Is There a Right answer?

SpokeSpoke Registered Users Posts: 6
Hello All,

I live in the Phoenix Arizona area and have a 1950,s style ranch house with a full South facing roof unshaded. My neighbor who lives in a comparable house just installed solar and now I am bitten by the bug. I have additional attic insulation new thermal pane high efficiency windows . A year ago we installed a new 3 phase ac unit., not a super high seer, 3 phase don't have the really high ratings. I know there is always one more thing I could do for efficiency but at this point I would like install solar. My furnace , water heater and clothes dryer are gas and I don't want to change them.

I have a proposal to install a 5.145 system ( 50% of my usage) the price is good at about $4.40 a watt. the plan is for 21 Suntech Pluto M245 panels and using Enphase M215 micro inverters. ( I kind of like the idea of micro inverters)

Since I have a broad expanse of unshaded roof should I increase the number of panels, is there a point of diminishing returns? Is more better?

Ideally I would like to produce 60% to 75% of my electric usage.

One last question I would like to install an American made product and was looking at the Solar World 240, how much more should I expect to pay to use Solar world I was guessing at $50 to $75 more per panel.

Thanks for any help

Comments

  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: Is There a Right answer?

    I have a comment. You mention that you know there is always more conservation you can do, and yet you reject two of the simplest out of hand. Hot water recapture heat pump sytem that recaptures heat from the AC while providing " free"hot water while making your AC run more efficiently.

    The second is that you get much more bang for your buck by installing solar hot water rather than PV. Now granted you may have expensive power and cheap gas, but if your goal is to reduce over all energy use solar hot water make great sense,especially in AZ.

    As for y our question, you have to pencil out the numbers and see what makes sense. Depending on tax credits, utility rebates, TOU/net metering schemes, each situation is different, and it often comes down to what you are comfortable spending.

    Good luck, welcome to the forum and keep in touch. There are some very smart folks here who nave forgotten more about PV than most of us will ever know.

    Tony
  • SpokeSpoke Registered Users Posts: 6
    Re: Is There a Right answer?

    Thanks,

    To modify our water heater for solar would involve significant plumbing having to relocate it. I just don't want to change that around. My problem is that we have a new AC unit and I would be stuck shelling out thousands of dollars in additional expenses changing out a new AC unit. Had I thought this out a couple of years ago I could have planned better, but I am stuck with the situation as it is.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Is There a Right answer?

    spoke,
    welcome aboard. you said,
    "5.145 system ( 50% of my usage)"

    now we don't know what 5.145 is. is that kwh? assuming it is kwh and you said it is half of your usage then your usage is 10.290kwh. you would not need a system as large as 5.14kw to produce 10.290kwh in arizona and in fact most places. it won't be less than 3.9hrs of full sun anywhere in az using your latitude for aiming. as such,
    10.29kwh/3.9hrs=2639w divide that by .77 to get a good stc rating of watts for pvs and is 3427w in pv. 14 pvs will be just under that, but should work just fine and being you intend to put enphase inverters on them you can always add more later on if your loads go up.

    that 3.9hrs of full sun at latitude is the worst case seen in all of az by this site: http://rredc.nrel.gov/solar/pubs/redbook/PDFs/AZ.PDF and it could be that you may not need as much in pv as i calculated and it does depend on where you are in az for that. summer may have more sun time, but with it comes more heat that will degrade output some, but even still you will reap quite a bit more over the worst case scenario most of the time.

    our forum host sells them currently at $550 per module. it changes periodically so check on it. http://www.solar-electric.com/hiposopa.html
  • SpokeSpoke Registered Users Posts: 6
    Re: Is There a Right answer?

    Thanks Neil,

    My average KWH for last year was 13543, (13543/12=1128 monthly average) the highest month was August at 2075 KWH and the lowest April at 601KWH. Over the last ten years my average monthly usage was 1210KWH. That 1210 figure was before I upgraded my windows and AC unit. These are the numbers I am working with.

    It sure is hot and dusty here in Arizona right now!
  • cptdondocptdondo Solar Expert Posts: 76 ✭✭✭
    Re: Is There a Right answer?
    Spoke wrote: »
    Thanks,

    To modify our water heater for solar would involve significant plumbing having to relocate it.

    My solar water heater is plumbed as a preheater to the regular water tank. Very little plumbing change required. You need room for the solar tank and the associated piping but the return is pretty good. And if you run out of solar hot water you still have the original tank to provide hot water.
  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: Is There a Right answer?

