What’ca Got There Partner? Not Much

Hi everyone. This is my first post. I want to set up a small emergency solar/battery storage system. My plan/hope is to run my refrigerator, a deep freeze, some CFL lights and ceiling fans. I would really like to plug all of this into my circuit breaker panel for ease of use. Until there is an emergency I would like to use it just to make sure everything is setup correctly and to help off-set a little of the cost.

Knowing I don’t know anything (that is why a joined this forum, to get help and learn) I want to start small. I have spent days and nights reading material on solar.

I just purchased four sets of Harbor Freight (please don’t scream at me, I know this is light weight stuff) 45 watt panels. So I have 180 watts of solar panels. But what does that mean?

1. How much “power” can I generate and store in a day?
2. What is the best/good/affordable way to set this up?

Thanks so much for your comments and recommendations.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What’ca Got There Partner? Not Much

    Welcome to the forum!

    This has to be the #1 request for solar power. :p
    It's also about the worst use scenario. Sorry to be the barer of bad news but ...

    "My plan/hope is to run my refrigerator, a deep freeze, some CFL lights and ceiling fans."

    Right. Refrigerator or freezer = more than 1 kW hour per day, plus the need for a pure sine wave inverter. Let me translate that in to one simple word: expensive.

    Those HF panels you've got are notorious for not even reaching their nameplate rating, btw.

    Realistically, the loads you want to run would need quite a lot of inverter, battery, and panel. Take a look at my set-up in the sig. That runs a refrigerator (no separate freezer) plus a few other things like water pump and office equipment. It is barely adequate. It needs more panel and battery capacity as it is. To run both a 'frige and freezer, it's practically X2 as they are large power consumers.

    Your looking at $10,000, frankly.

    Now consider buying a small inverter generator like the Honde EI series, 2000-3000 Watt could handle it if judiciously managed. It should be about 1/5 the cost too.
  • System2System2 Posts: 6,290 admin
    Re: What’ca Got There Partner? Not Much
    Welcome to the forum!

    Right. Refrigerator or freezer = more than 1 kW hour per day, plus the need for a pure sine wave inverter.
    Your looking at $10,000, frankly.

    Thanks for the feedback. Like I said I don't know much.

    How many kWh can I make a day with this number of solar panels?

    I did check the amp draw on my appliances. My frig draws 1.16 amps, or course more on start up. But it doesn't run all day. That is why I thought I'd be able to run it on batteries.

    I have seen on the show "The Colony" last season and this season they used battery banks to run lights, welders, skill saws, saws awls, etc. It makes me think it is possible, in some way.
  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: What’ca Got There Partner? Not Much

    Quick rule of thumb: Solar panel name plate rating/2*4 will give you an average available power out the inverter.

    180/2=90*4=360 watt/hours/day, on average.

    People usually over estimate solar power input capability, at the same time they under estimate their loads.

    Your fridge alone, 1.16 amps*120=139 watts, duty cycle ~50%=1.6 kwh/day.

    Buy a Kill-a-Watt meter to test your loads before you buy any more stuff to build a solar system.

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What’ca Got There Partner? Not Much
    Thanks for the feedback. Like I said I don't know much.

    How many kWh can I make a day with this number of solar panels?

    I did check the amp draw on my appliances. My frig draws 1.16 amps, or course more on start up. But it doesn't run all day. That is why I thought I'd be able to run it on batteries.

    I have seen on the show "The Colony" last season and this season they used battery banks to run lights, welders, skill saws, saws awls, etc. It makes me think it is possible, in some way.

    Oh, it's possible. It's just a matter of how much for how long at what cost!

    Here's refrigerator from an actual unit (mine):
    Average 120 Watts running, approximately 20 minutes out of each hour. That's 960 Watt hours per day, not including start-up surges and defrost (500 Watts) cycle. Refrigerators vary in their usage quite a bit due to ambient temperature and humidity and how often you open the door. The start-up is more, and the more it cycles the more start-up. Plus, after the defrost runs the compressor has to work extra hard to re-cool the refrigerant. Big power users over time, even though they draw relatively little when actually running. The opposite would be a microwave, which will use 1000+ Watts, but is only used a few minutes a day.

    The readings you got for your 'frige indicate about 140 Watts draw, which is not too far off mine. But 20 Watts difference over a day can be a lot of Watt hours: 160 with the same cycle time.

