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Questions about Solar

Discussion in 'Charging Standards and Infrastructure' started by nleggatt, Feb 24, 2013.

  1. nleggatt

    nleggatt Member

    Joined:
    Dec 7, 2011
    Messages:
    389
    Location:
    Abbotsford, BC
    Hello everyone, seems like since getting my car I have more and more reasons to post!

    I'm trying to learn a bit more about solar systems and the lingo that goes with them. Currently I'm using 50-100 or so kWh of power a day on electricity. I would like to get that down to 30-60 a day and so am trying to figure out how many solar panels I would need to lower my over all power usage. The car draws 60kWh over a period of 5-6 hours while charging (I don't need to provide a steady 60 kWh but figure if I just lower my hourly usage through-out the day then over the day it would effectively = 30-60kWh therefore making the car almost free). So short of it is, Curious if I can just get a simple solar system, plug it into my 120v plug in my house, and have it supplement my hourly usage so that over all it's lower, hopefully combining over the day to be half or equal of my car use.

    So my confusion lays on when I'm reading about solar panels and it says, 250W solar panel, does that mean it provides 250W (.250kW/hour?) so over the course of a day (8 avg hours of sun) it would be app 2kWh of my power mentioned above? or is .250 kW steady stream and then how do you calculate how much it impacts your hourly power usage??? sooo confused.

    Anyways, just trying to get the usage down.
     
  2. Sparky

    Sparky Member

    Joined:
    Aug 13, 2012
    Messages:
    211
    Location:
    Glendale,CA
    According to the PVWatts calculator

    http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/International/inputv1_intl.cgi?siteid=24288

    (Output below)

    For Abbotsford, an optimally arranged 4 kW (DC) set of panels (so, 16 of your 250W panels) will yield about 10 kWh per day average.
    So, if you want to offset an average of 30 kWh per day, you'll need a 12kW system.
    BTW, you're not to going to be plugging this kind of juice into any 120V outlet. Getting an estimate of the work from a local solar contractor for your site would be prudent. There may be other issues.
    I have no idea if this is cost effective for your location (cheap hydro power may trump cost of solar).
    Hope this helps.

    Station Identification
    City: Abbotsford
    Country/Province: BC
    Latitude: 49.03° N
    Longitude: 122.37° W
    Elevation: 54 m
    Weather Data: CWEC
    PV System Specifications
    DC Rating: 4.00 kW
    DC to AC Derate Factor: 0.770
    AC Rating: 3.08 kW
    Array Type: Fixed Tilt
    Array Tilt: 49.0°
    Array Azimuth: 180.0°
    Energy Specifications
    Energy Cost: 0.0862 dollars CAN/kWh
    Results
    Average Solar Radiation per day: kWh/m2 = 3.64
    Energy per Year 3724 kWh
     
  3. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Location:
    Texas
    That's about 10,500 Model S miles per year (assumes 350 Wh/mi).
     
  4. montgom626

    montgom626 Active Member

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    Location:
    USA
    Reduce usage is the most rational and cost effective approach. Get an energy. Solar is not the first choice.
     
  5. nleggatt

    nleggatt Member

    Joined:
    Dec 7, 2011
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    Location:
    Abbotsford, BC
    Thanks everyone.

    Here's some more of my crazy logic. When I look at my usage graph for the day, I see I very rarely go above a 1kWh (ie, hourly chart shows mostly 0.7 kWh). SO! Couldn't I just get a 1kWh panel, connect it to my house (however) and then even out all of my low demand times during the day? So the house on "stand-by" isn't costing me anything? Sure, its only like $0.10/hour, BUT, $over the course of a 8 hour day, that's $0.80 /day x 60 (billing period) = almost $50 off my util bill. The panel might cost what, $500?

    Am I missing something?
     
  6. montgom626

    montgom626 Active Member

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    Location:
    USA
    Not at all. Like I mentioned before, reduce usage before you go solar.
     
