One way grid-tie scenario possible?

SystemSystem Posts: 2,511 admin
Hi guys. I stumbled on this forum while researching how to add solar power to my business. Seems like a friendly/positive place to hang out! I have a question regarding the possibility to set up a system as follows:

What I'd like: A system where I am adding to my solar system over time, when money permits (ie: expandable modular system) and that would first use what is available from the solar array to run my shop, and 'top up' with power from the grid (which will be always). I'm not interested in a grid-tie system where I'm selling power to the grid (or the hassles/approvals. etc). I simply want to only use the grid to provide power over and above what my solar system can provide to run my shop. I don't expect my slowly expanding solar system to be able to run every load in the shop any time soon (if ever), even when optimal conditions exist, so I don't foresee a scenario where I have excess power to sell back to the grid (even for seconds, never mind long enough to make it worth doing) during normal daylight hours. Is there hardware out there that would allow such a scenario? Ideally at a pre-individual load circuit level (ie: residential style 200 amp circuit breaker panel that takes power first from the solar system, and automatically/seamlessly takes from the grid the power needed to meet the remaining load).

Thanks in advance for any advice!

Mark.

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: One way grid-tie scenario possible?

    selling to the utility is somewhat of a misnomer for most of us. what is happening is that the power you are generating is being used by you and any excesses generated by you are sent out to your neighbor causing the meter to go the other way. most times one does not have a system large enough to offset all of one's usage and get lots of $ in power being sent out (aka sold) in excess. basically the sun doesn't have full intensity all of the time or it becomes dusk/night and power comes in from the utility and starts turning the meter forward again. this uses the grid like it's a battery.
    a smaller system that you propose will only offset part of the usage from the utility because some is feeding your loads directly and any excess power consumption will come from the utility and will be reflected in the meter reading. the way you were thinking was like an off grid system being backed by the utility and that would work a bit differently as your off grid system cannot be engaged with excess coming from the grid. anyway, this won't happen with 100% efficiency either as some power will be lost to operate the inverter plus minor other losses, but it is far better than a gt system with battery backup or worse yet an off grid system. in a sense you are selling with a gt system, but you are buying too as it depends on your loads and how much sun you are getting for how long. a small system means you'll take in more than what goes out and you pay for it.
  • mike95490mike95490 Solar Expert Posts: 8,471 ✭✭✭✭✭
    Re: One way grid-tie scenario possible?

    Well, I think it's sort of a waste, to not do a bi-directional grid tie.

    So, just get a battery charger of what ever size you want, and set it to keep the batteries charged. if your solar can't keep up, the charger will kick in.
    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 ,

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: One way grid-tie scenario possible?

    the batteries would come into play only if he wants battery backup which is a gt with battery backup system. not as efficient as a straight gt system as i stated already.
  • BB.BB. Super Moderators, Administrators Posts: 29,746 admin
    Re: One way grid-tie scenario possible?

    I think that this could be done with a Xantrex XW Hybrid inverter--you may be able to program it to not pump any power back out the grid...

    The whole issue of incremental growth is actually a fairly big one here...

    One large 3-6 kW inverter is typically cheaper than a bunch of 1-2 kW inverters.

    Also, it is really not a great idea to start with a small battery bank and add batteries to the string over the years. New batteries (and different brands/model/size of batteries) tend not to play well with the existing battery bank (new batteries tend to cycle deeper than the old batteries in the bank--and can age to roughly the same life as left on the old bank)... Or you end up with replacing bits and pieces of your bank as the different cells age out and fail.

    If you where willing to accept Grid Tied Solar--the Enphase (and a few others now) inverters look interesting. Basically each panel has its own inverter--and the inverters directly tie to the 220/208 VAC branch circuit.

    However, normally any major electrical work (adding GT inverters, adding other inverters and circuits to your shop to support the added solar panels, etc.) typically need building permits/inspections each time it is done. Obviously, adding a few panels at a time and calling up the building inspector (and possibly the utility) is an expensive/time consuming pain in the behind.

