panel watt size

[john.b]

Hi, My question is about the difference between panel size in watts, i'm new to solar and have a 300 watt panel but after watching many videos on Youtube i mostly see people with large amounts of smaller pannels like 100-150 watts, this kind of got me thinking why do people do that instead of using larger panels especially when short of space, my 300w panel is around 1m x 1.5m and i'd think 3 x 100w panels would be bigger in size so i was wanting to know is there any advantage to having more smaller panels than fewer larger ones, will 3 x 100 watt panels give more current than 1 x 300 watt panel ?

Many thanks
john

[sensij]

With PWM charge controllers on 12 V systems, sometimes smaller panels are a better choice. For most systems, the 300 W panel you have will be more cost effective.

[john.b]

With PWM charge controllers on 12 V systems, sometimes smaller panels are a better choice. For most systems, the 300 W panel you have will be more cost effective.

Thanks Sensij, sorry i should have said my controller is MPPT, the system is 12v for now but may change that later on as i will need to run long cable when i build the array, the 300 panel is just sitting on a shed roof just to give me some idea of what to expect, what caught my eye was the panel labels on different panels, mine says 9.5A but i'd noticed some100w panels say 5.5A so was thinking 3 of these have the potential make more power than the single 300w, i've probebley got my wires crossed so that's why i thought i'd post up to get some thoughts on it.

Thank you again for your reply
Take care
john

[littleharbor]

The difference is the voltage those amps are coming in at. The amperage of a 24 volt, 72 cell panel would be half of an equal wattage @ 12 volt panel. When converted by your MPPT controller the amperage would actually more than double because the voltage step down would be at battery voltage which is even lower than the 12 volt panel's Vmp.

[SunEagle]

Thanks Sensij, sorry i should have said my controller is MPPT, the system is 12v for now but may change that later on as i will need to run long cable when i build the array, the 300 panel is just sitting on a shed roof just to give me some idea of what to expect, what caught my eye was the panel labels on different panels, mine says 9.5A but i'd noticed some100w panels say 5.5A so was thinking 3 of these have the potential make more power than the single 300w, i've probebley got my wires crossed so that's why i thought i'd post up to get some thoughts on it.

Thank you again for your reply
Take care
john

Simple rule of thumb concerning CC's

PWM - amps in = amps out
MPPT - watts in = watts out

So if you took 3 x 100watt panels with an Imp = 5.5amps and wired them in parallel into a PWM CC you will get 16.5amps of charging.

If you took a 300 watt panel with an Imp = 9.5amps and wire it to an MPPT CC you will get 300w / 12volt = 25amps of charging.

[citabria]

Just my thoughts on why there are pv systems out there with panels of lessor wattage:
1. Many of the pv systems (especially on youtube) started as a (hobby).
2. No planned design of a complete pv system was taken by the owner/builder, because they did not understand what their ultimate goals of a completed system were to be. For example: The builder just wanted a couple of night lights and a way to charge cell phones, etc... But, along the way they decided to power a refrigerator, freezer, or well, etc..
3. The builder did not plan a monetary budget for a completed system and thought they would slowly migrate to a larger system as funds allowed.
4. The builder got a (heck of a deal) on salvaged or unused panels that no one else wanted.
5. The builder got a heck of a deal on salvaged telecom batteries and decided to build a pv system to make use of the batteries.

Good luck with your project..

[SunEagle]

Just my thoughts on why there are pv systems out there with panels of lessor wattage:
1. Many of the pv systems (especially on youtube) started as a (hobby).
2. No planned design of a complete pv system was taken by the owner/builder, because they did not understand what their ultimate goals of a completed system were to be. For example: The builder just wanted a couple of night lights and a way to charge cell phones, etc... But, along the way they decided to power a refrigerator, freezer, or well, etc..
3. The builder did not plan a monetary budget for a completed system and thought they would slowly migrate to a larger system as funds allowed.
4. The builder got a (heck of a deal) on salvaged or unused panels that no one else wanted.
5. The builder got a heck of a deal on salvaged telecom batteries and decided to build a pv system to make use of the batteries.

Good luck with your project..

You have hit the nail on the head of how off grid systems get built first and then designed later at a big cost.

[john.b]

Thank you Littleharber and SunEagle, right that's real interesting and explaines a high amp reading i had on the watt meter that i'd just assumed was a glitch and wrong.

So if i understand you correct the 300w panel is capable of producing 25A in a 12v system using MPPT, with it having 9.5 on the back i was thinking this was it's max output.

As i said i noticed a while back the watt meter said my Amps peeked over 16A one day and i thought it was just a glitch.

