Reply
 
Thread Tools Display Modes
 
Old 12-07-2016, 11:31 AM   #1
Mini-Skoolie
 
Join Date: Dec 2016
Posts: 43
Micro-Inverter vs Power Optimizer

Researching the solar system now and I know that I do not want my solar panels in series. With the curved roof, my pannels will be in multiple orientations and I don't want this or shading to impact my entire system. This means that I need to install either micro inverters or power optimizers on the back of each panel. The question is...which one.

Micro inverters convert the DC to AC at the panel. However, I would then need to convert back to DC to charge my batteries...and then convert from DC to AC when there is no sun to run my AC items like the fridge.

Power Optimizers condition the DC at each panel so the power can be combined in its DC state before you do whatever you want (either send through inverter or directly to the DC charge controller to feed the batteries)

I'm leaning towards the Power Optimizer right now...but what are your thoughts?
PappySki is offline   Reply With Quote
Old 12-07-2016, 12:07 PM   #2
Bus Crazy
 
Join Date: Nov 2011
Location: Sault Ste. Marie, Ontario
Posts: 1,677
Year: 1997
Coachwork: Thomas
Chassis: B3800 Short bus
Engine: T444E
Rated Cap: 36
Neither?

How many watts and volts are the panels in question? Just wire the panels in parallel to a bus bar and connect that to the charge controller. Charge controller runs straight to the batteries. Inverter pulls directly from the batteries.
__________________
My build page: Armageddon - The Smell of Airborne Rust
jazty is offline   Reply With Quote
Old 12-07-2016, 12:50 PM   #3
Mini-Skoolie
 
Join Date: Dec 2016
Posts: 43
Only issue is that shade on any of the panels will reduce the efficiency of all the panels in this setup. That is what I am trying to avoid. Both the micro inverters and the power optimizers allow the panels to operate independently of each other.
PappySki is offline   Reply With Quote
Old 12-07-2016, 01:02 PM   #4
Bus Crazy
 
Join Date: Nov 2011
Location: Sault Ste. Marie, Ontario
Posts: 1,677
Year: 1997
Coachwork: Thomas
Chassis: B3800 Short bus
Engine: T444E
Rated Cap: 36
Only if you wire them in series is that true. If you want to increase voltage then you wire them in series. If you want to keep each panel independent and have the current increased then you wire them in parallel.
Panels wired in parallel are independent in that if one is completely shaded it has no effect on the other panels. Your total array output is reduced, of course.
I have my panels wired in parallel. One can be completely shaded and the other can be producing full power.

Here's a 2-second google search page I found on the subject: How to Wire Solar Panels in Parallel or Series | HES PV Blog
__________________
My build page: Armageddon - The Smell of Airborne Rust
jazty is offline   Reply With Quote
Old 12-07-2016, 01:34 PM   #5
Mini-Skoolie
 
Join Date: Dec 2016
Posts: 43
Makes sense...so is there any benefit to the micro-inverters or power optimizers?

Also, I'll be charging a 48v battery bank. I'm leaning towards keeping my panels wired in parallel (300w, 25amp, 12v) and using a 12v to 48v DC/DC converter? Thoughts?
PappySki is offline   Reply With Quote
Old 12-07-2016, 01:49 PM   #6
Bus Crazy
 
Join Date: Nov 2011
Location: Sault Ste. Marie, Ontario
Posts: 1,677
Year: 1997
Coachwork: Thomas
Chassis: B3800 Short bus
Engine: T444E
Rated Cap: 36
I'll chime in again here..

No, I don't think there's any benefit to using micro-inverters or power optimizers on a small scale solar array that isn't grid-tied. It would also be added complexity, which is often not a good thing.

Uh oh. So your panels are 12v and you want a 48v battery bank.. Hmm.. Well, you could maybe use a DC step-up converter, but it'll take some fiddling with and, again, adds complexity. A problem I see is that with the varying output of the panels a step-up converter will be constantly cycling off and on. I would expect it to burn out quickly.. Have you been able to find a reasonably priced step-up converter that can handle the necessary watts? All this extra stuff just makes me think it's going to be unreliable.

You'd be better off using higher voltage panels and an MPPT charge controller. I don't know of any charge controllers that can take a lower voltage and increase it on their own. It's usually the other way around. I have a Tracer MPPT charge controller that can take up to 100 volts input and charge a 12 volt, 24 volt or 48 volt battery bank.

Honestly, with those low-voltage panels the most direct solution is to put them in series, despite the shading issues you'll encounter. Otherwise it might be worth putting them in parallel and going with a 12 volt battery bank.
__________________
My build page: Armageddon - The Smell of Airborne Rust
jazty is offline   Reply With Quote
Old 12-07-2016, 01:59 PM   #7
Mini-Skoolie
 
Join Date: Dec 2016
Posts: 43
Learn something new every day and I really need to stop making assumptions. I just assumed that solar panels were 12v DC. Time for more research

Thanks
PappySki is offline   Reply With Quote
Old 12-07-2016, 02:09 PM   #8
Bus Nut
 
Join Date: Jun 2016
Location: Orange County, CA
Posts: 859
Year: 1990
Coachwork: integral
Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
As Jazty said, your plan is too complicated, inefficient, expensive and potentially unreliable. On any moving vehicle you need to keep it simple! If you have a 12V house battery bank, use grid-tie panels (about 30V and 8.5A each, and well less than $1 a watt) in parallel, with their combined current feeding a MPPT charge controller that will charge the batteries. This way one shaded panel doesn't cut the entire output, and the CC is working efficiently because it's stepping down voltage and stepping up current by only about a factor of two. The batteries' output then powers an inverter for your AC loads. Simple!

