: doesn't sound like you are that familiar with grid-tie installations. Your country might not have requirements as in the US. For safety reasons, try to use local electrician knowledgeable in installing solar. This document might give you some of these safety areas being addressed here.