  7. astrotoy

    astrotoy Member

    Joined:
    Jan 24, 2013
    Messages:
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    Location:
    SF Bay Area
    I have solar in my home. Remember, the panel cost is only part of the cost. You need to have it installed and buy an inverter to get you to match your grid. I have a 42 panel system (pretty big) that I bought in 2009 from Solar City (before I heard of Tesla). It has produced slightly over 10,000 kWh per year for the past 3 years (I am in the SF Bay area with a southwest facing roof and no obstructions - pretty close ideal). Back then, including the tax credits, I think I paid in the low 30's, or about $750 per panel installed and including two inverters. TOU pricing works well for me, since I generate electricity at the peak rates and use the Tesla charging at the lowest rates.
     
  8. richkae

    richkae VIN587

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    I put solar on my roof about two years ago. I dont have a lot of south facing roof so I could only fit 3.8kW of panels on the roof. ( That's rated DC, I really get about 3.5 kW max output on a perfect day at peak time which is very close to noon )
    It has produced a total of 6957 kWh, about 9.5 kWh per day. The Seattle area has historically averaged about 3.57 sun hours per day ( Solar Insolation - Sun Hours Per Day ) but the last 2 years have been below average.
    The best summer day I have ever had, it produced 24 kWh, unfortunately Seattle summers are short and frequently cloudy.
    When your panels are illuminated via a shallow sun angle, they make much less energy ( energy output is a function of the solar angle ), so the early morning and late evening do almost nothing unless you have active solar tracking.

    I actually reduced my energy consumption from the utility more with conservation. Every bulb ( but 3 I can not easily reach ) in my house is now an LED or a CFL ( I am actually now phasing out the CFLs in favor of LEDs ). I had the attic and crawlspace insulation improved, and all my HVAC ductwork sealed up ( testing showed I was wasting energy heating and cooling my crawlspace with leaky ducts ). I put key electronics behind power bars with accessible switches and turn the whole mess off with one switch.
    All of that reduced my energy consumption more than the solar panels did - and more than the Roadster consumed.
    Of course now we have a Model S and the Roadster, and the Model S averages more than 2x the kWh consumption than the Roadster does. ( The Model S gets driven more )

    8kWh from solar will only eliminate your base load if your base load is 0.33 kW because you've got 24 hours in the day ( most of it "darkness" ). As well as thinking about solar, you should look into reducing your base loads.
    To put it another way: Seattle only averages 3.57 hours of sun per day and 3.57/24 is about 1/7 so energy I save from the base load is 7 times more effective than additional solar.
     
  9. nleggatt

    nleggatt Member

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    Location:
    Abbotsford, BC
    Thanks for the detailed response. We are taking steps to reduce our usage:

    1. cancelled cable for the spring and summer months as we will be spending more time outside
    2. started replacing all the lights with CFL and LED
    3. put bathroom fans on timers
    4. put closet lights on motion sensors
    5. sealing some heat loss areas in the house (doors, and a fireplace vent that isn't sealed correctly)
    6. unplugging my 2 computers and printer when not in use
    7. trying to do laundry once/twice a week rather than daily

    We have an electric heat pump with a gas furnace, we we've changed the schedule on that to just keep the house at a steady temp. rather than lowering it at night (takes more energy in the morning to get the house back up to the daily temp - that's my theory anyways (15-18 degrees at night to 21-22 during the day).

    Not sure what else I can do.
     
  10. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    Thermostats and Control Systems | Department of Energy

    "A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. In fact, as soon as your house drops below its normal temperature, it will lose energy to the surrounding environment more slowly. The lower the interior temperature, the slower the heat loss. So the longer your house remains at the lower temperature, the more energy you save, because your house has lost less energy than it would have at the higher temperature. The same concept applies to raising your thermostat setting in the summer -- a higher interior temperature will slow the flow of heat into your house, saving energy on air conditioning."
     

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