Four questions about solar

[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.

[Jammer]

Originally Posted by Dirk01

Question 1: Can I imagine an MPPT Solar Charger as an "electricity sink"? If, for example, I connect two solar modules with different output voltages - say 18VDC and 20VDC - in parallel to one MPPT Solar Charger input, will a 12V battery get the full power of each individual solar module?

As posted upthread: a) it isn't recommended, and b) typically you give up some of the output from the higher voltage panel.

Question 2: What power do the solar panels give - say + / - 15° north or south of the equator? The performance specifications of the manufacturers refer to a "sun light output" of 1kW per m². However, the solar power in the area of the equator is (assuming a cloudless sky) about 2kW per m². Consequently, the modules (assuming constant efficiency) would have to deliver about twice the power. This in turn means double the current at the same voltage (to my knowledge the voltage does not get higher). This, in turn, would be important for dimensioning the maximum charging current that the solar charger can process. Is this assumption correct?

Some of the replies upthread may be confusing. Panels are rated based on nominal "standard" conditions. They will exceed their rated output, slightly, in unusually favorable conditions, but will never deliver "twice the power" they are rated for. As noted upthread, higher quality MPPT controllers will limit output power to the controller's rated maximum, or are thermally limited so as to avoid damage to the controller.

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

Somewhere around 0.8 to 1.0 kwh per day per m², for general planning purposes. Typical commodity panels are running around 200 watts nominal per m², and in typical areas the average output is equivalent to 5 hours of rated output per day.

It is clear to me that many other parameters (i.e. degree due to age of the modules, salt crystal coating, angle to the sun, etc. etc. etc.) make differences also. The more qualified information is provided, the sooner a "feeling" can be developed for where the journey is going. And maybe in the course of the posts there will be a hint for one or the another how to harvest the missing bit of energy without much effort.

The higher-efficiency panels are sometimes used in space-constrained applications but are expensive. You get maybe an extra 20% power for double the panel cost. Location, weather, shading, and efficiency of the rest of the system including the battery matter more.


Good luck in your journey. Solar is much better understood and easier to design, install, and use than was the case 10 years ago, and people do things with it that used to be met with harsh public ridicule when suggested.

[StuM]

Originally Posted by Shanachie

After a night at anchor, the very good controller starts charging the batteries after first light here in Florida. By the time the sun is up, the bank is getting 14-17 amps an hour on a normally sunny day.


But that charge rate doesn't last because the batteries accept amps at a lower rate as they charge. By early afternoon, the bank is accepting a couple of amps an hour as they approach capacity.

...
The good mppt controllers -- I have Victron -- will produce decent power on a cloudy day. The sweet spot is when you have enough panels to fill up on a cloudy day.

...
For me, that's 320 amps.

If you're going to offer electrical advice, it would be a good idea to learn what the units are


1. There is no such thing as "amps an hour". Amp is an instantaneus measure of power.


2. If your system is generating 320 Amps, I hope you have VERY thick wires and a huge battery bank to absorb that sort of power.

[Shanachie]

Originally Posted by StuM

2. If your system is generating 320 Amps, I hope you have VERY thick wires and a huge battery bank to absorb that sort of power.

Obviously, I made a typo and meant to say 320 watts, referring to the solar panels. On the other hand, my battery bank is 320 amps, so ,,,

[StuM]

Originally Posted by Shanachie

Obviously, I made a typo and meant to say 320 watts, ,

A typo is an accidental spelling or punctuation error. Not knowing how to spell a word or using a totally different word with a different meaning is not a typo

Originally Posted by Shanachie

On the other hand, my battery bank is 320 amps, so ,,,

Really?

Is that 320 CCA, 320 CA, 320 HCA or 320 PCHA?




Or are you perchance talking about the bank's amp hour rating.?
My original comment stands

[Dirk01]

Originally Posted by Shanachie

Yield from the panels is the wrong way to think about the problem.You need to think about how much amperage your batteries will accept.


The good mppt controllers -- I have Victron -- will produce decent power on a cloudy day. The sweet spot is when you have enough panels to fill up on a cloudy day.

Hybrid catamaran. 2 x 12kWh@48VDC@80%SOC, 1 x 6kWh@24VDC@80%SOC, all LFP, genny with 8kW (or nearby)
That means they eat what they are offered until they are full. I've not enough space for PV to overcome the limits. My SOC will normally not exceed 80% (unless there's a special situation coming up) and not less than 30% (exception: during night SOC 20% is the minimum allowed).

And YES, you're right with your statement "he sweet spot is when you have enough panels to fill up on a cloudy day." My intention is to run the genny only to prevent rusting.

That's what I've learned too.

Cheers
Dirk

[noelex 77]

Originally Posted by Shanachie

Yield from the panels is the wrong way to think about the problem.You need to think about how much amperage your batteries will accept.

You have to be able, on average, to produce more energy than you are using. This is the key to solar happiness .

If your energy input is less than your consumption how much amperage your batteries will accept is unimportant.

Solar (plus the other energy input devices) yield vs consumption is vital to the success of the installation.

The batteries just store energy and enable some limited short term averaging.

[Shanachie]

No such thing as amp hours? Perhaps you should tell the battery, solar and alternator industries about your finding.

