A unique solar question

[SWbySWesty]

Whatever you do, be sure to spend the $$ on a MPPT controller.

A lot of people are saying that on a system so small, a MPPT controller is a waste of extra money that could be spent on a bigger panel...thoughts?

I've decided to skip the pelican case idea. FYI for those following the thread.

 

[Xterabl]

Well, then in that case, I'd look into 2X KC40T panels for 80W (I believe someone else recommended this amt of power). Occoasionally, i've seen someone on eBay selling (2) for <$300. But right now it seems the cheapest offering is $275 for only one:
http://cgi.ebay.com/Kyocera-KC40T-4...079?pt=LH_DefaultDomain_0&hash=item19af9f393f

From what I can tell based on research only (I do not own any "real" solar yet), this is a robust and proven solar panel platform.

Re: MPPT,
I hate wasted potential, especially when it comes to solar where you get so little bang for the buck/hassle/area. How exactly due you quantify "waste of money"? Here's an attempt to do so for, in on case, a single 65W Kyocera panel (PDF DOCUMENT LINK):
http://www.amerescosolar.com/Files/SS MPPT Benefit White Paper.pdf

I'm sure there's much more out there to help you make your decision.

 

[SWbySWesty]

single 80 watt panel: $209 - http://www.ul-solar.com/80_Watt_12_Volt_multicrystalline_solar_panel_TSS_p/stp080p-tss.htm

Morningstar regular 6A controller: $45 - http://www.ul-solar.com/Morningstar_Sunsaver_12_Volt_6_5_Amp_Charger_p/chg-ss6-12v.htm

Morningstar MPPT controller 15A: $200-250 - http://www.solarbatterycharger.org/morningstarsunsaverchargecontrol-ss-15mppt-15l.aspx

Wiring: $40-50

So the MPPT controller is adding nearly $100-150 to the price tag. Based on the white paper, there is a convincing argument for it. So now I pose this question:

With a MPPT controller, can one go with a smaller panel? I was planning 80watts, but most of these people saying 'go big' having been using regular controllers. Will a MPPT controller allow, say, the use of a BP-350J solar panel? (55w)

 

[dwh]

When thinking about MPPT, don't forget something that was specifically mentioned in that white paper - the real gains come when the battery is nearly dead. However, in general it's recommended to not take a battery below 50% if you want long battery life.

So, how much actual benefit you'll see from MPPT depends on how low you drain your battery.

If you regularly take your battery down below 50%, then you'll get more benefit from MPPT, but if you size your system so that the battery only goes down 50% and then gets recharged the next day by the solar, you won't see much benefit on average.

EDIT: So, if you design a system to get maximum benefit from MPPT (regularly discharge below 50%), you not only have to account for the extra cost of the MPPT charge controller, but also for the extra cost in terms of shorter battery life.

If you're trying to recharge a battery that is already above 50% charged, then the difference between PWM and MPPT isn't much; You can expect maybe 10%-15% overall better harvest with MPPT, often less. On a big solar array, such as for a house, 10% is a big deal, on a < 100w system...not so much.


EDIT: On your pricing figures, you left out shipping, which can add up to a significant number.

 

[Xterabl]

dwh makes some good points. Except with one clarification: what he calls "nearly dead" should be "low voltage". With a good deep cycle aux battery, you can repeatedly go to low voltage, and it absolutely will not be "nearly dead"

Also, for small solar, I recall someone on this board recommended these folks:
http://www.amsolar.com/index.html
You might want to search around and see if you can find him/her and ask about their experience.

 

[dwh]

dwh makes some good points. Except with one clarification: what he calls "nearly dead" should be "low voltage". With a good deep cycle aux battery, you can repeatedly go to low voltage, and it absolutely will not be "nearly dead"

When the lights are too dim to see your hand in front of your face, the water pump doesn't pump, and the inverter won't invert...I call that a dead battery. I.e., "drained below usefulness".

Perhaps you are thinking of "dead" meaning "ruined". Draining a battery until it's dead doesn't mean it's ruined. Of course, if you do it too many times it will be.

 

[expdtnoffroad]

Did you ever find out what you wanted to know about FTL?

I have to apologize for the delay in getting back to everyone on the FTL Solar stuff. I have been running around dealing with a flooded basement at home. :snorkel: I will see what I can dig up next week.