    As for how much power you can actually expect out of any given solar panel, the first thing you have to understand is that they do not produce their rated Wattage all the time. That rating comes from a laboratory "flash" test, and is dependent on fixed lighting and temperature. The light that falls on them in the real world varies greatly over the course of the day. As a rule-of-thumb you can count on about 4 hours of "equivalent good sun" per day and an averaged output in that time of around 80% of the nameplate rating.

    Thus 180 Watts of panel will perform like 144 Watts over 4 hours = 576 Watt hours per day. That doesn't include loss or gain for high or low temperatures nor the amount of power used within the system itself. By the time you "convert" rated DC panel Watts to usable AC outlet Watts up to 50% of the power may disappear. Daunting, isn't it? Some systems do better, of course.

    A rule-of-thumb estimate for off-grid solar power is that it costs about $1 per Watt over the life of the equipment (batteries need to be replaced no matter how well maintained, and components do wear/fail). Now how much is the electric rate in your area? It's ten cents here, if "here" weren't 15 miles from the nearest power pole!

    This is why for occasional power outages a small generator is usually a much better way to go.
  • BB.BB. Super Moderators, Administrators Posts: 29,720 admin
    Re: What’ca Got There Partner? Not Much

    And when you see something like 360 Watt*Hours of energy... That, roughly, means that you can draw 360 watts for 1 hour, 36 watts for 10 hours, 180 watts for two hours, etc...

    In real life, it is not so "clean"... Batteries, the more current you draw, the less efficient they become--Add variability due to weather, seasons, etc... You usually have to design the system larger than your minimum load requirement and/or do something else (backup generator, turn off loads when the weather is bad, etc.).

    The whole exercise does give you a new appreciation for Utility Power... How they can get power to your home for $0.10-$0.20 per kWH, and to generate your own (and provide battery storage) cost you ~$1-$2+ per kWHour...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: What’ca Got There Partner? Not Much
    icarus wrote: »
    Quick rule of thumb: Solar panel name plate rating/2*4 will give you an average available power out the inverter.

    180/2=90*4=360 watt/hours/day, on average.

    People usually over estimate solar power input capability, at the same time they under estimate their loads.

    Your fridge alone, 1.16 amps*120=139 watts, duty cycle ~50%=1.6 kwh/day.

    Buy a Kill-a-Watt meter to test your loads before you buy any more stuff to build a solar system.

    Tony

    That is great news Tony. If I understand your math I can potentially make 360 watts per hour per day. If there are roughly 7 hours of "watt making hours" a day I'm can make 2.5 kWh/day, (360x7=2.5kWh). That is more power then my frig needs if the duty cycle is 50%. If nothing else I could keep my frig going and some low voltage lights. Right?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What’ca Got There Partner? Not Much
    That is great news Tony. If I understand your math I can potentially make 360 watts per hour per day. If there are roughly 7 hours of "watt making hours" a day I'm can make 2.5 kWh/day, (360x7=2.5kWh). That is more power then my frig needs if the duty cycle is 50%. If nothing else I could keep my frig going and some low voltage lights. Right?

    No. Not "360 Watts per hour"; 360 Watt hours. That's running a 60 Watt bulb for 6 hours.
    Nor will you have "7 hours" to work with. Maximum Wattage Equivalent is far less than the total daylight hours. Solar panels put out very little without direct sunlight on them. That's why we talk about 4 hours of "equivalent good sun".

    180 Watts of panel is never going to run a refrigerator for a day or a night. 360 Watt hours will run your 140 Watt 'frige for five hours at the absolute most. And that is optimistic.
  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: What’ca Got There Partner? Not Much

    I'm sorry, but you are not understanding me (or more likely I am not writing it correctly!)

    A watt/hour is a quantity of energy, that translates into 1 watt draw for 1 hour. In more realistic terms, a 100 watt light bulb burning for 1 hour, consumes 100 watt/hours or WH.

    So instead of making 360 watts for an hour, you are more likely to make 90 watts (at best, and over 1 hour you will "make" 90 wh.