    Just an FYI

    http://www.air-conditioning-and-refrigeration-guide.com/heat-recovery-air-conditioning.html

    http://www.trevormartin.com/hru.asp


    Solar guppy is the resident expert on hot water heat recovery A/C.

    I believe there are add on units for some systems. Dropping the A/C draw makes the solar pencil out faster, for a comparatively small investment. As we often say on this forum, every dollar of conservation will yield about $10 in PV savings.

    Tony
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: Is There a Right answer?

    "and using Enphase M215 micro inverters. ( I kind of like the idea of micro inverters)"

    if you have a full sunny roof a central inverter is typically what is used since they are about half the price you might save around 50 cents a watt. Enphase is realtively new and hasn't been tested for as long as their warranty is.

    As far as the water heater is concerned others are right, but honestly, most people only need hot water in the morning for a shower. You can get a gas timer for $110 and set it to run for an hour in the morning.
    http://gaswaterheatertimer.com/index.php?page=purchase

    I turn my hot water off for half the year, and don't really miss it.

    That will decrease your hot water bill tremendously and not be that much of a hassle or expense. Solar hot water systems professionally installed are pretty expensive $3000 to $10,000 depending on where you live. Probably closer to $3000 in AZ? is my guess.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Is There a Right answer?
    Spoke wrote: »
    Hello All,

    I live in the Phoenix Arizona area and have a 1950,s style ranch house with a full South facing roof unshaded. My neighbor who lives in a comparable house just installed solar and now I am bitten by the bug. I have additional attic insulation new thermal pane high efficiency windows . A year ago we installed a new 3 phase ac unit., not a super high seer, 3 phase don't have the really high ratings. I know there is always one more thing I could do for efficiency but at this point I would like install solar. My furnace , water heater and clothes dryer are gas and I don't want to change them.

    I have a proposal to install a 5.145 system ( 50% of my usage) the price is good at about $4.40 a watt. the plan is for 21 Suntech Pluto M245 panels and using Enphase M215 micro inverters. ( I kind of like the idea of micro inverters)

    Since I have a broad expanse of unshaded roof should I increase the number of panels, is there a point of diminishing returns? Is more better?

    Ideally I would like to produce 60% to 75% of my electric usage.

    One last question I would like to install an American made product and was looking at the Solar World 240, how much more should I expect to pay to use Solar world I was guessing at $50 to $75 more per panel.

    Thanks for any help
    Microinverters are great if you have shading issues, or if module level monitoring is important to you, or if expandability is a must-do, but they can be significantly more expensive if your system is larger than about 3kW.

    In increasing your system size there is a point of diminishing returns where your production exceeds your usage, but whether that is an instantaneous value, over a month's time, or over a year depends on your utility's net metering policy.
  • solar_davesolar_dave Solar Expert Posts: 2,346 ✭✭✭✭
    Re: Is There a Right answer?
    Spoke wrote: »
    Thanks Neil,

    My average KWH for last year was 13543, (13543/12=1128 monthly average) the highest month was August at 2075 KWH and the lowest April at 601KWH. Over the last ten years my average monthly usage was 1210KWH. That 1210 figure was before I upgraded my windows and AC unit. These are the numbers I am working with.

    It sure is hot and dusty here in Arizona right now!

    OK so are you an APS or SRP customer? What rate plan are you on or do you plan to use?

    Both questions make a big difference on your planning for a solar system. The E-6 rate plus you purchase rate make a difference on how to account for the watts generated. Early in the year you can build a kWh bank to use against you summer usage, but there is catch. If you are on TOU plans with APS the on peak and off peak banks are separate. So consider that in you calculations.

    You can poke around here and see my system in the PHX area.
    PV watts shows this for a 5.125Kw system:
    
    "Station Identification"
    "City:","Phoenix"
    "State:","Arizona"
    "Lat (deg N):", 33.43
    "Long (deg W):", 112.02
    "Elev (m): ", 339
    "PV System Specifications"
    "DC Rating:"," 5.1 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 3.9 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 22.5"
    "Array Azimuth:","180.0"
    
    "Energy Specifications"
    "Cost of Electricity:"," 8.5 cents/kWh"
    
    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.63, 527, 44.80
    2, 5.66, 582, 49.47
    3, 6.45, 709, 60.27
    4, 7.67, 798, 67.83
    5, 7.98, 836, 71.06
    6, 7.85, 769, 65.36
    7, 7.58, 772, 65.62
    8, 7.40, 760, 64.60
    9, 7.06, 705, 59.93
    10, 6.37, 685, 58.23
    11, 5.11, 549, 46.66
    12, 4.37, 503, 42.76
    "Year", 6.51, 8197, 696.75
    
  • SpokeSpoke Registered Users Posts: 6
    Re: Is There a Right answer?

