So many solar options. Is there a standard?

[Serapium]

Hey all. Could use some advice as I plan our solar installation. I'm finding a whole lot of solar panel options that all kind of leave me stumped. In particular, knowing that the end goal of the system is to charge a 12V bank of batteries, do the panels have to be 12V panels, or does a MPPT charge controller regulate the voltage to the correct output?

Take for instance this 315 Watt panel at $1.00 per Watt. It is a 35.83VDC/8.8A panel. Does that translate linearly through a MPPT charge controller to 12VDC/26.25A output?

Astronergy ASM6612P-315 Silver Poly Solar Panel - Wholesale Solar

How important are the values for 'open circuit voltage', 'short circuit current' etc when planning an installation?

[noelex 77]

Originally Posted by Serapium

Take for instance this 315 Watt panel at $1.00 per Watt. It is a 35.83VDC/8.8A panel. Does that translate linearly through a MPPT charge controller to 12VDC/26.25A output?

Yes a MPPT controller will convert the voltage as you describe. However, solar panels will only output their specified wattage under exceptional conditions. Also a 12v battery will normally be at say 12.6-14.8v when it is subject to a charge current.

So around 19A into a 12v battery would be considered reasonably good in the best part of the day from a 315w panel.

With a MPPT controller the voltage of the panel does not make much difference providing you do not exceed the max voltage of the controller (leave some leeway). The controller will need to be rated for the full output current into the battery so you cannot use a 10A controller with a 315W panel even if the input current is less than 10A.

[jeepbluetj]

There are other advantages of MPPT.

1. You'll get more power into your batteries (as opposed to a PWM controller)
2. You can use smaller cable from the panels to the controller. (Higher voltage will carry the same power at less current)

[socaldmax]

Originally Posted by Serapium

Hey all. Could use some advice as I plan our solar installation. I'm finding a whole lot of solar panel options that all kind of leave me stumped. In particular, knowing that the end goal of the system is to charge a 12V bank of batteries, do the panels have to be 12V panels, or does a MPPT charge controller regulate the voltage to the correct output?

Take for instance this 315 Watt panel at $1.00 per Watt. It is a 35.83VDC/8.8A panel. Does that translate linearly through a MPPT charge controller to 12VDC/26.25A output?

Astronergy ASM6612P-315 Silver Poly Solar Panel - Wholesale Solar

How important are the values for 'open circuit voltage', 'short circuit current' etc when planning an installation?

Excellent questions!

Yes, an MPPT controller will convert the 35v/8.8A input to the battery voltage, let's say 13v under charge, at around 24A. They're usually about 96-99% efficient, so there will be a little loss there. That's why I prefer newer panels like the one you posted, it produces far higher than charging voltage at peak times, so it will produce at least 13-15v much earlier in the day and later in the evening than a panel that produces only 19v peak. Every little bit helps, higher efficiency panels, higher voltage, larger cabling, etc.

The open circuit voltage is important in regards to the MPPT controller. Let's say your controller has a max. input V of 100V, you could hook 2 of the 35V panels in series and end up just over 70V, but you could not hook a 3rd one in series. An MPPT controller with a max. of 150V could take 4 panels in series. Always leave a few volts headroom, in some rare instances, they can produce higher V.

[socaldmax]

Another feature I prefer in an MPPT controller is user adjustable bulk charging voltage. You can check your battery mfr's website, find out the recommended charging voltage and set it to that. Most charge controllers are set to very conservative levels if using generic battery settings and will only charge your batteries to 80 or 85%, leaving the upper 15 or 20% unused. This translates into 30 to 40% of usable capacity. That's a lot to miss out on!

[noelex 77]

Originally Posted by socaldmax

That's why I prefer newer panels like the one you posted, it produces far higher than charging voltage at peak times, so it will produce at least 13-15v much earlier in the day and later in the evening than a panel that produces only 19v peak.

Under low illumination solar cells produce lots of volts, but little or no current. So higher voltage panels don't start any earlier. If a 12v panel is used the panel voltage will be above the battery voltage before the cells can generate any useful current.

MPPT controllers actually miss out slightly very early, and late in the day, because their self consumption is higher. The better units do not start tracking until the solar panel output exceeds the self consumption.

Originally Posted by socaldmax

Another feature I prefer in an MPPT controller is user adjustable bulk charging voltage. You can check your battery mfr's website, find out the recommended charging voltage and set it to that.

I agree user adjustable charge voltages (and absorption time) are an important features, but these are available in many non MPPPT (or so called PWM controllers) as well.

[Snore]

Don't get too hung up on the controller. There is a huge difference between panels!

Do some searches on CF about solar panels. Also check Maine Sail aka compass marine website for a good education on solar panels.





Sent from my iPhone- please forgive autocorrect errors.

[Serapium]

Thanks, everyone. I'll take all that into consideration. Now that I have a better grasp on the tech, can I follow up with a more philosophical question (backed with math)?

