Adding Solar Panels - Looking for best practices

[Happ]

Flexible panels regardless of rating do not compare in output apples to apples. Your local marine store will vouch this out. If using a hard panel be sure to leave at least 1” clearance underwriting for ventilation. It will add to the output and last a lot longer.

[Randy P]

I installed 2 170W rigid panels to the hardtop of our boat. They are wired in parallel and give about 18 amps current in bright sun. They are fused at the connection outside and go inside the cabin via 10 awg solar cable (adequate current capacity with much thicker insulation) to our house bank via one Victron 100/30 MPPT controller. The positive cable from the panels to the MPPT goes through a 30A fused breaker allowing me to turn off power from the panels to the MPPT when I want or need to. The Victron MPPT is Bluetooth connected so I can get all data via my smart devices (iPhone/iPad - but it also is Android friendly). My old house bank was 2-110AH FLA deep cycles but this year I’m going to Lithium from Battle Born: 2 -100AH. Denser power profile, quicker charging, longer draining, etc and a LOT lighter. Due to the move to LFP I’m installing Victron Orion 12/12-30 DC - DC charger between the FLA engine battery and the new LFP house bank. I have an internally regulated 70A alternator and don’t want to fry it when the LFP bank gets full and sends all that extra power back when I’m under power. I’m also installing a Victron Smart 712 monitor to keep track of what’s what. All of this stuff is on a power boat BTW so not sure if any of this helps you.

[bradm85]

I installed solar panels 2 years ago. I drove myself crazy researching flexible vs rigid; series vs parallel, single controller vs multiple, etc. In the end I decided on three 150W rigid panels through a single controller for 450 total watts. I have a Hunter 41DS and went the past 2 summers with never having to run the engine to charge the batteries even after being at anchor for 2 1/2 days and I was running my frig and freezer continuous. I did do power consumption analysis before deciding. You can find power consumption tools on line which will help you greatly in your decision.

[Dave52]

Emarine in ft lauderdale will answer your questions and help plan, fabricate and ship your system with all parts and install instructions. Helped me 5 years ago to build a system which still operates flawlessly today.

[littledave]

Great thread. My input from experience rewiring an old launch for 12v with 4x trogan 6v as house battery and Victron MTTP 100/30 (Bluetooth app is awesome for keeping on top of what's happening) hooked up to 2 rigid 150w solar panels. Then adding isotherm fridge & freezer compressor kits to cool existing seperate fridge & freezer. Main challenge is keeping up with fridge & freezer when boat on marina berth. Altering mounts of solar panel so can tilt ~ 26° (recommended summer angle, panels face ~ solar north on berth ☺️) has made large improvement in generation. Be hard to do with flexible panels. Note I drop panels onto cabin roof when we use boat.

[Sailor-Gene]

Something this thread is needing... a bottom up analysis. OP desires 100AH per day usable. FLA, AGM, GEL. All have the same low efficiency charge profile... bulk to 80 + 90%, and absorb till full. That does not fit solar power availability. Solar is good for 4 to 6 hours depending on location & weather.

Li batteries are very efficient charging, most accept 0.5 to 1 C and just quit sucking in power when they are full.

A 400 W solar array could yield 1600 WA or 135 AH @ 12V in prime time to your two 100 AH usable batteries. And Li are getting cheaper.

Happy �� Sailing

Gene.

[bcboomer]

Firefly batteries will take .5c and are a simpler, cheaper way to get a fast recharge. Assuming a better charging system.

[Adelie]

Originally Posted by bcboomer

Firefly batteries will take .5c and are a simpler, cheaper way to get a fast recharge. Assuming a better charging system.

Firefly is cheaper up front but in the long run LiFePo is cheaper. High Quality FLA is even cheaper in the long run. DIY LFP is the cheapest but you need to design and maintain the system yourself.

If you have weight limits, LiFePo is probably a better bet.

If up front cost is an issue then the charging system costs need to be considered too.

AGM including Firefly are probably equal to LFP for up front costs because they don't like being charged at a low rate unless no discharged very deeply. If you are discharging to near 50% then you should be charging at 0.2C minimum, 0.3-0.4C is recommended. For a 500Ahr bank that means charging at 100A minimum. That's about when you need a much better than stock charging system including high output alternator, regulator and probably a serpentine belt.

