Can someone explain which is better?

I live on a boat and am looking t install 2 solar panels but can't decide between 220 watt or 260 watt. Is there a huge difference between the two as far as power output? I am new to solar panels and would appreciate any help!

Comments

  • mike95490mike95490 Solar Expert Posts: 8,500 ✭✭✭✭✭
    Re: Can someone explain which is better?

    The one that fits best in your space, is the best one. Look into the type of cells in the panel, and if the panel is rated for marine use.

    Boats have more vibration and water than a house, and what might be a sane choice for a house, would do poorly on a boat.

    Panels over 150W often are 20 or 30V panels. You would need a MPPT charge contoller to downconvert to 12V, or you are just wasting half your panel wattage.

    Is this a power boat or a sail boat? Panel use - for battery top-off, or to run a cooler for a week of cruising ?

    Mike
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Can someone explain which is better?

    Cost can also be a consideration: you can pay a pretty healthy premium for the latest high-wattage panel designs, which may not deliver a good watt/dollar value.

    As always, start by figuring out what your power requirements are.
  • System2System2 Posts: 6,290 admin
    Re: Can someone explain which is better?

    Thank you for replying! I live on a 44' sailboat and the panels would mainly be for battery top off. My husband and I plan to go cruising next October to the Bahamas. We wanted to have some sort of back up (other than shore power) if we stay at anchor. We do have a generator and an inverter on board.
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Can someone explain which is better?

    Those panels are also, physically, very large. Will they be well out of the way so that people won't drop tools and things on the panels? They are just glass and will shatter pretty easily if hit or the frames are not properly mounted and protected against twisting.

    Also, they need to be pretty clear of shadows. Any antennas, lights, masts, cables, etc. will dramatically reduce output.

    Regarding the 2x40 watt difference between the panels. Using this solar calculator, you can figure ouSolar Electric Discussion Forum by Northern Arizona Wind & Sun - Reply to Topict how much power they will generate. Assuming Sterling VA, off grid using derate factor of 0.52, mounted at 39 degrees facing shouth (assuming you are moored at a dock and have a flat roof on a house boat, or something similar), and using 1kW in program (program not allow any smaller solar panel ratings):

    Aprox 60-75 kWhrs per month (812 kWhrs per year) per 1,000 watts of panels

    812kWhr * (2 * 220w)/1,000 watts = 357 kWhrs per year
    812kWhr * (2 * 260w)/1,000 watts = 422 kWhrs per year

    422kWhrs-357kWhr/365 days per year = 0.178 kWhrs per day (178 watts*hours per day)

    Say you have 3 x 13 watt CFL (compact florescent lights)

    178 watt*hours / (3*13 watts) = 4.6 hours per day additional for larger panels

    Your daily average power for 2*220 watts of solar panels, in the winter months will be around:

    60 kWhrs per month (winter per 1kW of panels) * 1,000 w/kW * 1/30 days * (2*0.220 kW panels) = 880 watt*hours per day

    Overall, solar panels do not generate a lot of energy--so you will have to have conserve as much as possible with your loads.

    If you are not at dock and need to mount them flat, you will collect a lot less energy:

    694 kWhrs per year per 1 kWatt of solar panels mounted flat

    694 kWH per year flat / 812 kWH per year angled = 85%

    So, you will collect 15% less power overall, but in the winter, you average daily power will drop by ~2/3rds (in the summer you will collect more power).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,500 ✭✭✭✭✭
    Re: Can someone explain which is better?

    On a sailboat, you NEED a location with no shade. The shadow of one line, or stay, will shut down a panel, till the shadow is gone. That's the toughest problem on a sailboat. So the cost of a 240W panel, and charge controller, close to $6-800, and then the mounting and wireing, is it better to carry an extra couple gallons of gas for the generator ? While I'm all for solar, is it the best way to spend your money?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Can someone explain which is better?

    I see you have a sail boat and since you cannot control which direction the boat is moored, you will probably need to mount them flat.

