Matching solar panels to batteries to consumption

[socaldmax]

Originally Posted by newhaul

Not really how things work in the real world. The mppt only really benifits in the last. Ten or so percent of charging. Btw I guess you missid the part from the op that he is looking to update a bit from his.current pair of 11watt panels that are over 30 years old.

No, I'm sorry to tell you, you are wrong.

A PWM is simply a chopper circuit. It shuts off the incoming power from the solar panel to make the average voltage out equal the battery voltage. All of the power from the solar panel while the circuit is off is WASTED power. At least 20%, more like 25% is WASTED power. MPPT controllers convert higher voltage to the desired voltage at a higher current - very little loss, just a couple %.

During bulk phase, the MPPT far outperforms a PWM controller. During absorption phase, the controller holds a fixed V and the battery resistance controls the rate of current flow into the batteries. At this point, most MPPT controllers behave like a PWM since they usually don't use max. power during absorption.

[Littlechay]

Originally Posted by newhaul

) and all I install are mono panels with an efficiency in the 20% range.

Your better off installing poly panels on small boats with the high likelihood of shading. Cheaper panels too.

[mitiempo]

Originally Posted by newhaul

Not really how things work in the real world. The mppt only really benefits in the last ten or so percent of charging.

You need to do more research. MPPT works in bulk only - all controllers are using Pwm after absorption.

[socaldmax]

Originally Posted by Sauntress

And cross the Atlantic.
Now, we have 10 Amp per twenty four hours estimated of which 6Amp for the masthead tricolour and the compass. I actually question whether people 1,000 miles from land religiously run with nav lights. I suspect the answer is no, just when something hoves in view. The suggested setup is a 50 Watt panel, which theoretically, and if I have understood your discussion, should knock out 4Amps at peak charge, over 5 hours= 20 but I am sure that is not right for all the reasons you two are talking about. One view says the MPPT squeezes 20% more. The other says it ain't worth it, or words to that effect. This seems key and the cost differential given all the rest, possibly academic. I did write up all of this properly but cannot attach the Word document.

A 50 watt panel is rated at Standard Test Conditions. This means that you will never see that kind of output in the real world, even if you mounted it on an expensive solar tracker. Most people see about 75% odrated output with an MPPT controller with flat mounted panels in the summer. In the winter, this drops to around 65%. If you're using a PWM, then reduce those numbers by an additional 25%.

If you factor in that your boat will be heeling over under sail, the sun will be somewhere else in relation to your panel, you can't even count on 50% output reliably. If the sun is rising in the east and you're healing in any other direction, your solar panel is going to get very little sun, possible well below 50%. The only time you'll get anywhere close to the most power you'll ever get is when you're becalmed at noon, or just happened to get lucky and your heeled over with your panel facing the sun.

That's all assuming you're not somewhere where it's raining or cloudy most of the time. A few days of clouds or rain and your batteries are going to be undercharged.

All of the math you've been presented so far was under ideal, laboratory conditions. Unfortunately, the world, and especially the sea and weather doesn't work that way. If you install a 100w panel with an MPPT and it keeps your batteries charged up at all times, that's great, no harm done. If you install a 50 watt panel with a PWM controller and it doesn't keep you fully charged due to all of the factors mentioned above, you can't just pull over in the middle of the ocean and add another panel. You're out of power until you can pull into another marina and add more.

[socaldmax]

Originally Posted by mitiempo

You need to do more research. MPPT works in bulk only - all controllers are using Pwm after absorption.

Exactly!

[Sauntress]

All of the math you've been presented so far was under ideal, laboratory conditions. Unfortunately, the world, and especially the sea and weather doesn't work that way. If you install a 100w panel with an MPPT and it keeps your batteries charged up at all times, that's great, no harm done. If you install a 50 watt panel with a PWM controller and it doesn't keep you fully charged due to all of the factors mentioned above, you can't just pull over in the middle of the ocean and add another panel. You're out of power until you can pull into another marina and add more.[/QUOTE]

OK understood.

[DawnTreader]

We cruise full time. We have PWM controller and 55 watt panel. Our range of production is between 4ah on a cloudy winter day to 35ah on a cloudless summer day. Our average consumption is probably 15ah per day but we can throttle up or down based on battery state.

