I have 700Watts worth of Solar Panels - What Can It Do For Me?

KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
edited January 11 in Solar Beginners Corner #1
Hello, I have 7, 100Watt 12v solar panels in storage that I've never used. I'm wondering it it's worth the time to install them and put them to use. Basically, I pay 11 cents / kWh plus an $8.00 "Customer Fee" per month in South Florida. I can install them and the controllers etc myself. Would a 700watt bank of Solar panels even make a difference? Would it be worthwhile to install and use these? Thanks

PS, my monthly electric bill is usually around $300
PEAK usage of 71 kWh/Day in August
Total Billed Usage: 2261 kWh
We feel our electric bill is high
1300SQ FT Residential home
2 occupants
No swimming pool
2.5 ton AC

Comments

  • softdownsoftdown Solar Expert Posts: 2,173 ✭✭✭✭
    S Florida usually enjoys cheap energy. A lot of numbers would have to be crunched to answer your question. In short, I doubt there is any economy to installing 700 watts for a $300/mt customer. I'd guess they might produce about $5/mt worth of energy - in S. Florida. Very rough guess. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
    edited January 11 #3
    Yikes, that wouldn't be worth it at all
    Thanks
  • softdownsoftdown Solar Expert Posts: 2,173 ✭✭✭✭
    I'm guessing it might take closer to 17,000 watts to produce $300/mt of electricity in S Florida. And you could not find a rougher guess.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
    edited January 11 #5
    I thought like this.....but I definitely could be wrong....
    700Watts x 8 hours = 5,600Watt hours per day (or 5.6 kWh / day) = 498kWh/month
    That would be almost 25% of my monthly usage or about $75.00 worth of power per month?
    Where did I go wrong?
  • BB.BB. Super Moderators, Administrators Posts: 28,997 admin
    Some quick math... Fixed array, grid tied (panels+GT inverter, no batteries):
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Miami
    Average Solar Insolation figures

    6Measured in kWh/m2/day onto a solar panel set at a 64° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    4.61
     
    5.25
     
    5.54
     
    5.88
     
    5.58
     
    4.90
     
    JulAugSepOctNovDec
    4.94
     
    4.86
     
    4.69
     
    4.96
     
    4.56
     
    4.43
     

    Let say ~5 hours a 2day average sun over a year:
    • 700 Watts * 0.77 GT system eff * 5.0 hours of sun per day = 2,695 WH per day = 2.695 kWH per day average
    • 2.695 kWH per day * 365 days per year * $0.11 per kWH = $108 per year
    Vs $3,600 yearly electric bill. Depending on local requirements--Bolting to hurricane proof roof or ground mounts, building permits, electric utility approval... I personally would suggest that you spend your time and money on insulation, conservation, looking at your HVAC system, etc.

    You could make this an off grid system for 700 Watt array emergency power:
    • 700 Watts * 0.52 off grid system eff * 5.0 hours of sun average = 1,820 WH per day
    And a battery bank:
    • 1,820 WH per day * 1/0.85 AC inverter eff * 2 days of storage * 1/0.50 max discharge * 1/24 volt battery bank = 357 AH @ 24 volt battery bank
    Use 8x 6 volt @ 200 AH "golf cart" batteries in 4 series * 2 parallel strings for a 24 volt @ 400 AH battery bank.

    The suggested array for such a battery bank at 5% to ~13% rate of charge (5% minimum, 10%+ rate of charge is better for battery bank life):
    • 400 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 753 Watt array minimum
    • 400 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,506 Watt array nominal
    • 400 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,958 Watt array "cost effective" maximum
    Unfortunately, you would need 8x 100 watt solar panels to charge a 24 volt battery bank and reach 5% minimum rate of charge. You could cut back on the battery bank size (1/2 number of batteries) and/or reconfigure to a 12 volt battery bank. (smaller bank, less backup/overnight storage).

    A solar power emergency backup system can be nice--But may be hard to justify (you still need to mount the solar panels). And golf cart batteries, whether used or not, probably have a useful life of 3-5 years in warm/hot location.

    Enough to run some LED lighting, laptop computer, cell phone charger, and possibly a small DC fan (if needed) for air circulation at night/sleeping.

