How to get SunPower Solar Panels for a skoolie?

[Truffles]

Hi all,

I've been looking into various solar panel arrangements, and it looks like the only panels that fit my needs will be the ones with the highest efficiency, SunPower. If we go with their 420 watt solar panels, we should be able to fit 10 of them on the roof (4200 Watts of Solar!) and still have room for a small rooftop deck.

I have contacted SunPower, my local dealer, dealers in neighboring states, and WholesaleSolar.com, and none of them are able to sell these panels to RV's. This isn't because the panels can't take the forces of travelling down the road. They are actually very durable panels. The problem is that majority of the SunPower dealers will only sell you these panels if they do the installation, and they don't do installations on RV's.

Does anybody have a local hookup on the SunPower 420Watt Solar Panels? I just want to pay cash and get them shipped directly to our house for us to install.

Any help sourcing would be greatly appreciated.

[JDOnTheGo]

I've purchased mine via Craigslist.

[Truffles]

Originally Posted by JDOnTheGo

I've purchased mine via Craigslist.

Hah, yea, you're the reason I'm so darn determined to get these!

Love the build by the way. The number of time's that I've exclaimed to my girlfriend "This guy's so good!", while watching your videos, would make you blush.

On a side note, how happy are you with your Leaf batteries? We are right on the tipping point of pulling the trigger on a 20kwh LiFePO4 bank and the major holdup seems to be the idea of leaf batteries.

[dzl_]

Santansolar.com usually has sunpower panels for sale (<400W), and often has 400W plus panels. But I've yet to see them selling 400W plus sunpower panels.


What is it about the sunpower panels that make them a must have for you? What specific dimensions are you trying to accommodate?


I really like Sunpower panels so if you do get a line on the newest generation of Sunpower panels (especially the commercial ones), let me know.

[DoxieLuvr2015]

Following this thread for sure!!

[JDOnTheGo]

Originally Posted by Truffles

Love the build by the way. The number of time's that I've exclaimed to my girlfriend "This guy's so good!", while watching your videos, would make you blush.

Thank you!! You may have me confused with someone else though - most people just shake their heads after watching my videos!

Originally Posted by Truffles

On a side note, how happy are you with your Leaf batteries? We are right on the tipping point of pulling the trigger on a 20kwh LiFePO4 bank and the major holdup seems to be the idea of leaf batteries.

My 10kWh LiFeMnPO4 bank is from Elite Power Systems and purchased from StarLight Solar. I am very happy with the system - it just works. When we spend a load of money on a thing, we tend to love it regardless of reality to justify the expenditure. In this case, this bank has served me very well for just over three years now. I haven't had to do anything with it since installation which almost makes me feel guilty. I used to spend some time with the FLA banks in my previous motorhomes. Not a huge amount, of course, but seems like they needed watered or terminals needed cleaned, needed to clean up/paint the tray where corrosion was occurring, or something. Not this lithium bank - it just sits there and does its job. It has worked so well I've never even went back and finalized the wiring and mounting of the BMS.

I can't speak for any other lithium solution but I am most certainly sold on the advantages, in spite of the cost. Obviously, a lithium bank is not appropriate for all situations and certainly not "required" in any (??) RV/motorhome. However; they are pretty sweet if you rely on stored electrical power. Why? Size, weight, capacity, ability to charge quickly, ability to power 'large' loads, and extremely low maintenance.

[Truffles]

Originally Posted by dzl_

Santansolar.com usually has sunpower panels for sale (<400W), and often has 400W plus panels. But I've yet to see them selling 400W plus sunpower panels.


What is it about the sunpower panels that make them a must have for you? What specific dimensions are you trying to accommodate?


I really like Sunpower panels so if you do get a line on the newest generation of Sunpower panels (especially the commercial ones), let me know.

For me, the reason I was leaning toward SunPower was because of their high efficiency, and ability to perform in partial shade,

which many panels lack

. After running the numbers on a few common panel manufacturers (SunPower, LG, and Renogy), it looks like I can afford to fit more solar on the roof if we go with LG, instead of SunPower.

Here are the panels with (Zero room between them) on my bus, just to see what was theoretically possible.

[Native]

How much are the three panels used in your diagrams?

[Truffles]

Originally Posted by Native

How much are the three panels used in your diagrams?

I saw the LG panels (with micro inverters) on Tandem Solar's website for $562.50, or $1.50 per watt

Renogy has their 320 Watt panels on their website for $329 a piece, or $0.98 per watt.

