Groundmount solar grid-tie system

System
System Posts: 2,511 admin
I've looked into solar a few times over the years while we lived in California, and ended up putting it off due to cost. Now I'm living in Texas (Austin, actually) and have a large, side-yard that is unused and pretty much gets no shade at all.

It seems perfect for a ground-mounted solar system that swivels to track the sun. Without needing a roofer to do the installation, I can do most of the installation work myself, including running the wires, and then hire an electrician to do the final grid-tie hookup.

What's is a good resource to get a ballpark estimate on how much generation capacity we need, how much it will cost, and what rebates are available? Looking at our power bills, we used around 21,000 kWh's last year. And I know if I install myself, the Texas rebates are unavailable to me.

Comments

  • System2
    System2 Posts: 6,290 admin
    Re: Groundmount solar grid-tie system

    I wanted to add a little more info. I used one of the simple calculators on the web and got these results for 100% electricity offset. Obviously I can start small and add on over time, but this is what would be needed for 100% electricity offset:
    System specifications for: Round Rock, TX
    Utility: TXU Energy Retail Co LP

    Solar Radiance: 5.26 kWh/sq m/day
    Avg. Monthly Usage: 1,750 kWh/month
    System Size: 13.80 kW
    Roof Size: 1,379 sq ft
    Estimated Cost: $96,574.34 (based on $7/watt)
    Post Incentive Cost: $50,382.04

    Now, this assumes a fixed, roof-mounted system. How can I adjust this for a swivel-mounted system (if that's the right term)? Also, I'm assuming $7/watt is for having someone install it. What is a good estimate to use if I'm doing the work myself?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Groundmount solar grid-tie system

    PV Watts website does a pretty quick and easy job of estimating solar output... Assuming you are in the Houston/Austin area (I chose Austin), use 1 kW of panel, fixed mount, default efficiency, etc.:
    "Station Identification"
    "City:","Austin"
    "State:","Texas"
    "Lat (deg N):", 30.30
    "Long (deg W):", 97.70
    "Elev (m): ", 189
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 0.8 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 30.3"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 9.7 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.32, 99, 9.60
    2, 4.96, 101, 9.80
    3, 5.47, 122, 11.83
    4, 5.52, 116, 11.25
    5, 5.54, 118, 11.45
    6, 5.93, 121, 11.74
    7, 6.21, 129, 12.51
    8, 6.22, 129, 12.51
    9, 5.77, 119, 11.54
    10, 5.65, 121, 11.74
    11, 4.60, 98, 9.51
    12, 3.96, 90, 8.73
    "Year", 5.35, 1362, 132.11

    So, 1,362 kWHrs per year (average):
    • 21,000 kWH per year / 1,362 kWH per year per 1kW of panels = 15.4 kW of solar panels
    If you wanted to have a 2-axis tracked array, as above, we get 1,804 kWhr per year:
    • 21,000 kWH / 1,804 kWH per 1kW of panels = 11.64 kW of solar panels
    Note that trackers can be expensive and require their own maintenance. And solar panels are really cheap right now--so most folks just choose the larger array. You can play with an adjustable array (tilt higher for winter, lower for summer, etc.) by plugging in numbers into PV watts.

    Currently, it sounds like GT solar is around $6-$10 per Watt installed--in your area and with a ground mount, you may be able to get down towards the $6 per watt number (I am not in the solar biz--just a rough guess on my part). And you can get the 30% federal tax credit.

    So, before tax credits, you would be looking at ~$90,000 + for such a system.

    Now--our recommendations here tend to ask people to look at extreme conservation first--before installing solar. It is almost always cheaper to conserve a watt than to generate a watt.

    Lots of attic insulation, double pane windows, energy star appliances, CFL/Florescent lighting, new/more efficient A/C or heat pump, look at computers/network power usage (laptops typically use much less power than desktop computers), turn things off when not in use, etc...

    One of the nice things about reducing energy use inside your home--for areas that require A/C, you are not paying first for excessive electrical and then paying again to move that heat out of the home.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Groundmount solar grid-tie system

    Regarding DIY costs--You can start with our host:

    Northern Arizona Wind and Sun

    They also have same sample quotes too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: Groundmount solar grid-tie system

    That's very helpful. Thanks for all the great info!!

    So, I need somewhere between 11 and 16 kW of panels, and according to the quotes, DIY pricing would break down like so:
    2 kW - $8,602
    5 kW - $17,913
    7 kW - $26,028
    10 kW - $36,054

    I'd like to break it into manageable chunks, cost-wise, so I'm thinking about a 5kW starter system, which will hopefully end up around $10-12k post-rebates. And then I can build out more panels and inverters over time, adding on more 5 kW stages in parallel. Does that make sense, or is there a reason to wait and build it all out at once?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Groundmount solar grid-tie system

    From a cost point of view--I think that building out in stages of 3kW minimum is a good starting point (below that, the cost of equipment goes up, and you have major costs for permits and just getting stuff on site).

    I think that the rest depends on your bank balance and other personal issues.

    From my point of view--if you have conservation investments to make--do those first.

    And don't get yourself underwater for loans and such... Solar is not a "great" investment (expensive up front/long time frame for return on investment--and you probably live in a low power cost region). At this time, having a cash/liquid savings buffer will help you sleep better at night.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    Re: Groundmount solar grid-tie system

    SDGator, here are some additional comments. I'm in TX (Dallas) and thus may have similar weather patterns to what you have in Austin.

    My '09 kWh consumption was 29 kWh (no solar).

    I put in an 8.1 KW (DC) system in Feb. of this year - this size was simply based on the maximum number of panels that could fit on my roof.

    If you remain a TXU customer, you don't have Net Metering. In my case I pay 9.9 ¢/kWh (varies monthly), and TXU pays me a fixed 7.5 ¢ for what I export to the grid.

    If you instead are a Green Mountain or Kinetic customer, you do have a form of Net Metering, but you'll pay about 2 ¢ more. I'm not aware of other companies doing Net Metering besides these two.

    For my 8.1 KW (DC) system, I'm currently running at about 80% DC-to-AC efficiency (producing about 880 kWh/mo). I have multiple panel orientations per string, and some shading. You should be able to do better with a pole system.

    My electrical usage pattern allows me to use about 76% of what I produce. The other 24% (about 210 kWh/mo) gets exported onto the grid - just can't use it all doing daylight hours.

    For what I do use (about 670 kWh/mo), it's reducing my electric bill by about 36%. This reduction of course depends on consumption.

    Installed kWh rate here in Dallas is about $6/W at the moment. Utility rebates and tax incentives cut this in half, to about net $3/W. At the moment, though, in my area, Oncor's out of rebate money.

    Hope this helps.

    Best regards,

    Bill
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Groundmount solar grid-tie system

    Ground mounts are great for ease of installation and maintenance.

    Ground mounts also makes the panels relatively easy to quickly cart away. You may want to consider protection of your investment.