Four questions about solar

[Adelie]

Originally Posted by PaulCrawhorn

LFP banks will immediately soak up every Ah produced, and have no need to charge to Full, in fact last longer if you don't.



Half the weight and space, and if cared for end up cheaper than lead per usable Ah per year so long as nothing goes wrong.

DIY LFP is the cheapest per Ahr returned over the battery's expected life.



For plug-N-Play high quality golfcart or solar batteries are next cheapest.



Next it was more or less a tossup between Fireflys and BattleBorns.



Personally, I would never use Fireflys on a sailboat unless it had a relatively small battery bank and an over abundance of solar panels. While Fireflys are much better at PSoC service than other AGMs they still require high charging currents which are very hard to provide on solar. Using the engine to recharge the batteries and meet the minimum needed charging current seems to defeat the goal of being on a sailboat. For a motor vessel no big, either way.



The following graphic was compiled 18mo ago. From a casual pursual, relative ranking has not significantly changed though the absolute numbers have. The prices for LFP have improved and will improve more now that they are coming off patent. At the end of the year I will update.

[COOGOR]

Originally Posted by Dirk01

Question 4: Which work (kWh) can realistically be harvested per day and per m² (specify current efficiency)?

Hello Dirk,
there is a great calculator at

https://de.sunware.solar/auslegung/index
(allow cookies for it to work)
It gives as well an idea about the harvesting depending on your location.
Cheers!

[Nepidae]

Admittedly I am NOT an electrical person, but I did stay at a Holiday Inn recently.

During that stay our 3-220W Xantrex Max Flex panels generated over 2.5kWh of power. We have a Victron 150/60 MPPT and 6-6V L16 400Ah AGM batts. The output gauges are a BMV-712 smart and a solar output gauge.

Remembering I am not an electrical person, regardless of where I stay, how does this work with a statement of panel limitation to the watt of the panel?

Thanks.

[valhalla360]

Originally Posted by Nepidae

Admittedly I am NOT an electrical person, but I did stay at a Holiday Inn recently.

During that stay our 3-220W Xantrex Max Flex panels generated over 2.5kWh of power. We have a Victron 150/60 MPPT and 6-6V L16 400Ah AGM batts. The output gauges are a BMV-712 smart and a solar output gauge.

Remembering I am not an electrical person, regardless of where I stay, how does this work with a statement of panel limitation to the watt of the panel?

Thanks.

3 - 220w panels are 660w total.

You can generally expect around 4 times the watt rating in watt-hours.

660w * 4 = 2640w-hr or 2.64 kwh.

That lines up pretty well with your results.

[StuM]

> During that stay our 3-220W Xantrex Max Flex panels generated over 2.5kWh of power.

Originally Posted by valhalla360

3 - 220w panels are 660w total.

You can generally expect around 4 times the watt rating in watt-hours.

660w * 4 = 2640w-hr or 2.64 kwh.

That lines up pretty well with your results.

That assumes he stayed for one full day.
If he arrived late afternoon and departed early the next morning, that's a phenomenal result.

If he stayed for a week, that's a pretty poor result.

[goboatingnow]

* Buy a top-quality MPPT controller. It makes a huge difference. Also, if you're originally installing 300 watts of solar, buy a controller that will handle more, in case you need to expand the system.

Mppt controllers do NOT make a “ huge difference “ the answer like many is it depends see https://www.victronenergy.com/upload...WM-or-MPPT.pdf

Nor would I recommend oversizing the controller , if you expand buy a new controller. Otherwise your wasting money.

* Buy name-brand rigid panels. Second-hand or cheaply made panels might save you a few dollars at first, but you'll probably end up spending twice. My flexible panels were not as good as rigid.

My experience differs , there is little difference between generic and branded panels of the same type. I would agree stay away from flexible panels. People often compare panels of difference specifications but this is misleading

* I've used one panel and two with a single controller. Practically, I could see no reason for using two controllers with two panels of the same model. The battery bank was still full at the end of the day.

A controller per panel has advantages especially for large high voltage panels , as the mppt point may not be identical. In practice the gains are likely to be small

* Reduce the risk of fire by using quality fuse blocks and oversized wiring. You should fuse between the panels and the controller, then between the controller and the batteries.

Fusing the panel output is uncommon , largely because PV panels are largely current sources and not voltage sources and can be shorted without issue.

Fuses should always be places near the battery connection point on the output of the solar controller to protect the wiring from battery short circuit

The process of selecting solar requires answering a few questions and making some choices

In a 24 hour period ( as an example ) how many ampshours are consumed ( assuming your batteries can actually support 24 hours of operation ) by the boat , This is a measure of battery capacity consumed

Given a number of daylight hours , how quickly do you want that energy restored to the batteries , making allowances for shorter days or reduced sunlight

If you have an ammeter you can log hour by hour the energy demand of your boat , ie average of 20 A for an hour is 20 AH , so you can assemble a consumption profile.

Let’s say your boat therefore uses 100AH over 24 hours

Now a good rule of thumb is to assume panels generate half their stated output during daylight hours , so 120W panel,via a 12v comtroller might average 5 A per hour of sunlight. Ie 5AH , this would require 20 hours to recover your daily consumption clearly this panel is too small. Doubling the panel brings this to 10 hours etc, Clearly in good days you’ll exceed these calculations , in others you’ll be behind.

