Solar panel upgrade questions

[scross]

#1. If you are planning to upgrade your solar panel(s) which is better - one big watt panel of two smaller sized panels?
For my upgrade the primary factor was space on the Sports Rack. One large 340 Watt panel was the best space available solution. We have a Yakama sports box on the starboard side of the sports rack so locating the panel to avoid shading was important. But, if two smaller panels were possible, are two small panels a more energy efficient solution?
#2. If you use two smaller panels (e.g. each under 200 watts) do they need to be matched exactly in output specs?
#3. If you use two smaller panels should they be wired in parallel or series? What are the benefits of each wiring setup?

 

[Toucan]

If you use two similarly sized panels in series, you can use the original wiring coupled to a higher voltage MPPT controller. However, if one panel is shaded more than the other, you loose more. It takes little shading by an antenna or storage box to kill the output from a solar panel or pair in series.

Barry Thompson
TOUCAN, R-27 Classic

 

[Submariner]

#1. If you are planning to upgrade your solar panel(s) which is better - one big watt panel of two smaller sized panels? For my upgrade the primary factor was space on the Sports Rack. One large 340 Watt panel was the best space available solution. We have a Yakama sports box on the starboard side of the sports rack so locating the panel to avoid shading was important. But, if two smaller panels were possible, are two small panels a more energy efficient solution?

Wattage is wattage. I am not aware of any difference in having one large panel vs several smaller wattage panels. When I researched my solar upgrade I had a hard time finding a selection of large wattage panels (above 250 watts), and the few I did find weren't available (out of stock).

Space is an issue on a boat. The efficiency of a solar panel is what mattered most to me. Take for example the factory 160 watt panel that came with my boat was 16% efficient. The 200 watt panel I replaced it with was 24%. That may not sound like a lot. But both the 160 and the 200 watt panels were the same width. The 200 watt panel was 40 more watts and 3 inches shorter. Thus, it took up less space.

Space is always going to be the primary issue when upgrading solar. Two smaller panels may provide better mounting options than one big panel.

#2. If you use two smaller panels (e.g. each under 200 watts) do they need to be matched exactly in output specs?

It would depend on how you connect the panels. If you run an independent solar controller for each panel it wouldn't matter. If you're hooking them up in series they should be identical panels. If you're doing them in parallel then I believe they can be different.

#3. If you use two smaller panels should they be wired in parallel or series? What are the benefits of each wiring setup?

Series will add the voltage while keeping the amps the same.
Parallel will add the amperage while keeping the voltage the same.

To charge a battery the voltage of the panels must be higher than the voltage of the battery. The voltage of the panels is highly dependent on the intensity of the sunshine.

Connecting in series will increase the voltage substantially thus you may capture more sunshine earlier in the morning and later in the evening resulting in a higher daily output (since the voltage is way higher than the batteries). Amps generate heat from the resistance in the wire. Heat is lost power. Connecting in series minimizes this loss. If any part of the panel is shaded it will negatively affect the entire array. Depending on the panel's resistance to shading and how much is shaded, it could result in zero output. If you're going to have a shading problem you won't want to connect them in series. As a matter of safety, I also wouldn't recommend connecting more than 2 panels in series. As an example, using my pair of 200 watt panels connected in series, If I were to do 4 panels in series it would exceed 130 volts. Folks working on electrical systems don't usually expect to see such high voltages on DC. The solar controller you choose also must support the higher voltage. The factory MPPT controller (DMT1250) on the LE's only supports up to 50 volts but can handle up to 700 watts of solar. This mandates parallel connections for additional solar panels. The Victron MPPT 100/30 controller I installed supports up to 100 volts.

Connecting in parallel will keep the voltage the same while increasing the amperage. The panels will operate mostly independent of each other. If one panel is shaded and the other isn't, only the output of the shaded panel is reduced. The disadvantage of parallel is that the amps increase, and thus the gauge wire between the solar panel and the solar controller must be rated to support the higher amperage. If it can't support the higher amperage then bigger gauge wire will be needed. It's far easier to increase the wire size from the solar controller to the battery than it is to run new wire from the solar controller to the solar panels up on the roof.

Here's an example of series vs parallel using the 200 watt panels I have as an example. Note, the 200 watt panels I have are 24 volt panels.

From the solar panels to the controller:
2x200 watt panels connected in series: 400 watts = 63 volts at 6.3 amps
2x200 watt panels connected in parallel: 400 watts = 32 volts at 12.5 amps.

From the solar controller to the battery
400 watts = 13.6 volts at 29.4amps.

