Cinderella in Latitude 38!

Thanks Latitude 38

The May issue of Latitude 38 has been released, Ava and I are featured!

We would like to extend a big THANK YOU to the crew at Latitude 38 for helping us share our story and show others how easy and affordable it can be to sail sustainably.

You can find the full article in Latitude 38 here

If you want to read up on our full conversion to electric drive, you can find that here

Cinderella’s Solar Setup

Sailing around the world on 100% renewable energy. It really rolls off the tongue nicely, doesn’t it. Well, our message here at Sailing Cinderella is not only that it’s possible, but anyone can do it.

But how?

By harnessing that giant thermal-nuclear reactor in the sky! With solar panels.

Aboard Cinderella we have a little more complicated electrical system than the typical sailboat with our electric drive system. But in the end, it isn’t very complicated either. Below is a schematic of our solar charging system onboard . We will continue to improve the system and report back on our findings.

If you read one of our earlier posts Planning Your Solar Install you will learn why we chose the components that we chose. We are going to dig a little deeper now.

Before that, I would like to say upfront that…


I understand the principles of electricity and I have researched the standards that exist for sailboats. I recommend all readers do the same before attempting an installation of a solar array.

Before I got into the wiring bit, there were a few questions I had to ask myself

What size wires are required?

Thanks to Ohm’s law we know V=IR. Basically, the lower the voltage the higher the amperage, and the bigger the wire diameters that are required. Bigger wires cost more money, and it will be harder to feed them through the tight crevasses of a boat. Fortunately there are charts to help us here. I always use the chart to find the wire gauge needed.

How much input voltage can the charge controllers handle?

This is the maximum voltage coming from the solar panels. For basic PWM controllers this is lower than their MPPT counterparts. All charge controller will have this stated in their manual. The MidNite Solar Kid we used on Cinderella can handle up to 150V coming in from our solar panels. We can even programm it for 12, 24, or 48V battery banks.

Will the panels see equal shading?

If the panels see equal shading, it may make sense to wire them in series. If the shading is very different, parallel may be the better option.

On Cinderella, both of our Solar World panels on our bimini are the same. This allows us to wire them in series or parallel. We decided to wire them in series giving us a high enough voltage to charge our motor battery bank.

The smaller solar panel that we installed on our dodger is wired to its own PWM controller. Since it is wired to its own controller, we do not need to worry about how it will affect the other panels. 

Is there space near the battery bank for a controller?

The wire run from the controller to the batteries can carry a very high amperage. Since amps = heat, these wires will need to be a large enough to handle the heat created by the resistance of the wire.

The longer the wire run is, the bigger the wires need to be. Big wires don’t bend easy, and they take up lots of space. The closer you can keep you controllers to a clean dry battery compartment the shorter the wire run, and the smaller they need to be.

Note: charge controller can get pretty hot when they are operating near maximum capacity. Make sure the installation area has some sort of ventilation.

Our Plan

cinderella's solar schematic
Cinderella’s onboard solar charging schematic

The goal was to wire our two SolarWorld 345w panels in series and install them over our cockpit. The power from the panels will run through a switch where we can select to charge either our 12V or 48V battery bank.

Each bank will have its own dedicated MPPT charge controller to handle the 80V coming in from the panels.

Our solar panels are capable of producing more power than our MidNite Kid can handle when charging our 12V system. This means we will max out the controller when the sun is shining high in the sky. This also means that we will miss out on some available power.  Hopefully we won’t need it.

When we are charging our 48V system, the Midnite Kid can easily handle all of the power that our panels can produce. This is because the V=IR. As voltage is increased, the amps (heat) are decreased.

Since the Midnite Kid could be configure to charge at 12V and 48V, we decided to purchase two of the same controller. Using one for each system would give us redundancy in the event of a failure. 

Since Cinderella came with a Morningstar 10 amp PWM charge controller, we decided also to get a smaller flexible panel to put on our dodger. I figured it couldn’t hurt to supplement our 12V bank and the panel was relatively inexpensive at the time.


The ideal mounting system for solar panels is definitely a dedicated robust arch. Track down your local marine welder and I am sure they could come up with something that not only functions, but is aesthetically pleasing. 

If you are on a budget, craftier options are required. Many sailboats already have a folding bimini frame of some sort. A few supports in key areas really opens up the square footage for a solar install at a minimal cost. 

