My Portable Solar System

RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
Figured I would share and as some questions as I tweak out this little portable solar power system I put together for times of emergency or times of play or what ever.

Here is a Foldable 76 Peak watt Amorphous solar panel

64.8 watts; 3.6 amps; 18 volts.* Its open circuit voltage is 24 volts.*

In peak mid-day sunlight, it produces up to 76.7 watts and 5.56 amps.**

The panel weighs 6.6 pounds, and measures 66.4 x 31.5 inches unfolded, and 16.5 x 7.1 x 3.2 inches folded.*


The Battery is a 24 Ah 266Wh Lithium Polymer battery specifically designed to accept the wide range of voltages that a solar panel will output of a day. The battery will accept a 4.5amp max charging current. So the battery can be charged to full on one full sunny day of solar power.

I use a Watts UP power meter to measure my current Voltage, Amps, Watts, and Amp Hour Input total for the day. It will also scroll though the Peak AMPs, Peak Watts, Lowest Voltage, Watt Hours, Amps Total for the day. When the sun goes down the meter shuts off, When the sun rises the meter starts up, the battery starts charging and the meter logs all the data all day long. Pretty nice.

The Pelican case is Crush/Water Proof and I'm still figuring out exacty how I want to stuff it full of my batterys I have 2 right now, my Short Wave Radio and Antenna, My Scanner, My DC to DC converters, My DC to AC converter, Battery Chargers, Rechargeable Batterys, CFL lights, ect... It all already fits I just have to get it just how I like it.

I want to get one more panel for a total of 150 peak watts of panels.

I also want to get a Morning Start MPPT 15amp max charge controller so I can also use the panels for charging a AGM battery with the help of MPPT.

I would have been cheaper to go with 80 watt glass panels but I can't fold them up to the side of a large book like I can with the fold able panels.

So my question is how much of a gain do you think I could expect to see by tilting these panels 15 degrees? I live in Indianapolis Indiana and the charts call for 15 Degrees I think is the best angle.

What angle do I get maximum light to the panels?

The 76 Watt Peak reading was captured during peak sun with the panels laying flat on the ground in summer in Atlanta, I didn't do that reading but I am doing my own testing right now.

Is the sun just as strong in the winter as it is in the summer when it comes to solar power production? Or is it just that there is less sun time during the winter vs the summer?

Comments

  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: My Portable Solar System

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  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: My Portable Solar System

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  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: My Portable Solar System

    A couple of simple answers.

    First, the most efficient angle is when the panels are 90 degrees to the sun, so this angle varies both with time of day AND time of year,, (unless you are on the equator) The following link will provide you with a way to play with the angles to maximize gain. With a small portable system, tilting the panels to the right elevation, and turning them throughout the day for the proper azimuth will give the greatest harvest. http://www.pvwatts.org/

    As for insolation in the winter. For all intents and purposes, full sun is full sun. There can be regional variation due to local climates that may change the net insolation at some times of the year, summer humidity or winter fog for example, but the real limit is the length of the day. On the other hand, most solar panels put out significantly more power when the panels are cold. Where I live, we have about 6 hours of daylight in December, but 18 in the summer. In the winter we have MUCH higher output per hour because we often are VERY cold (-30-40f) and we get considerable reflection off the snow and ice.

    Good luck,

    Tony
  • MoeMoe Solar Expert Posts: 60 ✭✭✭✭
    Re: My Portable Solar System

    Maximum output will come with the sun perpendicular to the panel. Insolation will fall off with the cosine of the sun's angle away from perpendicular to the panel.

    The rule of thumb for fixed installation is to have the panel faced due south and titled at your latitude for year-round operation, or tilted at latitude +15º for winter or latitude -15º for summer.

    But as Tony says, the ideal tilt ("elevation") of the panel varies throughout the day. Obviously, so does the ideal "azimuth" with the sun rising and setting north of east/west in the summer and south of it in the winter.

    Here's a program that will generate AZ/EL curves for different times of the year and times of day for your location.
  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: My Portable Solar System

    Thanks guys. I'm gonna have to play with the angels and see how it affects outputs.

