One Inverter or Two for different Azimuth

System
System Posts: 2,511 admin
One Inverter or Two, for a 5.5KW to 6.0 KW DC (STC) System

Hello,

I’m new to the forum and I need some good solid advice on solar systems, panels, and inverters. I’ve read several of the various threads and this is a forum with very knowledgeable people.

A little about myself: my wife and I are retired and live in Bakersfield, gets very hot in the summer. Our house has a Southern Exposure of 160 deg. and West is 250 deg. The South side can hold about 18 – 20 panels and avoid any shading problems and / or relocating roof vents. The West side can hold about 12 to 16 panels. We are trying to eliminate tiers 3,4, and 5 from PG&E’s electric rates. We’ve had various contractors at the house, and to get the job they will tell you anything, including moving pluming and roof vents, to who knows what. Each contractor has the best and latest PV system.

I guess I need to get to the point. I’ve been looking at Fronius, SMA, Xantrex, and Sun Power SPRx inverters. Panels I’ve considered would include Evergreen ES-A Series 210w, Schuco SMAU-1 SPV 210w, Mitsubishi PV-UD 185MF5, and the Sun Power 225.

I’ve been to the sizing tool site for SMA and Xantrex but it’s a little confusing when trying to figure string sizing and different azimuth orientations, and minimum & maximum ambient temperatures with minimum and maximum open voltages.
One contractor say’s one inverter is enough and another say’s I need two due to South and West issue. Another say’s move pluming and roof vents and maximize the South side and forget the West.

My thought was no more than 18-20 panels on the South side and the rest on the West to get the benefit from the sun in the mid to late afternoon for a system total of 5.5 to 6.0. D.C.

Are there any issues with Sun Power having a positive ground as opposed to others that have a negative ground?

Having no real word experience with PV-System’s and knowing no one personally that has one, I’m inclined to the SMA and Schuco. It seems however that many on the forum favor Xantrex inverters, and the Evergreen panel’s.

KWH monthly average around 1,350. For the year, low is in the 900,s and high’s in the 2,200 range.

Any and all advice is welcome.

Please forgive me for such a wordy post. I’m just trying to get the most reliable system on a limited retirement income.

Thank You
Charlie

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: One Inverter or Two for different Azimuth

    PG&E does favor afternoon Solar production over morning with Time of Use billing.

    In the summer, Peak vs Off-Peak can be a 3:1 ratio in cost difference... So, if you lose 20% by facing west, but get "paid" 3x as much for the power--you may still come out a head.

    Depending on how deep you want to get--you can use the PV Watts Program for a south vs west array and click on the "Output Hourly Performance Data" and paste that into a spreadsheet. And load the winter/summer pricing * kWhr output by hour--and add it all up. You can tell very quickly (OK, less than quickly with an E6 tiered power bill to cut and paste into the spread sheet--you will have to make some simplifications and assumptions--if you need help, ask and I will see if I can help) which will work better for you.

    But--if you are trying to also save money--Have you done everything you can regarding conservation? In general, money spent on conservation will be a better investment before you spend you first dollar on solar power.

    As in the other threads, >R40 ceiling insulation, >15 SEER A/C, double pane windows with low E glass, energy star appliances, use less power inside the home (lap top computer instead of desktop left on 24 hours per day) so you don't pay for A/C to get the heat out, etc...

    In my old homes, even when we did not have wall insulation--just changing to double pane low E windows (that sealed well) made a huge improvement in keeping our west facing bedrooms cooler in the summer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: One Inverter or Two for different Azimuth

    Bill

    I would consider Time of Use metering but being retired it's kind of hard to leave the AC off during the very hot days.

    House we live in: New construction in 2005. AC is 14 seer, low eWindows dual pane, at least R40 in the ceiling, and exterior walls R19, and all interior walls are insulated. PolarPly roof sheeting under tile roof. Electric range and electric dryer are the big users. I have a tower computer that I built with parts from an online vendor, (don't want to advertise for them). We've started to change out all the lights we can to CFL's. It would seem that two people could get their KWH usage down. I may need to get the Kill-A-Watt or an ammeter with a small clamp to see exactly where all the juice is going.

    I would think that the SMA inverter with copper coils and low frequency transformation would last longer but I don't have enough information,(first hand or otherwise) to hang my hat on.

    I'm still searching the forum to see who favors various inverters and panels.

    Of course any recommendations would be welcome

    Thank You for your response.