    What you have asked for--basically a grid tied inverter that never sells to the grid has been asked for many times. But, as far as I have heard (mostly through this board)--nobody has ever created or sold such a device.

    For the most part, if you where to connect such a GT Inverter to the house/shop wiring--the building department would treat it just like a normal GT installation. And the utility would probably treat it just the same too (require their approvals). The fact that it dd not "sell power" to the utility may be a minor point to them and they would probably deny it anyway (if this where a utility that did not allow grid tied solar anyway--many of the smaller/coop utilities seem not want grid tied solar--many probably claim safety issues; whereas the real issue is that it costs them revenue if done as one year net metered billing and/or software/billing issues).

    As you have stated the problem--I don't think what you are asking for will be cost effective.

    If you where to save your cash and build the system all at once -- or at least stage it out this way:
    1. Xantrex XW Hybrid Inverter + minimal battery bank (6kW inverter plus around 600 AH minimum of 48 volt battery bank). Wire up loads to "protected subpanel"--basically a large UPS system.
    2. Add backup AC generator to XW Inverter (if you want backup power beyond that of the battery bank)
    3. Add solar charge controller + panels
    4. Add additional panels (+ additional solar charge controller if needed).
    I would check with the XW support folks to see if you can program a XW inverter to "support" the load but not sell back to the utility.

    Normally, the XW behaves like a grid tied inverter collection all of the solar power it can and supplying local loads with excess "Turning the utility meter backwards".

    If the AC Mains fail (storm, etc.)--the XW will behave like an off-grid inverter and run your local loads until the AC mains come back on and/or start the backup genset for continued off-grid power (large integrated UPS system). The XW Inverter will use whatever solar power is available seamlessly while off grid (solar panels will reduce generator run-time).

    If your utility supports One Year Net Metering--It can actually be a big win for you. I live in California and other than signing some forms, the process was pretty painless (first bill the utility messed up on big time) as we used an experienced installer. Just the usual building inspection and a new meter (for our Time of Use rate plan) from the utility.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: One way grid-tie scenario possible?
    niel wrote: »
    selling to the utility is somewhat of a misnomer for most of us. what is happening is that the power you are generating is being used by you and any excesses generated by you are sent out to your neighbor causing the meter to go the other way. most times one does not have a system large enough to offset all of one's usage and get lots of $ in power being sent out (aka sold) in excess. basically the sun doesn't have full intensity all of the time or it becomes dusk/night and power comes in from the utility and starts turning the meter forward again. this uses the grid like it's a battery.
    a smaller system that you propose will only offset part of the usage from the utility because some is feeding your loads directly and any excess power consumption will come from the utility and will be reflected in the meter reading. the way you were thinking was like an off grid system being backed by the utility and that would work a bit differently as your off grid system cannot be engaged with excess coming from the grid. anyway, this won't happen with 100% efficiency either as some power will be lost to operate the inverter plus minor other losses, but it is far better than a gt system with battery backup or worse yet an off grid system. in a sense you are selling with a gt system, but you are buying too as it depends on your loads and how much sun you are getting for how long. a small system means you'll take in more than what goes out and you pay for it.

    Thanks for the quick reply! I will never have excess power from a solar array to spin the meter backwards. From the moment I step into my shop in the early morning to when I leave 10-12 hours later there are heavy and constant loads well above what my solar panels could provide. I'm simply trying to reduce/offset my electrical bill from the utility, and keep adding/upgrading the solar system as savings are realized (and build 'equity' in the solar system itself - by adding value to my building when it's eventually time to sell)

    The idea of adding batteries could be more feasible if/when the size of my solar system begins to provide more power than I need during daylight hours when my shop is in full operation. I don't see this happening though because the total possible square footage for PV panels on my (flat) roof is limited to just offsetting my electric bill from the utility). I'm also trying to minimize my initial cash outlay for hardware, so if I can make the system work without using batteries (at least until my system grows) all the better.