    I have another question.

    This panel has an open circuit voltage is 24 volts, and 64.8 watts; 3.6 amps; 18 volts normal operating conditions.

    So my question is under noon sun light as the current from the load drops, should the voltage from the panels rise closer to the Open Circuit Voltage as the current from the load drops?

    I am noticing that when the panel is hooked directly to the Lithium Ion battery for charging that the voltage is from 11v up to 15 volts from 9am up to 12pm, the amperage will increase along with the voltage as the panel gets more sun.

    No I notice that the panel is outputting 26v, .03 amps.

    So when should I expect to see 26v out of this panel? Why am I seeing 11v-15v normally up till now which is the first day I have receive a full day of cloudless sun.

    Thanks for the feedback.
  • mike95490mike95490 Solar Expert Posts: 7,286 ✭✭✭✭
    Re: My Portable Solar System

    Your battery will limit the amount the PV voltage will rise to.
    This is the advantage the MPPT controllers have, they can harvest the "extra" voltage, and convert it to more amps for your battery. Does your panel have a
    MAX POWER or POW Max Voltage or PMV spec ?
    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 ,

  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: My Portable Solar System
    RWB wrote: »
    This panel has an open circuit voltage is 24 volts, and 64.8 watts; 3.6 amps; 18 volts normal operating conditions.

    So my question is under noon sun light as the current from the load drops, should the voltage from the panels rise closer to the Open Circuit Voltage as the current from the load drops?

    It would be handy if you could find the data sheet for your panels, but here is a data sheet for another solar pane (210 watt)l. Of course your numbers will be different--but the curves will be very similar (just relabel the graph with your voltages and currents).

    A battery, is a voltage source--no matter how much or how little current you draw, the output voltage will fixed (to a first approximation).

    A solar panel is a current source, and once there is enough light, Vmp (voltage, maximum power) will be reached... Then the available output current will be proportional to the amount of sunlight available.

    Open circuit (Voc) voltage is when current = 0 amps. And Voc is (when there is a minimum amount of light) not dependent on how much sun there is (9am vs noon vs under light cloud cover--Voc will not change). (Voc is somewhat affected by panel temperature)

    So, the output voltage of a solar panel is really, more or less, dependent on the load attached, how much current the load demands, and how much current is available from the panel.

    I am noticing that when the panel is hooked directly to the Lithium Ion battery for charging that the voltage is from 11v up to 15 volts from 9am up to 12pm, the amperage will increase along with the voltage as the panel gets more sun.
    No I notice that the panel is outputting 26v, .03 amps.

    So when should I expect to see 26v out of this panel? Why am I seeing 11v-15v normally up till now which is the first day I have receive a full day of cloudless sun.

    So, on a cool day, with some sun, and no load, you will see Voc (24-26 volts seems OK).

    The 11v-15v is the voltage that is "set" by the battery--Or, more likely the battery charger.

    I assume that the battery charger is a "12 volt" charger, and when the battery is low (needing charging), the battery charger is drawing as much current as it can (taking the panel voltage down to ~12 volts).

    Once the battery is nearly charged, the charge controller will take less current and the panel voltage will begin to drift up.

    Finally, once the battery is fully charged, the charge controller will "turn off" and with near zero current draw (0.03 amps is pretty close to zero with this solar panel), the solar panel will approach Voc of 24-26 volts.

    Depending on how much charging the battery required and how much sun is available--it may take several hours to several days of sun to fully charge your battery pack.

    And, you should check that the battery pack / charge controller can operate safely with your solar panel (basically from 0v to 26+ volts). A charge controller made to run from a cigarette lighter may not operate very long if connected to a solar panel that can output 26 volts (when lightly loaded).