Seems like I have a couple of options in designing a system from the ground up. Here are two examples that highlight the main differences. Let's assume that the panel I end up choosing is the same for both of these examples, and matches the characteristics of the panel above. So it's a 315 Watt nominal panel at 35.83VDC/8.8A. Let's further assume that I have a budget of $2,500 (an arbitrary number) to invest in panels and controllers. Real estate isn't an issue as we have a 46' trimaran that includes a 25'x6' hard top pilot house and a full width rear davit/deck that is 25'x4'. Would you rather:

Install 4 panels at $1,245 with two banks of two panels wired in series and each series connected set of two panels connected to a TriStar (or similar) MPPT controller at $550 each (dual controllers for redundancy and added efficiency should one set of panels experience shading - total of $1100).

- OR -

Install 7 panels independently at a total cost of $2205 and couple each panel to an inexpensive Chinese controller (30 AMP "MPPT" at $19 each - 30A 12V 24V Auto Switch MPPT Solar Panel Battery Regulator Charge Controller KJ | eBay). The idea would be to purchase 12 of these cheap controllers so that backups are on hand for a total cost of $228.

Version A has a theoretical output capacity of 1260 Watts for $2,345
Version B has a theoretical output capacity of 2205 Watts for $2,433

I realize that the efficiency of the cheaper controllers would be lower and that even though they are called 'MPPT' controllers that they will not perform anywhere near the higher dollar units. However, it seems that some of that loss (or all of it and then some) would be offset by having each panel isolated and therefore not subject to shading effect on other panels in the series.

Thoughts?

[leftbrainstuff]

Originally Posted by Serapium

Hey all. Could use some advice as I plan our solar installation. I'm finding a whole lot of solar panel options that all kind of leave me stumped. In particular, knowing that the end goal of the system is to charge a 12V bank of batteries, do the panels have to be 12V panels, or does a MPPT charge controller regulate the voltage to the correct output?

Take for instance this 315 Watt panel at $1.00 per Watt. It is a 35.83VDC/8.8A panel. Does that translate linearly through a MPPT charge controller to 12VDC/26.25A output?

Astronergy ASM6612P-315 Silver Poly Solar Panel - Wholesale Solar

How important are the values for 'open circuit voltage', 'short circuit current' etc when planning an installation?

There are no standards perse. And there are good and bad panels and controllers. Check wikipedia and the DoE for some facts.

Due to losses in converting sunlight to electrical charge in a battery you need significantly more than 12V output from your panel.

Each cell will output about 0.5V per cell. Count the cells in the panel to calculate the max open circuit voltage. 16+V is min open circuit voltage you need to charge 12V batteries. A good Kyocera panel will have an OCV of 20+V.

You'll then get about 5 hours of max sun, about 1000W/m^2 on average over a year.

A good panel will give 15 - 25% efficiency. Current research gives 50ish% so might be available in a few years.

Shading will reduce your capacity. So alignment is crucial to maximising performance.

Panels are cheap. Fit as many as you can. An MPPT controller will convert excess voltage to current. A little free lunch compared to shunts. Use any excess to heat water.

Start small. Just one panel and a controller. Measure and adjust. You'll soon gain confidence and some much needed data to drive your ultimate design.



Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[StuM]

Can those cheap controllers handle the 35.83VDC ?

[socaldmax]

Originally Posted by Serapium

Thanks, everyone. I'll take all that into consideration. Now that I have a better grasp on the tech, can I follow up with a more philosophical question (backed with math)?

Seems like I have a couple of options in designing a system from the ground up. Here are two examples that highlight the main differences. Let's assume that the panel I end up choosing is the same for both of these examples, and matches the characteristics of the panel above. So it's a 315 Watt nominal panel at 35.83VDC/8.8A. Let's further assume that I have a budget of $2,500 (an arbitrary number) to invest in panels and controllers. Real estate isn't an issue as we have a 46' trimaran that includes a 25'x6' hard top pilot house and a full width rear davit/deck that is 25'x4'. Would you rather:

Install 4 panels at $1,245 with two banks of two panels wired in series and each series connected set of two panels connected to a TriStar (or similar) MPPT controller at $550 each (dual controllers for redundancy and added efficiency should one set of panels experience shading - total of $1100).

- OR -

Install 7 panels independently at a total cost of $2205 and couple each panel to an inexpensive Chinese controller (30 AMP "MPPT" at $19 each - 30A 12V 24V Auto Switch MPPT Solar Panel Battery Regulator Charge Controller KJ | eBay). The idea would be to purchase 12 of these cheap controllers so that backups are on hand for a total cost of $228.

Version A has a theoretical output capacity of 1260 Watts for $2,345
Version B has a theoretical output capacity of 2205 Watts for $2,433

I realize that the efficiency of the cheaper controllers would be lower and that even though they are called 'MPPT' controllers that they will not perform anywhere near the higher dollar units. However, it seems that some of that loss (or all of it and then some) would be offset by having each panel isolated and therefore not subject to shading effect on other panels in the series.