    Not enough energy to (reliably) run a single refrigerator. A genset (natural gas or propane) would probably be more useful (and run much more of your loads). Gasoline or diesel could work too--But you run into fuel storage issues (nether keeps well past 1 year for gasoline, a few years for diesel).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
    edited January 11 #7
    Oh wow.  Ok, I figured in WAY too much efficiency
    Great
    so I can use these panels MAYBE for emergency power in case of an extended power outage for example.

    Changing course and looking into better insulation, more efficient appliances, new AC etc
  • KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
    So to cut my bill in half, I would need approximately 38kWh per day
    And to get 38kWh per day I would need approx 4.75 kW per hour
    And that would be 4750 Watts per hour
    So I would need about 20 of the 250Watt panels just to cut my bill in half?
  • KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
    edited January 11 #9
    I need to do some additional research into 24v panels
  • softdownsoftdown Solar Expert Posts: 2,173 ✭✭✭✭
    I pay for energy on two S. Florida homes. One utility brags about offering among the cheapest energy in the nation. That makes a huge difference of course. In LA, your energy bill would likely be over $1000/mt. Then panels make a lot of sense.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • BB.BB. Super Moderators, Administrators Posts: 28,997 admin
    edited January 12 #11
    • 38,000 WH per day * 1/0.77 GT system eff * 1/5 hours per day (rough average) = 9,870 Watt array (break even)
    You need to look at the rate plans from your utility. In California we went from simple flat rate pricing (same rate all day long, 365 days a year) to complicated rate plans that change pricing by time of day, season, and tiered energy usage--Use more power, higher $/kWH pricing).

    GT Solar in its initial offerings (10+ years ago), was a subside from Government and Customers to those installing GT solar systems. Done in the name of "Green Power".

    Today, much less in the way of government subsidies, and having all customers subsidize a few GT Solar customers makes no business sense.

    In the early days... I buy power at $0.18 per kWH and sell back power at $18 per kWH. Later, I sell power a afternoon peak (upwards of $0.30 per kWH retail pricing) and buy it back (again at retail) night and morning at $0.10 per kWH). Not bad (and in a sunny area, GT solar costs $0.10 to $0.15 per kWH or even less to install over the life of the system).

    Now... You buy your power at "retail" and sell the power at wholesale ($0.02 to $0.05 per kWH) and instead of a $5 per month connection fee, I pay $10 per month, and some utilities start looking at $48 to $96 per month connection fees. Some of these reduce the retail cost of power to the majority of utility customers (not taking from one group of customers to subsidize another group of customers).

    If you have an older home and never have worked on conservation before... You can probably reduce your energy usage by upwards of 50%.

    Getting a Kill-a-Watt meter to measure your 120 VAC plug-ini loads.

    And something like this to measure you whole house loads (and they now have the option to measure major circuits like HVAC, hot water, ec.):

    https://www.theenergydetective.com/

    You will be very surprised at where some of your money goes... For example comparing your microwave to a desktop computer:
    • Microwave: 1/3 hour per day (20 minutes per day) * 1.5 kWatt load = 0.5 kWH per day
    • Desktop Computer System: 24 hours per day (no standby) * 0.3 kW (300 Watt) = 7.2 kWH per day
    If you have an entertainment system, satellite system, digital video recorder, etc. that are on 24x7, they too can draw a lot of energy.

    The other issue with warm climates... All that energy you dump into the home (1-2 kWH per day per fridge/freezer, stove, computer, TV system, non-LED/CFL lighting, etc.)--That heat needs to be pulled out of the home by your HVAC system.

    Insulating your ceiling and A/C Ducts, sealing air leaks, shading south/west facing walls and windows, double pane windows (for many folks the double pane windows reduce outside noise quite a bit), etc...

    I live in a moderate climate (just south of San Francisco California)--But others here can help you too.

    If you have (for example) electric water heating--There are "heat pump" solutions that give you (nearly) free water heating (or reduce your water heating costs by 1/2 to 2/3).

    The neat thing about many of the conservation solutions, they don't cost you anything more in the future (no batteries to replace, solar system to maintain). Use a 10 Watt Chromebook for web surfing, and only turn on the 300 Watt desktop when needed, etc.

