What do I need to create a solar power system

glock907glock907 Registered Users Posts: 7
I wish to purchase all the solar power items needed to operate a minimum of 1 full sized refrigerator and 1 large freezer and the instructions to connect it all together. I have no working knowledge of electronics and need all the help i can get. if the rig
will operate more the better. I need a detailed list of needed equipment diagrams would also be helpful. recommended products would also be helpful thank you

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What do I need to create a solar power system

    Welcome to the forum.
    The first thing you need is a Kill-A-Watt or similar meter. You run the appliance in question through it, get some real world numbers on its power consumption, figure out how much power you need to supply, then have a mild coronary when you find out what it costs.

    This is why the inevitable first question is: why do you want to do this?
    If it's for emergency back-up power when the grid goes down, usually a good generator is a more prudent investment. If it is to run an off-grid home, you need to take into consideration how much time you spend there; propane refrigeration can be cheaper for short-duration stays. If it is to save money on your electric bill, you're barking up the wrong tree as off-grid power comes at a cost that can be ten times utility power.

    Since I'm one of those that does run refrigeration off-grid I can tell you precisely what is involved.
    1). An inverter capable of handling the start-up surge of the refrigeration compressor. This inevitably means pure sine wave type and at least 1 kW capacity. Even though the running 'frige will only draw around 150 Watts, when it starts it will momentarily demand a lot more. If it has automatic defrost it will use around 500 Watts for that cycle too.
    2). Enough battery capacity to handle the daily Watt hour load. For instance a refrigerator using 120 Watts when running with a duty cycle of 1/3 of a day is: 120 Watts * 8 hours = 960 Watt hours. To get just that portion of the power on a 12 Volt system you need: 960 Watt hours / 12 Volts = 80 Amp hours. This does not include the start-up surge, defrost cycle, depth of discharge limitations, or system efficiency losses. Regrettably refrigerators do not have "fixed" energy demands, as weather and how often the door is opened will change the need for it to cool down.
    3). Sufficient solar panels to recharge the battery bank at a reasonable rate. This will vary not only by the size of the battery bank but also by your location; some sites get more sun, some are more efficient, some are not so lucky.

    If you look at my signature you'll see a somewhat cryptic description of the equipment that powers my standard 16 cu. ft. refrigerator (as well as the rest of the cabin). It is a tad "marginal" in specifications as I do a lot of load shifting and have a slight panel efficiency advantage over most locations due to high elevation.

    Still interested? :D
  • BB.BB. Super Moderators, Administrators Posts: 29,717 admin
    Re: What do I need to create a solar power system

    The order I would proceed:
    1. Get a Kill-a-Watt meter (or equivalent) and measure your daily energy usage (kWH per day--Kilo Watt Hours)
    2. Compare those readings against modern Energy Star Rated Appliances (a really good off-the shelf full size fridge is around 1kWH per day, and similar for a freezer). Note that making Ice Cubes, placing a lot of new items in fridge/freezer, hot weather, etc. will drive up power usage)
    3. Review your needs against your budget. For a true off-grid system, you will pay around $1-$2+ per kWH for your electricity (parts, maintenance, new batteries every 5-10 years, new inverter/charge controllers every 10+ years, etc.)
    4. Once you have addressed conservation and have a good idea of your daily power needs, we need to know (roughly) where you live and your minimum acceptable "pure solar" needs--i.e., for most areas, 9 months of pure solar and 3 months of the year using a backup genset in winter).

    Then is just a series of plug in the numbers equations...

    For many areas in the US, we can use 4 hours of sun as the minimum amount of noontime equivalent sun.

    And a 100 kWH per month or 3.3 kWH per day is a good sized system to give a person a "reasonably" useful amount of energy (can power a fridge + the rest of a small home with well pump, etc.).

    Battery sizing is 1-3 days of no sun with 50% maximum discharge (for longer life). Using 2 days:
    • 3,300 WH per day * 1/0.85 inverter eff * 2 days no sun * 1/0.50 max discharge * 1/24 volt battery bank = 324AH @ 48 volt battery bank

    (note that I used a 48 volt battery bank--For larger systems, the wiring and batteries are much easier to install/maintain for a higher voltage system)

    Two calculations for solar array size... First, design the solar array to properly recharge the battery bank. Typically, that is 5% to 13% rate of charge:
    • 324 AH * 59 volts charging * 1/0.77 panel+charger losses * 0.05 rate of charge = 1,241 Watt Solar array (minimum)
    • 324 AH * 59 volts charging * 1/0.77 panel+charger losses * 0.10 rate of charge = 2,482 Watt Solar array (healthy sized array)
    • 324 AH * 59 volts charging * 1/0.77 panel+charger losses * 0.13 rate of charge = 3,227 Watt Solar Array (rough cost effective maximum array)

    And then there is calculating the array based on the number of Watt*Hours per day you use and how much sun you have:
    • 3,300 WH * 1/0.52 system losses * 1/4 hours of sun per day = 1,587 Watt Solar Array minimum

