Increasing array size for panels that won't tilt

[Endurance]

My first post here. The site information looks good but I have a different application for which I'd appreciate some input. I am putting solar panels on a boat. The boat part brings up a few challenges. First, the battery bank has to be at 12 volts to operate a lot of existing 12v equipment. Second, because the boat moves around, the panels have to sit flat rather than face the sun. Third, safety says I need to keep the wiring between the array and the controller pretty close to about 50 volts. Last, my boat is at Lake Powell where typical daytime highs are over 100 degrees F. during the boating season.

I have used the string sizing tool for a set of sample panels: six Trina Solar 240 watt panels. Here are their specs:


    Number of Cells: 60
    Tolerance: +3%/-0%
    Vmp: 30.4 volts
    Imp: 7.89 amps
    Voc: 37.2 volts
    Isc: 8.37 amps
    64.96" x 39.05" x 1.57"
    43 lbs.
    MC4 locking connectors

The string sizing tool says that if I use three strings of two panels, I will be maxing out a Classic 150 controller's amps but not bad enough to need a second controller. That sounds like what I want, but I wonder if I should tweak the results a little. Since I have to keep my array voltage on the lower side, there's no way I will get into a hyper VOC situation. Maybe rather than the 1,440 watts that six of the 240 watt panels would give me, I wonder if I'd get more hours of production per day with something like six 290 watt panels. I realize that I would sometimes be "wasting" some panel capacity. I also realize that in the real world, completely flat panels at high temperatures don't often give their rated output. Besides, panels are getting pretty cheap these days.

I also wonder how happy a Classic 150 will be running at or close to its maximum output in a high ambient temperature for most of the day.

I will appreciate any thoughts.

[Resthome]

My first post here. The site information looks good but I have a different application for which I'd appreciate some input. I am putting solar panels on a boat. The boat part brings up a few challenges. First, the battery bank has to be at 12 volts to operate a lot of existing 12v equipment. Second, because the boat moves around, the panels have to sit flat rather than face the sun. Third, safety says I need to keep the wiring between the array and the controller pretty close to about 50 volts. Last, my boat is at Lake Powell where typical daytime highs are over 100 degrees F. during the boating season.

I have used the string sizing tool for a set of sample panels: six Trina Solar 240 watt panels. Here are their specs:


    Number of Cells: 60
    Tolerance: +3%/-0%
    Vmp: 30.4 volts
    Imp: 7.89 amps
    Voc: 37.2 volts
    Isc: 8.37 amps
    64.96" x 39.05" x 1.57"
    43 lbs.
    MC4 locking connectors

The string sizing tool says that if I use three strings of two panels, I will be maxing out a Classic 150 controller's amps but not bad enough to need a second controller. That sounds like what I want, but I wonder if I should tweak the results a little. Since I have to keep my array voltage on the lower side, there's no way I will get into a hyper VOC situation. Maybe rather than the 1,440 watts that six of the 240 watt panels would give me, I wonder if I'd get more hours of production per day with something like six 290 watt panels. I realize that I would sometimes be "wasting" some panel capacity. I also realize that in the real world, completely flat panels at high temperatures don't often give their rated output. Besides, panels are getting pretty cheap these days.

I also wonder how happy a Classic 150 will be running at or close to its maximum output in a high ambient temperature for most of the day.

I will appreciate any thoughts.

I'm running a similar set up at Lake Don Pedro with 10 -  140W. Kyocera panels due to mounting space limitation on my canopy. You didn't mention the temp coefficients for your panels but most of them are similar. I just changed to these panels in late September 2012, so have not had them in the real hot 100 degree weather. But I can tell you the performance on the panel will be no where near the manufacturer spec. With the high summer temps and the voltage drops and system efficiencies you can pretty much figure on 70% of the power specification in my experience. My Classic 150 is mounted in a closet inside and gets the benefits of the A/C to help keep it cooler. I have yet to have the turbo fan come on. The smaller fans run for a short period of time while in bulk and running more than 35A.  I'm using 4g marine wire from the combiner to the controller and 2g marine wire to the 850AH battery bank. When charging amps get above 35 Amps I start to see about a .1-.2v drop in voltage between the Classic and the battery bank which is about 18 ft of wire run one direction between the two. I'm about 13 ft of wire run one direction from the combiner to the Classic. And 2g marine wire does not fit the Classic terminals so you have to use some type of bus bar connections.


We are pretty conservative with the loads so my biggest draw with the Swamp Cooler and TV, Laptop, and radios is around 25-30 Amp. Don't use the Microwave for more than 1-2 minutes without using the generator as it will suck 150A to run.


Your mileage may vary. BTW I am extremely happy with the Classic 150 and Midnight as a company. There support is excellent as noted in these forums.

