solar panels

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Hi all, question, I found some 145w panels
from DM Solar, could someone tell me
if these are a good buy for the price of 120.00

I an doing a rv solar setup, and thought for the price 4
of these to charge 6 230ah bats. Will be using a 45amp mppt controller
and a magnum 2000w inverter.

Thanks in advance. BJ

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,478 admin
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    Re: solar panels

    A good start is to figure out the $$$/Watt price... In the olden days (10-15 years ago), you where looking at $10 per watt.

    8 years ago around $5 per watt. Today $2 to even $1 per watt... The "magical" $1 a watt for, a couple years ago, the goal of thin film panel manufactures--Which were about 1/2 the efficiency (need 2x the square footage of panels for same amount of power) and usually plastic face--Which can have less than 20+ year life in sun that we normally expect from glass panels (I am a pessimist regarding sun+clear plastics--they may last much longer than I fear).

    And the caveats... Check for costs at your front door (shipping+handling+insurance). Shipping a pallet load (packaged from factory) of panels via truck is sometimes not that much more than shipping a single panel via UPS/FedEx/etc... Most panels are single weight tempered glass--Very easy to break if scratched or a hard knock. And using "standard shipping", around 140 watt panels are about the maximum size that can be shipped without going truck.

    Note that on a $$/Watt basis, panels over ~200 watts are typically less expensive. And panels less than a 100 watts are typically much more expensive.

    Today, you are looking at around $1.40 to $2.80 per watt (from our host).

    Another thing to watch for when going >100 watt panels... Many of the "high power" panels are not standard "12 volt" Vmp panels (really Vmp~17.5 to 18.6 volts or so)... Meaning, that if you are looking at Vmp>20 volts or so, you may need/want to purchase a MPPT type charge controller.... Which is around 2-5x more expensive than a "cheap" PWM type charge controller.

    If Vmp is too low, it may not recharge the battery correctly (especially in hot weather). And if Vmp is too high, you lose a lot of efficiency when Vmp is >> Vbatt charging (i.e., a Vmp=35 volt panel charging a 12 volt battery with a PWM controller will be around 50% efficient).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,478 admin
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    Re: solar panels

    Regarding the battery bank... Assuming 6 volt @ 230 AH batteries, or a 12 volt @ 460 AH battery bank.

    The recommended rule of thumb for charging is from 5% to 13% of the 20 Hour Rating for charging current:
    • 460 AH * 14.5 volts charging * 1/0.77 panel+charger derating * 0.05 rate of charge = 433 Watt array minimum
    • 460 AH * 14.5 volts charging * 1/0.77 panel+charger derating * 0.10 rate of charge = 866 Watt array "nominal"
    • 460 AH * 14.5 volts charging * 1/0.77 panel+charger derating * 0.13 rate of charge = 1,126 Watt array "max cost effective"

    So, your 4x145w=580 Watt array is towards the small side--But that is not unusual for weekend use and/or RV use where there is not a lot of room for an array.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
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    Re: solar panels

    bjcarpetguy..

    Note the panels are not in stock.. I have 5 of them.. I bought from Amazon for $160 with FREE shipping..

    More do in tommorrow from Amazon for $160/each.. PM me if you want a link..

    I will be getting 1 more.. to make 6 panels and 870 watts..

    The true specs.. they are 145 watts just the panels numbers are slightly different.. see this sticker >>

    DMSpecSticker.jpg

    Here is the link to the review on this forum and video testing..

    http://forum.solar-electric.com/showthread.php?15999-DM-Solar-145w-Panel-Came-In