Hello: I am shopping for a solar system for my Hunter 33. I calculate that I need about 300 Ah and would like to meet that need with 600W solar panels and 400 Ah of LiFePo. Now I just need to decide on a brand (or brands). Do you like your system? Why or why not.
Thank you!
Let's do some math. Since solar panels are marketed in terms wattage, it is easiest to us watts as a measure to calculate your energy needs. A watt is equal to Volts x amp. The estimate of 300ah of daily consumption is equal to 3.6kWh at a nominal 12v. That is a lot of consumption.
A solar panel can be expected to provide about 3 times its nominal wattage per day. Somedays when conditions are perfect there will be more, on days that are cloudy there will be less. Better quality, higher efficiency panels will do better. After about 2 years on solar, that fits with my experience.
To generate the 3.6kWh you will need about 1200 watts of solar. If you have the real estate for 2 600 watt panels placed in clear sun without shading, then you will have adequate solar power for your daily needs.
However, your battery bank is woefully inadequate as there is no reserve or cushion for a few bad days. If you only get 50% efficiency on a cloudy day, you will not make enough power for one day and your battery will down to 25% SOC. Two bad weather days and your bank is pretty much depleted.
The real estate for solar panels on a boat is limited. While panels can be placed on the deck or dodger their efficiency goes down because of the shading inherent in those locations. It doesn't take much shading to significantly reduce the panel's output. Instead of 3x the nominal wattage, dodger panels may only produce 1 or 2 times the nominal wattage. A while back Delos looked at the energy production of their solar system and shared it on their YouTube channel. The performance differences are interesting.
One other note, panel output is rated based on standard conditions which allow for fair comparisons between different panels and manufacturers. Those conditions are rarely attainable on a sailboat, which means the panels will rarely produce their nominal wattage.
For a deeper dive into what makes a good panel, take a look at this article from Nigel Calder. It is a few years old, however it still relevant.
Advances in onboard marine solar technology improved efficiency and lowered the cost. But they also introduced more complexity.
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