    I'm not quite following what you say when you mentioned my "off grid system cannot be engaged with excess coming from the grid." What combination of hardware is best/most economical for my goal of seamlessly and automatically taking power from the grid only above and beyond what my solar panels can provide? (I would start with a (roughly) 3kw to 4kw system, and hope to add more capacity every 6 months or so.)

    Thanks!

    Mark.
  • System2System2 Posts: 6,290 admin
    Re: One way grid-tie scenario possible?
    BB. wrote: »
    I think that this could be done with a Xantrex XW Hybrid inverter--you may be able to program it to not pump any power back out the grid...
    -Bill


    Thanks for the reply Bill! I was reading up on the Xantrex Freedom SW Inverter/Charger (here: http://www.xantrex.com/web/id/2744/docserve.aspx), and from my understanding of the details in the Owners Manual pdf it sounds like I can use the grid as an option for power/charging (or a generator) in the event the solar panels aren't providing enough juice for my total AC load (which will be always).

    Thanks,

    Mark.
  • BB.BB. Super Moderators, Administrators Posts: 29,746 admin
    Re: One way grid-tie scenario possible?

    The most cost effective solution for you would still be a grid tied system... Even if you never turn the meter backwards.

    A grid tied inverter does seamlessly inject power into your wiring. Basically just like your car alternator injects DC power into the cars wiring to go to the headlights, running the engine computer, car radio and charging the battery...

    There is no transfer switch needed. No special hardware other than the solar panels and inverter.

    From what I have seen, cost effective GT systems start around 3-4 kWatts anyway--so you could add a new bank of 3-4 kW inverter+panels. The labor and building permits may be worth it at that power level for you to do several rounds of that (although--I would still get a quote on getting the whole 12 kW or whatever final system will be and see what the cost comparisons are).

    Avoiding batteries/transfer switches/hybrid inverters saves a lot of costs and maintenance issues (batteries need replacing ever 5-10 years or so).

    The only killer for a Grid Tied system is if your local utility prohibits it...

    Also, some utilities in the US have some rules where they meter the power you generate and sell it back to you (frequently with a subsidy--but not always).

    In California--we are required to go on a Time of Use metering plan--which could be a bad deal for a business that cannot shift power usage outside the peak afternoon billing periods.

    Also, if you are in Ontario area--are some place up there now offering really high subsidies for folks who install solar power? (IIRC $0.80 per kWhr or something crazy like that?).

    The only reasons to add batteries (ideally) is if you need emergency power... If your utility power is stable--Then Grid Tied is really the more cost effective solution.

    Lastly, at least in the US--I would not count on adding Solar PV Power to your building as increasing its value... Many buyers in the US residential market are "afraid" of solar or don't like its looks. And when power is cheap--the value of the solar array is frequently not worth the financing costs vs just simply purchasing the power outright from the utility. You may get some tax breaks from commercial solar -- but that is a local issue (in the US there are various tax breaks like no property tax on solar RE systems or a business can depreciate the system, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Ralph DayRalph Day Solar Expert Posts: 892 ✭✭✭✭
    Re: One way grid-tie scenario possible?

    Yes Bill, in the great white north (brown now actually), we have a feed in tariff program paying 80.2 cents per kwh (Ontario, microFIT program). You can use none of the power, it's all into the grid, and on a 20year contract. The difference between US and us is there's no rebates on the install. My install is pushing $80K right now, and the most I can get back is sales taxes of perhaps $4K.

    The payback time is 6-8 years, depending on how much you want to set aside for maintenance, replacements and such, and how much you just plunk on the loan. The response has been quite good. The local utility estimator told me there are 1000 systems in the que in the area (a radius of 75 miles or less from my site).

    Ralph
  • solarvicsolarvic Solar Expert Posts: 1,053 ✭✭✭✭
    Re: One way grid-tie scenario possible?