Recommendations
When upgrading solar, space to mount the panels is the first challenge, and is the primary challenge. That's going to determine everything else. Shading is second. If you have a mast that'll create shading, consider a port and starboard configuration with separate solar controllers. When sizing the panels for wattage, consider your electrical needs.
In the Pacific Northwest, as an easy rule of thumb, take the wattage of solar and divide by 4. That's how many amp-hours a day to expect, on average. (400 watts / 4 = 100 amp-hours a day).

With our 2x200 watt solar array connected in series and no shading problems at all:
In January, in the fog all day, I got 21 amp-hours.
In September in the pouring down rain all day I saw 50amp-hours.
The day before when it wasn't raining, (same location) I saw 110amp-hours.
My high-score thus far has been 225 amp-hours.
In general, April - September I can usually count on at least 100amp-hours a day.

This year up at Cap Sante Marina.
July 21 - 212 amp-hours
July 22 - 155 amp-hours
July 23 - 200 amp-hours
July 24 - 114 amp-hours

We just got back from a weekend at Kingston, WA. Saturday (August 13) I saw 166amp-hours.

We consume at least 120amp-hours daily on Channel Surfing.

 

[scross]

Thanks Martin!
Our Journey is set with its current solar configuration but your explanation helps me for how to set up our next boat!

 

[Mark_H]

Martin,
Thanks for your detailed reply. I am following this topic because someday I want to add a second solar panel to my 2022 R-27 LE. It has the DMT1250 MPPT controller and a CMP21190PK solar panel with an Open Circuit Voltage of 23.85V. I was thinking I could add a second panel in series and use the existing wiring from the panels to the controller. Two panels in series would result in a Voc of 47.7V, which is less than 50V. Is this not workable for some reason?

 

[Submariner]

Martin,
Thanks for your detailed reply. I am following this topic because someday I want to add a second solar panel to my 2022 R-27 LE. It has the DMT1250 MPPT controller and a CMP21190PK solar panel with an Open Circuit Voltage of 23.85V. I was thinking I could add a second panel in series and use the existing wiring from the panels to the controller. Two panels in series would result in a Voc of 47.7V, which is less than 50V. Is this not workable for some reason?

Do them in parallel as that's cutting it close unless you have one and can verify the voltage. I found out through a friend who's got an LE on the East coast, he installed a pair of CMP's 270 watt panels in series with a VoC of 46.2volts. 46.2 volts * 2 equaled about 103volts (as measured by a voltmeter) which errored out on the Victron MPPT 100/50 that only supports 100 volts. He called CMP and they said they need to go back and update their spec's at least on the 270 watt panel. He ended up buying MC4 Y cables and going with a parallel configuration.

 

[Submariner]

Martin,
Thanks for your detailed reply. I am following this topic because someday I want to add a second solar panel to my 2022 R-27 LE. It has the DMT1250 MPPT controller and a CMP21190PK solar panel with an Open Circuit Voltage of 23.85V. I was thinking I could add a second panel in series and use the existing wiring from the panels to the controller. Two panels in series would result in a Voc of 47.7V, which is less than 50V. Is this not workable for some reason?

I would also add...The DMT1250 can take power from the engine and solar, but not at the same time. I'd actually recommend not adding to the DMT1250. Simply disconnect the solar wires from it and install a Victron 100/30 or 100/50 controller. Then you could wire your panels in series and would be able to capture solar power while your engine is running.

Then the DMT1250 becomes your engine to house DC to DC charger, and the Victron (or similar MPPT controller, doesn't have to be Victron, but does need to support LFP) is your dedicated solar controller which would allow engine and solar charging at the same time.

That 600ah LFP battery is a deep bucket to fill back up, and AC is a huge drain. 🙂

 

[Mark_H]

Thanks for additional details.

I see that that Abso Charger manual for the DMT1250 states the CH2 solar input can be 14.5 to 50 VDC,
but the datasheet for the DMT1250 states 10 to 45 VDC. So, best to be safe and not put two panels like mine in series.

 

[Submariner]

If anybody wants to talk about solar for their boat, or wants some help with solar, or to evaluate options, or dive in deeper, have more specific questions, feel free to reach out to me directly. I talk to a lot of folks and I learn a lot by talking to other boaters.

Of all the upgrades I've done to Channel Surfing, the solar upgrade I rank as one of the top 3. It has had a huge return in quality of boating experience for us. In my opinion, the factory 160 watt panel is designed to keep up with the cabin refrigerator, and to keep the batteries topped off when trailering.

400 watts of solar was a game changer for us.

Three consecutive days at anchor is no problem for us. At a guest marina, I don't to have to run that shore power cable up and over the boat. Skipping shore-power at a guest marina is one less chore, and often saves the $4 - $7 per day hookup charge that some marinas charge... At home I pay about 11 cents per kilowatt-hour. Channel Surfing at most would consume 4 kilowatt-hours a day if I ran the hot water heater and the BBQ grill off shorepower in addition to normal 12 volt DC loads. There's 44 cents worth.

