MPPT vs PWM cotrollers?

[CatNewBee]

Originally Posted by GTom

Total = 45-125Ah or 500-1500Wh.

According to this test (200W NON-SHADED panels delivering ~ 6-800Wh/day), a 300W array wouldn't be oversized for the above needs:

when it comes to solar there is no such thing called "oversized".
You don't have un-shaded panels, there are clouds and rain and your panels are not oriented in the perfect angle. Also your power demands might be too optimistic. You need batteries than can cope with the incoming power and can store it efficiently, also need enough capacity to overcome some days with very little solar input. Lets say there is sh*t weather for 3 days, your batteries are almost empty, can your solar re-charge them the next sunny day? I guess it can recharge only the last day and will stay empty over a long time, maybe drain the battery after the next cloudy day.

Average values are useless when calculating the solar array for a boat or RV because you depend on the input. In a house installation you do not care about this stuff, average is OK, because the grid supplies you at any time with enough power and accepts any power you produce at any time. This is not the case on a boat / island system.

A good solar array is able to re-charge the battery at least within 2 days from empty to full WHILE covering the running daily load. So you need excess capacity at least 2..3 times of your demand - or a generator.

[john61ct]

Yes when using say 100AH per day, a 4-600AH bank is needed to cover poor weather conditions.

Even 1000w solar would not be "oversized", 600w may be enough if good solar conditions.

300w would only do when usage is light in very sunny conditions, and you have a genny to run in the mornings.

[thomm225]

Originally Posted by john61ct

This is supposed to be a cruiser's forum.

Most have much higher power requirements, and are away from mains for long periods in suboptimal conditions.

$350 is commonly the cost for one cell in the battery bank, or just the panels' mounting bracket.

I missed this part about the mounting bracket.

My main panel (65 watt) is lying (tied down) on my aft lazarette locker so I don't need a bracket for it. My 20 watt panel is kept inside the port lazarette locker and I bring it out at anchor or when on a long tack if necessary.

There's usually a way around cost problems......

I did get all the data off the panel plates yesterday though so I can see exactly what the best power output could be. I'm only running the 20 W panel right now to keep the batteries up so the 65 W Panel is below.

[GTom]

Originally Posted by thomm225

I did get all the data off the panel plates yesterday though so I can see exactly what the best power output could be. I'm only running the 20 W panel right now to keep the batteries up so the 65 W Panel is below.

It's not the best case scenario most of us are after, when sizing our energy supplies... Realistic conditions, clouds, non-ideal angle - and still the above mentioned power budget. Latter in your case might be significantly smaller thus you will feel well served with the panelage you actually use and which speak for a PWM.

I happen to have a need for a long-term maybe 50-100W solution: I'd like to keep the batteries in the boat during winter and a smaller panel should keep them charged. Depending how I'll install the rest, it's well possible that most panels will be taken off for wintering e.g. if I decide for a pole mount. This case a smaller panel would stay on, probably with a dedicated small (=<10A) controller, which can be PWM.

[thomm225]

Originally Posted by GTom

It's not the best case scenario most of us are after, when sizing our energy supplies... Realistic conditions, clouds, non-ideal angle - and still the above mentioned power budget. Latter in your case might be significantly smaller thus you will feel well served with the panelage you actually use and which speak for a PWM.

I happen to have a need for a long-term maybe 50-100W solution: I'd like to keep the batteries in the boat during winter and a smaller panel should keep them charged. Depending how I'll install the rest, it's well possible that most panels will be taken off for wintering e.g. if I decide for a pole mount. This case a smaller panel would stay on, probably with a dedicated small (=<10A) controller, which can be PWM.

Yes, I understand that but I just wanted to know what the best would be.

I got interested after I told you my optimal panel current output was around 6 amps with my 85 watts worth of panels, but when I actually checked on the panels plates, it's closer to 5 amps

The last 5 years or so I've had no problems just running my 65 watt panel (except for one period when I had a battery going bad) and that was when I had one starter battery and one deep cell in parallel.

Now with the two deep cells in parallel and 85 watts worth of panels, I'll have lots of power even on a cloudy day.

My power requirements are: lights, inverter (for charging phone, laptop, internet jet pack), autopilot, VHF, Depth, GPS but if I need to I can turn everything off and sail a few hours while the batteries charge.

When I do this I turn off the autopilot in the position that best maintains course and as needed steer with the mainsheet

This is the first boat I've ever owned that had any instruments at all. The other 12 or so didn't even have depth or radio

[sailorchic34]

As with all things, it does depend on the amount of stuff on the boat. My boat like some others is pretty bare bones and simple. A low amp draw autopilot, Tablet chartplotter, depth and vhf is all the instruments I have. I also have a 120V fridge run via inverter that uses no more power then the far more expensive marine fridges. That and a mix of LED and CCF lights is all I have. Well a water pump that runs for less then 2 minutes a day, hardly worth mentioning.