    Your idea about adding more solar panels every six months or so can cause you extra grief. I bought 8 panels of 1 model and about 8 months later I tryed to buy more> They were discontinued and was lucky to find 8 more but needed at least 20 to make 2 strings for inverter. So I could only use 1 string of 14 with 2 extra.s I couldn,t use. Then bought 8 panels of another brand. Decided later I needed 6 more. They became discontinued and was lucky to get 4 still 2 short for what I needed. So I got 2 more of another brand to go with them 12 and now they are discontinued. So It ended up I had to use 2 separate inverters instead of i because of the difference of solar panels. If I would have had all the same solar panels I would have only needed 1 larger inverter instead of 2 smaller ones. Best thing about having 2 inverters is if 1 breaks down I will still have power from other one. No one ever seems to bring up the problems I had by not getting the panels at 1 time. S:Dlarvic
  • BB.BB. Super Moderators, Administrators Posts: 29,746 admin
    Re: One way grid-tie scenario possible?

    Solar Vic,

    Since Belaro was planning on building out the array around 3-4kW at a time--a 3.5 kW array with 3kW GT inverter is not a bad step size... Below 3kW GT inverters (and by the time all of the building permits, labor, planning, etc.) goes into the mix--I would guess that smaller step sizes (2kW or less) for GT system build out is just not economically viable (higher $$$/watt component costs, relatively fixed overhead costs per job, etc.).

    I would still recommend getting a second quote with the full 10-20 kW (or whatever is his eventual planned system)--and see what the step vs 1-shot costs would be.

    If this was done with an XW Hybrid inverter and battery backed system--The recommended step sizes would be 1x 6kW XW inverter + 7kW of panels at a time... The XW system could be done as:
    1. install XW hardware + battery bank
    2. install 3.5 kW of panels + charge controller
    3. install 3.5 kW of panels + charge controller
    4. repeat
    But--I still do not believe that the XW system (when battery costs are included) really is a "cost savings" system.

    Even if the GT system never turns the meter backwards--the low cost/high reliability, little maintenance of the GT type system would would win big.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solarvicsolarvic Solar Expert Posts: 1,053 ✭✭✭✭
    Re: One way grid-tie scenario possible?

    Bill I am very glad I went to gridtied. At first I was going to go off grid and bought a lot of off grid components. I was thinking of setting up one of my offgrid inverters for power outages. I think I am going to try and sell all my offgrid stuff and just buy a guardian that only runs when the power is off. Lots simpler and cheaper. Got my first GTI electric bill , only $16 and some change. S:Dlarvic
  • BB.BB. Super Moderators, Administrators Posts: 29,746 admin
    Re: One way grid-tie scenario possible?

    I too love the idea of being able to run my system off-grid in an emergency (or when California government goes bankrupt in the next year or so)...

    But I am also cheap/practical... Conservation plus a small genset made way more sense than going Hybrid (XW did not exist when I installed my GT system--would have been a more difficult choice for me--but I probably still would stay with a small genset).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: One way grid-tie scenario possible?

    solarvic,
    if you wish to, you may sell your personal solar items here. we just don't want those in business or creating a business to do so here. you can describe and answer questions about each item and even put a price on it here, but leave the rest of it with pms or emails.
  • solarvicsolarvic Solar Expert Posts: 1,053 ✭✭✭✭
    Re: One way grid-tie scenario possible?
    niel wrote: »
    solarvic,
    if you wish to, you may sell your personal solar items here. we just don't want those in business or creating a business to do so here. you can describe and answer questions about each item and even put a price on it here, but leave the rest of it with pms or emails.
    Thanks niel. I won,t make a pest of myself. Probably when someone needs something I can make them an offer. S:Dlarvic
    27 kw today.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: One way grid-tie scenario possible?

    hey vic, i need a 2kw solar system with battery backup-make me an offer!!!:p
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