Calculation of Solar Output from PV

[john61ct]

With a good system you don't need to micromanage. Certainly the fridge cycling is automatic.

When solar only isn't enough, burn a bit of dino juice in the morning to give the bank some bulk before the sun starts, to get them to 100% Full.

A few times a week is enough for longevity.

[valhalla360]

Originally Posted by a64pilot

The 1/3 rule works and is I think sort of meant for boats cruising the Caribbean, mostly during Winter.

If we are talking typical which is really what rules of thumb are built around, seasonal variation tends to take care of itself.

If you look at Stu's chart (other than having a latitude of 100 deg which was confusing until you realized there was no data beyond 90 deg), it supports this.
- At latitudes below 20 deg, the output is pretty consistent.
- By the time you get up around 45 deg it levels out in the summer (warm season for the hemisphere) and isn't much higher than at the equator. At 45 deg, most cruisers put the boat to bed about the time the solar output starts dropping off significantly or they head towards the equator.

I'm betting daily variations due to clouds, dirty panels and other issues are at least as great as the change in available solar power.

[noelex 77]

This graph I think is a little easier to understand. It is based on averages. Individual regions will be higher or lower than this depending on the local climate.

It shows insolation by latitude and month.

Condensing this information down to a single number has its uses, but is similar to saying that the average cruising boat consumes 120 Ahrs a day. While this is may be helpful as a starting point it is important to understand that some vessels use far more power than this and some much less. Solar production also has a similar wide variation based on location, season and on the installation.

[rgleason]

Here is a good interactive website which helps determine irradiance at your location.
JRC Photovoltaic Geographical Information System (PVGIS) - European Commission
Scroll down a bit, Daily, Monthly etc.

[rgleason]

Solar Output is dependent upon many critical system choices and installation.

I'm finding solar is not as simple as I once thought.
I really like the Victron supporting information and controller features, which are new to me. Things have changed a lot in 5 years.

Controller choices - Which PWM vs MPPW? Fitting Solar Panels to boats

Solar Panel choices -Silicone, Amorphous, etc. How to pick?

Matching Solar Modules to MPPW Controllers.

Even Victron has a huge range of controllers

For learners, Dave Berry's "Fitting Solar Panels to Boats" pdf at the bottom of this blog article I found very helpful.

[barnakiel]

If you live in the US then your agencies publish all relevant insolation data.


If you live, or go, elsewhere, you may find this useful:


Global Solar Atlas


E.g.


a solar array at 5 A nominal
in a 5 hr insolation location
will average
25 Ah of daily output




Assumed average over 100 years period.


Cheers,
b.