How do Solar Cells behave from a Voltage perspective? There are often 12V and 24 V Moduls. What I want to know...

How do Solar Cells behave from a Voltage perspective? There are often 12V and 24 V Moduls. What I want to know, do they have constant Voltage output and the current changes depending on the Light or does voltage and current change with light intensity and the 12V or 24V are just the upper limit?

Other urls found in this thread:

solarquotes.com.au/blog/how-to-read-a-solar-panel-specification-part-1-power-temperature-specs/
solarquotes.com.au/blog/understanding-solar-panel-specifications-part-2-power-tolerance-efficiency/
electrodacus.com/
en.wikipedia.org/wiki/Maximum_power_point_tracking
batteryuniversity.com/learn/
youtube.com/watch?v=Iis9sJFIR3Q
twitter.com/NSFWRedditVideo

What you need to do is get yourself a cheap solar cell and a cheap volt meter and some resistors and play around. Learn about loads and current draw and voltage relationships. Nothing beats getting the real parts and experimenting/playing.

In short. The voltage will change much less when they are not powering something. Higher light will keep the voltage up and allow you to power more things without the voltage sagging.

The ultimate way to show this is to take the wires coming out of the solar cell and connect them together and measure the voltage. zero volts is what you'll get since your load is the wire. Have fun.

I don't have any to live test. My point for asking is because I wanted to use a solar charger with an bike dynamo and was wondering if I'd need beside a AC/DC rectifier a voltage converter too.

Most modules will have a data sheet. But iirc voltage goes up quite fast and stays at .5 to .6 volts per cell. If you want to charge a battery though, just get an MPPT charger, which converts the voltage of the cells' optimum power point to charging voltage. There should be a voltage-current-diagram in the module data sheet, which goes straight and then drops. The 'knee' at the start of the drop is that optimal power point.

Oh, and 12 and 24v modules are just rough estimates for lead acid battery charging voltages and how many cells are in series. It's not really the true voltage.

The datasheet seems to expect 12V or 24V for most chargers so with your description I most likely will need a voltage converter.

It's not just about charging batteries. I wanted to mount a small solar panel on a bike trailer. So while charging Batteries on one hand, I also wanted to use the solar charger to operate USB Devices and power a laptop with a 12V socket.

Makeing use of the Dynamo on the Bike, I could use a smaller solar panel and also charge when sun is down.

>do they have constant Voltage output
No.

And really, a solar panel's spec sheet has way more than just a nominal voltage.

solarquotes.com.au/blog/how-to-read-a-solar-panel-specification-part-1-power-temperature-specs/
solarquotes.com.au/blog/understanding-solar-panel-specifications-part-2-power-tolerance-efficiency/

And of course there may be even more specs, such as temperature coefficients for the Voltage.

>I most likely will need a voltage converter
Sure you do.

> I wanted to mount a small solar panel on a bike trailer.
electrodacus.com/

>electrodacus.com/
interessting. getting rid of weight is important. It's still a budget question, though. however if I can make it moneywise I'll probably go with the lithium batteries/ controller.

Lithium batteries like LiFePo4 are very likely cheaper. Not just because of the weight savings, but also because of massive difference in charge/discharge efficiency (you can make the solar part of the setup correspondingly smaller / cheaper).

PS: I saw aliexpress also has a few solar charge controllers for Lithium chemistry batteries by now. If you think that guy's pretty nice controller is too expensive you might venture to try the Chinese ones.

I have a question, ehat does controller do, i saw a solar sheet with panels, controller, battery and invertor. All are obvious except controller

It controls the battery charging.

It maybe also does this:
en.wikipedia.org/wiki/Maximum_power_point_tracking

Maybe it also keeps statistics so you can optimize the system and serves other functions.

PS: Battery charging / discharging for various chemistries and more is explained in some detail here:
batteryuniversity.com/learn/ , see BU-4xx and 5xx

You do need a controller for most chemistries - you can't just apply x volt y amp for 30 minutes (or forever) and expect good results.

these days, besides charging batteries, controllers come with additional fuctionality like direct output for something (lights for example) and also some even have 5V USB outlets.