    At this point with something like 2,000 to 3,000 kWH per month energy usage--You are looking for "big wins" first. Don't drive your family nuts with unplugging their cell phone chargers or turning off every LED light in the house the moment they leave the room.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
    edited January 12 #12
    Thanks BB!
    Very helpful info.   I'll look into that whole house thing.  And You're right I think I could use some attic insulation.
    I had no idea how much the power companies had pulled back from their incentives.  Sounds like greed?
  • KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
    softdown said:
    I pay for energy on two S. Florida homes. One utility brags about offering among the cheapest energy in the nation. That makes a huge difference of course. In LA, your energy bill would likely be over $1000/mt. Then panels make a lot of sense.
    OK.  So Florida's power is a real bargain compared to California?  Didn't realize it would be such a difference.
  • BB.BB. Super Moderators, Administrators Posts: 28,997 admin
    It is not greed... It is fairness. "Rich" people put lots of solar on their home getting lots of tax subsidies and rate subsidies. "Poor" people in apartments and rental homes pay high rates and taxes--Unable to put up their own solar panels.

    Also, GT Solar is not a "controllable" power source (by the utility engineers). When Solar/Renewable Energy was less than 10% of utility generation, it was too small to matter. When >10%, it becomes a major issue that the utility operators have to play lots of games to keep the line voltage and frequency stable for their systems.

    And for the accountants, having customers buying and selling highly variable output power at retail prices does not make business sense. In California, I sell power to the utility at ~$0.30 during sunny summer afternoons. And buy power at $0.10 at nights/mornings.

    Utilities buy power wholesale at roughly $0.02 to $0.10 per kWH (for base load power)--Solar/RE power is not worth $0.30 per kWH to a utility accountant/engineer.

    News I had not heard--Turns out China has put the brakes on Solar/Wind/RE power subsidies early in 2018. RE projects have to complete with all other energy sources without subsidies now.

    https://wattsupwiththat.com/2019/01/11/china-says-no-to-wind-and-solar-tech-unless-it-can-compete-with-coal-on-price/

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stmoloudstmoloud Registered Users Posts: 101 ✭✭
    edited January 13 #15
    I can tell you I have a little more than this but... I live in a really small space, a converted bus probably around 3/4 the space of a typical US school bus I have seen in TV shows and movies. My computing power comes from a raspberry Pi, very frugal to run. I have a few led lights which help me get around at night. There is also a 12v pump which helps with the water.
    My biggest extravagance is a new Samsung 'digital inverter' fridge-freezer (269 kWh per year - but can be less if you disable the ice-maker).  
    Yes, It can be done but you do need to be ever vigilant about your power usage. And understand battery management. 
    I like it. It's a challenge. It's one of them things which makes me tick. 
    But, do the finances, I would be better off on the grid. But there are other reasons why you might want to be out of the grid and all the associated crap. 

    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
  • t00lst00ls Solar Expert Posts: 200 ✭✭✭
    1300 Sqft...$300 electric bill
    first thing to do is change some of your energy habits, before thinking about installing solar....otherwise you would wait a long time for a ROI
  • KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
    edited January 13 #17
    t00ls said:
    1300 Sqft...$300 electric bill
    first thing to do is change some of your energy habits, before thinking about installing solar....otherwise you would wait a long time for a ROI
    Thanks and you're probably correct.  I've already started.
    I have two computers in my office that run 24/7 and I did not have them ever sleeping or hibernating.
    So yesterday I changed the power settings to turn them both off after 1 hour of non use.
    Next, my attic insulation needs to be improved. it's been up there 25 years and is thinning and has become compacted.  I used my thermal imaging camera to see where heat was making it through on a very hot summer day. I found a ew places where there was basically no insulation and the inside walls were 107 degrees. I'll be adding 2 inches of insulation soon.
    The Outside AC unit was replaced separately from the inside air handler and I think that may be an energy hog so I'll be looking into getting a new matched, energy efficient set.
    These changes might net me more savings than trying to use solar.
    Thanks
  • KnowledgeSpongeKnowledgeSponge Solar Expert Posts: 173 ✭✭✭
    edited January 13 #18
    Bill,

    Per your description, with your 3.5kW setup, you might qualify as one of the "Rich" ones.
    You get paid for generating electricity during the day at .30 and only pay .10 at night....that is definitely an advantage over the poor who could really use the savings.

