Incremental system upgrades?

AceNZAceNZ Solar Expert Posts: 104 ✭✭✭✭
As summarized in my signature, I have a hybrid on-grid / off-grid setup (runs from batteries at night), as well as evacuated tubes for hot water. The panels are sized at the maximum rated DC power input for the GT inverter (6 kW), which produces about 5.1 kW peak with mid-day clipping in summer. The inverter/charger is rated at 10 kVA AC load and up to 140A of charger current. Batteries are 925AH @ 48V.

I'm starting to think about ways that I might be able to slowly and incrementally upgrade and improve this system, over time. My main goals are increasing independence from the grid, improving reliability and maintainability, and keeping up with or ahead of the minor but steady decreases in system output due to component aging.

One complication is that the house has 3-phase power, and the solar is only tied into one phase.

Here's a link to a graph from a typical sunny summer day (shows generation and two of the three phases of consumption):

http://pvoutput.org/intraday.jsp?id=24188&sid=22036&dt=20131223&gs=0&m=0

Over the long term, I can imagine adding more panels, a backup generator, a second or third GT inverter and a second or third inverter/charger to support the other phases. (My consumption is also higher than I'd like, and I'm planning more on the conservation side as well.)

Any thoughts about the best way to approach this?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,229 admin
    Re: Incremental system upgrades?

    Do you need native 3 phase AC power (typically AC induction motors and sometimes electric heaters). Or are all of your home devices just single phase?

    It is possible to operate many 3 phase motors/equipment on single phase... But if you move your home to single phase power, it may require a fair amount of rewiring (and understanding the type of three phase wiring you have... In the US we call it Delta or Wye/Y/Star connected).

    And there can be grounding/neutral issues (3 phase is not nearly as "simple" as single phase/split phase power).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AceNZAceNZ Solar Expert Posts: 104 ✭✭✭✭
    Re: Incremental system upgrades?
    BB. wrote: »
    Do you need native 3 phase AC power (typically AC induction motors and sometimes electric heaters). Or are all of your home devices just single phase?

    No, I don't need native 3-phase. It was setup that way for capacity reasons. The maximum capacity available on a single phase residential is 60A (15 kVA @ 240V). I have 60A per phase (45 kVA).

    The big loads I have now that aren't on the solar phase are two electric water heaters (20A each), an electric oven, microwave, coffee machine, washer/dryer, and water pump.

    One of the features of the Quattro is the ability to set a current limit on the grid side. If the limit is exceeded, the difference is made up from the batteries.
    BB. wrote: »
    But if you move your home to single phase power, it may require a fair amount of rewiring (and understanding the type of three phase wiring you have... In the US we call it Delta or Wye/Y/Star connected).

    And there can be grounding/neutral issues (3 phase is not nearly as "simple" as single phase/split phase power).

    I believe the wiring here is the wye type, with separate wires for each phase, plus a single neutral. Each phase is 240V; it's not dual voltage like the 110/220 that's common in the US.

    When the solar was installed, since it's only on one phase, I wanted to re-balance a bunch of circuits by phase -- making the changes was easy and fast.

    The capacity fees are painful, and will only get worse. In October (before my hybrid system was working), I paid NZ$70 for energy (net, after export credits), and $125 for capacity.
  • BB.BB. Super Moderators, Administrators Posts: 32,229 admin
    Re: Incremental system upgrades?

    OK--I am guessing that you have 400 VAC 3 phase power (line to line) at 50 Hz. And you have 230 VAC from Hot to Neutral.

    You have 3 hot phases and 1 neutral and all of your appliances/loads connect from one of the hot leads to the common/shared neutral lead.

    The problem you will have converting your home from 3 phase to single phase is that in three phase systems, the neutral wire currents cancel if all three phases are equally loaded.

    If you were to power all three phases from one hot lead (single phase inverter), the three different phase currents would add up in the neutral (i.e. if you had 10 amps on each of the three "single phase" powered phases, the return current on the common neutral would be 30 amps.

    So--depending on how your home is wired, your neutrals may not be heavy enough cable to carry the sum of the A+B+C currents.