Micro inverters are for grid-tie systems, and not even all of them.

John
Iceni John is offline   Reply With Quote
Old 12-07-2016, 10:45 PM   #9
Bus Nut
 
warewolff's Avatar
 
Join Date: Sep 2016
Location: NY
Posts: 468
Year: 2000
Coachwork: Carpenter
Chassis: International 3800
Engine: T444E
Quote:
Originally Posted by PappySki View Post
Makes sense...so is there any benefit to the micro-inverters or power optimizers?

Also, I'll be charging a 48v battery bank. I'm leaning towards keeping my panels wired in parallel (300w, 25amp, 12v) and using a 12v to 48v DC/DC converter? Thoughts?
I sell solar for a living and microinverters are great for maximizing profits earned by big corporate solar companies when installed on otherwise low sun hour roofs. They're used mostly in private residential projects, producing just enough energy to save the homeowner their 20% or so on electric and with the federal rebates here in the US the company makes a killing. I would never fathom installing microinverters on my bus. Just install a heavy duty tilt system so you can angle the panels in the winter. The difference between an RV and a true residential install is that the homeowner is rarely going to want to get on the roof and adjust 20 panels. Even if you found a homeowner who was willing to get on the roof and tinker around, the liability that comes with 3rd party owned systems wouldn't allow it.

On your bus, however, get up there and tilt the 3 or 4 panels to the point that they get direct sun. Jazy is spot on in that if you're really concerned about shading, wiring parallel will overcome that concern.

Lastly, check out the 24v 305w Grade B solar panels selling on ebay. They put out something like 9 amps per hour, each, in optimum sun. ~$100 per panel, cosmetically flawed but otherwise work fine. If you can pick them up in Arizona on a desert vacation you save yourself freight shipping and can invest in a good MPPT charger so you don't have to worry about keeping the voltage the same on your roof and in your battery bank.
__________________
Roads? Where we're going, we don't need ... roads.
warewolff is offline   Reply With Quote
Old 12-08-2016, 10:03 PM   #10
Bus Crazy
 
ol trunt's Avatar
 
Join Date: Apr 2012
Location: So Cal
Posts: 2,449
Year: 1935
Coachwork: Superior
Chassis: Chevy
Engine: 317 ci/tid / Isuzu
Thanks J ,IJ and WW. I've copied your comments to my notebook as a reminder should I ever find myself in the position to build a true live in Skoolie. What you point out makes perfect sense.

Jack
ol trunt is offline   Reply With Quote
Old 12-09-2016, 04:44 AM   #11
Mini-Skoolie
 
Join Date: Dec 2016
Posts: 43
Thanks everyone. Appreciate the feedback and will include in my plans
PappySki is offline   Reply With Quote
Old 12-09-2016, 08:05 AM   #12
Bus Crazy
 
joeblack5's Avatar
 
Join Date: Dec 2015
Location: pa
Posts: 1,515
Year: 98
Coachwork: 1. Corbeil & 2. Thomas
Chassis: 1 ford e350 2 mercedes
Engine: 7.3 powerstroke & MBE906
Hmm I do not think all of this makes sense.

micro inverters are used in grid tie systems unless you get really fancy stuff. So on a bus that is already useless.

Power opimizers are system that short shaded panels out of a series loop so that they do not affect the whole string, mostly used in high voltage direct grid tie systems.
Not very usefull for busses either.

you first have to specify how many watt of solar you are planning to install, then you can decide if it is worth your while to go to higher voltage inverters. 48 volt inverters can be about 10% more efficient.

Lead acid batteries are very inefficient in charging the last 10% of charge because of the gassing. They need to gass to avoid sulfate buildup. So you will loose a lot of solar power to just charge the batteries to the fill 14 to 15 volt.

It is more efficient to go with lithium . That is way better / efficient for partial charging and also will have longer lifetime with being partial charged.

