[RE-wrenches] Module Voltage Question for Off-Grid Designers

Wed Dec 10 17:25:58 PST 2008

Hi Matt,

I use the Solar World 175's, very happy with them.

Also use, Evergreen and have tried the new REC but don't have any good  
feed back on they yet as to how well they do.

Most all my systems use a stepdown controller, and I can get away with  
3 x 24v modules in series due to my low temperatures here.

I wonder how much longer they will be around.

jay

peltz power
On Dec 10, 2008, at 2:54 PM, Matt Tritt wrote:

> My favorite is the Sharp 175 for off-grid and solar pumping  
> applications; a sturdy, well built and consistent module for most  
> applications. You can even get them fairly often!
>
> Matt T
>
> Kirpal Khalsa wrote:
>>
>> Allen..Greetings....yes indeed it is an issue. we have been  
>> addressing with multiple charge controllers per system. we don't  
>> fight the current (not electrical).  In the future the way i see  
>> it- the electronics will be more flexible and be able to handle the  
>> larger variety of string voltages.  For example the long long long  
>> awaited apollo solar t100 which will allow voltages to exceed the  
>> 150V limit we have had for a long time.  They have apparently even  
>> lined up some breakers which will work with these greater  
>> voltages.  3 modules in a series will no longer be a maximum.  I  
>> understand midnite solar also has a charge controller which will  
>> allow the 150V max to go by the way side.  We are trying to be  
>> flexible as modules become less standard and hope that the  
>> electronics will allow us to address thesee challanges as time goes  
>> by.
>>
>> One thing that we would love to see is more large wattage modules  
>> with j boxes rather than pre-wired MC cables.  In many of our off  
>> grid systems the array is located in readily accesible locations  
>> and crafting a fence or sticking the array over 8 feet of the  
>> ground is a big hassle/extra expense.  This has proven to be a  
>> bigger concern for us rahter than the voltage variety.  If you know  
>> of any 72 cell or for that matter 60 cell modules  which allow flex  
>> conduit between j boxes we would love some info.......
>>
>>
>> -- 
>> Sunny Regards,
>> Kirpal Khalsa
>> NABCEP Certified Solar PV Installer
>> Renewable Energy Systems LLC
>>
>>
>> On Wed, Dec 10, 2008 at 12:16 PM, Allan Sindelar <allan at positiveenergysolar.com 
>> > wrote:
>> Wrenches,
>> Here's an issue I haven't seen directly addressed, and I would like  
>> to know what the rest of you are doing.
>> It's getting harder to get 24V nominal modules. Because the bulk of  
>> industry growth is high-voltage grid-tied applications, modules no  
>> longer have to be a standard voltage. Just pick the number of  
>> modules to best fit the chosen inverter's string voltage range.
>>
>> But for off-grid, the odd cell counts and resulting  
>> "nontraditional" DC input voltages challenge the traditional rules  
>> of off-grid design. I may be fighting a losing battle here, as the  
>> industry changes so rapidly and fundamentally. I have been trying  
>> to stay with 72-cell modules for offgrid, as this most readily  
>> combines with existing systems with 36-cell modules (12V) and 72- 
>> cell modules (24V).
>>
>> For example, I will use the new Canadian Solar 170-200W modules.  
>> They are 60-cell modules, with a Vmppt of around 28 volts - too low  
>> to charge 24V batteries with a standard charge controller. We can  
>> use them in any new systems with an MX60 or similar voltage- 
>> converting MPPT controller. Two or three in series would charge a  
>> 24V battery; 3 in series would charge 48V. Four in series would  
>> violate Code, as low-temp voltage would easily exceed 150V.
>>
>> Unless 60-cell modules remain a standard in the future, any future  
>> array additions would have to be on their own charge controller, in  
>> order to match a different I-V curve and MPP voltages into the same  
>> battery bank. Is this prohibitive? No, it just runs counter to the  
>> longstanding standards of off-grid design that allow modules to be  
>> added in the future: these modules will not add well to existing  
>> systems, and will not easily allow additional dissimilar modules to  
>> be added later.
>>
>> I had this same objection to using Day4 modules, although they were  
>> better at 16Vnom. Three made up a standard 48V array, so strings  
>> could be combined with two-module strings of similar 24Vnom modules.
>>
>> Who else is trying to stay with 24V modules? Anyone still using 12V  
>> modules in off-grid (residential-scale, not little apps) designs?  
>> Who has a crystal ball and knows what modules will be like in 20  
>> years, or even two years? Wat are the rest of you doing?
>>
>> Thanks, as usual.
>> Allan
>> Allan Sindelar
>> allan_(at)_positiveenergysolar.com
>> NABCEP certified solar PV installer
>> Positive Energy, Inc.
>> 3225A Richards Lane
>> Santa Fe NM 87507
>> 505 424-1112
>>
>>
>>
>>
>>
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