Wind is better than solar. Discuss

[Na Mara]

Any substantial solar rig on my boat would require an arch and would add way more windage than two 50mm poles and two aerodynamic generators. Also I have calculated that the average output of this rig is 3.5 times my consumption at anchor. With the battery bank I am putting in I have 5 days of stationary reserve with zero generation. Finally, in anything over 6kn of wind I will generate more than I use on the hook from the generators alone. Even in regions with light winds wind speed is typically less than 6kn less than 5% of the time. Let’s say that at the generators this occurs 20% of the time, and let’s say that this coincides with poor solar performance 50% of the time. Then the conditions where I get less generation than I use might occur 15% of the time in light wind regions. That’s 5 days a month if it occurs altogether and so can be bridged by my batteries. Of course there may be outlier events occurring maybe once or twice a year where it is overcast with zero wind for over a week. For those one or two times a year I am absolutely willing to run my engine for power probably in conjunction with moving the boat and heating water. I don’t see that as poorly thought through or unreasonable.

[Anders]

Originally Posted by Pelagic

https://youtu.be/BxzkUTHaTPE
Can be deceiving, but doesn't seem noisy

We med moor a lot in the med and I get to listen to many wind gens and all the three bladed has been noisy including silent wind. I don't know for certain if i have heard silent wind pro but i don't expect it to be silent.
The only wind gen that I would have on the boat is the d400 since it is silent and have a decent output but in the med with often light winds I suspect most wind gens has a negative output since they often shade the solar panels.

[Na Mara]

According to my da they are pretty damn quiet and he owns one. You can only just hear them over the wind in the rigging if you are sitting right under them. Further, with my system I won’t have to run them all the time when it’s windy to maintain SOC. If they are noises over in 15-20kn of wind then you would shut them down once you got to 100% on the battery. Which you would do after only 4-5 hrs in those kind of conditions.

[Na Mara]

Your point about panels being shaded by the turbines is well taken though. I accept you often have to choose between a predominantly wind based system or a purely solar one. I am just arguing for and installing the former.

[Mike OReilly]

Originally Posted by Na Mara

According to my da they are pretty damn quiet and he owns one. You can only just hear them over the wind in the rigging if you are sitting right under them. Further, with my system I won’t have to run them all the time when it’s windy to maintain SOC. If they are noises over in 15-20kn of wind then you would shut them down once you got to 100% on the battery. Which you would do after only 4-5 hrs in those kind of conditions.

This is my experience with my Silentwind over nearly a decade of seasonal use. I even posted a video a while back with a couple of us chatting in the cockpit while the Silentwind was whirring away just aft and above us. As I said, it's not silent, but you can tell there is no need to raise your voice to be heard.

But I do think specific installations can make a big difference. I think most of the noise that people hear is actually coming from vibrations from the boat. I find if my mast is not secured in place properly it can produce vibrational noises through the boomkin.

Anyway, I'll be interested in hearing how things go for you Na Mara. I hope you'll come back and report some real-world experience after a season or two. I do think you are being optimistic, but it will really depend on your location.

[Na Mara]

Originally Posted by Mike OReilly

Anyway, I'll be interested in hearing how things go for you Na Mara. I hope you'll come back and report some real-world experience after a season or two. I do think you are being optimistic, but it will really depend on your location.

Will do.

If anything I am expecting better performance than I predict as I assumed a light wind region with mean wind speed of 10kn. My local sailing ground is off Denmark and it’s windy there. Mean wind speed is more like 15-20 kn. But experience will tell.

[DGH]

Please tell me if I'm on the wrong thread, but I'm looking for some up-to-date solar panel advice. I want to replace a couple of 20 year old 80 watt panels. One is dead I think and the other has quite low output. The existing sizes are 1460 x 500 mm and I could go up to 1600 x 700 maximum. They are mounted on my coach house roof. Bearing in mind that I am in Sydney, Australia, what is the best brand and type to purchase?
(BTW in all my travels the only wind gen I've had to be near that does not make an annoying noise is the D400. They seem to start in very low wind velocity too. No personal interest!)