    Charlie
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: One Inverter or Two for different Azimuth

    Do you have electric hot water too? A desuperheater as mentioned by Solar Guppy (and others) might give you "free" hot water during the cooling season.

    If you like "fresh air" and loose a lot of conditioned air through open windows (or taking in hot air through the A/C)--A heat recovery ventilator may help.

    The Kill-a-Watt meter is about the best for checking your wall plug appliances. But if you are in the 900 to 2,200 kWhr per month range--your major electric appliances (A/C, heat, stove, etc.) are killing you.

    2,200 kWhrs / 30 days = 73.3 kWhrs per day
    73.3kWrs * 1,000w/kW / (24 hrs * 120 VAC) = 25.5 amp load 24 hours per day (at 120 VAC)...

    That is a lot of average power. Equivalent of 3,000 watts 24 hours per day. The average draw for my home (winter/summer) is around 300 watts 24 hours per day (no A/C, natural gas appliances, etc... I know that our situations are different).

    Telling you to dry clothes on the line and unplugging your cellphone charger when not in use will not help.

    It will not be cheap to offset your AC usage with solar PV GT system... To offset 6 months of A/C is going to be around 15kW of solar panels...

    Has anyone in your area tried the energy audits that we sometime see talked about?

    One Canadian poster here was not too thrilled with one done at his home (if I recall correctly).

    You might try a T.E.D. a whole house energy monitor... I don't think you can program them for PG&E's complex rate plans--and it will not work correctly with Grid Tied / Net Metering.

    Or wait a few weeks and see what the new unit WindSun (our admin here) say looks to be a very nice unit (with multiple measurement units? maybe...).

    Solar Equipment wise--the major vendors of mono and poly crystalline PV panels seem to be pretty good--generally buy on price (delivered) and avialability.

    GT Inverter wise--The major vendors seem to be doing OK--Xantrex, SMA, and others. We had one person here relate problem with their particular Fronius installation (apparently a known configuration issue that Fronus has refused to document).

    Our host (Northern Arizona Wind & Sun) is a good place to start when looking for "good parts/vendors". They seem to stand behind their vendors and get rid of any that create problems for their customers (I have to say "seem" because I am neither a customer or employee of NAWS--I just help keep spam down here as a moderator).

    Of course, price and service delivered to you is what is important--you may have local suppliers that you like. And with a Grid Tied system--unless you are going to do the work yourself, you will end up dealing with a turnkey contractor that will supply inverter+panel+permits+labor for your project.

    Talk to a few contractors and see what they recommend / would use for your installation. What kind of customer feedback they have. The usual stuff...

    And, if it seems to good to be true--it probably is. Take a look at the panel fire thread (if you have not yet) to see what a bad installation looks like / can do.

    I do not live in hot weather with an all electric house--so there is probably little more I can help you with on the conservation side other than to make everything a cost/benefit decision...

    Sorry.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: One Inverter or Two for different Azimuth

    Before you do anything, you need to find out where your energy is going.

    R40 structure with a SEER14 AC system can't possibly use that much energy .. something isn't what you think or you have loads like hot tubs or large pools your have not included in your assessment of you property?

    You didn't mention the size of the home or the AC in tons. Something that well insulated should need more than 3 tons figure 3kw when running for even a 2500sf home .. I would be surprised if the AC was more than 500kw month

    As for inverters, SMA and Xantrex are both high frequency devices, the only difference is SMA has the galvanic isolation on the Output, hence the large 60hz transformer, the Xantrex is high frequency galvanic isolation ( hence transformer 1/20th the size ) between the DC and AC stages. Xantrex come standard with 10 year warranty

    If you do go with GT PV, I would recommend two inverters, the often linked Fronious white paper is bogus in my professional opinion, its conclusions are not on measured arrays and did not take into consideration the thermal variations of the two arrays in different orientations, which is the single largest cause of vmp difference and why there is Mppt in the first place.
  • System2
    System2 Posts: 6,290 admin
    Re: One Inverter or Two for different Azimuth

    Solar Guppy also Bill,

    Oopps, I was wrong about SMA and transformation, thank you.

    We have a gas water heater, and gas forced air unit for heating with an electronic air cleaner. AC unit is 4 tons with variable speed blower, 2000 square foot house. Yes, there is a pool, what I would call moderate size, 13000 gal. that runs about 4 hours a day in the summer and 2-3 hours a day in the winter.

