Challenges with Solar on boats

[newhaul]

Originally Posted by rabbi

your 12v / 24v assumption is a bit oversimplified

I have a 12v Trojan battery bank, which is charged @14.8v bulk as per spec, and 16.2v for equalizing.

15Amps x 14.8v is 220W.

The question is: how often will the panel produce more than 220w? The real world answer is: On rare days for maybe an hour around noontime but only if I cleaned the panels with fresh water the same day and if there is absolutely no shade.


The 280W panel rating is valid only under controlled conditions that nobody can ever reproduce in a real world installation on a boat.

After a few year the panel's production will be lower anyway. Aging of solar panels does happen, even if its just tons of micro scratches from cleaning all the dust and salt crystals.

We will just have to agree to disagree then . My real world is significantly different than yours . I routinely see 12 amps out of my mere 200 watts .

[john61ct]

Can you link to your panel specs? What device is reporting the current?

[newhaul]

Originally Posted by john61ct

Can you link to your panel specs? What device is reporting the current?

I already posted all that information likely several pages back by now. Later today on the boat I will verify with my fluke clamp on .


Edit : I am disapearing (going sailing ) for a few days I will post my panel results when I get back . Pictures to follow.

[john61ct]

Originally Posted by rabbi

Overall I think that 280W panels are a good fit for the MPPT 75/15.
...
panels will age over time and will eventually no longer be able to make full use of the controller.

I was thinking maybe 250w would be my limit, it is a personal choice after all, but I think I would like to at least test in the 280-290w range. It is a choice between that last, and getting the most out of every watt produced by the panel (at higher SC pricing) as the others in the thread have been advocating so stridently.

Originally Posted by rabbi

I'd rather spend money on 350w panels than on a MPPT 100/30.

Now I'm confused. You would need the 100/30 in order to accommodate a 350w panel right?

The way I would phrase it, if the panels were $140, 75/15 is $100 vs $225 for a 100/30.

Starting with a pair of sets @$480 vs $730, the SC savings gets me a whole third set free!

[Steadman Uhlich]

Originally Posted by Btimmerman49

With the help of Alex at SeaTek Marine in Marathon I installed a single Sunpower 360W/70V panel on my little 27' Watkin's dingy davits using a Victron 100/30 MPPT. This setup works great. The Victron has a bluetooth interface to my iPhone which provides real time output as well as a 30 day history. When powering an isotherm ref/freezer, a PUR Survivor 35 watermaker, Simrad autopilot, large Garmin chart plotter, a 2000w inverter, a fan and various other items on the boat it often outputs slightly in excess of 360 watts. My house bank is 4-105 amp AGMs with a single 85 amp AGM for starting. I charge all of these at once using several Guest battery selectors. This just shows that you can add a lot of comfort to a small boat with a single high quality solar panel, MPPT controller, and adequate battery bank.

Howdy!

If you have not done so already, please copy your comment above, and go to this linked thread, and post your comment with answers to the questions asked in my Original Post #1, along with some photos of your boat showing your solar installation. I think your example would be helpful for others to see, especially if they have boats about the size of yours.

http://www.cruisersforum.com/forums/...ts-179638.html

This is also an open invitation to anyone else reading this thread, who has not already posted their installation in the linked thread up above.

[rabbi]

Originally Posted by john61ct

I was thinking maybe 250w would be my limit, it is a personal choice after all, but I think I would like to at least test in the 280-290w range. It is a choice between that last, and getting the most out of every watt produced by the panel (at higher SC pricing) as the others in the thread have been advocating so stridently.


Now I'm confused. You would need the 100/30 in order to accommodate a 350w panel right?

The way I would phrase it, if the panels were $140, 75/15 is $100 vs $225 for a 100/30.

Starting with a pair of sets @$480 vs $730, the SC savings gets me a whole third set free!

The 75/15 can accommodate any panel within 15A Isc and 75V Voc. So the are plenty of 350w panels out there that fit the 75/15.


Of course around midday during summer the panels would be able to produce more than the controller can use. But it doesn't do any harm.

In the morning or evening hours or generally when overcast, rainy, or just outside the summer season the output will be higher than a bigger controller on a smaller panel.

With a smaller controller I'm cutting off some of the peak production around noon but with a larger panel the total production is much more.
And since my batteries are full before the midday peak production cutting into this doesn't hurt at all.

