240 Watts Solar - How Big Battery ?

[Jim Cate]

G'Day Mark,

As it happens, we too have 240 W of panels, and have used a house bank of 4 Trojan T-105 golf cart batteries for years. Seems to work for us. More than two days of limited sun and not enough wind causes us to use the alternator for survival. Hate doing that!

Incidentally, we use a simple controller, and have a switch to bypass it. Unless we are leaving the boat, we switch the regulator off. Often this means that by late afternoon the charging voltage reaches the 15+ volt region, typically charging at a few amps. While many shriek at this, it mimics an equalizing charge, and seems to do no harm. This set of T-105s is about 4.5 years old, has been discharged to less than 12 volts resting repeatedly, and is still going well. YMMV.

Of course, now that Nic is not there running her hair dryer all day, your batts should last even better... unless the cooling of many beers makes up the diff!

Cheers,

Jim and Ann s/v Insatiable II lying Cairns, Qld, Oz

[Mark Johnson]

By far the best bang for your buck with both houses & boats, is in energy conservation rather than production & storage. The latter approach is 400% more $! On our self built 34' trimaran, (12 years live aboard cruiser), We have all the comforts... Inverter, Refrigeration, radar, SSB, watermaker, autopilot, dozens of lights & fans, windlass, etc... We use fluorescent or LED lights, vacuum panels for super insulating the fridge, don't make ice, the smallest of everything, and minimize the inverter use by running "black box" AC items like computers & TVs directly off of 12V DC. (Using a transformer / converter to step up the boat's 12V DC, to the 19V DC that these "AC black box" items actually use.) This uses half the amps of using the inverter and plugging in theAC black box that came with the TV!

By going "green" as it were... We only use about 40 AH / day while living on the hook. (with fans running 24/7, making water, and movies every night) We get this back exclusively from our 4 solar panels (that = 280 W), and we are charged up by mid day, 340 or so days out of the year. Only when doing overnighters... we consume about 80 AH, and to fill the slight energy deficit, (the solar usually gives us 50 to 60 AH/ day)... we run the engine for an hour before sun up. Otherwise it's all free energy.

We started with Lead/acid Trojan L-16 batteries= (380 AH), and have downsized to L-14s =(340AH) This huge bank for our needs, is never more than 70 or at worst 80 AH down, so should last perhaps 10 years. (with hydro-caps) we only top off the water 4 times / year! You do have to remember to water however, at the first day of each season for example, otherwise.... that's how we ruined our first set.

Being a trimaran, weight is important for us, so next time we may downsize yet again, to about 250 AH. This way we usually would be using 1/5th of our theoretical capacity, and never more than 1/2. This conservation approach works best if done in conjunction with the original build, or a total refit. Otherwise, the rule is to size your battery bank at a bit more than twice as large in AHs, than the max consumption before charging. Wind generation is loud, sometimes even antisocial, & very off & on. Diesel is nasty, consumptive & requires that you "be there", Solar is the champ. It will do the job if your W. of solar is sufficient. (Even factoring in very overcast days, my solar set up runs our boat 95% of the year) Put another way... We can rely on 50 AH/day from our 280 W of panels, 95% of the year. This was from Trinidad, to up the Rio Dulce, to the Chesapeake.

This does require an energy efficient boat however, OR a large one with a LOT of room for solar panels. Mark

[Cotemar]

We have installed 460 watts. Two 230 SunPower panels and a BlueSky SB3024iL Solar Boost 40A/12V MPPT PV charge controller.

Currently using three 100 Ah in parallel for total of 300Ah house. This has worked for the last six months of cruising Long Island Sound. Will be adding another 300Ah this winter for a total 600Ah.

1) The reason for going with 600Ah is when you get a couple of rainy days in a row you can still be running on your piggy bank.

2) With 3 batteries a few years old and 3 new batteries I will be able to rotate out the 3 older batteries and still have 3 newer batteries running all my systems on any old battery out rotation. This is better than the whole battery system dieing at the same time.

http://www.cruisersforum.com/forums/f136/solar-panels-and-associated-systems-38764-2.html#post488059

http://www.cruisersforum.com/forums/f136/solar-panels-and-associated-systems-38764-2.html#post491749


Mark

[sailorboy1]

I hope people realize that Mark has been cruising for while and knows what he is doing etc. :-)

[daddle]

The PO here installed far too many Ah of batteries. With that in mind I would suggest that on a sunny day with the fridge and all normal loads running it would be really nice if one could take the batteries from a normal discharge level to mostly charged.