Bimini Mount

Cinderella was a sleek racer, she came with no bimini. I knew the cost of a quality tubing bender’s time was outside of my budget, so I kept my eye open for ideas. I ended up finding a used bimini frame on Craigslist and figured I could add some structural support bits from and Bosun Supply. The resulting arch cost me about $500. 

Dodger Mount

We added the flexible panel I bought from Amazon to our dodger using canvas turn fittings. We got crafty with a soldering iron/hot knife to make clean holes in the Sunbrella fabric. The knife also worked perfectly when widening the holes on the solar panel’s plastic backing. 

Solar Panel - Dodger Mount


SolarWorld Panels

In order to charge a battery, you must apply a voltage higher than that of a battery. Simple enough, right? Most “12V” solar panels actually produce 18V. 

Cinderella has both a 12V battery bank and a 48V battery bank. Therefore we must produce more than 48V to charge both battery banks. Our large Solar World panels produce a maximum voltage of 47.8V. This is not enough to charge a 48V battery, so I knew we would have to wire them in series.

I installed breakers on the positive feed to provide safety to the system. I also installed a selector switch allowing me to select which battery bank I wanted to charge with these panels, either the 12V house bank, or the 48V motor bank. 

**This constitutes high voltage DC and you should take proper precautions**

HQST Panel

This panel I added on the dodger as a separate charging source since we had a PWM charge controller and the panel was relatively cheap. My hopes were that this panel could offset the house loads while we were charging our motor bank. 

Unfortunately, the Morningstar PWM charge controller fizzled out after it was splashed by saltwater. A wave pooped us on our first night in the ocean off the WA coast dumping several hundred gallons of seawater in into our cockpit and about a buckets worth down our companionway. By the time we replaced the charger with a matching cheap charge controller, the panel had worn out. 

I would not recommend cheap flexible panels, or the cheap charge controllers found on Amazon. While these may be fine for hobbyists, on ocean going vessels I have found it’s best to spend a little more money on quality equipment. 


48V Motor Bank

Making our 48V battery bank for Cinderella was pretty straightforward. Take four standard 12V batteries and wire them in series. The result is a 48V battery bank. 

When I first installed the system, I used the cheapest marine/starting batteries I could find at the local auto parts store. All in all, the cost was about $300 and I was able use the boat to race and daysail locally for two seasons. It was a cheap, easy solution, but I killed them in two seasons. 

Before we left Seattle to go cruising, we replaced those batteries with four 115 Ah DYNO deep cycle batteries. This suited our budget and almost doubled our range. DYNO is a Seattle company, and we got the chance to tour the facility before picking up our batteries. At their facility, DYNO recycles old batteries and uses the lead to make new ones. How Cool! This is definitely a perk to the older lead acid technology, local recycle-ability. 

I really hope that along with any new battery technology, there is equal thought into how to manufacture/recycle it sustainably. 

12V House Bank

Firefly G31 Carbon Foam Battery

Cinderella was a very simple race boat when I bought her. She had two 90Ah AGM batteries wired in parallel to run her house systems. Not only were these two batteries ageing, but I knew they were not up to the task of handling cruising sailboat loads. 

I started reading about these Oasis Firefly carbon foam batteries. Nigel Calder, author of many marine reference books, seemed to speak highly of them, that was a good sign.

Two big factors that convinced me to use Firefly for our house systems were their ability to handle deep discharges without drastically shortening their life, and how well they handled extended periods of time at a partial state of charge.  Other pros are that they are maintenance free and seemed robust enough for offshore cruising.

Our charging system was going to be 100% renewable and I wanted to be sure we could handle cloudy days with little sunshine. We ended up purchasing two 116Ah Firefly Energy G31 batteries. They could live in the same footprint of the two AGM batteries we already had, and should give us more useable power. 

Future Improvements

As battery technology advances, I expect the cost to drop. I would love to upgrade our motor battery bank to a Firefly or LiFePO4 batteries. Will be cruising, and will not have access to plugging in at the end of the day. A battery that can handle extended periods at a partial state of charge could be very beneficial. 

I would also love to link both the 12V and 48V systems together. Currently, we can only charge one battery bank at a time using our selector switch. Ideally we will connect both banks together with some sort of DC-DC charger, allowing the panels to charge everything at the same time. 


