Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 19-11-2014, 23:12   #1
Registered User

Join Date: Nov 2014
Posts: 17
Solar-Battery Load: Perfect Balance

The goal is to provide enough solar energy to power 24V electric propulsion, draining average 500W. My guess is I'll need approx. 1kW of theoretical max. PV power into MPPT controller charging 200Ah battery to keep it constantly topped while draining the required 500W. Assuming, of course, a nice summer day.

Am I on the right path?
__________________

__________________
Matthew Dobrski is offline   Reply With Quote
Old 19-11-2014, 23:30   #2
Registered User

Join Date: Jun 2013
Location: canada
Posts: 1,699
Re: Solar-Battery Load: Perfect Balance

500w motor? That's like 3/4 hp. You're not going to moving much.
__________________

__________________
smac999 is offline   Reply With Quote
Old 20-11-2014, 00:02   #3
Registered User

Join Date: Nov 2014
Posts: 17
Re: Solar-Battery Load: Perfect Balance

Indeed, but this is only alternative propulsion for relaxing slow driving, more like trolling. I can make 7-8 knots pushing the throttle whenever I need to, but that's not the goal. At full throttle the motor is sucking 4kW of power, which will drain the battery in a matter of minutes.
__________________
Matthew Dobrski is offline   Reply With Quote
Old 20-11-2014, 02:17   #4
Registered User

Join Date: Mar 2014
Posts: 36
Re: Solar-Battery Load: Perfect Balance

No. Prudence dictates that your available run time be based on your battery capacity not your solar capacity. It's far more reliable. Thanks.
__________________
sstuller is offline   Reply With Quote
Old 20-11-2014, 13:14   #5
Registered User

Join Date: May 2010
Posts: 666
Re: Solar-Battery Load: Perfect Balance

So you're talking about a trolling motor on a tinnie?. My diesel motor generates 36kw and will push me along at 7 knots max. My guess is that on a millpond with no current you might get 1/4 knot. You'll lose that when the first gust of wind hits the hull or when the tide changes.
__________________
dlymn is offline   Reply With Quote
Old 20-11-2014, 13:58   #6
Registered User

Join Date: Nov 2014
Posts: 17
Re: Solar-Battery Load: Perfect Balance

Dear dlymm, the efficiency of my electric propulsion is already confirmed and I'm happy with 6-7 km/hr average speed consuming 500W of power during calm day. Although it is not a seaworthy vessel, it is not a dinghy as well. And again, we're not talking about main propulsion. In more demanding conditions I'm using 60HP outboard to push my boat with 11-12 knots.

The topic of my post is roughly estimated total Pmax of solar array to keep the battery bank at relatively constant charged state needed for dark hours. I'm ignoring inevitable variances of power drain in reality, assuming theoretical scenario of static 500W drain from 24V solar system and a friendly weather.

Cheers,
Matthew.
__________________
Matthew Dobrski is offline   Reply With Quote
Old 20-11-2014, 14:56   #7
Registered User

Join Date: May 2010
Posts: 666
Re: Solar-Battery Load: Perfect Balance

So your 40kw outboard drives you at 20km/h and you 1/2 kw motor drives you at 7km/h- amazing.
My home solar system is 5kw and makes an average of 20kw perday. On the hottest day (>38 degrees C) it makes 30 kw.
You need 1kh per hour for say 5 hours. Your battery will give you at best 2.4 kw because lead acids drop below cut out voltage when half charged and there is a risk of damaging the battery if you try to drain more.
You need 2.6kw to be generated in the 5 hours that you are trolling. Given typical weather conditions etc this might mean that you might need more than a 1kw solar system to guarantee that you always have enough charge when you need it. You must generate the charge as you are trollin; any charging before or after trolling is merely topping up the batteries for the next time. This assumes that it is a perfectly sunny day, no, clouds, the panels pointing in exactly the right direction at all times and no shading by sails etc. Even so I don't think that this might be enough.

There is no such thing as a calm day. When you then put your dinghy in a 5 km/h heading breeze your 500w will be largely consumed countering this and so you will need to use more energy and so generate more power. If the tide is running against you, then more energy (if it's running with you, less) . If I am on open waters and floating, my GPS says I'm doing 1-2 knots on a "calm" day. That's current and breeze so light that you don't notice and not necessarily taking you in the direction you want to go.