Basically you might not need an extra inverter depending on your usage.

Usually each of the wafers in the OP picture only put out a few volts, and so you need to string them together in series (daisy chain) to get a sum voltage of each panel. Keep adding wafers until the panels are a few volts above the nominal voltage of the battery.

Hotter panels have higher resistance and so lower voltage (less wattage output).

The latter. As long as I remember my studies correctly.

Sure, that's the temperature coefficient.

Either way, you really want the full spec sheet, not just the nominal voltage when you buy a solar panel for more than just a bit of playing around.

Since I wasn't able to find reasonable priced things for my needs I probably go an build it myself. Since someone already thought about this, I post his conclustion.

If i have a battery of 120aH and output of 12v (going into inverter to 220v for household items), how much W would i have?

well it depends on what you use with it. the 120 Ah don't change. It's 12 hours on something that uses 12 Watts.

Oh, so it's 120ah times 12v so i get Wh. So it's 1440 kWh meaning 10 hours of sonething that uses 144w?

1440 Wh*

They have an internal resistance so they tend to hardly produce any voltage in low light then it will quickly ramp up as the sun comes.

made a mistake there. it's actually 120 Hours for something that uses 12 Watts.

144W/220V=0,655A
120Ah/0,655A=183 hours

well there is power loss on the inverter too so it's less that that.

wait, do i count 12v from a battery or 220v from a inverter?

>12 Watts
*headdesk*
There must ne something wrong with me. It's 120h @ 1Ampere. That's it. Forget the 12 Watts part.

if your device is on the inverter that puts out 220v you count 220v. P=U*I

If you want to learn about how to extract the most power from a given panel, look into maximum power point tracking.

Basically intelligently control your load resistance to match your panel's at-the-moment internal resistance. It's the maximum power transfer theorem applied to an erratic source.

Also take into account you don't want to discharge lower than about 50% on a normal flooded lead acid cell, or 30% on an AGM or deep cycle cell. Lower and you're really hurting your battery's cycle life.

When calculating your stored energy, multiply your amp hours and your battery voltage. When chaining batteries to form a pack, add ah when in parallel and add voltage when in series.
When you invert to 220, the current you pull to get the same power is proportionally smaller, so it all works out. You're just better off working out the math using your battery voltage because it's less complicated.

>When you invert to 220, the current you pull to get the same power is proportionally smaller, so it all works out. You're just better off working out the math using your battery voltage because it's less complicated.

So, how much Wh would i get from a 1 battery of 120ah and 12v goign into inverter to 220v?

the inverter is something that converts 12V to 220V. There is a bit of power loss on the conversion but the inverter itself shouldn't drain the battery unless you plug something into the inverter.

12*12=144
*10 because I dropped a zero earlier
=1440 Wh, or ~1.4 kWh

It doesn't matter what your inverter's output voltage is.
It DOES matter what your inverter's efficiency is. Multiply by your inverter's efficiency at the load you plan to put on it. This is usually 87-95% at the ideal load, but some shitty inverters drop off to like 50% when the load is too low or high.

so let's say you put a Light (9W), a Notebook (45W) and a Phone charger (5W) on the inverter. You pull 59 Watts.

59 Watts / 220 Volt = 0.268 Ampere
120 Ah / 0.268 Ampere = 447 Hours of usage.

In theory.

Only if you have a 240V battery bank. Recalculating with watt-hours and real math.
120Ah * 12V = 1440Wh
1440Wh / 59W = ~20h not counting losses

>120Ah * 12V = 1440Wh
I don't think this is a correct calculation. It's already 120 Ah @12V and 1Ampere. You can not calculate Wh unless you got a consumer... I think.

Most lead acid batteries are actually rated at like 10.8V or something, pic related.

(cont'd)
Meanwhile, glorious lithium chemistry batteries (note the much lower weight).

Never mind virtually all other characteristics also being better, like the self-discharge over time, battery life at a reasonable DOD, and so on.

Inverters convert power, not voltage. P = U * I. Energy = power * time. 1 Wh = 3600 J. Both potential and kinetic energy can be measured in watt-hours or joules.