SunPower has proven to be an impossible company to work with. You can't find installers that will sell you the panels, and they took 2 days to respond to me on the "Live Chat". Consequently, I can't find the price either. I recommend staying away from SunPower unless you are buying second hand like JDOnTheGo did. Especailly because you can fit even more solar on the roof if you buy from LG.

[Native]

For some reason, I had $0.50/watt in my mind. I do not know where I got that figure.

[dzl_]

I haven't heard of anyone using microinverters on a skoolie build. Is this something you are planning to do, or just the panels you happened to come across?


Some of the advantages of micro-inverters would apply to skoolie builds, but then there are disadvantages as well I would think.



Micro-inverters convert DC from the panel to AC, which makes sense for grid tied, but in an off grid situation it adds an unnecessary DC to AC to DC double conversion. Microinverters are pretty efficient but there is still a conversion loss, and then another (probably larger conversion loss converting it back).


This isn't something i've ever considered, so i might well be missing something

[Native]

I would think the micro-inverter technology would increase the cost of the panel as well.

[Truffles]

Originally Posted by dzl_

I haven't heard of anyone using microinverters on a skoolie build. Is this something you are planning to do, or just the panels you happened to come across?


Some of the advantages of micro-inverters would apply to skoolie builds, but then there are disadvantages as well I would think.



Micro-inverters convert DC from the panel to AC, which makes sense for grid tied, but in an off grid situation it adds an unnecessary DC to AC to DC double conversion. Microinverters are pretty efficient but there is still a conversion loss, and then another (probably larger conversion loss converting it back).


This isn't something i've ever considered, so i might well be missing something

Originally Posted by Native

I would think the micro-inverter technology would increase the cost of the panel as well.

I'm not a solar expert by any stretch of the imagination.

But my reasoning for choosing microinverters was because they allow you to have partial shading on some panels without affecting the output of the other panels. I figure that I will have limited options on parking spots, and that if I am unable to find a place free of shade then it may make the whole solar array unusable. As is shown in the youtube video linked below. I won't be offended if you tell me I'm dumb

https://youtu.be/QzzB1i1w_kM

[JDOnTheGo]

Microinverters are new to me so certainly not an expert. After reading a bit, I don't think they are applicable to the typical off-grid type of use (cabin, RV, etc.) since we are all using the DC output from the panels to charge a DC battery bank. As DZL says, they would seem to make sense in a grid tied system.

Panel shading is pretty easily handled by wiring them in parallel.

One of the reasons I like the higher voltage residential panels is that you can wire them in parallel and still have fairly high voltage so the wire from panel to MPPT can be longer-ish and not suffer too terribly from voltage drop.

[dzl_]

Originally Posted by Truffles

I'm not a solar expert by any stretch of the imagination.

But my reasoning for choosing microinverters was because they allow you to have partial shading on some panels without affecting the output of the other panels.

I see your reasoning and think you are on the right track conceptually but microinverters may not be the best tool for the job.



Here are couple options you can look into apart from Microinverters:

1. DC optimizers (also called solar optimizers). They are conceptually similar to Microinverters except that the output is DC. Like microinverters these are not commonly used in mobile builds, but they do have the advantage of outputting DC.
2. Per panel (or per string) MPPT controllers. You can achieve the same outcome of partial shade optimization if you use multiple small MPPT controllers. This is what is commonly done in the marine world for situations where partial shade is inevitable (sailboats for instance). Victron's small controllers, and Genasun controllers are often used for this.

Also as mentioned above, wiring in parallel can help as well (so long as the voltage is high enough to give the MPPT controller the breathing room it needs) as can choosing panels that perform better in partial shade (such as panels with 'half cut cells').

[Native]

Personally, I like option #2 because it adds redundancy. I also would think the multiple smaller MPPT controllers would be a bit less expensive.

[FatBoySTL]

Originally Posted by Native

Personally, I like option #2 because it adds redundancy. I also would think the multiple smaller MPPT controllers would be a bit less expensive.

The flip side of redundancy is complexity. More parts means more to go wrong.

Also, I don't think the cost of MPPT controllers is linear... A 40 amp controller does not cost the same as two 20 amp controllers.

[TomA]

The biggest issue with microinverters is that you will need a source of 60Hz sine wave for them to recognize as a functioning grid before they will put out any power. If the micros don't recognize the bus as a functioning grid, they shut down. That's a great way to control them super effectively if you have an inverter/charger that can vary its sine wave out of range of what the micros will produce into, say from 60Hz to 62.5Hz when the batteries are full.

