Solar panel question/Recommendations

rgranger · Jan 25, 2023

You need to get a charge controller for the solar panel... then... yes... it would be okay to hook it up to your one battery.

@Maine Sail has a few good writeups on this topic.

dlochner · Jan 25, 2023

artleyt115 said:
Hello everyone! It’s me again asking more power questions (Hooray!) so I have all my devices in the boat now and I drew up a little excel sheet of how much everything can consume and the hours we plan to run the devices. Now by my (poorly done) math I should expect around 4 day of battery usage of my one GEL 100ah battery with all electronic do-dads on the boat. Now some things (like the fridge) were put at the average consumption, though when I wrote the excel sheet, I put both the initial cooling wattage and the idle wattage (I plan to run that in the house over night before a trip to get the fridge to temp then put it in the boat).

So, my questions; if I add another battery in parallel, in theory it should give me 4 days of capacity. If I add another battery, can I put a 200w solar panel on the boat and expect the batteries to be able to take the possible 30amp it can (potentially) produce. And can I put the same solar panel on just one battery for now (Until I buck up and buy the other one) and expect one battery to withstand it? Also (I know sorry) I have a 10a (2 bank) battery charger that I am hooking up, if I get two batteries in parallel can I put one bank on each battery?

View attachment 212454

You're off to a good start.

If you are unsure of your math, please post the spreadsheet so we can check the formulas, much easier than doing the math ourselves.

A few comments:

Pick one unit of power, either watt hours or amphours, it is much less confusing that way.

Batteries placed in parallel should be of the same age and type to ensure the charges on the battery are balanced. This will lead to longer battery life.

Lead Acid batteries generally have a maximum usable capacity of 50% of the total capacity, if the battery is fully recharged between discharges. Realistically, when cruising or when shore power is not accessible, they have a useable capacity of 40%. There are a few exceptions, carbon foam batteries and a couple of high end AGMs have a larger capacity, up to about 70%.

Charging a battery is inefficient, it will take between 110% to 120% of the used ah to recharge the battery, i.e., for every 10 ah that is used, recharging will require 12 ah.

Solar panels will average efficiencies can be expected to produce 3 times the nominal power each day. A 100 watt panel will produce about 300 watts (25 ah) on average per day, less on cloudy days, a little more on bright sunny days. High efficiency panels (expensive) panels can get close to 4 times.

AGM batteries can generally absorb 20 to 40% of their rated capacity when charging in the bulk phase (constant current). This is written as .2C. A 100 ah battery can take a charge of 20 to 40 amps in the bulk phase.

Reputable battery manufacturers will use the 20-hour discharge rate to label capacity. Less reputable ones will use the 10 hour rate which tends to yield a higher capacity rating, but less actual capacity in real life settings.

A two bank charger can not deliver more than its rated capacity. When 2 batteries are connected, the charge current is divided between the two batteries. Your 10a charger will only put out 5a per battery, which will lead to under charging and very long charge times.

dlochner · Jan 25, 2023

artleyt115 said:
This is some really good information, from the sounds of it I should be able to use the 200W solar panel with no issues. (especially with a controller) I'll attach the sheet (though I did not use the formulas on the sheet I just hand did the math) I figured the charger was under powered for even one battery but I mainly figured it was a trickle charger to keep in the boat when I have it on a trailer. Though I didn't know about that absorption rate on the battery, that's awesome! Btw I heard through the grape vine that when a batteries are in parallel they have to be charged slower, is this true? (I don't think this is true but I thought I'd ask)

I didn't realize the site blocked excel files, probably because of macros that could hide malicious code.

You must use a controller. The Victron controllers with Bluetooth are a good choice, easy to program and efficient.

When batteries are in parallel or series they act as one large battery. Batteries in parallel will increase the ah capacity and the charge capacity will increase, but not the acceptance rate, it will still be .2C, but 20% of 200 ah instead of 100ah.

Ralph Johnstone · Jan 25, 2023

artleyt115 said:
The site wont let me post it :/

We'll have to settle for a screen shot.

Orbweaver · Jan 25, 2023

artleyt115 said:
... (especially with a controller) ...