I would suggest that you do some detailed calculations on the cost/benefits of your project. We did this for the home system and found that the cost of batteries was greater than the savings made. This is not including the cost of panels and the risk of damage to them. Electricity storage has a very long way to go.
__________________
dlymn is offline   Reply With Quote
Old 20-11-2014, 15:21   #8
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,045
Re: Solar-Battery Load: Perfect Balance

What I think you are really asking is how much Solar do I need to get a continuous approx 750W or so output? Oh and your not planning on lead acid batteries I assume?
__________________
a64pilot is offline   Reply With Quote
Old 20-11-2014, 19:53   #9
Registered User

Join Date: Nov 2014
Posts: 17
Re: Solar-Battery Load: Perfect Balance

Quote:
Originally Posted by a64pilot View Post
What I think you are really asking is how much Solar do I need to get a continuous approx 750W or so output? Oh and your not planning on lead acid batteries I assume?
Yes, more or less. To be exact 500W average output will suit me well. Taking Pmax value (specified maximum power produced by PV module under standard conditions) multiplied by number of panels in an array will render theoretical Pmax total. which in real life situations is impossible to harvest. What is the estimated average Pmax to Pactual ratio, ignoring extreme conditions?
__________________
Matthew Dobrski is offline   Reply With Quote
Old 20-11-2014, 22:21   #10
Registered User

Join Date: Nov 2011
Posts: 474
Re: Solar-Battery Load: Perfect Balance

How many panels could you fit on your boat?

Electric propulsion is not a 'new' thing. It works. There just needs to be some more work done on it and some advances to make it work even better.


Quote:
The goal is to provide enough solar energy to power 24V electric propulsion, draining average 500W. My guess is I'll need approx. 1kW of theoretical max. PV power into MPPT controller charging 200Ah battery to keep it constantly topped while draining the required 500W. Assuming, of course, a nice summer day.
500W / 24V = 20.83 Amps (@ 24 V obviously)

200 Ah battery using 20.83A + inefficiencies per hour @ 24 V would be a good sized battery.

If it is a Lithium battery, they can drain further and there is more of a cushion on either side to extend the life of the battery. You just don't want to overcharge it, and monitoring the charge and increasing speed might be one solution.

Make sure the charger/controller can handle the voltage range, but these specs make it look like you would need 5 panels to get 21 Amps in the Summer. 6 or so to get to 21 A in the Fall/Winter months when the Sun is lower. There are some inefficiencies with the panels converting to power because it is never the perfect temperature or angle. And power increases in the morning and decreases in the afternoon, so you won't get to 21 Amps for a lot of the day unless you have enough panels. Clouds can impact it too.

( There are plenty of vendors out there, and I'm surprised that the charge voltage is so high for 24V systems... but here are some specs
24v Solar Panels from Wholesale Solar )


http://www.bluepacificsolar.com/pict...s/iv-curve.jpg



This is a 12V graph, but the voltage changes a little bit based on clouds and time of day, but the amperage is what will change. And what you need to calculate to figure out how many panels it will take, or if you want to let the batteries recharge while at anchor.
__________________
SunDevil is offline   Reply With Quote
Old 20-11-2014, 22:47   #11
Registered User

Join Date: Nov 2014
Posts: 17
Re: Solar-Battery Load: Perfect Balance

Dear SunDevil, thanks for suggestions. I may be able to squeeze perhaps 1250W of total Pmax output from upgraded array, without turning the boat into grotesque solar panels carrier. The future upgrade includes 5.2kWh LiFePO4 battery sandwich, optionally charged with Honda EU2000 gen and Chinese Kisae Abso 24V/30A charger when the sun is down. Reinforced solar array should, however, supply at least .5kW in average summer daylight, I hope.
__________________
Matthew Dobrski is offline   Reply With Quote
Old 21-11-2014, 00:44   #12
Registered User

Join Date: Nov 2014
Posts: 17
Re: Solar-Battery Load: Perfect Balance

I believe a couple of pics may throw a bit more light on my project. Firstly, the vessel is designed and built from scratch for prolonged expeditions into British Columbia interior wilderness, threfore never exposed to harsh reality of sea. I feel almost guilty of posting here and expecting an advice from this noble sea cruising community ...



Anyway, strong winds, 10 ft. waves, tidal currents etc are not issue here. The vessel is behaving more like a tug boat or rubber boot and she'll never plain. This may explain relatively low power required for electric trolling at 5-6 km/hr, but rapid inrease above this threshold with not much speed gain. That's when main 60HP outboard is taking over the propelling duties.

