Phase alignment of Power Sources

SystemSystem Posts: 2,511 admin
I live in Oakland, CA and I am new to this web site.

I will be putting a Grid Tie system on my house.

- I have been studying John Wiles posts.
- Reading Pertinent sections of the NEC
- Refreshing my memory on Utility AC power distribution (reading a book)
- Looking at some example line drawings and an example 3 wire drawing.

The DC analysis seems straight forward and every thing looks good right up to the point where you backfeed through a breaker into the Utility grid.

So the issue I don't quite get is how Power Phase alignment is handled between the output of the inverter and the Utility Power Phase. Is this an issue? Does the inverter sense the Utility Phase and adjust to it?

This looks like a fun hspice simulation. But I already know what it will look like. You will get 2 Power Signals at 60 hz that are out of phase. The main distribution trunks are 3 Phase systems but the final distribution to residential is single phase.

How does this effect the Utility meter. IE if I am generating 3.5 Kwatts could I be spinning the meter back at a lower wattage becuase my phase is not optimum?

Also is there anyone else that is designing and installing their own system?


  • BB.BB. Super Moderators, Administrators Posts: 33,313 admin
    Re: Phase alignment of Power Sources

    From what I have seen and know--A single phase GT inverter sync's/slaves to the AC mains and pushes current back at a Power Factor of 1.0... I have a GE Utility Meter from PG&E and it will report back the voltage, current, Watts, and phase angles for my home (120/240 VAC, split phase).

    My meter is electronic (actually highly programmable) and spins forwards or backwards based on the number of kWhrs going through it (i.e., it is phase corrected, and does not charge for KVAR--Volt*Amp*Hour charges which is higher if PF is < 1.0). When the the GT inverter is not generating power, I have seen my meter report PV~0.6 or 0.7 (at a few hundred watts).

    Other utilities will have their own meters (some don't spin backwards, other spin "forwards" no matter which direction the power is going, and other utilities will install multiple meters for differential billing).

    As far as the Utility Network goes... There are several reasons they are current limiting the amount installed solar / RE power to 0.5-2.5% percent of network generation capacity (i.e., traditional power plants) or so... As long as the rest of the grid in the neighborhood is a "net sink" of power--the little amount of power supplied by distributed RE is "rounding error" for network management.

    However, if Solar RE becomes more prevalent--problems will arise. A few years ago, there was a development that was going to install GT solar on all of the homes. That would mean that the entire development could become a net generator of power during the day--and potentially the outbound power peaks would be higher than the traditional inbound peak power. The utility was firmly against allowing the plans to go forward (I never heard/found the final decision).

    From a business point of view, in California we are a net metered state--so I pay for power, and get paid for power at exactly the same rate. So, in the end, if my power in vs power out = ~$0.00 per month, I pay $6.00 per month. But--interestingly enough--my peak power consumption is around 1,000 Watts, and my peak power generation is around 2,500 watts... So, from the utility' point of view--my network reservation for generation is 2.5x that of my power consumption. And to boot--I am only paying minimum power cost (~1kWhr per day)... So, they have all that "copper" and transformer servicing my home--and little to show in the way of revenue.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Phase alignment of Power Sources

    gt inverters do sync to the frequency within tolerances and will track it. you also only need to worry about your single phase. if you plan on building something to sync with the grid this is out of my league and caution would be the word on doing this not only for safety, but this must be approved to connect to the grid. that's expensive and somewhat involved.
  • System2System2 Posts: 6,290 admin
    Re: Phase alignment of Power Sources

    Excellent Responses. I knew I would like this forum.

    I have no plans of building my own inverter. I plan to buy brand name components with the California required 10 year warranties.

    I am going draw up two system line drawings and I hope that it will be okay for me to post them here for review and input.

    With regard to PG&E I really can't predict where this is all headed but based on my look at this 7 years ago. Invertors were $7.5K for 2500Watts. Solar Panels for the brand name guys were $5-$6/watt (just for the solar panels)

    So if prices keep coming down the main power suppliers are going to have a big problem in Arizona, California, etc..

    SDG&E is building a Huge Dish Stirling engine Array that comes on line next year. And a small company in Washington has a 3Kwatt 15 foot diameter stirling dish with an XY tracker.

    I can't wait to see how my wife is going to react when I show her I want to put this huge thing in our backyard (just joking of course).:D
  • BB.BB. Super Moderators, Administrators Posts: 33,313 admin
    Re: Phase alignment of Power Sources

    Not a problem--if the drawings are simple/small (byte count)--you can upload the files directly... Otherwise you will have to use an external file/photo server.

    What kind of system are you looking for? Pure Grid Tie (no backup power) or the Hybrid system that supports battery backed power and backup genset?

    The prices for the parts is coming down... One thing I don't understand yet is what the new Smart Metering and Smart Billing plans are going to do for Solar GT...

    My guess is that for some of use, it Smart Billing will increase our bills (or at least, effectively not save as much money as our GT systems have in the past).

    At this point, check with PG&E (I assume) and see what their crystal ball says about Net Metering, GT, and rate plans before you spend any money.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Phase alignment of Power Sources

    Hi Bill,

    I am buying a house this fall.

    I will not do my drawings till next weekend.

    One will be for grid tie and the 2nd will be for Grid Tie with Battery Backup option as a future upgrade where the Array and output valtages would be compatible with a charge controller and batteries. For grid tie I can easily source 200V to a variety of inverters.