I hope this post helps you figure out what you need for your system. As you can see, there are a few factors to consider, but the end result can be decades of energy freedom.

If you like the open source information we continue to share, please consider a donation. Every little bit helps keep the Sailing Cinderella dream afloat!


Planning Your Solar Install

Choosing Solar Panels, Solar panes, solar charge contrller, MPPT

Sailing around the world on renewable energy. The concept is as old as sailing itself. Ever since the first sailors raised canvas, sailing around the world on renewable energy was a natural evolution.

It’s wasn’t until the first steamships appeared in the 1800’s that we actually moved away from renewable energy. So no, it isn’t a novel concept. But I’m not talking about the days of kerosine lamps and canvas sails. Fast forward a couple hundred years.

In our everyday lives we enjoy certain “luxuries” that help us feel like we are living a modern life in the 21 century. Running water, lights, phones, computers, tablets, fans, rice cookers, blenders, microwaves, these are all things that we have grown accustomed to in our everyday lives. Are we really willing to live without them just because we decided to go cruising? Camping is one thing, but let’s face it, most of us want creature comforts.

Sailing around the world on renewable energy is a little different in modern day. Cinderella is not bare bones, we have the luxuries aboard that most people have in their home (minus the microwave and flat screen tv), she is our home after all. And we power all of it with solar.

But where did we begin when sizing our solar system? This can be tricky. You might be tempted to break out the calculators and try to add up all of the energy draw aboard, use estimators to narrow down just how many hours of sunshine you expect to see, size you battery bank to make sure you don’t deplete it by more that 60% each day and so on.

I’m not saying you shouldn’t do that… I’m saying there is an easier way.

Tips on Selecting Solar Panels

Realize that there is no harm in having too much power.
When sizing Cinderella’s system I started backwards. How much space do we have aboard for solar panels?

Most modern sailboats (unless you have a very specialized raceboat) have lots of real estate behind the boom of the mainsail. That space is typically covered with a bimini of some sort to protect the people onboard from the sun. This is an excellent place to install solar panels!

On Cinderella, we measured the space from the end of the boom to her stern. We then measured the width of the boat in the same area. Once we had an idea of the available real estate, we went online to research what our options were.

It turns out there are three major options: rigid monocrystalline panels, rigid polycrystalline panels, and flexible panels.

Rigid monocrystalline panels are the oldest. They have been around for decades, and are getting better and better every year. Rigid monocrystalline panels produce the most power to area of any panel.

Rigid polycrystalline panels are newer than monocrystalline panels. They don’t produce quite as much power per area as monocrystalline panels, but they are far superior when it comes to shading. If the area you have available for panels has lot of shading, polycrystalline panels may be the way to go.

That leaves flexible panels. Flexible panels are the newcomers. They are light and flexible. They don’t produce anywhere near the power of rigid panels, but they can be mounted almost anywhere. Most marine brands also have the charge controllers built in, so you can wire them directly to your batteries. The biggest perk is that you can walk on them, so in theory you can open up quite a bit of real estate. Unfortunately thus far, I have not met very many cruisers that are happy with their flexible panels. They don’t seem to last as long as their rigid counterparts.

Knowing that we are not only running our home, but also charging our electric motor battery bank, I opted to go with the rigid monocrystalline option. The more power the better. Since we don’t have a wind generator, or a radar dome, there is nothing to shade our panels except for our thin backstay.

After measuring the available space (about 80″ x 90″) I started researching brands online. There are lots of threads on this subject. you will find brand diehards, you will find people talking about dollars to watts, you will find enough information to make your head spin.

I again offer a simpler solution: study at the spec sheets. All solar panels are made up of solar cells. These cells are wired together to make different voltages, but are roughly 6″ x 6″ regardless of their efficiency.

That translates to a standard width to all solar panels (with the exception of very small panels). Whether they are 190w or 360w, all of the panels are roughly 40″ wide.

Knowing that, we took that 80″ x 90″ area and decided to fill it with as much solar panel as we could. This came to roughly two 265w to 360w panels depending on brand and efficiency.

So, now that you have an idea of what you want based on your area to cover, where do you find them?

You may be tempted to go online and try to find the cheapest price, but you will quickly realize that shipping a 40″ x 80″ panel costs just as much as the panel! This may be ideal for covering a home roof, but not when you only need one or two.

