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Forum Index : Solar : Can Solar panel make more useable power?
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| Georgen Guru  Joined: 13/09/2011 Location: AustraliaPosts: 462 |
My small solar panel at times produces well or just below 12.5V so not even a single mA goes anywhere. Is it possible to have some kind of device that would “concentrate” power to make it 15V or something like that? I understand that amperage will be minute, but if battery doesn’t get power it looses power all the time. Would 2.5V or 2.7V Super Capacitor come here handy? That it would get charged to certain level then send power to 12V battery through some kind of converter. George |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Georgen How big is the panel, watts? Supercaps are not going to help you here. If the pannel is big enough then you could use a small boost converter to get a few extra volts, but it wont be worth it unless you have a big enough panel. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
My panel is tiny 10W I could probably ask here what size panel I need to comply with requirement? (Personally I thought of getting 80W as size looks that amateur installer like me could manage, If 80W is too small I could get two of them or 120W one if it needs be) And where to look for and what type of "small boost converter"? George |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Even a 10W panel should produce more volts if its a 12V type, perhaps you were measuring it while connected to the battery. Solar panel 101  : Take the panel by itself outside in full sun and connect a multimeter set to DC volts across the panel terminals. It should measure at least 17V or the panel is faulty.
If you get 17V or more when the panel is aligned to the sun then you can measure its short circuit current. Set your multimeter to the 10A DC range and connect it to the panel terminals. You should get a little under 1A max. When the panel is connected to a battery the max current is somewhat less. If your battery is a little discharged you can connect it to the panel with the Amp meter in *series* with just one of the leads. It will then indicate what charging current flows into the battery. As the battery charges up its voltage rises, when it gets close to 14V you need to disconnect the panel to avoid overcharging. This is what a solar regulator does automatically. Klaus |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Understand that and solar battery in good Sun gives bit over 17V My idea was when light gets lower and panel produces 3V or 6V or 12V, then battery is not charged at all. Understand that with so low voltages amperage would be probably negligible too and even if voltage could be boosted I would get single mA or portion of mA But I am curious if this “shoulder”, in normal circumstances unusable electricity production could be used somehow too? George |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Well, since you are the curious type here is a solution for those low light times:boost converter Its cheap too so why not get one and play with it? Don't expect miracles though, the electrical energy obtained from a solar panel is a small percentage of the incoming solar energy (<20%) at best. In low light very little is available but its fun to see how much *extra* a boost converter could recover. BTW, I have a few of these converters (different layout) and they are useful for all sorts of projects. Just remember there is usually no protection built in and a wrong connection could easily destroy them. Search the forum, we had a topic on them a while back here. Klaus |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Thank you for this info. Will probably have to dig up some material on how to implement it and when, as I don't want to pester you too much. My immediate worries are: - Should I have it connected only during low light periods or it is OK to have it connected all the time as long as I do not exceed 2.5A - How this gadget knows that I need 15V to 18V and not 35V ? George |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
In one of the posts I noticed this: Posted: 14 November 2005 at 9:09pm Gizmo http://thebackshed.com/forum/forum_posts.asp?TID=64&KW=boost +converter [quote] We are trying to charge a 12v battery. The sun is low and the panel only makes 10 volts, not enough to charge the battery. But the solar panel can still supply a few amps, say 10 amps at 8 volts if we loaded it. The MPPT converts this 8 volts/10 amps to 14 volts/5 amps, enought to start charging. Now in full sunlight, the panel makes 20 volts at 10 amps. If we put this across our battery and loaded it down to 14 volts, we might get 12 amps. The MPPT can convert 20 volts at 10 amps down to 14 volts at 15 amps. [/quote] Does it mean that MPPT could do this job too? Probably not as Amperage will not be high, when solar battery barely produces any voltage George |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Georgen Yes a MPPT will work, but only for larger panels. Devices like MPPT have their own power overheads, they need a couple of watts just to run. With your 10W panel, when the light level is so low that its only making 6 or so volts, then you can only draw a few hundrew milliwatts of power from it, not enough to run a MPPT. The little boost circuit Tinker pointed out may work, it's worth a try, but only if you can get it for a few dollars. At some point the money spent on gaining a few millWatts would be better spent on a 2nd solar panel. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