To echo dlochner and emphasize: YOU MUST USE A CONTROLLER with the solar panels. There are many styles/designs, so you'll have some research to decide which best meets your needs/budget. Do not, under any circumstance connect a solar panel directly to a battery.

If you put two batteries in parallel, you have one bank. So you should only connect one of the outputs from your charger to that one bank. Both batteries will charge to the same level because of the parallel wiring.

Timm R Oday25 · Jan 25, 2023

A couple of thoughts . We also have 25 Oday . A 200 watt solar panel is going to take up an enormous amount of room . We mounted a 30 watt off the back of the rear pulpit . I ran the wiring inside the railing ,under the cockpit and into the regulator mounted on the back of the bulkhead .
Most of the electronics you have listed most likely will only run randomly throughout the day .
We actually have two solar panels, one for each battery . The "charging" we get from the outboard is maybe 3 to 4 amps . Normally ,we draw down
one battery until we are at 12.3 volts . We then flip the battery selector switch to the other battery .
While we don't have refrigerator, the auotpilot uses several amps at a time when in use. We've been able to stay out for as long as a week this way

rgranger · Jan 25, 2023

Timm R Oday25 said:
A 200 watt solar panel is going to take up an enormous amount of room .

If you have a bimini, you might consider putting one similar to this over the top.

200 Watt 12 Volt Flexible Monocrystalline Solar Panel

The Renogy 200W Lightweight Monocrystalline Solar Panel enhances module efficiency while minimizing its weight. It is the perfect option for any off-grid solar system, especially for transportation applications such as RVs and boats. This solar panel frame features a lightweight substrate and...

www.renogy.com

rgranger · Jan 25, 2023

Here are some more ideas and products...

Highest Efficiency (up to 25.4%) And Best Flexible, Rigid, And Walkable Marine Solar Panels For Your Boat in 2024. We'll help you decide on the right solar panels to meet your power needs.

Marine solar panels with best Sunpower cells, 23.7-25.4%+ efficient, A+ grade solar cells only. All info and consulting available to help you choose the ideal solar panels for your needs. Visit or call, we're more than happy to help.

www.custommarineproducts.com

Maintenance of Flexible Solar Panels

maintenance of your flexible solar panels is easy, simply routinely keep them clean, check for structural integrity, and check the efficiency using monitoring functions in the charge regulators to ensure all is operating at optimum performance.

coastalclimatecontrol.com

rgranger · Jan 25, 2023

You know.... this rabbit hole is deeeeep! We could start talking about electric outboards, LiFePO4 batteries etc.

rgranger · Jan 25, 2023

artleyt115 said:
Yea it is, I dont plan to move to LiFEPO4 but I wanted an electric outboard originally just not too many good ones out there yet :/

Actually this Torqeedo Cruise is well reviewed and is equivalent to a 6 HP. My next pocket cruiser will get an upgrade to something like this...

Electric Boat Drives | Torqeedo

The number one for sustainable outboards and inboards - Torqeedo offers electric outboard motors up to 100 kW, inboards, hybrid-systems, intelligent battery technology and accessories

www.torqeedo.com

I go sailing for the silence and running an OB kind of ruins it for me.

mermike · Jan 25, 2023

I'm confused by the 87w/12w rating on your fridge. You listed 288.0 WH, which is 12w * 24H. 12 watts seems too low. Let's assume 30w on average.

Your inverter will draw power, even though you have N/A listed. A Victron Multiplus 2000 will draw anywhere from 3-9 watts depending on how search mode is configured. Let's assume 6 watts draw, 24 hours per day.

Your depth meter is only used when sailing, not 24 hours. Call it 6 hours.

Using your figures in addition to the assumptions above, I get a total of 3196.2 watts per day. A 200w panel will contribute around 800 watts per day. Figure in losses for voltage drop, battery efficiency and operating with an 80% depth of discharge, you'll need 227 AH of storage or 3 100AH batteries for 1 day away from shore power. Limit the PS4 to a couple of hours per day and you can eliminate 1 battery. But it might cause a mutiny.

The numbers seem high but math is math.

Solar panel question/Recommendations

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