Solar Choices

[deckofficer]

Originally Posted by RainDog

I cannot find a Genasun controller that works with a panel over 140 Watts. Am I missing them? I am looking for a controller to work with a single 220 Watt panel.

Genasun GV-Boost 105-350W Solar Boost Charge Controller with MPPT

[oceanshoretiga]

I haven't noticed whether any of the posts have talked about 24V panels; I think not.

after much research, I opted for a 24V panel through a Morningstar MPPT controller. I wanted about 200W and first looked at 2x12v panels of 110 each. It was then suggested to me that the single 24V of 195w would do a better job because a 24 volt panel starts at a much higher voltage and has much less voltage drop over the transmission lines from panel to MPPT to battery. As it turned out, the combined cost of the single panel and MPPT was only a little more than two panels with no controller; with controller, the 2x12 would have been more expensive. The single panel also made for a much neater installation.

A six month cruise from Perth to Bali and then the north coast of WA was the test. The single panel did the job and only once did I have to start the engine just because of low power.

Consider 24v.

Regards, Jim

[noelex 77]

The 24v 195w panel is the same as two 12v 97.5w panels connected in series. Two 110w panels connected in series would have produced more power, so I don't think the advice you received was correct.

With the latter you also have the option to connect the panels in parallel. There is still some debate on this issue, but the consensus is that parallel is better. Either way the 110w panels would be better in terms of output. Series connection does require smaller wire (or the wire losses can be less with the same sized wire) reducing cost and helping installation, but a MPPT controller is required.

However, the advantage of ease of installation (and probably a smaller area) is important and given the small power difference you probably made the correct decision.

A lot of people quote an earlier start up time (and later finish time) of a higher voltage as a major advantage of series connection.
In reality under low light a panel can produce adequate voltage before it can produce any useful current. However, what happens during shading is much more difficult to model and less clear cut.

[oceanshoretiga]

Whether one panel of 24 volts or 2 12s in series, everyone I talked to here agreed that 24 volts is better. Voltage drop is the key argument with less drop using 24 (appropriate wire, of course) and a higher starting voltage (up to 40v or more).

But, to most of us electrics is a mystery, and spiritual, science!

jim

[noelex 77]

Here is an example of very early in the morning. You can see the solar voltage (from 12v panels) is already over 18v (Voc). However, despite the high voltage the panel will produce very little current. So little that the controller has elected to stay in sleep mode as the current produced is so low that the power required to fire up the controllers circuits is greater.

Under low light solar panels are not limited by voltage. Boosting voltage does not help (or helps very little). The limitation is not voltage it is current. Series connection does not make any practical difference to the length of the solar day

(Sorry for the blurry picture it was quite dark, which I guess proves the point)

[CarinaPDX]

"Everyone" would not agree that 24V is better, unless of course you are using 24V battery banks. As Noelex 77 points out the main advantage is the smaller wire size (1/2 the cross-sectional area of a 12V system for the same loss), and I'll add that any diode drops have a smaller effect with the higher voltage - which can be countered by using Schottky diodes instead of silicon. The disadvantage is that a broken controller can't be bypassed with 24V as it would fry the battery. And a somewhat more expensive controller is required to down-convert to 12V, or a separate DC-DC converter, or an MPPT controller.

We have been giving examples of the calculation here, but if electrical circuits aren't your thing then I appreciate that this sounds like a foreign language. In that case I would recommend keeping it simple: 12V, suitable wiring, and a basic regulator (e.g. Morningstar). More efficiency requires a suitable system design for your specific situation (which you can certainly get help here to do). I am leery of a one-size-fits-all approach.

Greg

[s/v Jedi]

Originally Posted by noelex 77

With the latter you also have the option to connect the panels in parallel. There is still some debate on this issue, but the consensus is that parallel is better.

Nope; the consensus is that series-connection in combination with a good controller is better.

Only when you are willing to pay for a dedicated controller for each panel (the Genasun option), then connecting those controller-outputs in parallel makes sense.

Your outback controller would do better with panels connected in series.

[Tootsie]

There is one Genasun that operates in the range 105-300 Watts.

[noelex 77]

Originally Posted by s/v Jedi

Nope; the consensus is that series-connection in combination with a good controller is better.

Only when you are willing to pay for a dedicated controller for each panel (the Genasun option), then connecting those controller-outputs in parallel makes sense.

Your outback controller would do better with panels connected in series.

I agree it is a grey area. It would be great to get a definitive answer.
I tried to make some measurements a while ago, but at anchor it is difficult to controller the variables.

Installing a MPPT controller for each panel is an attractive option. The tracking can be much better when each panel is controlled independently. However, the self consumption rises significantly with multiple controllers. Low consumption controllers are available, but the tracking becomes worse especially in boats with rapidly changing shadows. I think this is the future, but at the moment suitable hardware is lacking and suspect the gain compared to the best single MPPT controller will be minor at best.