If you go with multiple small solar panels you can get real cheap mppt charger for 12 volt at 5 to 8 amp about $$8.
So it might be possible to use 75 watt panels and give each a cheap mppt.
Larger panels are often cheaper. ebay is full of new $.55/watt panels
joeblack5 is offline   Reply With Quote
Old 12-09-2016, 08:28 AM   #13
Mini-Skoolie
 
Join Date: Dec 2016
Posts: 43
I'm shooting for 2400 - 3000 watts of solar charging a 48v system with 200amp hour LiFeMnPO4 storage array. System will provide ample power as we build an off-grid home. It will run/charge power tools, air compressor, mini-split a/c unit, etc. Since using a mini-split, there will be ample space on the roof. Additional requirements for multiple telecomms options as I must always be connected to the internet. 3.5kw gennerator will provide back up power if needed due to heavy work load during the day or series of days with limited sun.
PappySki is offline   Reply With Quote
Old 12-09-2016, 09:34 AM   #14
Bus Crazy
 
joeblack5's Avatar
 
Join Date: Dec 2015
Location: pa
Posts: 1,515
Year: 98
Coachwork: 1. Corbeil & 2. Thomas
Chassis: 1 ford e350 2 mercedes
Engine: 7.3 powerstroke & MBE906
Sound like a good plan . we have 7200 watt on our barn with battery back up. 2 outback 3648 grid tie inverters and our 48 volt forklift doubles as battery bank.
Where are you located?
On our bus I am installing as we speak 3*300 watt panels at 24 volt. All small users .lights. Fridge and diesel heater are 12 volt as to avoid conversion losses. Then we have an older style sine inverter for short term load as induction cooking and microwave.

In our off grid cabin I wired for 48 vdc and 120 ac. There I use thin film panels. They are low efficiency but high voltage 100 volt range and take partial shading very well. They are also cheap. If you have enough space and do not need high efficiency then that could be an option.
joeblack5 is offline   Reply With Quote
Old 12-09-2016, 10:12 AM   #15
Mini-Skoolie
 
Join Date: Dec 2016
Posts: 43
Right now I'm in VA, but we will be going mobile in a few years (teaching online classes and picking up short term contracts). Plan is to build a home base and travel as we please.
PappySki is offline   Reply With Quote
Old 12-09-2016, 10:47 AM   #16
Bus Nut
 
Join Date: Jun 2016
Location: Orange County, CA
Posts: 859
Year: 1990
Coachwork: integral
Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
PappySki, why do you want a 48V system in a bus?

John
Iceni John is offline   Reply With Quote
Old 12-09-2016, 11:34 AM   #17
Mini-Skoolie
 
Join Date: Dec 2016
Posts: 43
48v system lets me run a 48v mini-split a/c system and it will match the system installed in our residence. Mini-split will allow me to have no large components on the roof which means I can maximize my solar collection. 48v a/c means I have no conversion loss and they are significantly more efficient and effective than any other DC A/C option. This will be an expensive system, but it will meet our short and long term requirements.
PappySki is offline   Reply With Quote
Old 12-09-2016, 12:00 PM   #18
Bus Crazy
 
joeblack5's Avatar
 
Join Date: Dec 2015
Location: pa
Posts: 1,515
Year: 98
Coachwork: 1. Corbeil & 2. Thomas
Chassis: 1 ford e350 2 mercedes
Engine: 7.3 powerstroke & MBE906
Great plan, do you want all your solar on your bus or are you planning to put some on your house. How much PV on the bus?

We are using lithium scavenged from Nissan Leaf and chevy volt. These have the longest life if you do not exceed 4.05 to 4.1 volt. Of coarse that gives you reduced capacity.
Our 48 volt house outback inverters are better of with a slightly higher voltage so 13 or better 14 cells in series.
I used to be a big fan of lead but now there is no way beside the use as starter battery.
Another good possibility especially with lithium is parallel stabilization that is charge to the 4.05 or what ever you decided and if there is more sun divert that load to whatever. If you have engine heater plug then that is good. No use in throttling back solar panels better use the energy in something even if that is not the most efficient use.

What online teaching are your doing?

Later j
joeblack5 is offline   Reply With Quote
Old 12-09-2016, 12:17 PM   #19
Almost There
 
Join Date: Aug 2014
Location: Oklahoma
Posts: 85
Year: 1984
Coachwork: Ward/Amtram
Chassis: International 36ft
Engine: DT466 w/ Allison MT643
hrmm... Micro inverters are pretty much always grid tie, which only make sense on a house grid connected system, EXCEPT that some power inverters such as Victron and *shudders* power jack inverters will recharge the batteries if connected to grid tie micro inverters. But, I wouldnt trust anything but a Victron or similar high dollar inverter/charger to actually apply proper charge curves to the batteries and not cook them. And, if your inverter goes out, you lose solar altogether.

Have you considered running each panel to a separate MPPT charge controller? Then if a panel gets shaded, all panels are still running at their max power point, including the shaded one.

You can parallel panels for sure, a shaded panel will slightly drop it's max power potential voltage below that of the other panels though, causing a greater power reduction on that panel than if it had a MPPT controller on it... but maybe that is a small enough loss that it's not worth the expense?
dalez is offline   Reply With Quote
Old 12-09-2016, 12:34 PM   #20
Mini-Skoolie
 
Join Date: Dec 2016
Posts: 43
How much on the roof really depends on the bus we find that we like. I should be able to put between 2400 and 3000watts...though I was looking at 12v panels when I did my measurements. I haven't had a chance to look at the dimensions of higher voltage panels.

What I'm teaching on line is tied into my three year plan. I'm currently working on my PhD in Cybersecurity.
PappySki is offline   Reply With Quote
Reply

Tags
micro inverter, power optimizer, solar

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 06:35 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×