It's quiet, it has no maintenance, requires no fuel, gives no exhaust.
I wake up in the morning to check my batteries only to find they are being charged as early as 7:00am. My panels start producing power around 6:00am. (June/July/Aug timeframe).

I've had my panels now for 15 months. I've seen all 4 seasons.
Nov/Dec/Jan/Feb expect not a lot, but not zero.
March - October in the Pacific Northwest is very usable. The weather is also better. 🙂

Channel Surfing Solar Power Upgrade
https://www.letsgochannelsurfing.com/solar-power

 

[briandunnington]

If anybody wants to talk about solar for their boat, or wants some help with solar, or to evaluate options, or dive in deeper, have more specific questions, feel free to reach out to me directly. I talk to a lot of folks and I learn a lot by talking to other boaters.

I am embarking on our solar journey and am gonna take you up on this. Thanks for always offering to share your knowledge gained.

 

[croakz]

I'm looking forward to adding my results when we get our R25SC at the end of the month.

I got two of these bifacial panels. Someone was saying that on the water bifacials work pretty well, as there is decent reflection. We'll see how well they work so close to the roof, we got the same mounts as Let's Go Channel Surfing.

https://www.ebay.com/itm/265783005128

- tom

 

[S@LTD]

Martin,
Thank you for the detailed discussion-very informative. I simply added a second solar panel of similar size two years ago (145 watt panels) and connected them in series. I still have the factory Sunsaver Duo controller. There have been a few times where we inadvertently drained the batteries below 50% DOC but for the most part we have been able to manage although I am sure we are on the edge of discharging more than optimal. We anchor a lot and admittedly I have been flying blind without a battery monitor.

Our batteries are 5 years old and being replaced as we speak. I just installed a Victron battery monitor and will be taking our first trip with it later this week to Octopus Islands and Desolation for 3 weeks. We would like to create a little power cushion (to occasionally bring along our CFX28 Dometic freezer) and trying to decide if switching to a more efficient Victron controller would be enough or should we be looking to upgrade panels as well? Since I have been flying blind as to usage I don’t have a feel. Frankly trying to decide if I dare load it up for this trip. Any thoughts?

 

[Submariner]

Martin,
I simply added a second solar panel of similar size two years ago (145 watt panels) and connected them in series. I still have the factory Sunsaver Duo controller.

We would like to create a little power cushion (to occasionally bring along our CFX28 Dometic freezer) and trying to decide if switching to a more efficient Victron controller would be enough or should we be looking to upgrade panels as well? Since I have been flying blind as to usage I don’t have a feel.

The spec sheet on the duo controller says it supports up to 280 watts and you have 290 watts. Upgrading to an MPPT controller will give you 21% more solar than you're getting today from the panels you already have. That's about 24ah more than you're getting today.

Testing illustrating a 21% gain between a PWM and an MPPT style controller.
https://marinehowto.com/mppt-vs-pwm-solar-controllers/

 

[scross]

We love our Iceco portable refrigerator/freezer. But it, like most portable freezers, is a power hog if you are using it as a freezer. In real world use it requires about 50 to 60 AmpHrs per day. That’s 50% of the power requirements of everything else in the boat combined. Getting the Iceco was the only reason I upgraded the solar panel from 160 watts to 340 watts. Even with the upgrade, the bigger panel doesn’t completely provide all the power the freezer requires.

 

[S@LTD]

Victron MPPT is added to the list. Yeah taking the freezer was a last minute thought given the new AGMs. I’ll leave it in the truck. Thanks all!

 

[Red Raven]

Martin,
Thank you for the detailed discussion-very informative. I simply added a second solar panel of similar size two years ago (145 watt panels) and connected them in series. I still have the factory Sunsaver Duo controller.

S@LTD,
Are you sure your panels are wired in series? Putting them in series would double the panel voltage. The Sunsaver Duo is a PWM controller and has a max input voltage of 25volts. As I recall, the stock solar panels can put out near 18v each so you would be over voltage most if not all of the time. Also, the max voltage from the panels that can be used at the battery is around 15 volts so the second panel would be wasted if in series.

The Sunsaver Duo works fine with two stock panels in parallel. That is what I have, though my panels are older and have a bit lower power (135 and 140 watts). The current is then doubled instead of the voltage and everything stays within spec. (Though the max current is near the limit of the stock wiring). Perhaps you meant to say yours were in parallel?

If you do change to a MPPT controller then you do want to put the panels in series as the MPPT controller can take advantage of the higher voltage to generate the maximum charging power for the batteries.