    Hi Ted and all,

    I am a SRP customer and as of right now I am not on any plan. Just usage. Any advice on what plan would be best to maximize savings would be appreciated.

    I know that micro inverters are probably not cost effective on a large unshaded array, but my understanding is that with micro inverters I do not need a DC disconnect and I think the overall wiring would be simpler and would yield a neater look on the building. I will discuss install issues with the contractor and decide what type of inverter at that point.

    My first install estimate shows 21 245 watt panels. I am thinking of having 25 installed this produces more wattage (6125?) but does not lead me into the situation where I am sending a significant amount back into the grid. With time and greater understanding I could add additional panels. ( another advantage of the micro inverter)

    I appreciate all this help
  • SpokeSpoke Registered Users Posts: 6
    Re: Is There a Right answer?

    Whoops

    Sorry Solar Dave I assumed that your name was TED. Though TED is a nice name.
  • solar_davesolar_dave Solar Expert Posts: 2,346 ✭✭✭✭
    Re: Is There a Right answer?
    Spoke wrote: »
    Hi Ted and all,

    I am a SRP customer and as of right now I am not on any plan. Just usage. Any advice on what plan would be best to maximize savings would be appreciated.

    I know that micro inverters are probably not cost effective on a large unshaded array, but my understanding is that with micro inverters I do not need a DC disconnect and I think the overall wiring would be simpler and would yield a neater look on the building. I will discuss install issues with the contractor and decide what type of inverter at that point.

    My first install estimate shows 21 245 watt panels. I am thinking of having 25 installed this produces more wattage (6125?) but does not lead me into the situation where I am sending a significant amount back into the grid. With time and greater understanding I could add additional panels. ( another advantage of the micro inverter)

    I appreciate all this help

    Sorry I can only speak to how APS does it, but a good place to start is here:
    http://www.srpnet.com/menu/paybillprice.aspx

    I would call SRP and talk about how they do net metering, what the rebate structure looks like, what the other solar customers do ...
  • solar_davesolar_dave Solar Expert Posts: 2,346 ✭✭✭✭
    Re: Is There a Right answer?

    First what is your goal and motivations? Net zero? reduce the bill? Most green person on the block?

    Second find a plan that improves your situation now without solar, then start your calculations. For instance if you go to TOU and can load shift to off peak, you will probably save some money now, Then look at how much of the on peak you can offset given a XXX amount of solar. Now you have a baseline for calculating you return over time.

    You might be surprised at how much of a reduction you can get in your bill with some minimal solar adds. As others have said, if you have electric heating/hot water, get off of that. Solar PV to heat water is an ugly uses of lots of watts. Solar hot water does lend it self to DIY projects.
  • rollandelliottrollandelliott Solar Expert Posts: 834 ✭✭
    Re: Is There a Right answer?

    "I do not need a DC disconnect and I think the overall wiring would be simpler and would yield a neater look on the building."

    The wires are hidden under the panels whether you use central or micro inverters hence they look about the same.

    The main benefit in using micro inverters besides shading is that it does simplify the wiring and system design to the point that any DIY handy person can install the panels pretty easily. You'd be looking at around $2.50/watt for the materials. Plus around .25/watt for the roofing rack structure.

    If you don't know anything about electricity you can hire an electrician to do the final wiring for $1000 to $2500 and save quite a bit over an installer doing it.

    There are many people on this board that have put up their own systems and saved $$$ by doing it themselves.

    I'd wait until november and see what kind of pricing enecsys micro inverters are going for. Their wiring system is IMHO better than enphase and pricing is supposed to be a lot better.
    http://forum.solar-electric.com/showthread.php?t=12408

    discusses these new micro inverters a little bit.
  • SpokeSpoke Registered Users Posts: 6
    Re: Is There a Right answer?

    My goal is just to reduce my bill and reduce the net effect of my energy use. We have gas for hot water and heat and clothes drying. Our gas bill are never that significant. I will research the plans and try to figure out what would be best.
  • FrxddyFrxddy Solar Expert Posts: 113 ✭✭✭✭
    Re: Is There a Right answer?

    If you plan on hiring the job out, the $4.40 watt seems like a fair price. Verify the installer is legit, pull the trigger and slam that bad boy system in. Then in a year you will know if more would be better, and also you'll have a good grip on how much more you'd like.

    <edit> PS In AZ you will make approx twice the power per watt of panel as I do in Maine.
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