[Uncle Bob]

Originally Posted by DGH

Please tell me if I'm on the wrong thread, but I'm looking for some up-to-date solar panel advice. I want to replace a couple of 20 year old 80 watt panels. One is dead I think and the other has quite low output. The existing sizes are 1460 x 500 mm and I could go up to 1600 x 700 maximum. They are mounted on my coach house roof. Bearing in mind that I am in Sydney, Australia, what is the best brand and type to purchase?
(BTW in all my travels the only wind gen I've had to be near that does not make an annoying noise is the D400. They seem to start in very low wind velocity too. No personal interest!)

You could try Low Energy Developments in Melbourne. I bought a pair of 75 watt long slender panels from them years ago, about 300mm wide from memory, and they have exceeded expectations.

[DGH]

Thank you Rob. I’ll check them out.

[Na Mara]

D400 is a good generator but it’s heavy and it doesn’t have electric braking. The latter necessitates tying it down in winds over 45 kn and precludes the kind of app based functionality I’m looking for. Finally performance at low wind speeds doesn’t match more modern units

[Adelie]

Originally Posted by Na Mara

Any substantial solar rig on my boat would require an arch and would add way more windage than two 50mm poles and two aerodynamic generators. ….

How did you calculate that?

[Na Mara]

It’s a simple matter of the presenting area. First an arch is going to have more tubing than a couple of masts, but if we ignore that and just look at the panels. If the boat is level then there is little windage from horizontally mounted panels, but monohulls rarely sail level. When heeled the presenting area to the wind is area of the panel multiplied by the sin of the heel angle. At 20degrees heel the presenting area of a 3m2 panel ( about 450W ) is 1m2. The force from the wind increases linearly with presenting area. Compare this to a 55mm swept radius wind turbine. The presenting area is 0.95m2 but very roughly about 60% of the airflow into that area passes straight through so effective area is more like 0.4m2. Now I want two of them so my effective area is 0.8m2. Thus the windage is a little lower when heeled underway than a solar arrays. Admittedly the difference is not as big as I thought and when level the advantage probably swings the other way, but my point is that windage is not an argument for solar over wind .

[noelex 77]

Originally Posted by Na Mara

It’s a simple matter of the presenting area. First an arch is going to have more tubing than a couple of masts, but if we ignore that and just look at the panels. If the boat is level then there is little windage from horizontally mounted panels, but monohulls rarely sail level. When heeled the presenting area to the wind is area of the panel multiplied by the sin of the heel angle. At 20degrees heel the presenting area of a 3m2 panel ( about 450W ) is 1m2. The force from the wind increases linearly with presenting area. Compare this to a 55mm swept radius wind turbine. The presenting area is 0.95m2 but very roughly about 60% of the airflow into that area passes straight through so effective area is more like 0.4m2. Now I want two of them so my effective area is 0.8m2. Thus the windage is a little lower when heeled underway than a solar arrays. Admittedly the difference is not as big as I thought and when level the advantage probably swings the other way, but my point is that windage is not an argument for solar over wind .

You need to take the drag coefficient into account. Wind generators sole purpose is to extract energy from wind, so the drag coefficient will be very high. Solar panels themselves and any arch are reasonably streamlined shape with a much lower drag coefficient.

I have no idea of the exact drag coefficient to use when estimating the total drag from a wind generator, but the total drag of a good streamlined shape is around 30x less than a shape with the same frontal area, but poor drag coefficient so this is a significant factor that must be included in any calculations.

[Na Mara]

The drag coefficient of a solid flat panel is 1. It’s the maximum drag object you can have. Because much of the air flows through a turbine it’s drag coefficient is significantly less than one (I took this into considerAtion in the earlier post when I talked about effective presenting area). Solar panels on an arch are only streamlined when close to horizontal. As soon as you heel appreciably they are fantastic wind catchers.

Boats with solar arches will tend toward rounding up when sailing upwind because of this. The wind gusts, the boat heels over, the balance in the sails shifts to the main which is exacerbated by the large panels way aft now catching a fair amount of the wind, the force exceeds the turning force of the rudder and the boat rounds up. As the presenting area of turbines doesn’t change as one heels, or rather it reduces marginally, it is easier to trim the boat to be balanced upwind with turbines than with panels.

[noelex 77]

Originally Posted by Na Mara

The drag coefficient of a solid flat panel is 1. It’s the maximum drag object you can have.

I am afraid that both of these statements are wrong.