[Kent0]

The appropriate spec to be consider here is that the Classic 150 is de-rated to 80 amps in environments over 40°C. For a 14.4 output voltage at 80 amps, the input power is about 1150 watts. That's 80% of the 1440-watt watt array's nominal rating. Because of the heat and flat mounting angle, the 240-watt modules are unlikely to exceed 1150 watts. But six 290-watt modules may be pushing your luck - that's like adding an extra 240-watt module!

[dgd]

..  I wonder if I'd get more hours of production per day with something like six 290 watt panels. I realize that I would sometimes be "wasting" some panel capacity. I also realize that in the real world, completely flat panels at high temperatures don't often give their rated output. Besides, panels are getting pretty cheap these days.

I also wonder how happy a Classic 150 will be running at or close to its maximum output in a high ambient temperature for most of the day.

I'd go for the additional larger panels.  Getting more power on 'bad' days is more important (for me) than being concerned about wasting power on 'good' days.  And as you say they are pretty cheap. Also, this would only occur when the Classic is in BULK MPPT where its trying to put everything it can into the batteries.  With an excess of PV power you could also look at a water heating element being switched on by the Classic to use excess power..

Driving the C150 to maximum should not be an issue but its easy to improve cooling with an external fan, there may even be an AUX1 option for this.

dgd

[Resthome]

"Operating Temperature

Min of -40c to 50C - Controller will auto derate as temperature rises above 25C"


Maybe Bob or Ryan can elaborate on this specification.


Kent0 stated that it derates at 40C. Is there a chart showing how much it derates above 25C?

[Halfcrazy]

Well the Classic itself starts to de rate around 80 degrees C on the Fet temperature. What we find is "IF" the Classic is running at 100% and the Ambient goes above 25C it will likely start to turn itself down to cool itself off. So while there is no hard fast chart if you will. If I where going to run a Classic in a 40C environment I would say load it to 75-80%. We have a chart somewhere that we used for ETL testing I will see if I can dig it up.

Ryan

[Resthome]

Thanks Ryan.. That makes sense. At around 36A I see the FETs at around 48C when the Classic is around 74F ambient.


@Endurance ... I think the message here is you need to keep the Classic in as cool as place that you can find. Maybe in a pontoon or somewhere it's not subject to the high outside temps or engine room temp. Remember at 100+ degree ambient outside temp the panels are going to be a lot hotter than that in the sun and that is going to de-rate the panels. The panel spec is at 25C cell temp. The other side of that is the batteries if used with the Temp Sensor will not require as much voltage when hot. But in the cooler winter temp you are going to be generating a lot more power and the batteries want more voltage when the temps are below 72F. So you need to look real close at the lowest temp for the area or be able to disconnect a string in the cooler months.

While the flat mounting loses some power I'm in Absorb mode by 9am PDT and Resting mode by 7pm PDT at this time of year.   

Just my $.02

[Endurance]

Thanks John and Ryan. This is good advice. Finding a cool place for my Classic 150 is a little like finding a cold place in Hell. Here are my three choices:

1. Under the master suite bed. This is low in the boat, but it is in a closed-off compartment that is about 40 inches by 80 inches and 18 inches high. I can punch some vents and add a computer fan to pull in air from under the floor between the pontoons. That is the coolest air I will find, but it would bring in moisture and possibly some bugs.

2. On the side of the master bed. This would have open air on the front, sides, and top. The bottom of the controller would pretty much have to be on the floor. It would have good air flow around it. It would pick up more lint from the floor and have a tendency to get bumped when you walked by it. The worst thing about this location would be when the controller woke up and started fans running before I wanted to wake up.

3. In a closet. This would be higher up on the wall and therefore more away from lint. I could leave the closet door open when I wanted more air flow. There is already a Magnum MS 2812 in the closet and it makes a lot of heat. The back wall of the closet is an outside wall, so it would be pretty easy to add a vent with a computer fan to exhaust hot air to the outside. If need be, under the floor an area on top of the pontoon where I could punch through a vent. That would bring in cool air with a little less bug and moisture problem than under the bed.

The pontoons are all sealed, so there's no chance of getting inside one of them. Given the three options I have, which do you think would be best?

[ChrisOlson]

3. In a closet. This would be higher up on the wall and therefore more away from lint. I could leave the closet door open when I wanted more air flow. There is already a Magnum MS 2812 in the closet and it makes a lot of heat. The back wall of the closet is an outside wall, so it would be pretty easy to add a vent with a computer fan to exhaust hot air to the outside. If need be, under the floor an area on top of the pontoon where I could punch through a vent. That would bring in cool air with a little less bug and moisture problem than under the bed.

This sounds like the best option to me, but I think it will take more than a computer fan to provide adequate ventilation for both the inverter and controller.  Putting a screen on the air intake vent would also help keep bugs out.

It sounds like this is not a V-hull with an engine room?  It's a pontoon style with outboard propulsion?  So you don't have an engine/house-battery room with bilge fans?  The reason I ask is because the engine room stays pretty nice and cool in our 58' Chris-Craft when the Detroit diesels aren't running because it's below the waterline.  We have a 24V PowerTech inverter in there that we're going to replace with a new Magnum this year and if I were to add solar to the boat that's where I'd put the controller.