    In the US, we have center tapped 240 VAC transformers which give 120 VAC hot to neutral power. We have the option of sending a Hot+Neutral lead to our 120 VAC loads, or send a Black+Red hot and a single White neutral wire out for branch circuits. For homes with "home run" two wire circuits (plus ground), there is usually no problem with "over subsribed neutrals" if converting from 120/240 split phase power to a single 120 VAC power source. However, for homes wired with 3 wire + ground, the shared neutral cannot carry the rated current of common single phase powered pairs of Black+Red hot leads.

    In the US, it is very common to have 125 or even 200 amp single phase house service power. That 60 amp limit per phase is a real issue for conversion to an off grid single phase inverter.

    So, how difficult would it be to wire your home for 230 VAC single phase? Would it be "legal" in NZ?

    Your billing of $70 and $125 for capacity (or reservation charges in the US) is a real pain... Further conservation and more GT Solar exporting power will still leave you with a $125 reservation charge (can generated power credits be used to reduce reservation charges?).

    The only way to get rid of the $125 reservation charge may be to cut from grid power completely. In California, even that is not a "legal" or easy option. If we were allowed to disconnect the meter--Then we would still need to pay for "stranded" charges incurred by the utility (the utility took out a 40 year loan "in our name" to build/maintain a distribution network for our home and to build generators to sell power to our home).

    Perhaps, you may be able to reduce the size of your main (from 60 amps to 20 amps as an example). Perhaps it will cost you less in reservation charges and your new conservation measures (and possibly AC inverters that have generator support) can manage the surge current (i.e., use battery energy for heavy current surges/short high power loads like pumps).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AceNZAceNZ Solar Expert Posts: 104 ✭✭✭✭
    Re: Incremental system upgrades?
    BB. wrote: »
    You have 3 hot phases and 1 neutral and all of your appliances/loads connect from one of the hot leads to the common/shared neutral lead.

    Yes.
    BB. wrote: »
    In the US, it is very common to have 125 or even 200 amp single phase house service power. That 60 amp limit per phase is a real issue for conversion to an off grid single phase inverter.

    125A @ 120V = 15 kVA, vs. 60A @ 240V = 14.4 kVA -- pretty close.
    BB. wrote: »
    So, how difficult would it be to wire your home for 230 VAC single phase? Would it be "legal" in NZ?

    It's definitely legal.

    The challenge in going to a single phase would be managing peak loads, so they don't exceed either the 60A per phase limit at the grid or the 10 kVA (40A) limit at the inverter. The way things are now, I'm not sure that's possible.

    The inverter also has a second AC output, which I'm not using at the moment, that's not subject to the 10 kVA limit, and just gets shed when the grid goes away. It's also possible to stack multiple inverters, to either support more phases or more load on a single phase.

    The way things are now, if the grid fails (or is disconnected), solar and/or the batteries/inverter drive a single phase. The other two phases are not connected.
    BB. wrote: »
    Your billing of $70 and $125 for capacity (or reservation charges in the US) is a real pain... Further conservation and more GT Solar exporting power will still leave you with a $125 reservation charge. (can generated power credits be used to reduce reservation charges?).

    Export credits are NZ$0.25 per kWh for the first 150 kWh per month, and $0.10 per kWh after that. The credits are applied against the entire bill, both energy and fixed costs. Import costs for energy alone, including taxes, are about $0.19 per kWh.
    BB. wrote: »
    The only way to get rid of the $125 reservation charge may be to cut from grid power completely. In California, even that is not a "legal" or easy option. If we were allowed to disconnect the meter--Then we would still need to pay for "stranded" charges incurred by the utility (the utility took out a 40 year loan "in our name" to build/maintain a distribution network for our home and to build generators to sell power to our home).

    It's legal here to disconnect from the grid. I don't want to completely disconnect, though -- I don't mind paying for a grid connection; I just don't want to 100% rely on it, and of course I don't want to pay more than I have to. The other option is to cut back on reserved capacity. The bulk of the monthly fees are per kVA. I believe the steps are 60A 3-phase, 40A 3-phase, 30A 3-phase (the beginning of true "residential" rates, which are cheaper), 40A 2-phase, and 60A 1-phase. They manage the steps with fuses at the street.