    We do have a hot tub but this is some of my dilemma. While using the hot tub in Dec of 2005 kwh was 1332, Dec 2006 kwh was 1321, no hot tub in Dec 07 kwh 1018, no hot tub in Dec 08 kwh 1700+, no hot tub in Jan 09 kwh 1600+ (circuit breaker was off). A smart meter was installed, not at my request, in the summer of 2007.

    I do need to get rid of the electric dryer. We brought it from our other house that didn't have gas. Wife wanted electric slide in oven at this home so that was that.

    Perhaps it's time I get in the "Survival Time" frame of mind. Maybe it's the fear game that the local solar companies are playing that's pushing me to solar?

    At present a couple of things are certain in California; no new generation plants or hydroelectric powerhouses, and rates will continue to go up and up.

    Thanks again for the inverter advice. If I do put panels on the south and west I'll do two inverters.

    Charlie
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: One Inverter or Two for different Azimuth

    I would say its time to really understand where your energy is going.

    Get a kill-a-watt and a DMM with the clamp on current probe, they are cheap and can be had on eBay for 25-30 bucks.

    Some thoughts:

    Have you verified that you have R40 in the ceiling everywhere? thats 16" deep loose fiberglass

    What is the HP of the pool pump, if you don't have thermal solar, no more than 1/2 HP is required for a pool of that size, 300 bucks you can swap out the pump assembly ( never just change the motor, the vane is matched to the HP of the motor )

    Do you have a pool heater ( my guess is you do and its a heat pump ), that will use more energy than anything else in the home

    Unplug the Hot Tub, if you do choose to use it, then set-it-up and heat it, keep it running is a large load, turn off the pool heater, get the thermal panels if you use for heating ( about 1500 if you do it yourself )

    Do you have yard/outdoor lights ... that can be a large load as well if run all night, every night

    I'd nix the "electronic Air Cleaner" I bet that runs 24/7 and also requires the blower motor in the air handler to run 24/7 ... its more marketing than Air quality improvement and can easily pull 5-6kw day

    Solar is good, its a fixed price for future energy but you need to get your current usage under control and know what it is before you venture into this. Payback wise its always better to increase energy efficiency than add generation

    For example, a Geo Thermal heat pump ( SEER ratings into the high 20's ) will be much lower cost and much faster return on investment than PV will ever be

    With Gas heat/Hot Water ... you should be much less in energy usage ... so some digging and more information would help in finding out where the energy is going
  • LucMan
    LucMan Solar Expert Posts: 223 ✭✭✭
    Re: One Inverter or Two for different Azimuth

    www.extension.purdue.edu/renewable-energy/docs/Heating-Fuel-Comparison-Calculator.xls -
    This calculator will help everyone to determine the energy savings for different efficiency equipment and fuels.
    Enter in your energy rates & change the efficiency rating and you can calculate your energy savings.
    Often the upgrade does not justify the savings.

    To add to some of the other suggestions, replacing your washer with one of the new front loaders will cut down on your drier energy use. Last year after replacing our 26 yr old top loader with a front loader our LP useage dropped from 400+ gals. per yr to under 200gals. Wish we had done it sooner!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: One Inverter or Two for different Azimuth

    Here is an older thread discussing high speed spin washers, driers, and extractors.

    If you do a lot of wash and dry, and the washer is an older model with "slow" speed spin, getting a little extractor (high speed spin drier--link was in above thread--don't know anything about the vendor or website) may be worth the extra step.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: One Inverter or Two for different Azimuth

    Have you verified that you have R40 in the ceiling everywhere? thats 16" deep loose fiberglass

    That was the spec for the home. I do need to personally verify that. I've been in the attic several times, did not measure the depth of the insulation but it looks pretty close.


    HP for the pool pump is 1hp 7.8-7.4 amps@230volts. So running the pool pump
    (4 ) hrs a day would come to around 200+kwhs a month, right??

    No heater for the pool of any kind.


    No yard lights, have coach lights which are on a photo cell and motion activated.

    Electronic air cleaner is in line with the duct work and is switched on all the time, it does have it's own switch so I can turn it off. There is no requirement for the blower motor to be running if the air cleaner is on.

    I need to get the kill-A-Watt and clamp meter and do the Sherlock Holmes routine.

    Thank You Everyone

    Charlie
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: One Inverter or Two for different Azimuth
    Oil Can wrote: »
    HP for the pool pump is 1hp 7.8-7.4 amps@230volts. So running the pool pump (4 ) hrs a day would come to around 200+kwhs a month, right??