They are adjustable - a little potentiometer sets the output voltage. Klaus |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
I tried few things with solar panel indoors in the evening and artificial light. Solar panel starts at below 1V and goes up to 8V even 10V just under 60W old type globe. Can booster have any input voltage from 3V to 32V and have output adjusted to 18V or 17V and stay there ? George |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Yes. Search for <SEPIC> buck/boost converters, but as mentioned they will use some power just to make them operate. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Hi Georgen, I am questioning the voltage rating of your little panel, a typical "12 volt" panel will have a max voltage between 18V and 23 Volt and a max output volt above 16 Volts. It takes a surprisingly small amount of light to get them over the 12.6 volt voltage threshold and start pushing against the resistance of the battery. I am guessing that your panel is rated to charge a 6 volt battery, if that is the case you most definitely need a voltage boost or an additional identical/similar panel and hook them in series. I'm confused, no wait... maybe I'm not... |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Found some info on : " buck/boost converters " But did not have luck on : " <SEPIC> " Maybe will have to look not on Forum, but on Back Shed Site George |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
http://en.wikipedia.org/wiki/Sepic Then go to Texas Instruments and look at all the ICs provided by ex-National Semiconductors. |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Quite possible. If I get 16V and 12V battery is 12.5V then it should be charged, or I am wrong and 18V - to 23V are needed to do charging properly? Davef, Thank you for link will study info when I get little bit more quiet time. George |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
The 18 to 23 is open circuit voltage (Voc) measuring the voltage with a multimeter attached to the positive and negative cables. No battery or load or resistance drawing on the panel. When you hook the battery up, it supplies a load to the panel that holds the voltage down. There are two exceptions to this, if the battery is not big enough for the panel or the battery is badly sulphated, in both cases the voltage will rise. The over 16 volts I quoted is maximum power volts (Vmp). for example if the spec sheet says Max Power is 4.76 Amps at 16.8 volts then 4.76 X 16.8 = 80 watts If the battery is half charged and is holding the voltage at 13.1 volts then 4.76 X 13.1 = 62.35 watts. In theory this is a loss of 17 watts that could be picked up with a MPPT gadget. In practice its a lot less and is not worth the effort unless the Vmp is a lot higher and the potential loss is quite large. The important thing is to fit a regulator so the voltage at the battery will not rise above its max charging voltage (for example a typical vented wet lead acid battery 14.8 volts) and then, at full charge it drops to a holding voltage, generally somewhere between 13.2 to 13.8 V depending on the battery chemistry. Deciding when a battery is fully charged is tricky. If you hook a decent sized panel directly to a battery then the battery will get to 90-95% charge then the voltage will rise above 15 volts and it will gas off rapidly and not completely charge. If the voltage is regulated and held at the batteries specified absorption voltage then full charge is the point when the amps going in to the battery stop reducing. This is usually between 1 and 2% of the battery banks rated amp hours, older flakier batteries are closer to 2%. A charge regulator matched to your battery size means it will look after itself. measuring battery voltage to estimate the state of charge is not practical in a working system. the batteries need to rest for 3 hours after a charge or discharge to get an accurate reading of resting voltage for your 12.5 volts to mean anything. Have a look it this page it might clear up a few things solar panels and voltage cheers yahoo I'm confused, no wait... maybe I'm not... |
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| Xmaswiz Regular Member  Joined: 14/04/2011 Location: United StatesPosts: 69 |
you could just use a CAP doubler as outlined in the windmill forums, very simple solution, very low cost. just search for cap doubler.  Santa Maria, CA. Noel |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Na that wont work, cap doublers only work on AC power, where a solar panel only provides DC power. The cap doubler uses the changes in current direction to charge/dump up the voltage, sort of thing. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Don B Senior Member  Joined: 27/09/2008 Location: AustraliaPosts: 190 |
Hi Georgen, Your 10 W panel is really too small to bother with voltage boosters or maximum power point trackers. As others have noted, the power overheads to operate these won't leave much to actually charge a battery, even in moderate sunlight conditions. If you want to get the absolute best out of your panel, then you need to rig some way of keeping it pointed at the sun as the sun moves throughout the day. Because of its small size, the tracking would have to be manual, but this would give you the maximum possible output. When you are in reduced lighting situations, the available power also drops dramatically as the voltage drops, so trying to boost the voltage in this situation to get a useful charging effect would be a waste of time. But don't be put off by these comments - keep reading and asking questions. Regards Don B |
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