[Rorzech]

The most Ive have from shading say 4 inches of the small edge was about 50% . Not sure how bad it would be if that 4 inches of shade crossed through the centre , but it can't be good. If your panels are pointed straight up to the sky on a cloudy day, you will get the most power out of the "Cloud Shine" I call it. Your panels will be picking scattered radiation from the whole sky down to the horizon 360 degrees around you, and shadowing will be of no consequence .You will collect much useful power on these days especially if you have extra capacity. You can never have too much solar panel collection power. I design my system to collect the power i need on cloudy days and I will have extra on sunny days that I can store in the battery bank. It's all how you look at it. You want enough power every single day so you don't have to go into emergency mode and have to start your engine to charge your batteries so your freezer doesn't start thawing out. Some clouds are thicker than others so it's better to over kill with panels then to cheap out on them. Look at SV Paragon, He's carries at least eight big panels under his dingy on deck. And I've seen them clipped on to his rails at times. I take my hat off to him. He's got the right Idea.

[john61ct]

Originally Posted by rabbi

The 75/15 can accommodate any panel within 15A Isc and 75V Voc. So the are plenty of 350w panels out there that fit the 75/15.


Of course around midday during summer the panels would be able to produce more than the controller can use. But it doesn't do any harm.

In the morning or evening hours or generally when overcast, rainy, or just outside the summer season the output will be higher than a bigger controller on a smaller panel.

With a smaller controller I'm cutting off some of the peak production around noon but with a larger panel the total production is much more.
And since my batteries are full before the midday peak production cutting into this doesn't hurt at all.

Yes I know no damage to the SC but for a 12V bank I'd only over-panel **that** much if I came across a crazy deal and the panels just happened to be that big (and fit the space, let's not forget **that** hard limit.

So maybe "highest morning amps per square foot" would be a good criterion to figure for, worth paying a bit more to optimize that.

[john61ct]

Re internal temp sensing only, on smaller Victrons

Originally Posted by rabbi

I don't consider this a huge issue. As the temperature compensation kicks in and the charge rate is reduced, the temperature of the controller falls and gets closer to the battery temp so the difference get smaller.

Yes, when others claim the smaller Victrons are inferior because of this, I think to myself I trust Dutch engineering, and for under $100. . .

[john61ct]

Re holding plate fridge

Originally Posted by rabbi

just a BDF 35 with a normal plate. But if you add enough beer it acts like a holding plate :-)

Not as fun as mass beerage, but a pet idea of mine, poor man's eutetics.

Google "polar tubes", just glue-capped 2" PVC, cut to the right length and filled 85% full with seawater.

I plan to work out clips to hang them from a cooler lid, so in the top of the space, no meltwater!

I would use a relatively small but very low-temp freezer, and would rotate between the cooler and a freezer

The tubes will likely stay frozen up to 6-8 days in a very efficient cooler, freeze faster than water jugs, no leaks, more space efficient. . .

I think I would use a SoC relay to turn on the freezer, as with Victron's BMV-702, whenever generating excess solar power, or manually when running the Alt for hours, just a way to store "free energy" as cold.

[Sailsgood]

Originally Posted by CapnCrunch

I'm not getting this. The Victron 100/15 specs read "Maximum PV power, 12V 1a,b): 200W (MPPT range 15V to 100V)"

My 290w panel specs show "Voc = 38.8VDC/ Isc = 9.58 A. I thought the Victron model numbers represented Voc/Isc?

If panel wattage is the determining factor, it looks like I would have go to the 150/35 at a cost of $295 ea vs. $90 ea for the 75/15. And, since the 150/35 is rated for 650W, I would need two of them . The damned panels only cost $175 ea, so I would be spending more for the controllers than for the panels.

As for your question about start batteries, for me, it always came down to the "oh s**t" factor. If one of two batteries in parallel went bad, it drags the other down with it. Whereas, if a single batty goes bad, I can always jump off the other if I need to start the engine quickly.

Just a suggestion, why not evaluate the WRM60 of Western Co.? Separate double MPPT (so you can enter with two PV strings)
Charge regulators for PV lighting – Western Co – Electronic Equipments

900W for 12V batteries
1800W for 24V batteries
3600W for 48V batteries

[rabbi]

Originally Posted by john61ct

I think I would use a SoC relay to turn on the freezer, as with Victron's BMV-702, whenever generating excess solar power, or manually when running the Alt for hours, just a way to store "free energy" as cold.