    I believe batteries are going to see big improvements for charge capacity and overall life and more cost reductions but not for at least 5 more years.

    I will screen capture the drawing as a .jpeg

    PG&E is not going to let everyone go to Solar and not charge them. That's why I want the Battery Backup option for the future.

    While the law dictates Grid Tie. They cannot prevent me from going to Europe for 4 months and telling them to shut off my power.
  • BB.BB. Super Moderators, Administrators Posts: 33,313 admin
    Re: Phase alignment of Power Sources


    When you look at battery backed systems... Include the Xantrex XW. Can do Grid Tied, Backup Power, and Off-Grid with the same system.

    At this point--unless you have a need for storm/earthquake backup power (or believe the State of California is an ungovernable/non-functional/bankrupt mess)--then, at least, do a very close cost comparison per $$$/kWhr and see which makes sense to you.

    If you believe there will be stable grid power for the decades to come--then the efficiency, cheapness, and low maintenance of a pure GT system is hard to beat.

    A hybrid / Off-Grid system is more expensive & requires battery replacement every 5-10 years--Realistically, the power generated off-grid costs ~10x what grid power costs (at least for normal rates--not those $0.60-$0.75 per kWhr rates for summer peak usage/warning days that are just around the corner).

    In the end, even though this is a "Solar RE" site sponsored/supported by a Solar RE retail/wholesaler--Strive to make all of the conservation improvements to your home (to be) that you can. It will both save you power costs and it will make your solar RE system much smaller and less expensive to build/maintain.

    Also, take a look at solar water heating--whether you save $30 in electricity or $30 in gas--it is still a net savings (solar hot water should be much less expensive to install--but the maintenance costs are higher than solar GT systems).

    And, lastly, you said that PG&E cannot do anything to you for disconnecting your AC mains (if you go to Europe for 4 months)...

    Technically, they probably can--if they wanted. California PUC has setup a method to charge people who go off grid by building their own power systems. Using the assertion that the Utility (and other investors) have built power plants for you on the assumption that you (or your property) will be consuming power for the next X decades. And if you go off-grid--you are stranding their investment based on your implied promise to use utility power.

    How often has this been done? I have no idea. I guess this is aimed at the larger industrial customers that could go with co-generation to provide their local power independently (and, effectively, become a private competitor to a public utility).

    Would they charge "you" for your solar RE system and going off grid? Again, I do not know--but I would not "advertise" or try to rub their nose in it (Ha--I just got my off-grid system installed and I am going to cut my ties to PG&E written in red at the top of the power bill).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Phase alignment of Power Sources

    Hi Bill,

    I totally agree with you. In fact I will not be buying batteries for at least 5 years.

    I have nothing against PG&E. I just am predicted that batteries will improve alot in the next 5 years and the whole solar system cost will be coming down.

    As more and more installations occur there may be some new laws or biz practices put in place. Maybe for the good but I really don't know for sure, so I just want to hedge my bets by having a a design that will allow me to go to battery back up at a later date.

    I really like the thermal water design cost but both my wife and I shower at the Gym 6 out of 7 days so we only use 2 HCF per month. So I would probable go with an Electric Water heater on demand. Cost is of course an issue but virtually no mantience.
  • BB.BB. Super Moderators, Administrators Posts: 33,313 admin
    Re: Phase alignment of Power Sources


    You just keep throwing things in here as asides. ;)

    It is is not easy to design/install a GT system such that it is "easy" to switch over to an off-grid system.

    The main reason being that GT systems run on Panel Voltage ~200-600 VDC. And Off-Grid/Hybrid systems typically run on 62-140 VDC wired solar panels. So, unless you bring the wiring down from the roof--it is a pain to rewire the panels two switch voltages...

    And since the Vmp ratings are different--you run into the whole Series/Parallel string configuration issue... You may use 10 panels per string for GT, and 3 panels per string for a Charge Controller (your integer multiples of panels may leave you a couple panels short or a panel long in the conversion).

    Also (I need my Thesaurus here to figure out the "on the other hand" paragraph leads), for GT systems, you can buy panels with high Vmp (over 35-40 volts)... They work great for GT systems... However, for Off Grid system, "high voltage" panels don't match well with Off-Grid controller's narrow operational range (today--~62-140 vdc).

    Things may change in the future--but is certainly an issue to assume the "conversion" is easy.

    Regarding your "Electric Water heater on demand"... Are you typing about true "demand/tankless hot water heaters" or just a 30 gallon tank you flip the switch on when you want hot water and wait an hour or two?

    One big issue is with the "true" tankless whole house hot water heaters... They require a very large electric service. And, many people complain that their home's lights dim/flicker when these big electric loads kick in and out.

    Or you could be thinking of small tankless/tanked electric hot water heaters on the sinks around the home (for tanked, only switch on when home)...

    Or--you can a regular gas hot water heater and only turn it on for weekends...

    Each of these has its pluses and minuses--but with where California Electric Rates are going -- I would look at a gas solution--unless I can prove to myself that an electric hot water heater really saves money (electric tends to be several more times as expensive vs natural gas--even though electric is much more efficient).

    A Tankless Gas Hot Water Heater sounds like it is made for your situation... It is off during the week, and only gets hot when you need hot water.

    For a "normally" occupied home--Tankless water heaters seem to (from reports here and other places) only save about 20% on the gas bill... Given that they are many more times expensive to purchase and install vs a tanked gas water heater--it is usually difficult to justify the cost/complexity of tankless gas water heaters.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.