The main difficulty is most of the development and research is directed towards domestic systems. These do not suffer significantly from shading over some of the panels, which is common, or universal, in boat systems. These conditions where there is isolated shading hold the key to separate the issue of series/parallel superiority.

Personally I think the evidence points towards parallel connection as optimum, but I keep an open mind.

[naclshaker]

when reviewing solar options I have found the 3 most significant characteristics to consider are #1 panel voltage (higher better performance) #2 efficiency ranges from 7.5% to 22% #3 sensitivity to shadowing. We have become conditioned to panels being marketed on watts at standard rating (1000 watts per sqr meter irradiance, 25 dg C, solar noon). Many panels look similar under those conditions. On boats with running rigging the game changer is surface area required and shadowing. If you buy based on dollar per watt rather than watts per sqr meter, you can easily double the area required to produce the same amount of energy per day. Mono-crystalline panels (18% - 22% efficiency) will always have a longer solar day to produce as compared to multi(poly)-crystalline (13% - 17% efficiency). Both genre have panel examples where long term rated performance is excellent, just remember you're buying watt hours per day, marketing would have you think you're buying watts at solar noon. Shadowing across cell rows (example 3" hard shadow), depending on the technology, can cut output by 80% down to as little as 4%. Efficiency and resistance to shadowing should be the biggest factor on designing an array on any boat with rigging and of course it costs more.

[s/v Jedi]

Originally Posted by noelex 77

I agree it is a grey area. It would be great to get a definitive answer.
I tried to make some measurements a while ago, but at anchor it is difficult to controller the variables.

Installing a MPPT controller for each panel is an attractive option. The tracking can be much better when each panel is controlled independently. However, the self consumption rises significantly with multiple controllers. Low consumption controllers are available, but the tracking becomes worse especially in boats with rapidly changing shadows. I think this is the future, but at the moment suitable hardware is lacking and suspect the gain compared to the best single MPPT controller will be minor at best.

The main difficulty is most of the development and research is directed towards domestic systems. These do not suffer significantly from shading over some of the panels, which is common, or universal, in boat systems. These conditions where there is isolated shading hold the key to separate the issue of series/parallel superiority.

Personally I think the evidence points towards parallel connection as optimum, but I keep an open mind.

- The Genasun controllers, one for each panel, are available today and in use by forum members; one has reported top results. They are costly but that doesn't mean they don't exist or that they don't work well. It's just a matter of choice on where to put money in, optimal solar system or some other gadget or a party etc.

- Series connection of panels has been reported by forum members as working measurably better than parallel on their own boats. No research on land-based systems, but actual hands-on measurements in actual operational, cruising circumstances.

I still didn't find the time to compare series vs parallel, but am sure of the benefit as Mark Cole has tested and reported on this in detail.

[Silverbullet]

I would always go with a volume of smaller panels rather than one large one because of redundancy. If you break one of the large ones, especially at sea, you may have lost it all. Additionally, using a 24vdc input , you may have the same problem rather than if you were using a 12vdc input. Yeah, Ive been dealing with solar for over 20 years.

[RainDog]

Originally Posted by deckofficer

Genasun GV-Boost 105-350W Solar Boost Charge Controller with MPPT

As I read the specs this will not work with a 220 Watt panel unless you have a 24V or higher battery.

[s/v Jedi]

Originally Posted by RainDog

As I read the specs this will not work with a 220 Watt panel unless you have a 24V or higher battery.

Correct. You're supposed to buy 140W Kyocera panels. If you go over 500W total, then you can consider 12V panels in series (up to 6, max. 150Voc) and feed that to an Outback Flex60 (60A @12V output) or Outback Flex80 MPPT. You can use 220W panels in that case.

When you have room for 1-4 panels of the 110-140W range, then the Genasun MPPT controllers (1 for each panel) should be considered.

Remember that it really matters how you mount the panels. They should not be across the center of the boat. It is very effective to put two on top of a bimini, one at port and one at starboard. Or mount them flip-up-style on the lifelines, like wings.
The reason is partial shading, study the shades over the boat as the sun passes over to see why this is important. You can never prevent shading, but you can prevent having many panels partially shaded at the same time.

When you connect the panels in series then the built-in bypass diodes take shaded sections out of the circuit. For parallel connections, you loose the whole panel when it gets partial shade.

[wdkester]

Jedi,
Could you give a link to Mark Coles testing results or his user name?

Also I'm wondering: 1. if you have series connected panels and you cover 100% of a panel, will it look like a direct short?
2. if you cover part of the panel you do get the same voltage but less current compared to an uncovered panel?
3. do most (all?) popular panels (e.g. kyrocera) have bypass diodes?