Right... okay, to a first approximation. Also I goofed up and divided by 69 instead of 59. Drunkposting is fun.
>virtually all other characteristics also being better
Except that they're intolerant of abuse and, as is a great concern to /diy/ers, expensive. Other than that they're fookin' awsum.

>a Light (9W), a Notebook (45W)
Jesus fuck, first step of getting good battery times is reducing your load as much as possible. Nine watts of light? Is that a fucking flood lamp? A 45 watt notebook? Is that a gayman laptop?

Seriously, the suggested power usage can be cut to third with some sanity.

If you want to play with solar on the cheap, hit up your local dollarstore/poundland for garden lights

cheap as fuck and neatly moddable

youtube.com/watch?v=Iis9sJFIR3Q

> Except that they're intolerant of abuse
Of massive abuse like puncturing it with a conductive material or charging it at a completely wrong voltage, perhaps?

But generally no. It's why every smartphone has such batteries (and on top of that even the slightly less abuse tolerant chemistries than LiFePo4).

> and, as is a great concern to /diy/ers, expensive
Nope again. For solar applications (or vehicle use - with the weight being a factor), they are almost always clearly cheaper.

And they are also generally cheaper per capacity over time.

All you get with lead acid is MAYBE a lower initial cost on just the batteries when you're dealing with some other kind of system than solar, like a combustion engine generator or whatever... and even that hinges on how much current you actually need to get in and out, because lead acid are very very much more limited in what is efficient.

>convert power
ah, now it makes sense. 59W/12V=4,92A and 120Ah / 4,92A = 24h including efficiency 20h sounds reasonable

>charging it at a completely wrong voltage, perhaps?
Am I mistaken in understanding that Li+ batteries are designed for use with a negative-delta-V charge termination criterion? Maybe these ones intended for motor cars are a bit smarter than that, or maybe alternators just never reach full charge voltage.
>they are almost always clearly cheaper.
Hmm, and charge and management circuitry is getting ever easier to design and apply. Fair enough.

> Am I mistaken in understanding that Li+ batteries are designed for use with a negative-delta-V charge termination criterion?
Aren't you thinking of NiMh?

Lithium battery chargers generally they just sense if the voltage is within a few percent of the target voltage and then terminate the charge. Before that the topping charge's voltage would usually be dropping as the cell gets more full and the current would stay more or less steady. IIRC. But I'm obviously using a charger to handle this might have ignored or confused some important details - I really don't actually need to actually know, it works regardless.

>Aren't you thinking of NiMh?
Fuggggg. You're right. In which case an alternator with a voltage regulator would never bring that battery to "full" charge as far as the Li-ion cells are concerned.
At single pricing, ~$500 for the Li-ion version vs. $225 for the lead-acid 33% larger version. Li+ is certainly getting there, if lithium supplies hold out.

>~$500 for the Li-ion version vs. $225 for the lead-acid
More like $470 for the one I posted, it has twice the service life if you assume even just 60% discharge, which is perhaps unrealistically little discharge. You might want to actually discharge to 20% just so you can drive around with less batteries, but lead batteries get *terrible* life the more you discharge them. If you regularly do 15% or under, you'll get like 150-200 cycles of battery life rather than a nominal 1000.

> 33% larger version
Not entirely that. I imagine you'll have about 6Hrs worth of power (in terms of near optimal sun) in total, with the solar panels not always being oriented and angled correctly, getting a bit dusty and scratched over time, weather, shade, and so on. Or rather, if you have more solar panels than will charge well for 5hrs or so, you'll be having an excess and discarding excess power a lot of the time, which you presumably don't want. [So I'm just going with the 90Ah rating for that kind of charging, making the batteries essentially equal.]

Never mind you'll have extra solar panels and rectifiers and stuff anyhow to compensate for the 30%+ discharging / charging inefficiency difference of lead-acid batteries.

And then the weight differences of the batteries? That's a major cost factor on its own already.

Lithium is not at all "close". It's simply cheaper in a mobile solar system, and even often cheaper in a stationary one.

I work in solar distribution and sell hundreds of kWs worth of panels a week and I've no idea how the fuck they work. Also QCELLS is top tier

What panels are currently best bang for the buck