    Next, one can seldom count on more than about 4 hours of "ideal" sun on average over the course of the day. (Your solar day may vary, but on a year round basis, 4 hours is a pretty good average. Remember, you may have 12 hours of daylight, but the first couple and the last couple of hours the sun angle will in most cases not be ideal. (if is ideal for sun rise, it stinks for sun set for example). Add to that, cloud cover, other shading issues, and basic crappy weather days. So, in my analogy, 180/2*4=360 watt hours per day average might be a realistic goal.

    That 360 wh is enough to run a 120 watt TV for 3 hours for example. (Or your fridge for a bit less than 3 hours.

    I hope this clarifies things.

    Tony

    PS Watts are an instantaneous measure of power, but until you add a time element it has little meaning. Watts*Time (in hours)= Watt hours. 1000wh=1kilowatt hour.
  • BB.BB. Super Moderators, Administrators Posts: 29,720 admin
    Re: What’ca Got There Partner? Not Much

    By the way:
    • watt/hours or WH
    Is actually:
    • Watt*Hours = WH
    Watts is a rate--Like miles per hour or gallons per minute. There is no useful measurement of Watts per Hour (Watt/Hours). It is a common mistake because we are all used to working with Miles or Gallons per Hour...

    watt*Hours is an amount. Like Miles or Gallons...

    Amp is a rate too... So Amp*Hours is an amount (like 8 amps for 5 hours is 40 Amp*Hours).

    For example, you can have a 100 AH battery bank... But is that bank 12 volts, 24 volts, or 48 volts.

    Amp*Hours is missing the "Voltage"... Amp*Hours*Volts is equal to Watt*Hours.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: What’ca Got There Partner? Not Much

    This forum is full of awesome people! Thank you very much for your feedback so far.

    From what I can tell I am a rank hobbyist at best compared to you guys. I love that you have your setups in your signatures. It helps me to know what is really needed to go off grid.

    I do have a portable 5,000/6,250 watt generator with a tri-fuel conversion kit that allows me to run it on gasoline, propane or natural gas. I got it from uscarb.com. I can easily run my entire house without the house air conditioners with that. But that is a different project.

    I think I will change my goal to seeing if I can just get this solar panel system setup and a few things running like my laptop. It should be fun learning something new.

    From what I understand I can possibly generate 360 watts a day. If each panel generates .92 amps for four hours a day I should be able to create around 44 amps. I now need to get a battery or batteries that will store the energy for use with an inverter.

    Does that mean I need one battery that has at least a 44 amp hour rating? Or should I get one that has a 100 AH or multiple ones with more AH so I can store more and not drain down the batteries so much? What would you recommend as far as the number of batteries and types of batteries?
  • BB.BB. Super Moderators, Administrators Posts: 29,720 admin
    Re: What’ca Got There Partner? Not Much

    Well,

    From PVWatts, you can estimate how much power you can generate from an off-grid solar system in Houston Texas.

    Assuming 180 watts of solar panels (I have to enter 1.8kW or 1,800 watts and move the decimal point--the program does not accept lower than 1kW or 1,000 watts), assume 0.52 derating (from solar panels to charge controller to battery to inverter losses), Houston, you will get:
    "Station Identification"
    "City:","Houston"
    "State:","Texas"
    "Lat (deg N):", 29.98
    "Long (deg W):", 95.37
    "Elev (m): ", 33
    "PV System Specifications"
    "DC Rating:"," 180 Watts" (really entered 1.8kW)
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.9 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 30.0"
    "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, 3.68, 9.9, 0.960 (really was 99, 9.60 till I moved decimal point, etc.)
    2, 4.12, 9.9, ..96
    3, 4.82, 12.7, 1.23
    4, 4.98, 12.4, 1.20
    5, 5.24, 13.2, 1.28
    6, 5.53, 13.2, 1.28
    7, 5.43, 13.3, 1.29
    8, 5.44, 13.5, 1.31
    9, 5.40, 13.1, 1.27
    10, 5.19, 13.2, 1.28
    11, 4.33, 11.0, 1.06
    12, 3.34, 8.9, .86
    "Year", 4.79, 144.3, 13.99

    So, you will generate around 8.9 (December) to 13.5 kWH (August) of "useful 120 AC power" per month or:
    • 8,900 WH per month / 30 day per month = 297 WH per day
    • 13,500 WH per month / 30 days per month = 450 WH per day
    Roughly, we normally size the battery to the loads--but in your case, you have the panels, so we will size the battery to your solar array.