Brian
www.sailingdawntreader.com

[StuM]

Originally Posted by newhaul

The mppt only really benifits in the last. Ten or so percent of charging.

Sorry, you've lost me there. Care to explain your reasoning?

[StuM]

Originally Posted by Sauntress

And cross the Atlantic.
Now, we have 10 Amp per twenty four hours estimated of which 6Amp for the masthead tricolour and the compass. I actually question whether people 1,000 miles from land religiously run with nav lights. I suspect the answer is no, just when something hoves in view. The suggested setup is a 50 Watt panel, which theoretically, and if I have understood your discussion, should knock out 4Amps at peak charge, over 5 hours= 20 ...

Again, please understand the difference between Amps and Amp hours and use the correct units.

But that's not my main point here. Anyone who doesn't religiously run with nav lights at night shouldn't be out there! If another vessel is running without nav lights as well, it won't "hove in view" until one of you runs into the other.

[Sauntress]

Still got it wrong? My apologies.

I was NOT suggesting we would run without lights. Never have. Just suggesting that some do. In fact we know they do.

[Littlechay]

https://www.victronenergy.com/upload...WM-or-MPPT.pdfSeems to be a lot of misconceptions here regarding both panel chemistry and the pros and cons of PWM v MPPT. This is quite a good paper from the Victron site. https://www.victronenergy.com/upload...WM-or-MPPT.pdf

[Adelie]

For low power applications PWM is likely to have an efficency advantage over MPPT. Also in hot applications.

The OP's anticipate setup is definitely in the low power category (<200w).

I vaguely recall that his anticipated cruising grounds include the Med which would put him/her in or near the hot zone.

I would go for PWM for now and change to MPPT if the panel system expands significantly. By then prices will have come down more and the total cost will probably be a wash.

http://solarcraft.net/articles/compa...e-controllers/

Page 9: http://www.morningstarcorp.com/wp-co...March-2015.pdf

[thomm225]

Originally Posted by socaldmax

I don't know about great - it could work considerably better if you increased the size of the wire to 12 or 10 ga and sprung for an MPPT controller.

I'll never understand this "works good enough" mentality. It's like saying your fuel tank sprung a leak 5 yrs ago and you patched it up with bubble gum and it's been holding fine. Never mind the correct way to patch a fuel tank, or the ever growing puddle of fuel sloshing in the bilge.

That's because you don't understand how much power I need. My setup works great and it's cost was less than $100.00. The old 14 gauge wire is what I found laying around which is why I used it. (if you check you'd see it's the right gauge also for my setup)

If it makes you feel better to spend more on electronics, I'm happy for you. I spend $1600 for my new 8 oz mainsail!

I have two more 20 watt panels but have yet to install them since my current system does the job.

I like the historical approach to sailing. I don't want a sailing condo so my power needs are less. I'm charging two 12 volt batteries in parallel and I don't need a starter battery (like the Op)

I have autopilot, GPS, depth, VHF, lights when absolutely necessary, and the inverter.

[Pete7]

Originally Posted by Sauntress

The suggested setup is a 50 Watt panel, which theoretically, and if I have understood your discussion, should knock out 4Amps at peak charge, over 5 hours= 20 but I am sure that is not right for all the reasons you two are talking about.

I think they are talking of a peak charge between say 10 and 3pm. If so what happens between say 7 and 10 am? and then in the afternoon between 3 and 9 pm? Well you won't have peak solar but will be generating some useful amps.

Without destroying the look of your 1913 yacht I think you have room for a pair of quality 50w solar panels. If you choose the flexible ones then can be walked upon. Whilst sailing you are going to have some shading as all ready mentioned and the panels will be flat so no 100% but with 100w and MPPT you will more than meet your needs with spare when its cloudy.

Now if you really want to start a long thread ask if two panels should be wired in series or parallel

[thomm225]

Originally Posted by Pete7

Without destroying the look of your 1913 yacht ......

Actually, his boat is really something. Here's a picture he sent me when I asked about it.

Sauntress,

If there is a problem with me posting this, I'm sure we can have the moderators delete it.

It's an awesome picture though of a beautiful boat......

Tom