    For example, here are the hours of sun per day for Nashville Tennessee based on a fixed array tilted to latitude (36o), and the monthly power for a 2,500 watt solar array and an Off-Grid system (using PV Watts website):
    "Station Identification"
    "City:","Nashville"
    "State:","Tennessee"
    "Lat (deg N):", 36.12
    "Long (deg W):", 86.68
    "Elev (m): ", 180
    "PV System Specifications"
    "DC Rating:"," 2.5 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 1.3 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 36.1"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 6.9 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.62, 143, 9.87
    2, 4.32, 154, 10.63
    3, 5.25, 201, 13.87
    4, 5.53, 194, 13.39
    5, 5.63, 200, 13.80
    6, 5.95, 199, 13.73
    7, 5.99, 205, 14.15
    8, 5.68, 197, 13.59
    9, 5.27, 177, 12.21
    10, 5.07, 183, 12.63
    11, 3.63, 132, 9.11
    12, 3.22, 122, 8.42
    "Year", 4.93, 2107, 145.38

    Such a system would generate a minimum (20 year average) of 122 kWH per month in December, and near 200 kWH per month for 6 months of the year.

    So--Your solar array should be somewhere in the 1,587 to 3,227 Watt range with ~2,500 watt array being a good sized system with some reserve power for poor weather/growing power needs. And will help ensure your battery bank is fairly rapidly recharged.

    A 2,500 watt system--Probably somewhere around $10,000 to $25,000 or so (you build with stuff on sale vs paying somebody to build it with all new parts).

    Note, I am not in the solar business--Just trying to give you some back of the envelope calculations so you can size your needs vs your budget.

    After we have nailed down your needs/expectations, we can go into the details.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What do I need to create a solar power system

    I forgot to mention the charge controller. How silly of me. :blush:
  • glock907glock907 Registered Users Posts: 7
    Re: What do I need to create a solar power system

    i live 50 miles north of nashville on i65 so those day light figures for nashville should be just about the same as here.
    i am going to have to build this thing one piece at a time. am retired police officer on a fixed income. i feel that a little ennergy to run frig and freezer min is a good start with a end product like the one you talked about so if i can build a system that is expandable that would be great. what would i need as a minimum to get started even if its only enough power to just the frig or a light. I am thinking adding a few pannels at a time as budget allows also where is the best place to go for the lowest prices
  • BB.BB. Super Moderators, Administrators Posts: 29,717 admin
    Re: What do I need to create a solar power system

    Problem is that a refrigerator and freezer are probably the biggest power users after heating, cooling, electric hot water (if use electricity). Although, running a couple desktop computers 24x7 and a Sat/DVR system can suck up the Watt*Hours too.

    It is very difficult to "expand" an Off Grid solar PV system... There are points where you have to change battery bank voltage from 12/24 to 48 volts (new inverters, rewiring battery bank or new batteries). And as you increase the array size, a new MPPT controller will probably require a rewiring of the solar array too--plus finding "matching" solar panels a few years down the road might be difficult too (between vendors going out of business and new/larger panels with different Vmp/Imp ratings).

    I am sorry to say that it almost always is not cost effective to slowly "grow" a solar power system.

    There are ways to approach the issues. For an "emergency power system" (say you have afternoon power failures/brown outs) you could:
    1. Battery bank + AC inverter/charger to power your loads (basically a large UPS system)
    2. Add a backup genset (plus fuel storage) to extend your power support past a couple days
    3. Add a solar charge controller + Solar Panels (you could add solar panels a few at a time over a few months or a year)
    4. Give system to relatives/sell on open market
    5. Start over with system sized to meet your needs after a few years of use

    Sorry, not trying to be a pain in the behind--It really is difficult to grow out a solar system. As the system "grows" you end up tossing old inverters and batteries (and frequently solar panels and charge controllers) to build out the "final" system.

    Some people have done it along the lines--Build a small system to power the RV/cabin while building out a larger home (usually using a generator for power tools during construction). Then keep the small system for RV/Cabin use.

    Roughly, you can probably (cost effectively) double the size of a system over time--But much more than that, it is a major rebuild (at the very least).

    Note the 100 kWH per month (3.3 kWH per day) system limit... Up to that size, many people are successful in building cost effective solar PV systems (with generator backup). Over that size, the size of the system (arrays, battery banks, etc.) make mistakes expensive and can be difficult to tackle as a first timer.

    A 100 kWH per system would barely keep a full sized fridge/freezer running with little excess power.

    That is why we always stress conservation. If you are trying to take care of a week or so of power failure (ice storms, etc.), then, many times a genset makes a better investment.

    If you are looking at a SHTF/EOTW type situation--You start having to look at what does a refrigerator buy you vs canning/root cellar/food preservation/etc... In those situations, a little amount of electric power may go a long way (lighting, radio, etc.). And use a solar oven for cooking (if you don't have wood on the property) plus solar thermal system for heating (hot water/hot air, home placement with respect to sun, glass, heavy drapes, etc.).

    -Bill

    PS: If you are looking for the best place to spend your money--I tend to push conservation. A kill-a-watt meter and taking notes of where your power is going--And new low power usage appliances/lighting/insuation/double pane windows/etc. is almost always a better place to spend you initial time and funds.