Thats what I thought, too. But in reality it turned out that SOC is not required. I just "charge the fridge" whenever voltage is above 13.2volt.
It does happen that the firdge cycles a bit in the early morning, turning on when voltage reaches 13.2v, drawing some energy which lowers the voltage, so it turns off again. But that is really something that happens just a few times. The load switch of the SC has a delay of a few minutes so the cycling isn't bad even if it does happen.

With the SOC relay this would be gone, and also I could make sure that only surplus energy goes into the fridge.
Right now depending on conditions it *could* happen that useful energy goes into the fridge instead of the battery. But from observation I have not had any rainy day where the batteries were not full in the early afternoon, and way before noon on sunny days.
And not a single day without cold drinks (even in more than just tropical heat, like 40° Celsius in Spain last week).

I'd love Victron to add a function that turns on the load only if there is surplus energy (i.e. unused panel output available in excess of xx Watt). Just to burn surplus energy.

[rabbi]

Originally Posted by john61ct

Yes I know no damage to the SC but for a 12V bank I'd only over-panel **that** much if I came across a crazy deal and the panels just happened to be that big (and fit the space, let's not forget **that** hard limit.

Or maybe chose a panel simply because its full black with black frame
:-)

I know black creates heat and reduces efficiency. But it looks good.

[john61ct]

Originally Posted by rabbi

Thats what I thought, too. But in reality it turned out that SOC is not required. I just "charge the fridge" whenever voltage is above 13.2volt.
It does happen that the firdge cycles a bit in the early morning, turning on when voltage reaches 13.2v, drawing some energy which lowers the voltage, so it turns off again. But that is really something that happens just a few times. The load switch of the SC has a delay of a few minutes so the cycling isn't bad even if it does happen.

With the SOC relay this would be gone, and also I could make sure that only surplus energy goes into the fridge.
Right now depending on conditions it *could* happen that useful energy goes into the fridge instead of the battery. But from observation I have not had any rainy day where the batteries were not full in the early afternoon, and way before noon on sunny days.
And not a single day without cold drinks (even in more than just tropical heat, like 40° Celsius in Spain last week).

I'd love Victron to add a function that turns on the load only if there is surplus energy (i.e. unused panel output available in excess of xx Watt). Just to burn surplus energy.

Yes I can see that voltage as a proxy for SoC could be good enough.

Some controllers do have that load diversion functionality, but I believe they're older, designed to handle wind and solar, likely not as efficient.

I'm curious how your bank gets to 100% full so quickly, is it just that you have such a large bank your discharge is always shallow?

Have you got a post you can link to that lays out the details of your setup?

[rabbi]

Originally Posted by john61ct

Yes I can see that voltage as a proxy for SoC could be good enough.

Some controllers do have that load diversion functionality, but I believe they're older, designed to handle wind and solar, likely not as efficient.

I'm curious how your bank gets to 100% full so quickly, is it just that you have such a large bank your discharge is always shallow?

Have you got a post you can link to that lays out the details of your setup?

The Votronic MPP 250 has an AES output, which is similar. AES is an "automatic energy selector" used by RV absorbtion fridges to switch between 12v, 220v and gas. As far as I know AES output is activated when on float and surplus energy is available.
But the Votronic SC is not as configurable as the Vitron MPPT.
In my previous boat I had a b-2-b charger by Votronic, not cheap but good quality. That was used to charge the house battery when motoring, but actually it was of very little use due to equally oversized solar.

We have 2 new Trojan T1275 150Ah batteries, so C20 is 300Ah in total. More would easily fit, but since the batteries only have to provide juice for one night its more than enough for us.


Our discharge is typically between 25 and 35Ah, or roughly 10% of capacity.
Sometimes we use up to 50 Ah if the inverter runs 24/7 to charge some slow charging gadget (electrical toothbrush takes ages to charge) or when doing a night passage with enough wind to sail fulltime.

So not much energy to recharge. 3 hours of morning sun are enough to get them to what I consider full, i.e. close to a 1% tail current on 14.8V. Of course only if there is no boom / mast shade.