[dmkkeng]

Originally Posted by RSB333

We are adding flexible panels to our Bimini this year, and we're looking for the latest techniques and advice. Will also replace our FLA batteries with two T31 AGM's and plan to install a Sterling "Alternator - to - Battery" charger to boost the output from our 55 amp original equipment alternator. We haven't been able to run our Adler Barber refrig. in the past as the drain on the batteries was unsustainable. But with the new system we plan a 100 AH daily electrical usage. Your advice and comments welcome!

Our sailboat has an 80 amp alternator however in never put out more than 50 amps maximum. I installed a Sterling smart regulator which increased the output closer to its rated output of 80 amps. This was a very inexpensive to implement however it did involve modifying my alternator. There are other options to further increase your charging output that involve installing a 2nd alternator or a higher output alternator, both require changes to your existing pulley systems. The higher output alternators also require a wider belt. The existing systems on most boats with 1/2" belt and pulleys typically only support alternators with outputs up to 100 amps.

We don't typically motor enough to keep the batteries charged sufficiently so my primary source of charging the batteries is solar. I have four 100W panels, this is adequate June, July and August however not so much during the other months. My original calculations indicated that I needed 450W however due to space constraints and panel size I opted for 400W. This was several years ago, over the past several years my power requirements have increased, at some point in the future I may look into adding an additional 200W of solar power. My back-up charging system is a 2000W Yamaha portable generator.

My house battery bank is 660 ah, the useable capacity is 80% of 660 Ah less 50% of 660 Ah, which is approximately 200 AH. This has been adequate for my needs however the next time I upgrade my battery bank I may look into some other technology other than the flooded cells that I currently have to increase battery capacity. Flooded cell batteries can only be discharged to 50%, when you are on the hook you never get your batteries back to 100%, it is usually somewhere between 80 and 90%, closer to 80% as your batteries age.

I am in the Pacific Northwest, at any point during the sailing season that I have 3 days in a row of no sun, out comes the generator, usually takes 4-6 hours to get the batteries back to 80%.

Hopefully the information that I have provided gives you some point of reference to help plan your system. My system has been in service for the past 4-5 years. We tend to do longer trips and mostly anchor at night.

[NCWDave]

Originally Posted by stormalong

Don't scrimp on wire size or quality. There is no point in using your solar to heat wire.

amen

[rgleason]

Originally Posted by bcboomer

Firefly batteries will take .5c and are a simpler, cheaper way to get a fast recharge. Assuming a better charging system.

Except, the daily usable portion of Firefly goes from .8 SoC down to .5 SoC, but lets say you drop them to .4 Soc so that's actually .4 x say 200ah=80ah whereas LFP is .7 x 200ah = 140ah So the effective size of two types of batteries is different.

[rgleason]

Adelie, that is a very useful spreadsheet thankyou.

[RSB333]

Adelie, love your battery chart. Not sure I can get the battery I want at the price you show, but the chart is great for identifying the trade-offs. Many thanks!
RSB333

[Adelie]

Originally Posted by RSB333

Adelie, love your battery chart. Not sure I can get the battery I want at the price you show, but the chart is great for identifying the trade-offs. Many thanks!
RSB333

I have an exceptionally good battery vendor here in San Diego, that's how I can get the Trojans at the price listed. Golf cart vendors would probably be similarly good.

[RSB333]

Originally Posted by guyrj33

looks like you're planning on two group 31 AGM batteries with a total capacity of about 200AH. You expect your daily energy usage to be 100AH.
That implies you will be relying on charging during the day and starting at 100% capacity to prevent your bank being discharged below 50% capacity.
I think your proposed bank is too small for your planned usage.
Also think you would be better off to stick with FLA batteries, as I understand AGM charging needs they need to get to 100% more often than FLAs.
Yes, as others have suggested a bigger alternator would be useful.
If you have the space I'd fit 4 FLA Golf Cart batteries giving you a total capacity of 450AHs, then a 100AH usage would represent a 23% capacity usage.
I haven't looked up the Sterling device you mention, but if you have a 55amp alternator that's the most you'll ever get out of it. In reality it will rarely output 55 amps and if you try to trick it into full output it will overheat.

After more reading, decided to take your advice and upgrade battery bank to 320-400 AH. Also going for 100 amp alternator with programmable external regulator. $$$ Thanks for the good advice!