    A rough rule of thumb for batteries is to charge them around 5-13% of their rated capacity. In your case, you have 180 watts of solar panels, and we will assume them to be 77% of "panel rating" (good average)"
    • 180 watts * 1/17.5 volts * 0.77 * 1/0.05 charge rate = 158 Amp*Hour @ 12 volts
    • 180 watts * 1/17.5 volts * 0.77 * 1/0.13 charge rate = 61 Amp*Hour @ 12 volts
    So, the "optimum recommended" 12 volt battery 20 Hour rating for your solar array would be around 61-158 AH...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: What’ca Got There Partner? Not Much

    Correction:

    "If each panel generates .92 amps for four hours a day I should be able to create around 44 amps."

    To throw another curve into your world. Amps is the measure of current flow through a wire. The way to measure power is Volt times amps equal watts (V*A=W)

    Amps are measured in Amp/hours. So in your case, .92 amps * 4 hours would be 3.6 amp/hours. In a 12 volt system, the equation would then be 12vdc*3.6 ah=43.2 Watt/hours

    A couple of formulae to commit to memory, and to under stand.

    Power is the product of Volts*amps=watts
    Power consumed (or produced) is measured in Watt/hours.
    Power is also measured in Amp/hours (amperes*time=AH)
    Amp hours * volts= watt/hours

    It all comes down to understanding the relationships between volts/amps/watts and time.

    Further muddying the waters,,

    Tony
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: What’ca Got There Partner? Not Much

    I started out similar to how you have, with the HF panels (only one set though!) and with similar goals for the project. After sitting through the cold and dark of a power outage after an ice storm, I resolved not to be in that position again! And I didn't want to have to have a generator running the whole time either. Besides, it is a fun new hobby to play with too! :D

    The first thing I figured out is that the HF panels are wildly optimistic in their ratings. A *few* have reported getting close to the 45W rating, but most have not and I was no exception. Fresh from the box, on a clear July day, carefully aimed at the noontime sun, the most power I've ever seen my set produce was a touch over 30W. Since then, they consistently produce in the 18-22W range, occasionally up to 25-26W on cool sunny days.

    On the plus side, they have been consistently doing that for a couple years now, in spite of being up on the roof the whole time. I was concerned they might not last but so far so good.

    The second lesson was how difficult / expensive it is to generate your own power! My fridge was the goal, and a bare-bones system to do just that was going to be several thousand. But I still had other things I wanted to run as well! Ouch... What I wound up with is a system that cost around $8k and fairly consistently generates 30-50 cents of electricity per day! :roll: Good thing saving money wasn't my goal! (We have very cheap power here, around 9 cents / kWh.)

    In the end, I pieced my system together over about a year. The components were selected specifically so I could do that, I planned to wind up with the full Outback system and bought things in stages. I now have 1080W (STC) in panels on the roof, feeding a 220AH 48V bank of T-105 "golf cart" batteries. With that, I have roughly 5kWh available before the batteries are at 50% DOD (don't want to go lower than that, and that far only on occasion) which with just the fridge and maybe a light or two would let me go 3 days without any sun in a bad storm / outage.

    In the meantime, I have it running my home computer network - about 150W continuous load, so 3.5kWh/day total usage! Long as it's sunny I'm fine but don't like taking it below 75% on a daily basis so I have written some software to control the Outback system and switch back to grid if I drop too low thanks to cloudy weather. At least I get some use out of it! It'll never pay back, but it's fun to tinker with and gives me some assurance I'll have power available should another ice storm come along...! (I also have a generator, just wanted to be able to run things without it going 24x7!)

    I have a bit more detail on my system (as well as the two smaller system - one the HF panels - I have) on my website listed below. You can also see what the big system is doing right now! :)

    A side note: Even better quality panels aren't going to give you "nameplate" wattage ratings. The nameplate numbers come from what's called "STC" - standard test conditions, or 1,000 W/sq.m. You'll only find that in a few areas - at the equator, at high noon on a cloudless clear day or something. For more "realistic" numbers look on the data sheets for the "PTC" rating (can't remember what that stands for) which is usually at 800W / sq.m. IIRC. My panels are 135W STC / 95W PTC and they consistently produce somewhere between the two, usually a little closer to PTC. But the PTC number is a great one to use for calculations, so you don't come up short on capacity.
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