24V solar power supply

KC-watts
KC-watts Solar Expert Posts: 37 ✭
in Off Grid Solar & Battery Systems #1
Have we done this before: panel direct to use? I connect my 36 cell panel (17V) into a 12 to 24 volt converter and let sunlight dictate when the fluorescent lamp lights. Don't lie, this is what we considered solar power when we first herd of the technology, ie. no batteries, chargers, or inverters.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Re: 24V solar power supply

    Led lamps plus a simple ballast would be much easier.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #3
    Re: 24V solar power supply

    I agree. Or go really old school and replace the solar panel with a skylight :-).

    I am available for custom hardware/firmware development

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #4
    Re: 24V solar power supply

    And sustainable tech for poor communities:
    https://www.youtube.com/watch?v=TSQ8LXXtv6w

    Hole in tin roof+flashing, clear bottle+water+bleach--Replace plastic bottle every ~5 years.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #5
    Re: 24V solar power supply

    Not only that, it could also provide free and effective water treatment.

    Solar_water_disinfection

    I am available for custom hardware/firmware development

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: 24V solar power supply

    Incandescent lamp = problem solved. Although why anyone would want lights on during the day ...

    DC converter isn't going to like the unstable Voltage of PV. Very few things like being run direct from PV. As a rule, the more complex the device the less likely it will function from an unstable Voltage source. (GTI's being the obvious exception as they are specifically design for this.)

    The whole point of batteries is to be able to shift the time when power can be produced to when power is needed for use. Embrace the technology; it's only three centuries old but it seems to work - so far.
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #7
    Re: 24V solar power supply

    Another lekker invention: http://thelightie.com/
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • KC-watts
    KC-watts Solar Expert Posts: 37 ✭
    #8
    Re: 24V solar power supply

    Works even better with my >15 V to 12 V output converter. Solar powered cigarette lighter plug, anyone? Both converters are switchmode and shut off at faults (dusk), though this one acts kinda funny at dawn/dusk. The other one is for a Humvee and is 8 times the size and faithfully blares it's alarm before shutoff

    Attachment not found.
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #9
    Re: 24V solar power supply
    Cariboocoot wrote: »
    Although why anyone would want lights on during the day ...

    My sentiments exactly.
    DC converter isn't going to like the unstable Voltage of PV. Very few things like being run direct from PV. As a rule, the more complex the device the less likely it will function from an unstable Voltage source.

    Thats not my experience. Most DC converters have extraordinaryly wide input ranges. Thats the point of them.

    Weve had an 7ah agm charging from a 10W panel (for an electric fence) with nothing more than a 2 dollar buck converter set to 13.8v. Obviously not ideal, but its still running 18 months later.

    However i think that dc converters would benefit from some extra input capacitance to help source power to the inductive sawtooth waveform.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: 24V solar power supply
    zoneblue wrote: »
    Thats not my experience. Most DC converters have extraordinaryly wide input ranges. Thats the point of them.

    Weve had an 7ah agm charging from a 10W panel (for an electric fence) with nothing more than a 2 dollar buck converter set to 13.8v. Obviously not ideal, but its still running 18 months later.

    However i think that dc converters would benefit from some extra input capacitance to help source power to the inductive sawtooth waveform.

    Have you ever actually run one from a solar panel?
    Accepting a wide range of input Voltage is not the same as being powered by a current source that lets the Voltage go anywhere from zero up to Voc depending on load conditions.
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  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    #11
    Re: 24V solar power supply
    zoneblue wrote: »
    Thats not my experience. Most DC converters have extraordinaryly wide input ranges. Thats the point of them.

    The cheap $25 converter I use accepts anywhere from 12v-72v dc and outputs a constant steady 12.0v dc
    Lasted for 2+ years now so I can't complain.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
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  • KC-watts
    KC-watts Solar Expert Posts: 37 ✭
    #12
    Re: 24V solar power supply
    jcheil wrote: »
    The cheap $25 converter I use accepts anywhere from 12v-72v dc and outputs a constant steady 12.0v dc
    Lasted for 2+ years now so I can't complain.

    Better than my expensive converter. The large power capacitors give power to the input low voltage alarm all too often. Something about that cheaper converter pictured, though it has almost no RF interference like my cheapest converter, does cut out at 15 volts.

    Although why anyone would want lights on during the day ...

