Planning Our Solar Array

January 4, 2015 by Jesse K on s/v Smitty 14 Comments

A cold and rainy January morning was a perfect time to finish up my research on our solar system. In a previous post, Trying to Make Sense of Solar, I laid out some of the options and design considerations. But just to review and make a clear list of what I plan to add here is a quick summary:

Living on the hook I am estimating we will use between 50-125 amp hours per day;
We are willing to run our diesel engine up to 1.5 hours a day allowing are alternator to generate about 65 amp hours, plus producing hot water as a by-product;
That would mean that we would want to generate about 50 amp hours of solar power a day;
Given that we are going in a small boat, efficiency is important, so we would like get the increased 15-20% efficiency you get from an MPPT controller over a PWM controller.
We may decide to add a watermaker to our boat and would like the ability to expand our solar array to offset some of that power consumption. So that would mean we would want to size certain aspects to allow for the easy upgrade in the future;
We like the aspect of the semi-flexible panels since they would allow us to disassemble and store the panels more easily in the event of a storm, and;
We are NOT independently wealthy and are trying to do this cruise in a very cost effective manner, so we can’t afford to splurge on the best available product for every component.

All that being said, here is what I have come up with for the our solar array:

Two (2) 100 watt semi-flexible solar panels mounted on our bimini;
A 30 amp MPPT controller with a remote panel, and;
An ability to expand the system by added two (2) 100 watt semi-flexible solar panels on the life lines or on deck.

Semi-Flex Solar Panels

My go-to source for electrical, Compass Marine aka Maine Sail, has a great write up on installing semi-flexible solar panels on a bimini.

Photo from Compass Marine

The steps involved with this process would include reinforcing the bimini structure, adding velcro, zippers or snaps to connect the panels and probably adding some wear patches to the bimini. You also have to be careful of the layout. The panels can’t cross over the bows that hold up the bimini or else you will create a flex point that can crack the panels. Below is a mockup of how I could layout panels on our bimini. We could actually fit two 100 watt and one 50 watt panels.

In the above mockup there are two additional panels on lifeline mounts. These would be the expansion panels if we choose to add some additional solar. I got this idea from a Solbian rep at a boat show. You connect the panels to the lower lifeline with some snap hooks and then use some line to position them. These could be angled to get a little more efficiency than laying flat if you are on the boat to make the adjustments.

Photo form Coast Climate Control

For the lifeline mount I would want to reinforce the panel by mounting it on something light weight. For that I would go with something like this thin-walled polycarbonate sheet that I heard about from a fellow cruiser (thanks Dani and Tate).

For panels, as much as I would love the Solbians, I can’t justify the added expense. Instead I have been looking at the less expensive semi-flexible panels. Based on reviews from others, like Dani and Tate on Sundowner, I have decided to go with Renogy 100-watt panels. These panels go for about $220 each on Amazon. But they have gone on sale for under $200, missed the Black Friday sale at that price. So I am hoping to get them on sale. And they are Amazon Prime eligible. According to the data from Dani and Tate, it appears that 5 amps per panel per hour is a realistic expectation for full sun.

One down side to the cheaper panels seems to be consistency. From reading reviews and recommendations, mainly from Maine Sail, on the sailing forums it appears that the best practice is to do some side by side testing as soon as you get them in. To do this I will make a 2×4 A frame that I can temporarily mount the panels on. I will then hook up the each panel separately to the charge controller and a battery. I will let each panel run for an hour and record the performance to make sure they are in the same ball park. I plan to record the starting, mid charge and ending volts and amps at the battery and the charge controller. If the results from each panel are not within the expected range I will send them back until I get a set I am comfortable with. This is another good reason to go with the Renogy because they are Amazon Prime eligible and that will help if I need to send them back.

Charge Controller

As I stated above, I want to go with an oversized MPPT charge controller. I looked at the Rogue MPT-3048, MidNite KID, TriStar 30, TriStar 40 and Blue Sky SB3024iL. This list primarily came from an article on the Compass Marine site about adding a small panel plus some recommendations I got from cruisers. I briefly considered some lesser brands such as the Renogy but decided that this piece was important enough to not mess around with off-brands.

Some of my key concerns were that I wanted flexibility to change the charge profile, the ability to equalize, a temp sensor and a remote panel. I plan to mount the controller in the stern compartment near the shore power charger and holding tank. I am concerned about the heat aspect. I don’t want to mount this unit in the cabin and have it dissipate heat into the cabin while we are in the tropics. I would also like some secondary ability to know what is going into the batteries besides the our Victron Battery Monitor.

In the end I found that the Rogue MPT-3048 had the best balance of options for the cost. It comes standard with a temp sensor and voltage sensors. The cost for adding the remote panel wasn’t bad. It didn’t hurt that it was among the cheapest. Still talking over $400 when all is said and done.

Installation & Cost Estimate

Here is my proposed wiring diagram. Getting a little busy and I might need to find a way to clean it up a little. I am attaching a PDF as well in case anyone wants to add comments on my wiring.

JK WIRING DIAGRAM_ADDING SOLAR

I plan to mount the charge controller on a piece of starboard next to the shore power charger.

The positive and negative solar busses will be mounted here as well. This will mean I will have about a 12-foot run from the controller to the batteries. Not ideal but I think have the heat go into this area will be preferable. Remembering that you count both the positive and the negative to determine the length of the run so that would mean I need coverage for 24 feet. According the Blue Sea Systems Sizing Chart (large PDF warning), 4 gauge wire would be sufficient for up to a 30-foot run. Using the same sizing chart, 4 gauge wire should be protected with a 100-amp ANL fuse when bundled. As shown on the wire diagram, I plan to use the same 50 amp fuse that protects the ACR in my current setup.

The bimini frame will be reinforced with cross bars on the edges and cross bars replacing the stern straps. With this configuration we won’t technically need the forward straps but I will probably just keep everything there.

I plan to wire the two panels on the bimini in parallel. From what I have read, you want to wire solar panels on a boat in parallel as that handles partial shading on a portion of one panel the best. If they are in series shading would degrees the output of the panels more. I am going to use the MC4 connectors for the panel wiring. This seems to give a good connection that can be disconnected easily when needed, yet another good Compass Marine article on this subject. I also plan to use the Renogy MC4 branch connectors to make the parallel connection at the bimini. I like how you can choose which side to make the male and which to make the female so you can make it dummy proof so you can’t connect them in reverse polarity. The Renogy panels come pre-wired this way.

Photo from Amazon

As I said above I plan to only install the two panels at this time. But I did include the possible expansion panels in my plan so that it will be easier to add these should the time come. Here is the cost estimate for the installation.

Solar Cost Estimate