Mixing Panels

[Offgrid]

Woohoo so I bought my first 100w solar panel today.Been makin them prior.Skrew making them! I got. 20 year warranty/80% efficiency.The watts surpass the sticker and pretty damn happy! It looks cool too compared to my made ones! I have one question though. The panels is rated 20v at 5 amps, I have 3 other DIY panels that produce about 17v with 3 amps.I have hooked all the panels new and old in parralel to increase the amps but also know will work at the lowest voltage which is the 17v. I didn't want to waste the extra 3 amps from the DIY panels but wanted to know if connecting them all together as they are now would be better or the single new panel would be better?

[Sunking]

Woohoo so I bought my first 100w solar panel today.Been makin them prior.Skrew making them! I got. 20 year warranty/80% efficiency.

No such thing as an 80% efficient panel. 20% is tops with 15 being good.

[Offgrid]

Why do most manufacturers keep going on about their panels will still have 80% efficiency after 20 years? Or do they mean 80% rated power? I think I worded my original statement incorrectly.

[Offgrid]

So Sunking do you think I should leave the old DIY panels and the new panel together? At least till the old one dies?

[Sunking]

Why do most manufacturers keep going on about their panels will still have 80% efficiency after 20 years?

They are not talking about efficiency, they are talking about the percentage of rated power output.

Example a 100 watt panel should generate 80 watts after 20 years.

With respect to panel efficiency, if a panel is 100% efficient, for each square meter of surface area; it will produce 1000 watts. A a panel with 1 square meter of surface area with 15% efficiency, will produce 150 watts..

So don't get to hung up on panel efficiency as it is mostly a non issue in most circumstances and only becomes important with limited area. To get those 18 to 20 % efficient panels cost big bucks, so unless space is limited, worry about the cost, not efficiency.

[Sunking]

So Sunking do you think I should leave the old DIY panels and the new panel together? At least till the old one dies?

Your only option is to wire them in parallel, and you will get decent results. Only problem is you turn your factory 100 watt panel into a 85 watt panel.

[Offgrid]

Thanks bud,your efficiency explanation makes perfect sense now.

[Offgrid]

Ok,Im getting a little concerned now.With my lower voltage (17V Voc +-) DIY panels and my Higher voltage (20v Voc) Factory panel in parallel my total charging voltage is only 13.56V (At battery terminals) This really concerns me because Im obviously not getting full charge power.Either that or my batteries are completely dead and taking time to raise the voltage but I know 12.46v is only about 20% DOD. So here is my question If I take away my 50W DIY panels and ONLY have my 100W with the higher voltage (20v Voc) ,will my batteries charge quicker? Regardless of having less amps from the DIY panels?

[Sunking]

Lot of things can be going on here, not time to panic. I suspect assuming the battery was good to start with it is fully charged, and if that is true the battery will not take any current and what you see is the cherge controller in float mode set to 13.6 volts.

Try this first. Disconnect the battery from everything, let rest 5 or 6 hours then measure the terminal voltage. If it reads 12.6 volts it is fully charged. If not let us know what it reads and we will go from there.

[Crumb]

Your only option is to wire them in parallel, and you will get decent results. Only problem is you turn your factory 100 watt panel into a 85 watt panel.

This looks like an important question, because I can see people adding different size panels all the time.
Can we explore this more fully? I have this question too.

Say I decide to add a 10 watt panel to a 60 watt small system.
You are hinting at an adverse effect in output, but it isn't clear how/why this happens or the best way to deal with it.

Additionally, in this configuration -do we need to do anything fancy/special with diodes or wiring?

Edit: is it fair to assume the challenges are greater as the size difference gets bigger?
In other words a 50 and a 60 watt panel together is not a big deal but a 5 watt and a 130 watt can have a bigger problem?

[Sunking]

This looks like an important question, because I can see people adding different size panels all the time.
Can we explore this more fully? I have this question too.

You can ask a question but this subject has been beat to death.

Mixing panels should be avoided. there are work around but expensive to implement and adds a great deal of complexity.

For example a good work around for a grid tied system is using microinverters. A inverter for every panel. Down fall is expense and very complex requiring a stand alone monitoring system.

For battery systems it forces you to use 12 volt panels and can only configure them in parallel which is very inefficient. One work around is similar of grouping matched panels in series to take advantage of higher voltages and MPPT controllers, and use another system matched with it own MPPT controller. In other words you make 2 or more panel arrays serving a common battery. Again that gets very expensive using multiple controllers, extra wiring, combiners, fuses etc and adds complexity.

I have said this a million times. Buy panels from manufactures where solar is a micro fraction of their business like BP, Sanyo, Sharp, Kyocera who have been in biz for decades and will still be around decades from now to offer warranty replacements and expansions. Most of the solar panel manufactures will be out of biz before long. If you own Evergreen solar panels you are SOL now. Most of the rest of the panel manufactures are near bankruptcy struggling to survive.

[Mike90250]

Panels in parallel, run at the voltage of the lowest panel
(your 20V panel will run at 17V)

Panels in series, will be limited to the lowest amp panel in the string.
(3, 6 amp panels in series with a 4 amp panel, the string will only produce 4 amps)

So, panel matching is important. the 17V / 20V combo you have, is not fatal, and should work to charge the batteries.

[Crumb]

Panels in parallel, run at the voltage of the lowest panel
(your 20V panel will run at 17V)

Panels in series, will be limited to the lowest amp panel in the string.
(3, 6 amp panels in series with a 4 amp panel, the string will only produce 4 amps)

So, panel matching is important. the 17V / 20V combo you have, is not fatal, and should work to charge the batteries.

Excellent, thank you! - This and a little ohm's law can fill in the blanks nicely.

[s.xavier]

always keep panels close together and use the same brand (preferably a reputable one)... skimping here and there doesn't make much sense and i'm sure most people have better things to do

if you owned a classic 65 mustang you wouldn't want to use crap parts from a 80s hyundai

[Mike90250]

... if you owned a classic 65 mustang you wouldn't want to use crap parts from a 80s hyundai

Just grind down that heavy steel and the cheap tin pieces fit fine.