question

you would need to do a test on each solar panel string to see what each string is outputting. there is no other way that I am aware of, shading on any one panel makes a huge difference to the string output. this will more than likely be panel or wiring related issue.

Presuming that all mppt units are not being output restricted because of absorption voltage being reached that is.

Might also be panel temperature. Output lowers as temperature increases. In bright sun, panel temp is likely to be well above ambient.

@Dbgiuffre

The word 'yacht' suggests to me lots of metal pointing upwards. Just a little shade from a handrail or even rigging wire can impinge output. Even the way the shade crosses the panel. And shade on one panel in a string can affect the whole string.

Totally agree with the above comments but also a solar panel has a sweet spot (angle to sun) and as yours are on a "curved surface" you are unlikely to get full power from them. (depending on curve)

Please see below the answer from the shipyard. Do you think it is correct?

The major components onboard are:

· Multiple 100W - 36V solar panels (4200W total), connected in series at 72 V

(Standard testing condition 25 °C, with a solar radiation of 1000W expressed in W/m² )

· Four Victron MPPT 100/50 (meaning 100V max input, 50 A maximum output)

· Eight x 200Ah 24V Victron Smart Lithium Batteries

Factors to keep in consideration when measuring the output:

· Actual solar radiation

o On a clear, warm and sunny day like yesterday (19^th of February 2023) the peak solar radiation is 737 W/m² at 13.00 (see attached file)

The average solar radiation in the 4 central hours of the day is 705 W/m² (70.5 %) and for the central 6 hours of the day 661 W/m² (66.1%)

4200 W x 70.5% = 2961 W with the Miami solar radiation

https://en.tutiempo.net/solar-radiation/miami-miami-international-airport.html

· Temperature of the solar panels

o Although solar panels use sunlight to produce energy, they do not require heat in any way. In fact, the hotter the ambient air becomes, the less efficient your solar panels will be.

Standard testing condition for all solar panels is 25 °C (77°F).

“If you really want to understand how much energy your solar panels may produce depending on the temperature outside, check the temperature coefficient on the manufacturer’s data sheet for your solar panels. The temperature coefficient tells you, in a percentage per degree Celsius, how much power a solar panel will lose when the temperature increases by 1 degree over 25°C (77°F).”

“For example, the temperature coefficient for most panels is -0.38% per one degree Celsius. This means that for every one degree Celsius above 25°C, the maximum efficiency of a solar panel will decrease by 0.38%. Conversely, for every one degree Celsius below 25°C, the maximum efficiency of that solar panel will increase by 0.38%. (Yes — cooler, sunny weather is best for solar panels and can help offset any decreased efficiency in the summer.)

So, if the panel surface temperature (black surface under the sun) was 60°C (or 140°F), solar panel efficiency for that solar panel will decrease by 13.3%.

So in addition to the sun radiation the real output drops because of the heat 2961 W – 13.3 % = 2567 W

· Panels orientation and angle

o All efficiency calculations are always based on sun beams reaching the panel a 90° angle.

Obviously with the solar panels following the shape of the vessel, it is impossible for all panels to be directed “together” at the sun at a 90° angle.

There would be no direct calculation for this, but common sense must allow for an additional percentage of “theoretical output” not to be gained.

As a conclusion, after raising the matter with the Victron engineer and service, the 4200W solar panels, with an output of 2400-2500W in the current conditions, appear to be working well.