Sigineer makes inverter/chargers that do that. This is how I will be going. The big advantage to microinverters is you are generating relatively low loss AC power just when you need it most, e.g. running the aircon full blast in the heat of the day. This is especially the case where your minisplit is 240v. Its a good solution for a higher power system with 3-5kW of solar and enough battery to run everything up to 24 hours, but I don't think it makes much sense on a smaller system that's only marginally big enough for the load. I'm planning an all-electric off grid 40' coach with 5-6kW of panels, 240V systems, full n+1 redundancy, and at least 20kWh of storage. Keeping my generation AC makes a lot of sense for this architecture, but such a system is not for the uninitiated, and requires a lot of space.

I'm a year or two away from building, maybe more given the world as it is, but for almost everybody planning a modest system, an integrated electronic component package, (think Vicor) Battleborn or other packaged LiFeO4 storage and DC output from the panels is probably the most sensible way to go.

[TomA]

Originally Posted by FatBoySTL

The flip side of redundancy is complexity. More parts means more to go wrong.

Sort of, but of course it depends. If you have a single MPPT controller, when it goes down your coach won't charge. If its an integrated inverter as well, you are dark with no power until you can replace it.

Micro inverters are highly reliable, (grid utility grade components) but even if you do lose one, or the panel its paired with, or god forbid two or more on-roof components in a lightning strike, accident or something really unlikely, the rest of your system remains operational. That's one of the things I really want in a big rooftop array with microinverters- they are dependent on a grid sine wave to output any power, so if I clip a low overpass, tree branch falls on me or I get in any kind of accident, any mechanical loss of system integrity will result in the affected micros shutting down. No output. Zero. I will also put a collision switch relay on the inverter charger to cut the 60hz signal in a wreck as well, so that I will never have thousands of watts of uncontrolled DC power on the roof or coming into the coach. With a big system, that's a huge plus.

No simple answers here, really, just compromises...

[dzl_]

Originally Posted by Native

Personally, I like option #2 because it adds redundancy. I also would think the multiple smaller MPPT controllers would be a bit less expensive.

Me too, redundancy, and simplicity in some respects. As FatBoySTL states often there is some tradeoff in added complexity, but its not too bad in this case, and its not really anymore complex than what its being compared to (microinverters and/or DC optimizers)

Originally Posted by FatBoySTL

The flip side of redundancy is complexity. More parts means more to go wrong.

Also, I don't think the cost of MPPT controllers is linear... A 40 amp controller does not cost the same as two 20 amp controllers.

I agree that there is usually tradeoff between redundancy and simplicity.

Depends what brand you are talking about, and even within brands can differ. With Victron its pretty linear (in some specific cases it is actually cheaper to use multiple smaller SCC's)

But comparing a single MPPT vs multiple MPPTs, is not really the issue here, since OP is looking at micro-inverters for shade tolerance. The comparison should be between microinverters, individual MPPT controllers, and DC optimizers.

I don't know a ton about micro-inverters, or DC optimizers, so I can't say how they compare to multiple small mppt in terms of cost, resilience, or complexity.

Originally Posted by TomA

Sort of, but of course it depends. If you have a single MPPT controller, when it goes down your coach won't charge. If its an integrated inverter as well, you are dark with no power until you can replace it.

Micro inverters are highly reliable, (grid utility grade components) but even if you do lose one, or the panel its paired with, or god forbid two or more on-roof components in a lightning strike, accident or something really unlikely, the rest of your system remains operational. That's one of the things I really want in a big rooftop array with microinverters- they are dependent on a grid sine wave to output any power, so if I clip a low overpass, tree branch falls on me or I get in any kind of accident, any mechanical loss of system integrity will result in the affected micros shutting down. No output. Zero. I will also put a collision switch relay on the inverter charger to cut the 60hz signal in a wreck as well, so that I will never have thousands of watts of DC power on the roof or into the coach uncontrolled. With a big system, that's a huge plus.

No simple answers here, really, just compromises...

You bring up some really interesting points!

It seems like you know a decent bit about micro-inverters, can I pick your brain a bit.

Your comment implies there is no single point of failure. Does this mean they are fully decentralized, no centralized unit or anything needed?

second, can you elaborate on this:

they are dependent on a grid sine wave to output any power, so if I clip a low overpass

What does "dependent on a grid sine wave" entail

What is the process of getting the energy from the microinverters into the batteries? Do you just wire the microinverter outputs to the AC panel and let the inverter/charger take it from there?



Finally, have you looked into the dual efficiency loss associated with converting DC to AC and then back to DC? Do you have any estimate on efficiency penalty we are talking about.