Curt

 

[Submariner]

Martin,
Thank you for the detailed discussion-very informative. I simply added a second solar panel of similar size two years ago (145 watt panels) and connected them in series. I still have the factory Sunsaver Duo controller.

Are you sure your panels are wired in series? Putting them in series would double the panel voltage. The Sunsaver Duo is a PWM controller and has a max input voltage of 25volts. As I recall, the stock solar panels can put out near 18v each so you would be over voltage most if not all of the time.
Curt

I thought the same thing at first glance. There are two versions of the Duo controller, a 10amp and a 20amp version. I read through the instructions manual which states that the maximum solar voltage may be 30volts or 55volts. I assume from reading the manual that to mean 30volts for the 10amp version and 55volts for the 20 amp version. A pair of 12 volt panels in series shouldn't go past 55 volts.

Regardless, upgrading to an MPPT controller offers a substantial gain over PWM.

Interestingly enough, why PWM controllers and not MPPT?

The PWM controller draws 4mA at night, and 10mA during charging. (2 watt-hours a day).
A MPPT controller (Victron 100/30 MPPT) is going to consume 30mA for its operation. (9watt-hours a day)
At least according to their specification data sheets.

PWM controllers consume a lot less power and are thus more suited for small wattage panels.
MPPT controllers are better suited for larger wattage panels.

2 and 9 watt-hours a day are not large by any means, but they do make 10 watt solar panels, and they make 400 watt solar panels.

https://www.custommarineproducts.com/uploads/1/4/3/7/1437708/solar_controller_instructions.pdf

 

[doke01]

Try to get the largest panel you can for the space you have. Failing that get two. Less issues if they are both the same wattage. I installed two 380 watt panels (Hitachi) in series that are normally used on houses (about $360 each) from a local place here in NJ. Put them in series, get a good MPPT controller (it has to handle the voltage of the panels in series). If not now, get LiFEPe04 when you can (higher power density, deeper discharge, lighter (2 200AH weighs the same as 2 100 AH lead acid and can discharge down to 10% vs. 70%, with voltage staying at the top until the end...super gains). Make sure the controller supports the batteries you are charging. I have two 200AH LiFePO04 in parallel for a total of 400 AH with a 60 Amp MPPT controller (you can throw 250Amps at these batteries if you have it. The more Amps the faster it charges). A 60 Amp MPPT and a 30 AMP 115V charger are near the top from a size perspective you can put on a Ranger. On Ranger's you are limited to what you can do by the space you have.

That being said, I can draw down with everything I have on board turned on and the batteries last almost 3 days (no sun, including the fridge and deep freecer, not the microwave of course). With sun, or just daylight I basically never run out of power. Install a Victron shunt and it will tell you how long your batteries will last. It doesn't predict longer than 10 days. I was overnight on the hook last weekend. Using power all day I went to bed at 1AM at 97%charge. By the time I woke up at 9AM I was at 100% charge. Get as much as you can afford in that fits the space you have. You won't regret it.

 

[Submariner]

On Channel Surfing, an RT27-OB, I upgraded solar in May 2021.

I removed the factory CMP (Custom Marine Products) 160 watt solar panel and replaced it with a pair of CMP 200 watt panels. The panels are fixed/rigid panels, monocrystaline panels, with an efficiency of 23.7% using SunPower Maxeon cells.

I have 400 watts total and I connected the two panels in series and upgraded the solar controller from a PWM controller to a Victron MPPT 100/30 controller.

This is real-world data I've captured over the past 15 months of solar on Channel Surfing around the Pacific Northwest, year round.

I've done the math in the spreadsheet to proportionally downgrade or upgrade my actual numbers to a smaller or larger wattage panel. The idea is to help others get some insight to what you might expect with a different sized solar array.

Obviously, solar depends on the weather, rain, fog, overcast, clear blue skies... and time of year, January, March, July, all cause drastic variations in output.

But consider this... If you have 100amp-hours a day in your battery bank and you consume 100amp-hours a day, you get 1 day away from shorepower. But if solar were able to provide you with 75ah a day, you now get 4 days.

If you're not sure what your average consumption is on your boat assume 80-100ah a day as a starting point. The cabin refrigerator will consume about 20-30ah, daily. The cockpit refrigerator is about 12-20ah daily.

Solar wattage comparison spreadsheet
https://www.letsgochannelsurfing.com/solar-power?pgid=kxcvhybj-984f2fdc-512b-4708-af84-e932b613eda6

 

[briandunnington]

If you're not sure what your average consumption is on your boat assume 80-100ah a day as a starting point. The cabin refrigerator will consume about 20-30ah, daily. The cockpit refrigerator is about 12-20ah daily.

Some us are 'lucky' enough to have boats so small that they only have one refrigerator. Look at all that power that we save!

But this is a really great resource - thanks for pulling all of this together!