How Many Watts of Solar?

[newhaul]

Originally Posted by GILow

This ^^^^^^^^^^^^^!

No point having a tiny battery bank that is filled in moments from the solar, only to have it run out two hours after sunset.

Also, as I learned the hard way, battery capacity is not JUST about Amp Hours of capacity, the bank needs to be able to deliver adequate CURRENT, without too much voltage drop, to run your heaviest load. So my original (temporary) house bank of 2 x 105 AH batteries were more than adequate in terms of storage capacity, but really struggled to run my coffee machine, and would not have had a hope of running the smallest microwave I could find. (750 watts)

that's where alternative chemestries hit their stride like Lfp the current sag is negligible.

[thomm225]

Originally Posted by Razoo

How many watts of solar is need for a 34'-38' sailboat? I'm trying to figure out what I need to run lights, laptop, micro wave etc.

Thanks.

If the above is all you are running, you can probably get by with 150-200 watts worth of panels if you have close to 200 ah worth of batteries

Right now I have two 80 ah batteries hooked up in parallel, and I'm using 115-135 watts of solar panels

My only needs are running lights, cabin lights, fan (I just bought a 12 volt fan to replace my 120volt fan) Inverters (for charging phone, laptop, drill, vac), depth, autopilot, VHF, GPS

My outboard is pull start.

Anchor light is a battery powered LED Lantern


***Btw, if you haven't bought the batteries yet, the 6 volt batteries are probably the best with some near 225ah plus each which is what I will buy next time. Two of those in parallel would be quite nice***

[sailorboy1]

Originally Posted by Razoo

How many watts of solar is need for a 34'-38' sailboat? I'm trying to figure out what I need to run lights, laptop, micro wave etc.

Bet about now you are wishing people would just give you an answer

I'm staying with 600W for a straight up answer as I expect you are will have a 150-175AH daily load.

[mjscottinnc]

I returned in 2018 from a 3 month trip to the Bahamas researching your exact question. I'm an electrical engineer and prepare the boat to test a number of possible power configurations.

The electrical system was setup with 2 - 45 amp solar chargers, 2 - 315 watt 36 volt solar panels, 2 - 200 Ah battery banks, a single engine driven 55 amp alternator, and a single 400 watt wind generator, AC-DC power supply Dual 36V @ 10 A, 3500 watt inverter, and an energy management/monitoring system I designed. One of the battery banks was 2 new Group 31 Trojan AGM, and the other was 2 new Group 31 Interstate floods.

Daily loads at anchor; Refrigeration, interior and anchor lighting (4 LEDs, 4 incandescent), CPAP, VHF & Satellite radio, Portable VHF recharge, Laptop recharge, 2 - Tablet recharge, 2 - Cell recharge.
Daily loads underway; At anchor loads plus auto-pilot.

One battery bank (Trojan)was designated as the engine start bank, the other was the house bank. The energy management systems could route any energy input (except the alternator when the engine is running) to any charger and any charger output to any battery bank. It worked off of priorities that I set up in the code, starting bank first, followed by the house bank. It was designed to provide redundancy in the event of any system component failure, but nothing failed so this was only simulated by unplugging things.

The results in a nut shell, with 630 watts of solar the system never failed to top-off both battery banks. There was a fair amount of daily load from the refrigeration, CPAP, occasional inverter use. On those times with 3 to 4 days of overcast, the wind generator would supply power occasionally (you can tell from the blade noise when its outputting and when its not), but it was more of a comfort to hear it supplying charge then was actually needed. There were other devices which only ran when motoring, like the radar, but I did not take that into consideration since the engine was supplying charge.
As a final test I had to leave the boat on the hard and return home for a month. I left the refrigeration, lights, and radios on and when I returned both banks were at 100% as if I had never left. All on solar alone, the wind generator was turned off and no land lines plugged in.

[a64pilot]

Well, we have a Kilowatt on a 38’ boat, and use right at 130 to 150 AH per day.
On a sunny day the Kilowatt is enough in the Bahamas in Winter, I suspect it’s going to be easily enough in Summer.

It’s not just a how many amps can an array make, it’s also an it takes x hours to charge a battery bank and you only have less than x worth of good Solar in a day.

Then remember it takes up to 110% of the energy removed to be replaced to be fully charged, for a lead bank.

A 30 min run of the Honda in the morning guarantees a fully charged battery bank, even on a cloudy day, besides we need the Honda or other generator anyway to make water, wash clothes etc.
So my advice is to carry a Honda or other generator so you don’t end up running your propulsion motor just to charge the batteries, and do not do what I see so often, and that is run a motor to charge batteries in the afternoon as that is really inefficient, cause in the afternoon the bank acceptance rate is way low and you can only dribble in power.
Run it in the morning when the bank can accept all the charger can make and still be in bulk, bulk charging is very efficient.
By running the generator in the morning, that ensures we are in absorption before Noon, which means of course that we have excess Solar that we can run the inverter and make ice, watch TV, wash clothes or whatever we want to.

The other thing is stuffing a kilowatt onto a 38’ boat likely means that all panels are not perfectly positioned and you have more shading issues, so it’s unlikely that 1000W makes double the power of a 500W array due to shading.

[john61ct]

Each boat's setup and usage patterns are unique.

Many do not like how their boat sails, or looks, if completely covered in panels.

Best to not just depend on one source input.

[kas_1611]

First figure out how many amps everything draws, which is basic maths as it is Watts over Volts, then multiply it by how many hours (realistically) you will use them. Count absolutely everything on your boat and not just the luxury items like laptops, coffee pots (what's wrong with a kettle and a coffee press?), microwaves (realistically how much do you use the one at home?).