They use amp hours as a common term to describe the relative electrical power of their various devices. I'm sure they will see the error of their ways, though, if you inform them of your brilliance.


Here's a definition for your own knowledge. https://en.wikipedia.org/wiki/Ampere_hour


If you know anything about boats and electricity, you know what I was referring to with a 320-amp battery bank. If you don't, tell me and I will send you a longer explanation.



Cheers.

[PaulCrawhorn]

It could mean a 320Ah bank.

Using amps (320A bank) doesn't just flag you, but leads to confusion.

Many would think you meant the max peak or continuous current your pack can output.

[StuM]

Originally Posted by Shanachie

No such thing as amp hours? Perhaps you should tell the battery, solar and alternator industries about your finding.

Who said that?

I repeat:There is no such thing as "amps an hour"
Obviously "amp hours" are a valid unit of energy.

They use amp hours as a common term to describe the relative electrical power of their various devices.

No they don't! You really need to learn the difference between power and energy. That lack of knowledge appears to be the root cause of your incorrect statements.

Power delivered or drawn is measued in Watts or Amperes, no hours involved.

Amp hours is a measure of energy, not power and is used to describe the storage capacity or use over a time period. (Such as a battery can deliver 100Ah at the C20 rate or a fridge uses 50Ah per day).

Here's a definition for your own knowledge. https://en.wikipedia.org/wiki/Ampere_hour

And you may like to read this post that I wrote a few years ago
https://www.cruisersforum.com/forums...ml#post1933764

If you know anything about boats and electricity, you know what I was referring to with a 320-amp battery bank.

It’s not what you don’t know that kills you, it’s what you know for sure that ain’t true. - Mark Twain

[Dirk01]

Hi folks,

don't make it too complicate.
Joule (J) = Wattsecond (Ws) = Volt (V) x Ampere (A) x time (s), or J = VAs. Due to 1 h = 3600 s this results in: 3600 J = 3600 Ws = 1 Wh = 1 VAh.
Work is the amount of energy you can put into something So W=E(later) - E(before).
Quite easy, isn't it?
Most important at all - don't mix up the units and take the units as a proof of your calc.

For me, I'm calculating NOT in VAh. Calculation in J, Nm or Ws does not need permanently the voltage you have to consider. Makes it easier and avoids failures if you have different voltage levels.

However, this discussion seems to be a bit off topic...

Cheers
Dirk

[noelex 77]

Ahrs has traditionally been used because batteries store electrons rather than watts. Hence all battery monitors count Ahrs.

[PaulCrawhorn]

The Wh unit lets people compare the overall capacity of packs at different voltages, yes that is useful.

But when discussing a given pack type, stick to Amps and Volts, much more directly applicable to the critical performance factors, how we actually use batteries, motors and other loads.

The problem with using Wh directly for capacity testing is that the Peukert effect makes results **much** more variable depending on the C-rate used.

Ah more directly relate to the actual chemical reactions inside the battery, Wh are affected much more by SoC and C-rate at that instant.

For example a LI battery might have an efficiency well over 99% using Ah but only 80% in one set of conditions, then 70% in others.

So, best to use CC load test, get your Ah capacity (if secondhand % of original also gives you SoH)

and then multiply that Ah number by nominal volts in order to publish a Wh figure.

Then the impact of Peukert's Law is much less a wild card.

Consider V and A as your "realer" foundation variables to measure, power in Watts is just a calculated value derived after the actual measurements.

[Ardbeg]

OK I do not know much about the technical stuff however I have had 2 x 250W Kyoceras on frame above my bimini for 12 years. I have 1500 WATT MPPT. I have 2 x 4D batteries with cranking power of 1200W each. This runs my boat all sailing season at 44 deg N ( Lake Ontario). I notice that the power coming off the panels seems about double what goes into the batteries. I have fridge and separate freezer. I have all electronics I need incl radar. Also TV and stereo. Never had a problem except when connection came apart one winter. If power is low in morning after an overnight at anchor, they charge up within 1 hour of morning sun. I notice there is still a charge on cloudy day, much less of course. I figure I am spilling power generated by about 1000am in the summer. No need for more. I almost never plug in unless maybe I am at a marina where power is free with dockage and I want hot water in the morning. Hope this helps.

[StuM]

Originally Posted by Ardbeg

I have 2 x 4D batteries with cranking power of 1200W each.

Cranking watts (more commonly expressed as cranking amps) are essentially meaningless when talking about a boat's house batteries.

I'd guess you have around 400Ah @ 12V nominal in that bank, which is the only really relevant figure.

This runs my boat all sailing season at 44 deg N ( Lake Ontario). I notice that the power coming off the panels seems about double what goes into the batteries. I have fridge and separate freezer. I have all electronics I need incl radar. Also TV and stereo.

Most of the other half will be supplying those house loads

If power is low in morning after an overnight at anchor, they charge up within 1 hour of morning sun. I notice there is still a charge on cloudy day, much less of course. I figure I am spilling power generated by about 1000am in the summer.

Unless you batteries are Lithium, that is not possible. It takes a lot moe than an hour to fully charge lead acid batteries which have been draining all night.