Said that, the existing solar system is not efficient enough to provide targeted average .5 kW of power for electric motor and keep the 225 Ah battery bank at relatively charged state for small nightime activities (i.e. LED lighting, laptop etc.). The plan is to double the solar estate, getting approx. 1250 W of total Pmax value. With new MPPT charge controller it should spit at least .5 kW of actual power, considering typical summer conditions and less than ideal panels positioning.



Please correct me if I'm wrong.
Attached Thumbnails
Click image for larger version

Name:	woodmag_lores 02.jpg
Views:	180
Size:	226.1 KB
ID:	92069   Click image for larger version

Name:	New Torqeedo_lores.jpg
Views:	203
Size:	276.0 KB
ID:	92072  

__________________
Matthew Dobrski is offline   Reply With Quote
Old 21-11-2014, 05:13   #13
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,045
Re: Solar-Battery Load: Perfect Balance

You need as much solar as you can afford or have room for, any "extra" can simply be absorbed as a slight speed increase. Matter of fact, that is exactly what I think will occur, that is speed will vary based on solar output, cloudy days you'll be a little slower than nice bright sunny days, but you'll be making way on both days.
Why such a big outboard? You do trim it out when under electric? Thought of selling it, losing a lot of weight with a smaller one? You would end up being faster on electric and use lots less gas when not etc. I think keeping your vessel as light as possible will go a long way towards making the electric thing work
On the Chinese charger, just off the top of my head, I think the little Honda could run twice that size charger and LIFE batteries could accept the charge rate, but maybe it would be working hard and be loud, maybe 30 amp lets it purr along in Eco mode?
__________________
a64pilot is offline   Reply With Quote
Old 21-11-2014, 06:12   #14
Bailing as fast as I can.
 
GILow's Avatar

Join Date: Sep 2008
Location: Adelaide, South Australia
Boat: Swanson 42
Posts: 3,585
Re: Solar-Battery Load: Perfect Balance

I love that boat.

You'd fit in really well on the Murray River here in oz. I had a plan to pinch half the panels from our roof for a few weeks and travel the Murray (again, did it once when I was 18) on a slinky little multihull a bit similar to yours just without the superstructure. I can't remember the exact numbers but I calculated that 800watts of panels would have driven two small 250 watt trolling motors at about 70% output for enough hours a day in summer to make the journey practical. ( but the Murray River runs through a particularly cloudless part of Oz and I would have had the current with me the whole way)

But that was for a much, much lighter boat and I think you will hit an efficiency curve problem where the weight of the boat demands more panels and batteries which in turn adds to the weight of the boat which adds to the structural loads which need stronger members which adds to weight and so forth.

Anyway if you make it work please post back here. I shelved the idea as I bought a bigger boat than I had then and now I have absolutely no free time whatsoever ( at least no free time that I would not rather be sailing)

I'd love to hear how it worked out. Or better still if it works come and do the Murray River and I'll be your river pilot.

Matt


Sent from my iPhone using Cruisers Sailing Forum
__________________
Very funny Scotty, now beam down my clothes.
http://www.swansonsailor.id.au
GILow is online now   Reply With Quote
Old 21-11-2014, 06:17   #15
Bailing as fast as I can.
 
GILow's Avatar

Join Date: Sep 2008
Location: Adelaide, South Australia
Boat: Swanson 42
Posts: 3,585
Re: Solar-Battery Load: Perfect Balance

Ps. A64pilot is right. Ditch the big engine. My original river raft weighed 1. 6 tons and moved effortlessly with a 10 hp outboard and the raft pontoons were made from 44 gallon drums not lovely professional looking hulls like yours. We have friends with a 10 ton houseboat who move it around with a pair of 9 hp Yamaha engines no problem. Sheltered water makes life so much easier. I reckon a 6 hp would move your boat very easily.

Matt


Sent from my iPhone using Cruisers Sailing Forum
__________________

__________________
Very funny Scotty, now beam down my clothes.
http://www.swansonsailor.id.au
GILow is online now   Reply With Quote
Reply

Tags
battery, loa, solar

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
"What makes the perfect boat woman...perfect" Celestialsailor Our Community 221 10-10-2017 11:38
Battery load or battery leak? jimthom Electrical: Batteries, Generators & Solar 5 09-05-2013 20:24
Perfect Boat or Perfect Place? Hanna&Chris General Sailing Forum 22 08-10-2009 20:27



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 13:07.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.