    RE: News from China....
    Are they no longer subsidizing RE projects or Solar panel Production? (or both) If they stop subsidizing SP production, wouldn't we see some big spikes in panel prices?
  • softdownsoftdown Solar Expert Posts: 2,173 ✭✭✭✭
    Desk top computers use roughly 300 watts when running. I'd see what happens with the computer changes and insulation before replacing the attic air handler. Why? I am a bit skeptical of the massive energy savings claims due to "newer technology". 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • BB.BB. Super Moderators, Administrators Posts: 28,997 admin
    edited January 13 #20

    “It's tough to make predictions, especially about the future.”

    ― Yogi Berra

    Who knows, may see a dip in the costs of solar/RE products as lots of factories/suppliers are looking for new customers to replace China's lost projects... Then many will fail due to lower demand and falling prices/proffits, and what is left will raise prices...

    I and family are doing OK... When government is throwing money around (solar subsidies), it seemed like a good idea to get in line. But I realized that this could not go on forever. I still think it was a very poor idea/use of money. It Solar/RE was a good idea, it would not have needed subsidies.

    Running ~600 Watts of computers is like leaving a 1,500 Watt room heater on 1/2 time. And you are paying for A/C to remove that heat (in hot weather). A Kill-a-Watt meter can tell you accurately what major plug-in appliances are costing your--And monitoring the whole house usage and/or A/C circuit will tell you how you are progressing.

    Computer circuits have been dramatically reducing energy usage on a "per transistor" basis. However, the amount of data and software has pushed for ever higher numbers of transistors per device. And, as a whole, the actual energy usage of computers has remained pretty flat or even increased over time.

    The first PC had an 8088 with approximately 10,000 transistors in the main processor... By 2011 high end "PC" processors were >>2 billion transistors. And today, >>20,000,000,000 (20 billion) transistors in high end processor:

    https://en.wikipedia.org/wiki/Transistor_count
    ~
    The 256 GByte memory has about (8 transistors per byte * 256 GBytes=) 20 ~2 Trillion transistors (2,000 Billion)...

    To me, it is just amazing how the integrated circuit (and related computer) industry has moved so fast with technologies.

    I have a couple Raspberry Pi B+ single board computers (about the size of a pack of cards). 4x 64 bit core 1.4 GHz, 1 GByte of on-board memory. And use a 32 GByte micro-SD card... Consuming ~2.5 Watts or so...

    Connect a keyboard and mouse (I use a wireless mouse keyboard) and a 4k TV... And it browses the web pretty well and can just barely play a 1,080P HD Youtube video without stuttering. $35 for the processor, $8 for the 32 GB micro SD card, $8 for a plastic case, and a USB power supply in the AC power strip. Plugged into the family TV. Running multi-user Linux (Raspbian--Running in 32 bit processor compatibility mode).

    https://www.adafruit.com/product/3775
    https://cdn-shop.adafruit.com/product-files/3775/Raspberry-Pi-Model-B-Plus-Product-Brief.pdf

    I am running one of the Raspberry Pi computers with (free) Pi-Hole software (actually, my 18 year old daughter's project)... A nice program that "kills" known advertising sites (software will run fine on a $5 Pi Zero too). You program your Router to point to the Pi-Hole computer (static IP address) and now computer on your network has most of the advertising blocked (PCs, MACs, cell phones connected over WIFI, Roku boxes, devices that "phone home" like Roku and smart TVs, etc.).

    https://pi-hole.net/

    A bit off thread--Just wanted folks to appreciate what a special time we live it. Nothing like it before, and probably nothing like it again.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,235 ✭✭✭✭✭
    ......I have two computers in my office that run 24/7 and I did not have them ever sleeping or hibernating.
    So yesterday I changed the power settings to turn them both off after 1 hour of non use......
    I like to use SLEEP settings at 15 min, if I'll be back to them often during the day, otherwise, HIBERNATE is a power off version that takes a little bit longer to wake from.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • NANOcontrolNANOcontrol Registered Users Posts: 120 ✭✭
    That is a good amount of panels to heat water.  That cost could be eliminated. Arn't a lot of options unless you do it yourself. And you would still always have a backup system for when electric went out.
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