No watermaker, no radar, no AIS, tv, stereo, etc. So for the smaller low cost cruiser, ok which must folks on CF are not, there are options that reduce the cost of cruising.

For me 300 watts of solar, do me proud with 4 6v GC2 batteries reaching float by 1 pm on the typical day. Rainly / foggy days can be an issue but generally there is enough power with 300 watts to do ok.

As to mounting cost. I laminated 1/4" oak strips together with a few SS bolts, nuts and U-clamps for about $25 per panel. Sure I could have spent big $$$ too.

Some people cruise on $3000 a month. Some cruise on far less then a $1000 a month, How one accomplishes that requires adjustments. It's not a one size fits all. For the budget cruiser, buying a $30 30 amp charge controller gives 90% of the power of a more expensive MPPT.

While MPPT's claim up to 30% increases, it's more in the 12 to 15% range (in real world output), and then only during bulk charge. Absorption is about the same efficiency with either PWM or MPPT controllers.

While I generally travel less then 1000 miles a year, average is 700 miles, most of my time away is on the hook. Last year that was 7 months on the hook.

From a power standpoint I assume no more then 65 percent of rated output from my solar set up. This as it's near impossible to have all panels shade free. 1/2 of a single cell being shaded can drop output of the panel by 80%. A single stay shadow is now so bad. But the boom or mast are killers as the boat swings, and the sun moves about, on the hook.

[FionaJC]

Ouch what a thread!
My setup is as follows and I have an MPPT controller I paid £41.53. I have 200w of semi flexible solar on the roof. I have a 2 x 110Ah wet battery system with a single 110aH auxiliary battery plus the engine starter. I charge by solar, alternator 80A, shore 40A or generator. I am on a non powered pontoon so I only use shore charging when I am "away"

I have the following;
1000wInverter for fridge & microwave
Garmin Radar
Garmin chartplotter
Autohelm 4000
Battery monitor BM1 NASA
Wind NASA
Depth NASA
Log NASA (never works)
GPS repeater
AIS receiver
Navtex
Satellite TV
Terrestrial TV
2 x stereo systems
VHF +GMDSS
Forward looking sonar on Garmin
Wireless hub for on board usage.
Computer system for engine management & sensors, Burglar alarm and essential sensors while away.
Computer system as backup OpenCPN chart plotter / logs
LED deck & forward flood lights 48w +48w +36w
Led internal lighting
LED tricolour
LED anchor
Windlass
5Kw diesel heater and booster / blower
3 x 12v Fans
2 x bilge pumps
2 x USB phone charging points
I think that's all and I have surprised myself at the list. I might have room for electric blankets!

And it all seems to work but my essential in winter is bilge pumps and alarms because the solar cant keep up.

I have to add, I am an electronic engineer so I keep three torches, charts, compass and sextant etc, just in case. I know how "reliable" electronics can be.

[thomm225]

For those of us that are never hooked to shore power, there's really not a lot to figure out as far as how much solar we will need or which controller

I can "cruise" for a couple weeks with my present setup and since I'm a coastal cruiser there is ice available if I need it.

The bay is only 30 miles wide at most here so that makes it quite nice. You can sail "offshore" but still be within range of supplies if necessary

This is a great way to prep for a longer cruise later if one can adjust to the slower paced lifestyle of constant cruising

One guy mentioned that this site is for real cruisers, but I'm thinking he meant real inexperienced cruisers that will spend lots of money sometimes unnecessary for his type of help

[GTom]

You make several compromises (turning off autohelm, don't use a fridge, etc) and you haven't mentioned what you are doing on consecutive cloudy days. Thanks, but that doesn't help me too much. If I want, I can also make my compromises eating dried food instead of using the fridge, steer the whole Oban - St Kilda trip (usually pretty cloudy up there...) manually with no autohelm, use the foghorn instead of the Radar (!), refrain from using the cabin heater (diesel but needs a ventillator) and be proud that I saved 200£. On a 30k £ boat, where selecting the right yearly berth makes 2k £ difference.

I am not a very experienced boat fitter but basic maths haven't left me and I think I can judge my power budget.

[thomm225]

I'm still experimenting so until I decide exactly what I want out of my present boat I'm not going to spend too much on it

So far I'm at around $8,500 with the boat cost, it's improvements, and maintenance over the past 7 years or so

Next year I might decide to sell this boat and get something that will perform a bit better and is a little larger, but then I'd have to pay for a larger slip and boat I don't really need yet

I have only sailed so far with out the autopilot because it was getting on my nerves with it's racket, and once when I had a battery going bad which I fix/removed while heaved too. Usually I can steer with an adjustment to the mainsheet every now and then while still reading my book etc or enjoying the view

Cloudy days don't affect my setup much because I don't have a lot of electronics running, and as an in season coastal cruiser there aren't a lot of cloudy days in a row