    Also, shade can kill 50% or more of your solar panel output. To be honest, I am not sure if you would be better off with the two large panels you are looking at or a bunch of smaller panels (at least some will be in full sun instead of two large panels which will almost always have some shade).

    There are a couple threads here concerning sailboats. If you put "sail boat" in the Search, you will find them.

    Like Mike said, bringing a small (and efficient) gasoline generator (Honda eu1000i/eu2000i or Yamaha Inverter/Generator), if your boat uses gasoline, may be a better bet for backup power.

    Also, in one of the threads, they showed the solar panels mounted off the stern of the boat--Your large panels probably will not be practical there and a set of smaller panels would be better (because of less shading).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Can someone explain which is better?

    It looks like I have a lot of calculating to do!! We were planning on mounting the panels on the frame work of the bimini. Nothing would be dropped on them. It would be the safest place for them on the boat. There would not be anything that I can see to be in the way except a very small shadow now and then from the 2 backstays. I found an entire kit at Altersystems.com (marine grade) that includes:

    2 Mitsubishi 110 watt modules
    Morningstar 20L amp series charge controller 12V with TC, LVD
    2 Mounting kits
    2 6' Multicontact array output cables
    30' mulitcontact array output cable
    MC branch coupler (male- 2 female)
    MC branch coupler (female- 2 male)

    for $1347.00

    There is also the 260 watt kit that has the same parts but has 2 Sharp 130 watt modules. It goes for $1523.00.

    My husband seems to thing that "more is better" when it comes to the watts.

    Any thoughts??
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Can someone explain which is better?

    Regarding the Morning Star 20L controller... I would suggest two, near manditory, options for you to look at:

    1. A remote battery temperature sensor... Battery charging voltage requirements fall as the temperature increases. The problem is, the internal temperature sensor is measuring the Charge Controller's internal temperature, not that of the battery. Charge Controllers tend to get warmer because of "self heating" by the fact they are electrical controllers (perfectly normal). In the worst case, your controller could stop charging the battery at 80-90% state of charge. Since you don't want to discharge your batteries below 50%, that means that you are losing 20-40% of the useful storage capacity of your battery.

    2. Some sort of dial/display on the charge controller. An LCD current/voltage meter is very useful to diagnose problems and to estimate just how much power you can collect and use. Saves having to guess or get out a meter to check things out.

    If you have a computer (laptop) on board, a Morning Star MPPT 15 amp controller will manage ~200 watts of solar panels nicely. You can plug in your computer and download the history. Plus you can order a Remote Battery Temperature sensor. But they are not cheap (compared with the controller you are looking at).

    wind-sun_2031_1362431Morningstar SunSaver MPPT Solar Charge Controller

    Also, battery wise, try to get true storage batteries rather than Marine/RV batteries... They will last longer. Marine batteries are just a compromise between a car starting battery and a true storage battery (deep cycle battery FAQ).

    Another suggestion is to install a Battery Monitor. This will tell you at a glance, how much charge is in your battery bank at any time (without using a hydrometer or having to shut off all loads and charging sources for several hours to measure voltage). The Trimetric is good for the price. The Xantrex units have programmable output that can be use to turn on an alarm (or turn off your loads) if the batteries are being discharged too deeply. If it saves you killing one battery bank, they probably will have paid for themselves.

    Obviously, I missundertood your panel wattage--the math is there and you can recalculate for your system.

    In the end, calculate your power needs. Solar systems are not cheap, and don't generate a lot of power... Great for a GPS, radio, anchor lights, and a sump pump. Will not run a desalinator or fridge.

    Regarding lighting, check into replacing any filament lights (especially those that run for hours or all night) with LED's... Conservation will be critical to your installation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Can someone explain which is better?

    Thank you very much for your help! We have changed as many bulbs a we can to LED. I will have to do some more research before sinking any money into this particular project. Thanks again to everyone! I'll be back with more questions I sure!
Sign In or Register to comment.