As it is here I don't think I'll ever get a proper charge without some engine time. I can sustain, but I cannot top up. It's a sad waste of weight, cost and space.

In the tropics I'd estimate you can get 25% of the panel's Ah rating per sunny day, figure 6 hours.

Ah? What a horrid non-engineering unit of energy. Sheesh. Drives me bonkers. But that's the way this goofy industry is.

[rebel heart]

Originally Posted by Shrew

Along the same lines, I'm also looking at capacity planning. I currently have a couple of group 31 AGM's. I was looking at upgrading to 4D or even an 8D. I've seen a lot of other's doing like Rebel Heart and going with 6V batteries in a series.

Anyone know the pros/con for mult. 12v in parrallel, a larger 12v, or 6v in a series?

BTW- I'm hoping this is inline with the thread and didn't intend on hijacking it. My apologies if you feel I'm trying to hijack the thread Mark.

One pro/con you might want to consider for 6v vs. 12v is the physical weight of the battery. A comparable 12v will be roughly double the weight as two 6v models. I'm a pretty fit guy, and there's just no way I can get a big enough 12v all the way into the back of my battery compartment (which is under the quarter berth). It's almost impossible with two individual 6v; not going to happen with something double the weight unless you rig some sort of A-frame trolley.

[rebel heart]

Originally Posted by Don Lucas

I hope people realize that Mark has been cruising for while and knows what he is doing etc. :-)

Yep. That's why I just answered his question roughly exactly as he asked it.

[Mark Johnson]

A good average is that a 5 A panel should give you it's 5A rating X 5 hours / day. It is actually a totaly different curve than that... sort of a bell curve, but this is a good expectation, and surprisingly accurate. 25 AH out of a 5 A panel. This is IF it is horizontal and non tilting. IF you can tilt it toward the sun in the beginning & end of the curve, say 3 times / day, your expectation goes up! IF it has DARK shading across it, (like that created by the wind generator on the same radar arch), then the output drops to useless... BUT, very overcast / cloudy days only drop that 25A expected output (max), down to perhaps 15A. Not "0".

If you figure your normal days consumption in AH, and have enough solar to provide that... X2, then you are good for cloudy places, (like Panama). For overnighters, the best time to hit your batteries with an hour of alternator made amps, is when the batteries are lowest, (say, 4:30 AM). This is when your batteries can accept the 55+ amps. When they are only 25A down vs 80A, they can not accept much more than a fraction of the amps created by an alternator. It might as well be a 10A alternator! A double sized solar array will provide 100% most of the time, and when doing overnighters... after an hour of alternator, the solar will do the 90% of "finishing off" at a rate that the batteries can accept. It works perfectly this way. We ALWAYS bring our batteries back to 100% each day. You don't have to, but your batteries will last twice as long if you do. (wet batteries)
Hope this helps... The other Mark

[Mark Johnson]

Regarding batteries with the longest life in cycles, not necessarily the best in performance but lifespan, which was our goal... Trojan 6V batteries in series is the best, second only to Rolls/Surette @ much more $! There are several different grades of L-16.

Two L-16s @ 380 AH, are quite tall, due to the large resavoir at the bottom, but they were meant for "stand on" fork lifts that run them DEAD daily! The harshest treatment there is! The plates are thick & robust. I don't know weather they are more weight than one @ 12 V and 380 AH, (if there is one), but the weight is split over TWO batteries for easier handling. If connected carefully, they are VERY tough, and will deliver FAR more cycles than the 12V equivilent. (we expect 10 years) Mark

[jenny2]

I am getting ready to upgrade my solar system to 2 banks of 4 each trojan t-105 with 400 watts of solar and a mppt charge controler that will run everything on my boat plenty of power and won't take long to pay for its self not feeding the generator also quiet

[cfarrar]

Re: post #23 (the other Mark),

That's a perfect explanation of how to use the alternator. An average of 5 hours of the max panel output is a sound, conservative planning tool.

[Maverick]

quote
Trojan 6V batteries in series is the best, second only to Rolls/Surette @ much more $
unquote

I agree with your choice. But not really with your mention of the $ difference. We sell both and at real similar Amperage, we sell the Surrette cheaper than the Trojan. The Trojan L-16 has very different models.

Both are very good anyway for a liveaboard use, meaning they SOMETIMES get really discharged!!!