I thought I would do a quick post about our power production on the boat. As we live completely “off-grid” I thought some people might find it interesting how it works. In the 3 months we have been cruising we have only run our Honda 2000 generator 5 times to charge our batteries. So %95 of the time we generate enough electricity to power all our equipment (freezer, fridge, lights, laptop, tablets, electronics, auto pilot, ect), except the watermaker. Our watermaker is the only 120V device on the boat, so it requires the Honda to run it when we want to make water.
In a way, we were lucky as I got to completely design our system from the ground up. Although our boat had some solar panels when we bought it, the Cubans had disconnected everything. They had installed a small house battery and basically relied on the diesel generator to produce enough power for each charter. Since this would not work for long term cruising, I had to design, build and install a completely new system.
First, batteries. I went back and forth on this decision as there are numerous options and each has its advantages and disadvantages. Originally I was leaning towards lithium iron phosphate batteries as they provide the highest energy for their weight. In the end I decided that they were just “too new” and although others had been successful with them it would be a huge amount of work to design and build a system. Abandoning that track left me with 3 options.
- Regular lead acid golf cart batteries
- Absorbed Glass Matt batteries
- Carbon Foam batteries
After tons of research, thought and number crunching I settled on standard lead acid golf cart batteries. The decision mostly came down to price and availability. It was not just the cost of the batteries, but the cost of the charging sources that pushed me to lead acid. Choosing lead acid meant I could use standard “off-the-shelf” alternators with the original equipment on the boat (battery isolators, switches, relays, ect). Not having to replace that equipment was a HUGE cost savings.
Once the batteries were chosen, I needed to determine how much solar production would meet our needs. We originally started our cruising with just 600 watts of solar but quickly found it lacking. After our shakedown cruise to Dry Tortugas I ordered and installed 200 watts more bringing our total to 800 watts. Although this 800 watts has been enough %95 of the time, we are going to add another 100 watts to help with cloudy days (cloudy, not overcast). The key to our solar array is that it has very little shade (if any). Many people don’t realize how much even small amounts of shade can affect solar production. Even the shade of a single line (rope to non sailors) can cut the production of a panel in 1/2. On overcast days with sun completely behind clouds, our array will put out almost NO power. Those are the days we must run the generator. On bright sunny days in an open anchorage our batteries will be completely full by 10:30am. Once our batteries are full we start charging the laptops, tablets and external USB power banks. The USB power banks have been a huge help as they allow us to keep the tablets going on days with limited sun.
The final key to our system is taking the free amps from the solar and stuffing them into the batteries. The standard accepted solution for this is to buy a big expensive solar controller and feed all the panels into it. I didn’t like that solution as not only did it provide a single point of failure but it provided challenges in wiring (really heavy wiring required). Instead, I opted for the array to be broken into 3 banks and each bank fed into its own solar controller. This way, I could use cheap Chinese controllers and not have a single point of failure. If one controller failed, only 1/3 of the array would go down. Since the controllers were so cheap, I could carry a spare aboard in the event of a failure. I choose cheap MPPT solar controllers that I researched and felt were a solid design. So far they have performed flawlessly even in the +40c heat of the Mexican summer last year.
Now, the astute among you will notice that our system is completely devoid of wind power generation. This is true as when I was designing and laying out the system I could not find a spot that the wind generator wouldn’t shade our solar panels. Doing the math, I didn’t think the power produced by the wind generator would offset the reduction for the shade it provided. However, I have been rethinking this and think I have a spot that will allow for minimum shade. I’m still thinking it through, but I will probably install a wind generator this summer. This will be a huge help during those overcast days.
Our solar array with Sea Squirrel (NOT Sea Frog) in the background.