Hence quickly you can determine what your expectations are and what size your panels need to be to match those expectations.

In my case mine recharge period is 4 hours in summer falling to 8 hours in the shoulder seasons.

[Adelie]

I would consider a 15-23% improvement significant if not huge.

[goboatingnow]

Originally Posted by Adelie

I would consider a 15-23% improvement significant if not huge.

In areas of relatively high irradiance, and high high panel temps , performance from a simple PWM controller is compatible to an mppt, especially in relTively low voltage panels.

With high panel voltage , low irradiance and medium ambients , mppt will typically give 10-15% more output

[Adelie]

Mainsail’s actual testing showered a bigger difference in Spring in Maine in varying sub-optimal conditions.

[StuM]

Originally Posted by goboatingnow

Let’s say your boat therefore uses 100AH over 24 hours

Now a good rule of thumb is to assume panels generate half their stated output during daylight hours , so 120W panel,via a 12v comtroller might average 5 A per hour of sunlight. Ie 5AH , this would require 20 hours to recover your daily consumption clearly this panel is too small. Doubling the panel brings this to 10 hours etc, Clearly in good days you’ll exceed these calculations , in others you’ll be behind.

A more common "rule of thumb" is 4 to 5 times "full sun equivalent". i.e. daily Wh is 4 to 5 times the rated output in Watts.

So a 120W panel is likely to run about 480 - 600Wh per day, which is 40-50Ah @ 12V.

In good conditions it can be a little higher, in poor conditions it can be a lot lower, but that's a good planning figure before you factor in local climate and time of year.

[HeywoodJ]

Originally Posted by goboatingnow

In areas of relatively high irradiance, and high high panel temps , performance from a simple PWM controller is compatible to an mppt, especially in relTively low voltage panels.

With high panel voltage , low irradiance and medium ambients , mppt will typically give 10-15% more output

I think what gets lost in this analysis is that it is only true of 18-20V nominal output modules, or those in the 32-40 cell range. Put a PWM on a 72-cell 40V module (all the modules on my boat are 72-cell) and you lose 50-60% of the output. Comparing PWM and MPPT only works if you're talking lower voltage panels, otherwise you need the the DC-DC buck converter that is an inherent part of the MPPT design.

[redneckrob]

Originally Posted by StuM

A more common "rule of thumb" is 4 to 5 times "full sun equivalent". i.e. daily Wh is 4 to 5 times the rated output in Watts.

So a 120W panel is likely to run about 480 - 600Wh per day, which is 40-50Ah @ 12V.

In good conditions it can be a little higher, in poor conditions it can be a lot lower, but that's a good planning figure before you factor in local climate and time of year.

It's important to remember that latitude and time of year can easily render that or any other "rule of thumb" that covers less than a year absolutely useless. In the mid-atlantic latitudes for example, a solar array will make nearly double the power in a given day in June then that same array in a day December just based on the length of the day. Again I don't know why anyone would rely on "rules of theumb" when they can plug their actual system specs into the free and easy to use pvwatts tool that DOE provides (which works worldwide btw) and get real numbers?

[noelex 77]

Originally Posted by redneckrob

It's important to remember that latitude and time of year can easily render that or any other "rule of thumb" that covers less than a year absolutely useless. In the mid-atlantic latitudes for example, a solar array will make nearly double the power in a given day in June then that same array in a day December just based on the length of the day. Again I don't know why anyone would rely on "rules of theumb" when they can plug their actual system specs into the free and easy to use pvwatts tool that DOE provides (which works worldwide btw) and get real numbers?

Spot on .

These solar “rules of thumb” are often quoted on the forum without the qualification that they only apply to narrow geographic zones and seasons.

Solar on cruising boats is a fantastic power source, but when designing a system the variability of output needs to be incorporated into the plan. Batteries can average out good and bad solar days, but do not store enough energy to average out good and bad seasons or locations.

Rather than relying on these rules of thumb you need to look at solar insolation in the areas and seasons where you plan to cruise. If you want a system that can function using solar as the primary power source without relying on a generator (and this is my preferred approach) the boat still needs to function in the areas and seasons with the lowest solar insolation. The battery bank will not average this out therefore rules of thumb quoting average production are of little value.

[StuM]

Originally Posted by noelex 77

These solar “rules of thumb” are often quoted on the forum without the qualification that they only apply to narrow geographic zones and seasons.

You mean something like "In good conditions it can be a little higher, in poor conditions it can be a lot lower, but that's a good planning figure before you factor in local climate and time of year. ."

[noelex 77]

Originally Posted by StuM

You mean something like "In good conditions it can be a little higher, in poor conditions it can be a lot lower, but that's a good planning figure before you factor in local climate and time of year. ."

I think people that have lived with a solar system on a boat (as you and many other members of this forum have done) understand how solar production works. They have a good feel for the output they can expect in their sailing areas.

People new to cruising expect a simple answer to “how much power will my panels produce”.

This is where the rules of thumb are quoted. This is fine if the question is qualified by including the cruising location and season (and preferably some information on the installation, such as how much shading the panels will experience), but these rules of thumb are quoted so often they create the impression that these numbers are set in stone.

In practice there is enormous variability in solar production. There really is no simple rule that works when defining an average output that can vary by 10x just between seasons in some locations.