Go to your local electrician’s supply! They exist in nearly every major city. In Seattle, it was Platt Electric.

I walked in to Platt with my tape measure and told the staff what I was doing. They led me into their warehouse and showed me the options. Since they basically buy full pallets of panels for resale, they were excited to cut me a deal on the leftover panels on each pallet. After looking through a few pallets, I found two 345w Solarworld panels that measured 40″ x 80″. the panels were $250 each, so I got 690w of solar for $500!

Not bad considering that has covered our “power bill” for over a year now and allowed us to be fully off the grid, fully sustainable with all of our “luxuries” plugged in.

Selecting your Battery Bank and Charge Controllers

Once you have your panels selected it’s time to have a look at your battery bank, and what controller you will put between the panels and your batteries.

Charge controllers come in two basic types PWM or “pulse width modulation” and MPPT “Multiple Power Point Tracking”.

Both of these use electronic circuitry to prevent the panels from destroying your batteries. The circuitry is how they differ.

Pulse Width Modulation is an older technology that works by breaking up the DC current heading to the batteries with a series of switches. These switches open and close so fast that the battery doesn’t even notice it. Using a set charge curve for the battery type, these charge controllers very the width of the energy pulse from the panels to meet the battery’s ideal charge voltage. This leads to an efficient charger that doesn’t boil your batteries.

Multiple Power Point Tracking is a newcomer. It is more efficient that PWM and it was designed for passive energy like solar. MPPT chargers work by a neat little trick discovered by Nicola Tesla, the transformer. The chargers invert DC power to AC power using electronic circuitry. All of that AC energy can then be transformed from very high voltage to the exact voltage the battery needs. The AC power is then converted back to DC power and fed to the batteries.

What does this mean? It means that you can feed very high voltage to an MPPT Charge controller and the controller can take the extra voltage and turn it into useable amperage that won’t boil batteries. Since higher voltages have less energy losses, we can send more useable power to the batteries! And use smaller diameter wires to do it.

Obviously, we went with the MPPT charge controller option.

Next step: Sizing the charge controller

Charge controllers are essentially sized by the amount of heat they can dissipate. In the world of electricity, amperage is heat, so we can say that charge controllers are sized by the amps they can handle.

Since our panels can produce 690 watts, we can divide 690 watts by 12 volts and get almost 58 amps. Thats quite a bit! It’s more than most standard alternators output. But that is also the theoretical best case scenario. I assumed that we would normally produce about half of our maximum, so I found a charge controller that could handle 30 amps.

I chose the Midnight Solar Kid. The Kid was reasonably priced at about $350 and was designed for the marine environment. They also have the option of paralleling, so if I decided I wanted to utilize the most from my panels, I could get a second Kidd and wire them together to handle the extra amps.

Since the Kid could also charge a 48V battery bank, I purchased a second one to charge our 48V electric motor drive. This also gave me redundancy at sea. If anything happened to one, we have a backup onboard to get us to the next port.

The last piece of the puzzle: the battery bank!

The battery bank is where you store and draw power from when the sun isn’t shining. There have been huge improvements in battery technology over the past few years, and it seems like the prices of the new technology is always dropping. Since I purchased our house bank for Cinderella over a year ago, we have noticed that the prices have dropped by about 30% on LiFePO4 technology!

We again sized our battery bank based on the space aboard Cinderella. She had two tired old 110ah agm batteries when I bought her, so we replaced them with two new batteries.

At the time Lithium was out of my price range, and I didn’t see a huge benefit to the weight difference in just two batteries. Although the new LiFePO4 technology looks very good.

Fortunately, there was a new carbon foam battery technology in the market. A company called Ocean Planet Energy partnered with Caterpillar and brought us the Firefly Oasis Battery. They coated standard lead acid plates with some type of carbon foam that prevented sulphation, a lead acid battery’s arch nemesis. This resulted in a battery with lithium like characteristics, at much lower prices.

We purchased two of these carbon foam batteries from Fisheries Supply in Seattle, and have been happy with them every since. Unlike standard lead acid batteries, we could discharge them almost completely without damaging their lifespan. We essentially got four 110ah batteries in half the footprint.

There you go! I hope this helps you design your solar system from Mercury to Pluto.

Obviously, its best to have a plan before you purchase all of your pieces. If you are curious how we wired our system click here.