So if i've understood this right that is great, it has now made me think about the array size which i'll need to be careful not to over step, my controller has a max output of 80A so would i be correct to make sure the array can not go over this amount ?

Thanks again, much appreciated
Take care
john

[john.b]

Just my thoughts on why there are pv systems out there with panels of lessor wattage:
1. Many of the pv systems (especially on youtube) started as a (hobby).
2. No planned design of a complete pv system was taken by the owner/builder, because they did not understand what their ultimate goals of a completed system were to be. For example: The builder just wanted a couple of night lights and a way to charge cell phones, etc... But, along the way they decided to power a refrigerator, freezer, or well, etc..
3. The builder did not plan a monetary budget for a completed system and thought they would slowly migrate to a larger system as funds allowed.
4. The builder got a (heck of a deal) on salvaged or unused panels that no one else wanted.
5. The builder got a heck of a deal on salvaged telecom batteries and decided to build a pv system to make use of the batteries.

Good luck with your project..

Hi Citabria
Your correct and this is a new hobby for me so not really sure where it will go or how much i'll end up doing, right now i've just got lights and the use of a pressure washer on a everyday basis but would like to add to this in time, the one pannel i have is not really in the best location so all being well when i build the array it should give me more as it will be in a place that gets more sun for longer. the whole thing is a new learning curve for me.

Take care
john

[J.P.M.]

OP:

Spend $20 on a copy of "Solar Power Your Home for Dummiies". No insult intended. It's a good primer with a name the thin skinned find upsetting. You need information on the basics.

Welcome to the neighborhood.

[SunEagle]

Thank you Littleharber and SunEagle, right that's real interesting and explaines a high amp reading i had on the watt meter that i'd just assumed was a glitch and wrong.

So if i understand you correct the 300w panel is capable of producing 25A in a 12v system using MPPT, with it having 9.5 on the back i was thinking this was it's max output.

As i said i noticed a while back the watt meter said my Amps peeked over 16A one day and i thought it was just a glitch.

So if i've understood this right that is great, it has now made me think about the array size which i'll need to be careful not to over step, my controller has a max output of 80A so would i be correct to make sure the array can not go over this amount ?

Thanks again, much appreciated
Take care
john

Just a reminder that some charge controllers labeled as "MPPT" are not. They are usually much cheaper then a true MPPT and have a tendency to draw the unaware to them since cost is usually a factor when people build a system.

Out of curiosity what it the make and model of your MPPT CC?

[john.b]

OP:

Spend $20 on a copy of "Solar Power Your Home for Dummiies". No insult intended. It's a good primer with a name the thin skinned find upsetting. You need information on the basics.

Welcome to the neighborhood.

J.P.M No offence taken, i know those dummies guide books are work a look, i didn't know they did one for solar so will have a look and pick one up. thank you

[john.b]

Just a reminder that some charge controllers labeled as "MPPT" are not. They are usually much cheaper then a true MPPT and have a tendency to draw the unaware to them since cost is usually a factor when people build a system.

Out of curiosity what it the make and model of your MPPT CC?

My controller is an SMK, it's quite a big heavy thing and looks to be well made, i did buy a PWM at first but found it not all that good, the SMK made a big difference. link below

http://www.smksolar.com/product/detail/22.html

[SunEagle]

My controller is an SMK, it's quite a big heavy thing and looks to be well made, i did buy a PWM at first but found it not all that good, the SMK made a big difference. link below

http://www.smksolar.com/product/detail/22.html

The SMK looks like a true MPPT CC so you should be good to go.

[AzRoute66]

So if i understand you correct the 300w panel is capable of producing 25A in a 12v system using MPPT, with it having 9.5 on the back i was thinking this was it's max output.

. The the panel is still producing the 9.5 amps, it is the charge controller that is converting the power into 25 amps.

As i said i noticed a while back the watt meter said my Amps peeked over 16A one day and i thought it was just a glitch.

Those watts/amps are coming out of the charge controller, not the panel.

So if i've understood this right that is great, it has now made me think about the array size which i'll need to be careful not to over step, my controller has a max output of 80A so would i be correct to make sure the array can not go over this amount ?

No, you still don't quite have it. The controller will accept however much power from the panel that the battery and loads will accept from it. If your battery is close to fully charged, and light load, the controller will be providing minimal amps so drawing a minimal amount of amperage from the panel. If the battery/load is charging heavily, the controller will be taking as much power as possible from the panel, up to the panel maximum or the controller rated maximum, whichever is lower. So you can see, even if the array was capable of providing enough power to create ___ amps, the 80A controller will only take enough power to create 80 amps at 12 V.