It might be best, based on the fact that your boat has a 12V house power system, and you plan on pushing it to the limit in high temps, to look at either:
-putting in two controllers to reduce the amp load on them
-switch the boat over to 24V
Sure, it's more expensive, but I've never seen anything with boats that isn't   

It's not too hard to switch an RV or boat to 24V for the inverter and leave existing DC house power systems on 12V.  That's the way our boat is set up, with two separate battery banks, one at 12V for the DC house power lighting and fans, and the other at 24V for the inverter.  When we hook up to shore power (or have our onboard generator running) the PowerTech inverter charges the 24V bank and there's a separate marine charger that charges the 12V bank.  The starting batteries (8D's) for the engines are separate from both of the house power battery banks.
--
Chris

[Resthome]

3. In a closet. This would be higher up on the wall and therefore more away from lint. I could leave the closet door open when I wanted more air flow. There is already a Magnum MS 2812 in the closet and it makes a lot of heat. The back wall of the closet is an outside wall, so it would be pretty easy to add a vent with a computer fan to exhaust hot air to the outside. If need be, under the floor an area on top of the pontoon where I could punch through a vent. That would bring in cool air with a little less bug and moisture problem than under the bed.

I would opt for the closet. Like you said you can always prop the door open. That's where I have mine mounted. My FEt's temp run just below 50C most of the time. I think the smaller Classic Fans turn on at 50C. Not sure when the Turbo Fan comes on, never had it come on yet. By the time it gets real hot here I'm already in Float and usually only have a small load. We were 88 yesterday and the Classic fans never went on. Granted we were not running the A/C at this time of year.

[JerryB]

I just saw this series of postings and thought I would offer my experience. I have a 50 foot yacht fitted with 9 240 watt solar panels fashioned as the "hard top" for the flybridge. I have a 12 volt electrical system, with a 1200 AH battery bank and a Classic 150. I live in Olympia WA. The system has worked very well for the one year that it has been in operation. The 2200 watt nameplate capacity array is NOT overkill for the Classic since the panels are horizontal and there are indeed clouds in the NW... The array is set up as 3 strings of 3 panels each for a 90 volt nominal feed to the Classic.  A couple of observations: The Classic REALLY needs external cooling when it is anywhere near max output. I have a temperature controlled 8" fan directed on the case. While the Classic is mounted in the engine room, most of the time the ambient is quite cool (at anchor) and it still needs the fan. With this array, the Classic only occasionally is maxxed out, so don't be afraid to "overbuild" on panels. Also I have found the "Solar" algorithm to be pretty poor in optimizing the power delivered. It can easily get "stuck" in a very sub-optimal point. The user-set %VOC mode works wery well at abut 83%. During the summer months I can harvest 7-9 KWH per day from the array; more than enouygh to provide all my electrical needs including domestic hot water (via the inverter). In your climate/lattitude, you will probably get a good deal more..... Anyway, hope this helps/insipres you.....

Jerry B

[ChrisOlson]

I just saw this series of postings and thought I would offer my experience. I have a 50 foot yacht fitted with 9 240 watt solar panels fashioned as the "hard top" for the flybridge.

Jerry - I'd like to do something like that on our boat and sort of interested in how you did your racking or mounts for the panels.
--
Chris

[vtmaps]

I have a 12 volt electrical system,
<snip>
The array is set up as 3 strings of 3 panels each for a 90 volt nominal feed to the Classic.
<snip>
The Classic REALLY needs external cooling when it is anywhere near max output.

Your classic will run cooler and more efficiently without so much (90 v --> 12 v) down conversion.  You could put your 9 panels in parallel and down convert from 30 v --> 12 v.

--vtMaps

[JerryB]

I understand completely about the down conversion efficiencies, but in order to utilize a 30 volt primary bus, the wire size would become prohibitive especially for routing through crowed wire channels on a boat. For equivalent power loss, it would have to increase 9 wire gauge sizes.....

On the racking for the panels, this is a unique arrangement. The panels are not mounted on the roof; they ARE the roof. The frame is a free-standing, edge-supported aluminum channel grid, custom welded. The channels are standard unirac extrusions which have been cut, fitted and welded. The panels are then mounted onto the frame which itself is supported by stainless steel tubing, screwed and glued to the boat hull. The water proofing of the panels turned out to be quite an exercise...... The small photo attached may give you a better idea. This structure supports 6 panels and three more are located aft on the roof of the sunbridge. The aft panels are mounted on a standard set of rails and they are removable since I do an elaborate light show on the boat every Christmas... Hope this helps.

Jerry

[ChrisOlson]

That's pretty cool.  Our boat is built a bit different because it's a steel hull and doesn't have an open flybridge.  I measured it and I got room to install eight 250 watt panels on the pilothouse (attached).

How did you handle the panel frame grounds?  Just leave them floating?

Thanks!
--
Chris