    Charlie--Maybe, maybe not... (I always like that answer. :p )

    7.4 amps * 230 VAC * 4 hrs per day * 30 days * 1k/1,000 = 204 kVAh per month...

    The issue is that for AC power, Volt*Amp*Hours is not Watt*Hours...

    It has to do with the phase relationship between the voltage and the current... What the power company charges a home is not the kVAhr, but kWHrs (this is a good thing).

    One way of writing the formula between VA and Watts is to use Power Factor, which is the Cosine of the angle between voltage and current:

    VA*PF=Watts

    For a resistance heater or a filament light bulb--the angle between Voltage and Current is Zero Degrees... Cos (0) = 1.00 (one). So, measuring the voltage and current with a simple meter will give accurate results.

    VA*1.00=Watts

    For motors, they are "inductive" which means that as the voltage rises, the the current will "lag" the voltage and start up a bit later. When all is said and done, depending on how far the motor current is "out of phase" with the voltage, there will be some sort of conversion (Power Factor) between VA and Watts.

    For an electric motor the Power Factor may be as low as 0.6 PF. So, now the above equation becomes:

    kVAhr * PF = 204 kVAhr * 0.6 = 122.4 kWhrs

    Now--from here I cannot tell the Power Factor of your pump motor... If it was 120 VAC--the Kill-A-Watt meter would be a great way to measure the PV and the VA vs Watt reading for the motor.

    It is possible to design the motor / capacitor set so that it runs near a "unity" power factor (>0.95)--but without test equipment (more expensive Fluke DVM or other)--it is not something that is easy to measure cheaply.

    I believe that a T.E.D. will give you the Watt (and not the VA) and kWhr charges correctly (as will the Kill-A-Watt meter)--but if you go around with a clamp AC Current Meter checking your loads--you may end up with some sort of missing PF correction factor that will have you scratching your head over how you think you should be paying 204 kWhrs per month, but can only find 122 kWhrs on your bill.

    You said you have a "smart" meter... My "less dumb" electronic meter can give me all of that information kW, kWh, VA, PF, etc. if I hold a magnet on the side of the meter for one second... Is there something similar you can do with your meter (either directly or through the PG&E website)?

    One thing I have done in the past--buy or pick up for scrap an old utility kWhr meter and socket--wire in some heavy electric cordage and you can splice it into your loads for a week/month to measure their individual usage. Just read the meter when you connect it up, and a week/month later at the same time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mradtke
    mradtke Solar Expert Posts: 53 ✭✭✭✭
    Re: One Inverter or Two for different Azimuth

    Charlie,

    You have been given an incredible amount of information by people who know about these things, but I have one small thing to add. There are some inverters available that have dual MPP tracking inputs. I don't know about the brands that might be available since my inverter research was limited to my specific arrays that were already installed. One advantage of a single, dual input inverter is less clutter in the installation. Power-One is the manufacturer that I chose, but it is a "transformerless" inverter which trades a slightly higher efficiency for a more difficult array installation (electrical code). You can see my review at http://forum.solar-electric.com/showthread.php?t=4559

    Mike
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: One Inverter or Two for different Azimuth

    Bill, that's likely the name plate rating and yes for a pool pump that's right for a "Energy Efficient" 1HP pool pump and your 200kwh number is correct .. it's likely much more as in the summer you need 6-8 hours run time for a clean pool

    pool pumps are really inefficient, less than 50% is typical for 1 HP motor. there are a couple of options

    pentairpool makes just about all the pumps out there

    http://www.pentairpool.com/products/products2.php?s=43

    Seem to match your name plate:

    http://www.pentairpool.com/products/products3.php?id=41 is a 1HP 7.6 amp unit

    Bump down to a reasonable HP ( 1/2 HP ) and save 1/3 the energy according to the data sheets, still huge flow, if you look at the data sheets, your probably getting 120 gpm or more with 1HP , even the smallest pump with low head gets better than 60 gpm with a 13K gallon pool that 100% exchange every 3 hours

    A neat new pump out, is the variable speed models ... I found one here on sale I'm considering getting

    http://www.poolsonly.com/sta-rite-intellipro-variable-speed-pump-vs3050-p6e6y4h-209l/prod_756.html

    Whats nice about this, is you can run at low speed most of the time, if you need to run the pool vac, then press a button for more flow. According to this calculator
    http://www.pentairpool.com/pool_pump_calc/index.htm

    I could save about 300 year minimum using this Hi-tech pump over the 3/4HP I have now