    People with off mains sheds, root cellars, lots of reasons. With a converter, motors could run an attic fan, water features, and any other inductive type loads not needed in the evening without needing a battery and controller.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: 24V solar power supply
    KC-watts wrote: »
    Better than my expensive converter. The large power capacitors give power to the input low voltage alarm all too often. Something about that cheaper converter pictured, though it has almost no RF interference like my cheapest converter, does cut out at 15 volts.

    Although why anyone would want lights on during the day ...

    People with off mains sheds, root cellars, lots of reasons. With a converter, motors could run an attic fan, water features, and any other inductive type loads not needed in the evening without needing a battery and controller.

    Sounds good.
    Until you actually try it.
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  • South Africa
    South Africa Solar Expert Posts: 295 ✭✭✭
    #14
    Re: 24V solar power supply
    Cariboocoot wrote: »
    Until you actually try it.

    I think I am going to try it. :-)

    Want a 12v computer fan on if there is sun which inevitably means there is heat.

    Have all the parts in the infamous 'shed'. :-)
    5kVA Victron Multiplus II, 5.2kW array, 14kWh DIYLifepo4 bank, all grid-tied.


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  • KC-watts
    KC-watts Solar Expert Posts: 37 ✭
    #15
    Re: 24V solar power supply

    See, there are active and potential users of a voltage regulated solar panel. I wish the best of luck to NA Wind & Sun in evaluating options and marketing a product for these applications.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #16
    Re: 24V solar power supply

    Just a quick note--Marc (Cariboocoot), Tony (Icarus), and I are volunteer moderators here... We have no connection with NAWS other than through helping to keep the spam down on the forum here.

    The issue with DC to DC converters and solar panels is that "standard" DC to DC converters assume that they have a (relatively) stable voltage on the front end with lots of current (i.e., a battery or other low impedance power source) and arbitrary loads on the output.

    With solar panels, they are "high impedance" current sources. And this gets complicated because:

    DC to DC converters are generally "constant power" conversion devices. Or (ignoring losses):

    Power In = Power Out
    Vin*Iin = Vout*Iout

    Looking at the input power, if Iin is current limited by the solar panel... Then Vin is (more or less) the variable that is affected by total power transfer. And as Vin falls, the DC converter is going to "want" more Iin to maintain constant power on the output.

    With a solar panel that can output only an Imp max (based on amount of aviable sunlight at that moment in time)--Once the load (steady state or surge) "demands" more power than the solar panel can supply, the input voltage will fall (as the DC converter tries to pull more current). This is an "unstable" operating condition and will cause the Vin to collapse--And the DC converter will shutdown/reset.

    If you have more power (and current) than the DC converter+loads needs--The system will run fine--As soon as the available solar power is less than the load needs, the input voltage will collapse.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #17
    Re: 24V solar power supply
    BB. wrote: »
    As soon as the available solar power is less than the load needs, the input voltage will collapse.

    DC-DC converters have a lower Vin limit. Once the converter drags Vin to that level, then my guess is that the converter will allow Vout to drop.

    I am available for custom hardware/firmware development

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  • KC-watts
    KC-watts Solar Expert Posts: 37 ✭
    #18
    Re: 24V solar power supply

    BB, great explanation on how a solar panel is inverse of battery. Battery provides more amps as voltage is dropped, yet a solar panel reduces amps as voltage drops. Mods, I only mentioned NAW&S because I am indebted to their forum having inherited my 60W "hobby" panel. I only wish them the best is why I offer they be the first to carry the fully electronic MPPT buck-boost go no-go solar panel voltage regulator. Casey Watts.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #19
    Re: 24V solar power supply

    Not a problem KC.

    I just want to be clear for the newer readers here--None of us Moderators are connected with NAWS (in a business sense)--And we cannot/do not speak for them.

    NAWS, for the most part, leaves the forum alone and lets the users manage it (with some basic rules--More or less, a business/family friendly environment with on topic posts--Renewable Energy, conservation, and some RE politics).

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #20
    Re: 24V solar power supply

    Actually solar panels provide Voc @ zero current. Apply a load and the Voltage comes down and current goes up. Under 'ideal' load conditions you will see maximum power of Vmp * Imp. But they will provide Imp at near zero Volts. This is why they are not suitable power sources for so many things: they provide "current first, Voltage second". With load fluctuations and no regulation the I*V curve will go up and down wherever as the variation in input Voltage to the load varies its current demand. Most all loads want a stable input Voltage, even if they accept a wide range. They do not want I*V going all over the place from Imp*0V to Imp*Vmp to 0I*Voc.

    Good for charging batteries though. :D
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