Then add 20% because we all underestimate.

This will give you the daily amp requirement for your particular boat. And it has nothing to do with length as someone on a 30ft with all mod cons will use a lot more than someone on a 40ft living frugally.

As an example we use between 50 and 100amps per day depending if the chartplotter is on (ie we are sailing) or if we are bobbing on the hook. With my 100watt panel and 14hrs of strong sunlight I can see around 50 to 70amps put back into the 2x140amp-hr batteries I have so in theory my panel can provide my needs for a couple of days on the hook. I have 2 additional 32watt rollable panels I can add in but these are now dated and struggle to add an amp to the overall power.

For my situation another 100watt panel would mean I should be able to produce all the power I need daily assuming the Greek skies remain clear. In northern Scotland where I live (as opposed to the Ionian where I sail) 200watts might only give me 20amps if it is grey, miserable and pouring with rain.

You will also need to figure out where you can put any panels as they have a frustrating tendency to be just to big for that handy spot on the coach roof. And take into account shading by boom, mast, the large flapping things etc as shade kills performance of any panel regardless of its size or manufacturer.

[WhiteHill]

Originally Posted by Discovery 15797

It is more complicated than a simple energy budget.


http://emarineinc.com had a energy budget spreadsheet on their site, but seems to be a bad link now.

Click on the text, not on the image, to get the calculating pdf.

[Cherod]

Free range sailing ( yes the long haired bearded one who has morphed into short hair moustached one ) did a very good vid recently about fitting solar , what to expect and what you actually get for your money . ( between killing fish !! )

[moseriw]

200 Watts of Solar YES but consider that the output is not as commonly specified.
Use my calculation to calculate your setup:



My measures:


2x Phaesun Solarmodule PN SPR S130 1082 x 796 x 35 mm 0,86 m²
2x Phaesun Solarmodule PN SPR S85 795 x 669 x 35 mm 0,53 m²
ges. 2,78 m²
Standard Formula Watt/Peak (Wp * 0,3 = Ah)
2x 135 Wp 620 Wh/d
2x 85 Wp 390 Wh/d

Sum 440 Wp * 0,3 = 132 Ah/d
MEASURED: 8-16 A = 13,2Ah in 10h shall give 132Ah/Day


Though, in my case the variance comparison is TRUE

[skipgundlach]

Originally Posted by Mike OReilly

clip....

… then, just maximize your solar . I’ve never heard of a smallish sized mono cruiser who said they had too much solar.

Or any other sized boat regardless of hull count.

Corollary:

"I hate my wind generator," said Nobody, Ever, awaking to a zero F freezer and full battery bank...

Seriously.

The next step is to spend the big bux to get the very highest watts to area (known as efficiency rating), which currently means SunPower panels, or panels made by someone else using their cells.

Even Sunpower has less-than-top-efficiency cells, which is why the same footprint is available in several different wattages. Here's an article explaining all that:

https://us.sunpower.com/sites/sunpow...nical-spec.pdf

[skipgundlach]

Originally Posted by skipgundlach

clip....

Even Sunpower has less-than-top-efficiency cells, which is why the same footprint is available in several different wattages. Here's an article explaining all that:

https://us.sunpower.com/sites/sunpow...nical-spec.pdf

Online with Sunpower attempting to get a working link exceeded my time limit so can't edit; sorry - disregard the above.

Here's a working link:

https://us.sunpower.com/solar-resour...specifications

[MJH]

Originally Posted by Razoo

How many watts of solar is need for a 34'-38' sailboat? I'm trying to figure out what I need to run lights, laptop, micro wave etc.

Thanks.

As others have already pointed out there are many, many things to consider in determining the amount of solar to install but by all means do a "complete" energy survey for your boat, it will educate you on what the big users are and insight into possible future upgrades to save energy. My biggest 24 hour users are the bilge alarm, laptop on ECO mode, VHF (yes, ON-16 even offshore), and my CPAP (I have sleep apnea). AIS, GPS, don't use much. SSB on only for receiving weather and sending position reports. I also use a Monitor windvane instead of autopilot, a big saving.

If anyone knows what the power consumption of the InReach is I would appreciate it.

In my case for sailing offshore I corresponded with a guy in the Pacific who had lived there for a few years...he said to shoot for 600W and he also had a wind generator for cloudy days/nights. I have read enough about the drawbacks of wind generators to count them out...maintenance, noise, blade danger.

So I installed 4 x 140W fixed panels (560W), two above the dodger and two on a new stern arch. With fixed panels I never think/worry about adjusting them as some are always gathering energy and, besides, the boat is moving all over the place with the waves and swells. On my roundtrip to Hawaii my two 8D Gel batteries never got below 78% over night and were usually recharged to a "FULL" indication by the afternoon...I never had to run the diesel to charge the batteries.

Solar is great. Put up as much as you can afford and room to mount it. The panels per se are relatively cheap, it is all the other stuff to install them that runs up the total expense.

~ ~ _/) ~ ~ MJH

[sailorboy1]

Originally Posted by MJH

My biggest 24 hour users are the bilge alarm, ...................

WOW!

I doubt my bilge alarm has used 1 AH in its whole life (I test it once in a while)

[KP44]

Depends on your style of cruising as well.

I have a 3,000 watt inverter that will easily power a microwave.
But after 2 years of hardly using the microwave, I removed it. Left the bulky microwave ashore. I only used the inverter this past season for power tools and for grinding coffee.
We have a 100 watt inverter that powers our laptops, charges cell phones, etc. We have not needed as much energy as we thought we would.


Put up whatever panels you have room to install. Mono panels are slightly more efficient than poly, so use Mono to make the best use of what little space you have on a boat.