Peter Brenner: Help before I buy system

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  • BB.BB. Super Moderators, Administrators Posts: 29,751 admin
    Re: Peter Brenner: Help before I buy system

    Solar panels are pretty impressive from a longevity point of view--25-40 years of power without any maintenance (other than a quick washing--if you want). Price around $10 per watt a decade ago--now better panels are probably in the $2.50 per watt or less.

    A 6kW/12kW surge Hybrid inverter for $3,400--that is not bad either.

    So, just to pick some numbers for a back of the envelope calculation (I like to do this for a sanity check). Using PV Watts, Tulsa OK, 10kW of solar panels, 0.52 derating (off-grid, battery, inverter, relatively conservative assumptions):
    "Station Identification"
    "City:","Tulsa"
    "State:","Oklahoma"
    "Lat (deg N):", 36.20
    "Long (deg W):", 95.90
    "Elev (m): ", 206
    "PV System Specifications"
    "DC Rating:"," 10.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 5.2 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 36.2"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.7 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.01, 643, 49.51
    2, 4.46, 627, 48.28
    3, 5.33, 808, 62.22
    4, 5.88, 848, 65.30
    5, 5.61, 804, 61.91
    6, 5.77, 776, 59.75
    7, 6.06, 830, 63.91
    8, 5.95, 823, 63.37
    9, 4.99, 688, 52.98
    10, 5.41, 808, 62.22
    11, 4.11, 605, 46.59
    12, 3.70, 580, 44.66
    "Year", 5.11, 8841, 680.76
    Assume $5,000 for electronics, $2.50 a watt for 10kW of panels, $1,000 for used batteries every 5 years. Over 20 year "life of system":
    • ($5,000+$25,000+4*$1,000) / (20 years * 8,841 kWhrs per year) = $0.19 per kWhr
    Not a bad price--"free batteries" do reduce the costs. Note, the above assumes you use 100% of your power (only true for Grid Tied systems). Also, the inverter would probably need replacement after 15 years +/-. Does not assume genset use.

    Looking at an efficient gasoline genset (efficient at less than 50% loading)... The Honda uses 1.1 gallons over 15 hours to generate 400 watts. Assume $2.50 per gallon (cheaper than $3.00+ per gallon in California):
    • 15 hours * 0.4 kW / 1.1 gallons of gas = 5.45 kWH / galllon
    • $2.50 per gallon * 1/5.45 kWhrs per gallon = $0.48 per kWhr (generator)
    Add the cost of generator+maintenance will drive the kWH price higher. Running the genset to charge battery bank--more losses. Run genset at less than 50% or so of capacity, higher fuel flow, higher costs...

    You could choose a larger genset, possibly diesel, and get quite a bit better kWhrs per gallon--but larger gensets mean larger fuel flows and higher minimum load requirements.

    If this was a grid tied system, the government will "give you" a 30% Federal Tax Credit for the solar system, reducing its costs a bit.

    Depending on what you are looking for (and how much cash you can justify)--the Solar seems to have a significant long term cost savings over a genset--if you are preparing for an off-grid world.

    Note that the above calculations are pretty much the minimum cost for self generated electricity. Personally, I would plan on a cost cushion of 2x to allow for unplanned failures, future cost increases, less than 100% usage of power, etc...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Peter BrennerPeter Brenner Registered Users Posts: 14
    Re: Peter Brenner: Help before I buy system

    Hello Tony,

    You wrote:

    "Why would you buy Harbour Freight Panels, when you can get name brand panels from reputable solar retailers (Including our site sponsor) for under $2/watt?"

    My first guess is Harbor Freight Tools because I really didn't know much about the "name brand" panels except the high prices. About fifteen years ago, I was really interested in solar power panels but the high costs eventually turned me off.

    If the prices of name brand panels have fallen to fairly reasonable levels, then I must reconsider them. I hadn't done much homework for solar panels, yet. This forum is inspiring me to look towards solar panels again.

    You wrote:

    "PS My guess is that 3 HF panels you mentions are 3-15 watt panels for at total of 45 name plate. (the reality with these panels is a net of maybe 30 watts) so $200/30= $6.66/watt for a no name, POS panel."

    I can't deny the logic of your explanation. Thank you.
  • Peter BrennerPeter Brenner Registered Users Posts: 14
    Re: Peter Brenner: Help before I buy system

    Bill,

    Thank you for the explanation. It looks like I should reconsider solar power panels as part of my off-grid system. The high prices of solar panels turned me off several years ago but you and Tony are demonstrating that has changed.
  • BB.BB. Super Moderators, Administrators Posts: 29,751 admin
    Re: Peter Brenner: Help before I buy system

    Solar still is not cheap and easy... But it is getting a lot better. :D

    It still requires some backup capital... Who knows what stuff will look like in ten years--but, recent history has shown that any failed inverter/charge controller that is over 10 years old pretty much needs replacing rather than repairs (electronics are moving so fast that components are just not available for many repairs on older systems).

    -Bill

    PS: I should ad that conservation and efficiency improvements for appliances, Air Conditioning, and computers in the last 10-20 years has also made off-grid solar much more practical too--while keeping a "modern" life style.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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