    Lastly, your Li-Polymer battery pack must have some sort of battery charge controller built in... In general, Lithium batteries are very sensitive to charging (and discharging) and may have extensive electronics to protect the batteries (and the user) from fire and explosion if improperly charged/discharged.
    The voltage of a Li-poly cell varies from about 2.7 V (discharged) to about 4.23 V (fully charged), and Li-poly cells have to be protected from overcharge by limiting the applied voltage to no more than 4.235 V per cell used in a series combination. Overcharging a Li-poly battery will likely result in explosion and/or fire. During discharge on load, the load has to be removed as soon as the voltage drops below approximately 3.0 V per cell (used in a series combination), or else the battery will subsequently no longer accept a full charge and may experience problems holding voltage under load.
    If you are charging a "bare" Li-Polymer battery without a li-poly configured charge controller, stop right now. It is not safe.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: My Portable Solar System

    These are the only specs I have:

    Nominal power: 64.8W
    .Actual peak output power:72W
    .Nominal current: 3.6A
    .Nominal voltage: 18V
    .Open-circuit voltage: 24V

    I' have been charging a battery and it has a built in solar charge control for Lithium Battery. So I figured that the battery went into trickle charge mode and thats why the voltage rose to 24v. Not sure yet though, still running test.

    I just figured if there was no load on the panel it should read 24v, then as soon as you put a load on it the voltage would drop down to 10 to 18v max under load. But I can plug a 12v cigarette lighter directly to the panel and I can pull 13watts from the panel with the voltage only dropping to like 23 volts and pulling around 1 amp. I figured with the 13watt load and 1amp the voltage would drop down to the 10-18volt range.

    Any ideas?
  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: My Portable Solar System

    Also BB the outside temperature is 0 degrees. The coldest temp yet. Supposedly temperature does not affect these type of panels.

    Yes BB I think you are correct in what is happening right now with the voltage and the battery's charge controller is going though the Lithium Ions battery charge pattern.

    Yes this battery's built in charge controller is designed to be charged by these solar panels. They have a wide voltage input ranges and accept 4.5amps max current input with under and over current protection.

    The battery is 24 Ah so 5 hours of peak sun and you will have a full battery or pretty close to it.

    The battery seems to be starting to trickle charge which drops current input which raises voltage, the voltage is raising high enough to trip the charge controller to stop charging due to upper voltage input limit.

    So I'm gonna drain the battery tonight and see how it works out during the same hours tomorrow under bulk charge.
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: My Portable Solar System

    You may have missed my post just above yours...

    Solar panels are, more or less, current mode sources (vs batteries which are voltage mode sources/sinks).

    Throw in a charge controller (of indeterminate type), and it is a bit difficult to predict exactly how the whole system would operate without more information.

    Also, given the variable output of the solar panel (based on sun and load) and the variable power requirements of the charge controller (state of battery charge, amount of current and voltage available from the solar panel)--that it works well is sometimes surprising (if the charge controller was designed for use in a car with a battery instead of with a solar panel).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: My Portable Solar System

    Yes, I updated my previous post to answer your questions BB.
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: My Portable Solar System

    If the panel voltage is going too high, you can probably make a little circuit to load the panels (a little bit) so the voltage does not rise to Voc.

    Here are some data sheets for Amorphous solar panels... Look at the 64 watt specifications (probably pretty close to your panel's ratings).
    TEMPERATURE COEFFICIENTS

    (at AM 1.5, 1000 W/m² irradiance)

    Temperature Coefficient of Voc: -88mV/K (-0.38%/°C)
    Temperature Coefficient of Vmp: -51mV/K (-0.31%/°C)

    Temperature Coefficient of Isc: 5.1mA/K (0.10%/°C)
    Temperature Coefficient of Imp: 4.1mA/K (0.10%/°C)

    Temperature Coefficient of Pmax: -143mW/K (-0.21%/°C)
    I have seen other companies and evaluation reports say that this or that brand of panels is better because they are not affected by temperature as much as mono/poly crystalline panels--and so far, once you allow for the voltage ratings, the temperature coefficient numbers are about the same for Amorphous panels too.

    Lastly, read all you can about your Li-Poly batteries... Many Lithium batteries have very different characteristics vs other types of rechargeable batteries.

    For example, Li-Ion batteries should be stored about 1/2 charged (when not being used). Storing at full charge will lessen their operational life.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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