    It's also possible to add a second meter (for about $400) that would provide power to certain circuits only at night, at a lower import price.
    BB. wrote: »
    Perhaps, you may be able to reduce the size of your main (from 60 amps to 20 amps as an example). Perhaps it will cost you less in reservation charges and your new conservation measures (and possibly AC inverters that have generator support) can manage the surge current (i.e., use battery energy for heavy current surges/short high power loads like pumps).

    That's the direction I've been leaning.
  • AceNZAceNZ Solar Expert Posts: 104 ✭✭✭✭
    Re: Incremental system upgrades?

    So, in terms of incremental system upgrades, what's the best path forward?

    Reducing my capacity requirements in terms of kVA and/or number of phases would certainly help, but how to prioritize that against things like:

    -- Adding more panels
    -- Adding a (small-ish) generator
    -- Adding another GT inverter
    -- Adding another inverter/charger
    -- Upgrading individual panels from 200W to something more
    -- Moving to micro-inverters, either on new panels only, or on old ones too
    -- Add a small wind turbine
    -- Something else?

    It would be nice to be able to make small improvements on the battery side over time, too, but I can't think of anything that would be "small."
  • BB.BB. Super Moderators, Administrators Posts: 32,229 admin
    Re: Incremental system upgrades?

    That 125-200 Amp service is at 240 VAC (really 120/240 VAC split phase). Older homes may have 30 or 60 amp service (120/240 VAC).

    Conservation would still be my goal... But reduction of surge/peak current may be an important sub-goal.

    Single phase 60 amps at 230 VAC (and even 60 amp fuses should support some pretty heavy surge current) is still a lot of power... The only time it would not is if you have significant heavy loads such as an all electric home (cooking, A/C+heating, hot water, clothes drier, etc.). Changing to Induction cook top, convection oven, etc. are only going to be 20-25% reduction in power--Not factor of 2 or 3 reductions.

    If that is where your heavy power usage is going?--May be hard to really reduce your main drop ratings unless you convert to propane for cooking (or wood/dramatically changing your cooking practices) and using heat pump for heating/hot water.

    Otherwise, you are just looking at throwing more money at everything to increase your local generation capacity (inverters, batteries, solar panels, backup gensets, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AceNZAceNZ Solar Expert Posts: 104 ✭✭✭✭
    Re: Incremental system upgrades?
    BB. wrote: »
    Changing to Induction cook top, convection oven, etc. are only going to be 20-25% reduction in power--Not factor of 2 or 3 reductions.

    The cooktop uses LPG. The oven is convection.
    BB. wrote: »
    If that is where your heavy power usage is going?--May be hard to really reduce your main drop ratings unless you convert to propane for cooking (or wood/dramatically changing your cooking practices) and using heat pump for heating/hot water.

    The biggest peak power consumers on the non-solar phases include:

    -- Two 350L hot water heaters (20A each). One is connected to evacuated tubes for solar heat; I can turn the elements off entirely for about 4 months. The rest of the time it's needed for boost only. The other one is electric-only, but usage is light. If you look at my live output graphs on the PVOutput site, you can see the 20A spikes when it comes on.
    -- Oven
    -- Microwave
    -- Coffee machine and similar kitchen gear
    -- Washer and dryer
    -- Portable oil-type heaters (up to two at a time; 10A each; winter only)
    -- Heat pump (mostly winter)
    -- Water pump
    -- A few remaining halogen lights (most have already been replaced with LEDs)
    BB. wrote: »
    Otherwise, you are just looking at throwing more money at everything to increase your local generation capacity (inverters, batteries, solar panels, backup gensets, etc.).

    I have already done a lot on the conservation side, and will continue to do more, but I also want to make some small, incremental improvements on the generation side over time, to improve my ability to be independent in case of an extended grid failure, and to keep up with or exceed the small decreases in performance that happen over time as the solar gear ages -- yes: inverters, panels, genset, etc.

    I have a pretty good handle of what to do on the conservation side. What I'm trying to get my head around is strategies on the generation side (phase re-balancing is important, too).
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