Point of diminishing returns on Solar?

[Fishspearit]

Originally Posted by Maren

Are you looking for an answer in terms of dollars, amps, efficiency (amps/$) or lifecycle cost?

I was interested in the amps,efficiency, dollar terms.

Maybe a better way of asking is: How often, or if ever, does someone with a large solar array not charge(or reduce charge) because the battery is topped up at midday?

It's kind of sounding like never, from the responses so far.

I know there's a point of diminishing returns somewhere, sort of like adding a 500 amp alternator to a 400 amp hour battery bank. But I guess that point in solar panels is somewhere a lot higher than I can afford to go!!

[hellosailor]

Shade: right on the nose, Therapy!

Although as I understand it, with an MPPT controller you'd still be using the reduced output from a series string and somewhat effectively using the power, instead of seeing it reduced to a useless lower voltage (dropping out) with a conventional controller.

[Luders33]

Currently I have two battery banks, 2 golf cart batteries each. Each bank has its own 65 watt panel (135 watt panels soon to be added totalling 200 watts for each bank) and seperate charge controller (sunsaver mppt). I have noticed major improvements over the previous setup (110 watts of panel for the all four golfcart batteries, and a cheapo charge controller); 1. The batteries don't go dry as fast as before 2. At night when I turn on the charger it takes very little time to reach float state. One other thing... The two 65 watt panels are built into the dodger and get shaded but the battery bank voltage stays pretty high showing that they are still revieving charge even with significant shadows.
can't wait to see how paralleling a 65 watt and a 135 watt will work... I read it would be ok as long as their voltage outputs are similar.... but i was told that their difference in amp output would be a problem.

To me it seems that at some point it would be better to have an alternate electrical generating source instead of just more panels... for when it is dark. It is confusing haveing many alternate sources and a bunch of individual regulators. Which source will be dominate? oh... how about a pedal generator. Get some excersize and make some electricity.

[Therapy]

Originally Posted by hellosailor

Shade: right on the nose, Therapy!

Although as I understand it, with an MPPT controller you'd still be using the reduced output from a series string and somewhat effectively using the power, instead of seeing it reduced to a useless lower voltage (dropping out) with a conventional controller.

From what I read thus far the voltage drops significantly and thus the usable output is zero.

When/if I have panels I will fork over the extra $$/sweat/whatever to have all panels parallel.

[ess105]

The "in series" problem goes away if you install or the panels come preinstalled with bypass diodes. In this case, if a panel becomes partially shaded it just drops out the loop and the overall voltage of the chain drops. If you have an MPPT, it will handle the change and deliver the best voltage for you batteries depending on where they are in the charge cycle.

[Therapy]

Originally Posted by ess105

The "in series" problem goes away if you install or the panels come preinstalled with bypass diodes. In this case, if a panel becomes partially shaded it just drops out the loop and the overall voltage of the chain drops. If you have an MPPT, it will handle the change and deliver the best voltage for you batteries depending on where they are in the charge cycle.

Are any panels built with bypass diodes within groups of cells?

[schoonerdog]

Yes, look for "shade tolerant" panels, they have blocking diodes within groups of cells. Many manufacturers make them. Regarding the "large array" question, I installed 700 watts of panels on my current boat and consumption between a fridge and freezer and lots of fans, pumps, lights, of around 200 amp hours each day. My solar panels are sized so that they will fully charge the house bank by noon on a sunny day. They then go to float mode to compensate for the 10 amps or so being steadily drawn through different things like laptops and higher ambient temperatures for mid day creating more refrigeration load, so it's not "wasted" power, but there is also plenty of extra power for doing things like charging laptop batteries or tool batteries or flashlight batteries. There's also plenty of extra power for VHF, SSB, radio communications, etc. But at the same time, on a cloudy day then my panels may just be enough to recharge batteries from night time draw and typical daytime draw without having extras such as long laptop hours or talking on the SSB. So it's really not a question of too much. In fact, I'd look at it the opposite way, a good solar array should have the objective of being your primary sole source of power, so it should have a minimum rather than a maximum. The minimum would ideally be enough power to be able to eliminate something like a generator. For our boat we have large solar arrays and then high output alternators on each engine.

One note is the first thing I see destroy cruising plans is excessive costs and repairs, and they almost always revolve around the engines and often generators. If you can therefore forego a generator or running the engine for charging the batteries daily, it really boosts your chances of a fully successful voyage. Having lived off the hook for a year while cruising with just solar power on my last boat while replacing two engines and just about every other system with a moving part including the wind generator, I'd really say solar power is aside from the wind, a sailors best friend. At the end of your voyage I'd lay money that you'll be able to point at your solar panels, and only your solar panels, as the one thing on your boat that didn't break. As to sizing your battery bank, with a good solar setup your battery bank is no longer compensating for fulltime draw, but only night time draw, therefore it can be proportionately smaller, typically half the size.

Originally Posted by Therapy

Are any panels built with bypass diodes within groups of cells?

[hellosailor]

700 watts? Dang, I bet it helps to have, what, 80-85 square feet of bridge cabin roof to spread that on?

I guess monohulls don't stand a chance! :-(

[Ex-Calif]

Originally Posted by hellosailor

700 watts? Dang, I bet it helps to have, what, 80-85 square feet of bridge cabin roof to spread that on?

I guess monohulls don't stand a chance! :-(

Imagine a day when your sails are lightweight, durable and are made from material that produces solar power...

How about 1,000 sq feet of solar generation?

It's coming someday.

[Maren]

Originally Posted by Ex-Calif

Imagine a day when your sails are lightweight, durable and are made from material that produces solar power...

And the only way they will charge is if people actually go sailing.

How about 1,000 sq feet of solar generation?

The efficiency will be a key factor.

It's coming someday.

I hope so. But I'm skeptical.