Thoughts?

I would go with version B, but not with that controller. One indication of a crappy controller is price. You cannot build a decent 30 amp controller and sell it for $19. Between the lack of heat sink fins and the documentation claiming "thunder protection" , I don't have any faith in that controller.

Your concept of using one controller per panel is a good idea. Theoretically, if you lose 1 panel or 1 controller, you still have the other 6 cranking out power. All else being equal, it seems like having 7 controllers instead of 2 would make it 3.5x more likely that one would fail, but if one does fail, again, it's much less loss until you can get a replacement. The other advantage is if you get shading on one or more panels, each controller is capable of maximizing harvest without losing power from any other panel.

If you're interested in a less expensive quality 20A controller that would work with your example solar panel, take a look at Eco-worthy. $102 ea, delivered, I'm sure you could get a big discount buying 8 or more.

[Serapium]

Alright. Based on the earlier comment I did the due diligence and it looks like the controller I referenced above will not support the voltage of 35.83 VDC.

So taking into consideration the recommendation of the eco-worthy controller that presents Version C.

I'd have 6 panels at $1,890 plus a total of six controllers at $612 (assuming no bulk discount) for a total of $2502 with no backup controllers in stock. This gives a total theoretical output of 1890 Watts.

It's this better than Version A?

[socaldmax]

Originally Posted by Serapium

Alright. Based on the earlier comment I did the due diligence and it looks like the controller I referenced above will not support the voltage of 35.83 VDC.

So taking into consideration the recommendation of the eco-worthy controller that presents Version C.

I'd have 6 panels at $1,890 plus a total of six controllers at $612 (assuming no bulk discount) for a total of $2502 with no backup controllers in stock. This gives a total theoretical output of 1890 Watts.

It's this better than Version A?

Yes, it puts out 50% more power than version A and if you lose a panel or controller, you still have 5 left. If you buy a 7th controller, you'll have a spare.

Don't forget cabling, fasteners, sealants, connectors, brackets, heat shrink, zip ties, grommets, etc. That could easily add up to another $200 or more. Don't cut any corners, you don't want to have to redo anything later, possibly in some remote location.

[Catamoron]

I have to put my 2 cents in even though I haven't read through all the responses - not sure if somebody has posted about not (and I mean NOT) going with a Chinese MPPT controller - we made that mistake and was the biggest waste of $200 I've ever spent. Whoever said to not get hung up on the controller is incorrect - IMHO its the controller, not the panels that you'll get your most difference in output. Go with big solar panels - as big as you can get, and get a MidNite MPPT controller. Our old controller would only put out a max amp of around 25 and any given time - we installed the MidNite with the same solar panels and were making into the 70's at times and regularly seeing up towards 60 amps during most of the day (using an array of 840 watts) - please don't waste your money on anything other than a good controller. Sorry if somebody's already posted this.

[noelex 77]

The first priority is to fit as many solar watts as you can. Differences in controller efficiency (like the difference between MPPT and non MPPT controllers ) only makes a small difference. If you have room, this can be easily compensated for with only a slight increase in the wattage of the solar panels.

Most boats are limited by the amount of panel space that is available so they need to go for the most efficient system possible. Multihulls have much more space and fitting more watts with a less good controller will generally give you much more power for the same money.

However, the cheap MPPT controllers tend to be very unreliable. Sometimes they are not even MPPT. I would not recommend them even with multiple back ups. If you are using high voltage panels you need a good MPPT controller and unfortunately that is expensive.

One option that is worth costing is nominal 12v panels (these will have 36 cells). They can be used with much simpler non MPPT controllers. These so called PWM controllers are less complex and even inexpensive models tend to be reliable. Second hand models are also available when people upgrade to MPPT. There is no efficiency advantages in using multiple PWM controllers (even the gain from fitting more than one MPPT controller is only very small). A single large PWM controller could potentially be picked up cheaply. You loose redundancy, but they only fail rarely. In an emergency direct connection to the battery, bypassing the controller can be used, providing you monitor the battery voltage carefully.

Anyway, it is an option that is worth throwing into the mix. Large high voltage panels are more readily available and are usually a little less expensive, but the controller costs are very significant. If you have few space restrictions 12v panels with a PWM controller is often the best bang for the buck.

Don't forget to include the delivery costs. Some couriers put a surcharge on large glass objects and delivery on large panels can be much more than you would imagine. If buying on-line these costs are not apparent until the end. Sometimes a larger number of smaller panels are significantly cheaper if the overall size fall below the threshold when the surcharge applies. Fitting a greater number of smaller panels is sometimes easier and sometimes harder depending on the mounting location. There is a small gain in output from the same wattage of smaller panels as shadowing is less of a factor, but the overall area is usually a bit larger.