    Then, when you look at solar--the costs can be significantly reduced because of your smaller energy footprint.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • glock907glock907 Registered Users Posts: 7
    Re: What do I need to create a solar power system

    well then in the event of economic crash and we were to forgo the refrigerator and freezer,use canned foods, fire place, warm cloths with sleeping bags and blankets for heat, use of a grill,smoker and solar oven for cooking only needing light and emergency radio etc
    what would you suggest for me with a limited budget, thinking pannels on the back patio or on the roof with a bank of batteries in the attic.
    as far as batteries in the attic is that safe?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: What do I need to create a solar power system

    guys,
    he did not ask for a refrigerator/freezer combo, but 2 separate appliances. this doubles the drain and doubles the potential of the at one time load capable of being presented to the inverter.
  • BB.BB. Super Moderators, Administrators Posts: 29,717 admin
    Re: What do I need to create a solar power system

    Batteries will last longer if cool. But, too cold, and then to (temporarily) lose capacity (appear to have less capacity).

    Size matters with solar power... For example, a couple threads to read:
    BB. wrote: »
    Emergency Power

    Basically a very long thread that starts from the beginning with a few vague requirements through design and assembly for a "portable" solar RE off-grid power box.

    And here is another example by Mike90045 called the Solar Monolith:

    attachment.php?attachmentid=384&stc=1&thumb=1&d=1234752636

    attachment.php?attachmentid=385&stc=1&thumb=1&d=1234752653

    Update pictures/information here.

    And a middle sized "lower cost" system (talking about a "portable" garage--But the basic power discussions apply to a home system):

    Semi-mobile garage


    The semi-mobile garage would use around 4x 6 volt 220 AH "golf cart" batteries and around 700 watts of solar array--For 1.5 kWH per day (enough for an efficient fridge or freezer for your area).

    Our host has good quality components at fair prices (the posters and moderators here are all volunteers--Only the two Admins here work for NAWS). Take a look at price some equipment out (~700 watts of solar panels, a MorningStar TS 45 amp MPPT charge controller, 4x 6volt 220 AH batteries, 300 watt MorningStar Inverter, etc.). And see what that runs you and if that would be useful. Note the 300 watt inverter is way too small for powering your fridge/freezer... You would have to look at 1,500 watt inverter and probably a 24 volt battery bank.

    Add a Honda eu2000i Generator ($1,000 or so delivered). And a battery charger (maybe around 45 amps maximum on the eu2000i for Iota/PowerMax @ 12 volts). If you want to go with more efficient chargers (a worthy goal), read this thread: Question about battery charger selection with EU2000 generator.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • glock907glock907 Registered Users Posts: 7
    Re: What do I need to create a solar power system

    so if i went with the 700 watt system what kind of price might i be looking at and how many solar pannels would i be looking at
  • BB.BB. Super Moderators, Administrators Posts: 29,717 admin
    Re: What do I need to create a solar power system

    "It depends"... A panel that is relatively easy to ship and handle by one person is around 135 Watts:

    700w/135 per panel = 5.2 panels

    You can place 5 Kyocera 13 watt panels in series and connect that to a MorningStar TS 45 amp MPPT controller and have sweet little setup. But that would cost you around $1,625 plus shipping and handling (not cheap for S+H either--I would guess).

    You could also get 210 Watt Kyocera panels:

    700w / 210 w per panel = 3-4 panels

    Which would cost you around 900-$1,200 plus S+H

    Big panels are typically less expensive (on a $/watt basis). Also, fewer electrical connections, less mounting hardware, etc. But >175 watt panel, you probably will need two people to move them around and help install. Also >135 watt panels probably have to go by truck/pallet.

    Solar panels are expensive to package and ship--So, you will have to take the cost on your door step into account. Also, sometimes you can work out deals with a local Grid Tied solar installer to add some panels for you into their next order. Shopping around helps.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • glock907glock907 Registered Users Posts: 7
    Re: What do I need to create a solar power system

    i nave not seen any that big the ones sold at harbor freight are is a 45 wat system for $189
  • glock907glock907 Registered Users Posts: 7
    Re: What do I need to create a solar power system

    going to bed now thank you
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: What do I need to create a solar power system

    To answer your basic question, you will need a minimum around 1600 watt-hours per day to run an Energy Star rated refrig and freezer, more if they are in an area that gets over 80 degrees F.

    You are not going to get that with a pile of 15 watt Harbor Freight panels, you will need at least a pair of 135 or 140 watt panels, and that would be marginal unless you get more than 6 hours full 100% sun per day.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: What do I need to create a solar power system

    BB,

    I ordered a couple of 175w panels recently to finish up an array I already had, and they came FedEx. I was surprised as well.....everything I'd ordered in the past ( but was more panels ) came motor freight.
  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: What do I need to create a solar power system
    glock907 wrote: »
    i nave not seen any that big the ones sold at harbor freight are is a 45 wat system for $189

    PLEASE do not buy solar stuff from Harbor Freight if you're serious about making power. Please.
  • glock907glock907 Registered Users Posts: 7
    Re: What do I need to create a solar power system

    bill thats a cool portable unit, how much did that cost to buiild and what will it power
    Glock907
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