[RE-wrenches] Solar Boost Controller in Senegal

Tue Jun 30 14:40:16 PDT 2009

Larry,

You're absolutely right in your first paragraph about one thing that I
stated incorrectly: MPPT is for harvesting the most power possible from any
voltage being produced above the battery voltage. I meant the difference
between Vmp and Vbatt, not, not the difference between Voc and Vmp. Thanks
for catching that. Sorry all.

In a hot climate the MPPT benefit is greatest if the array is wired at a
higher nominal voltage than the battery. Hot 12V or 24V modules don't have
enough of a voltage window between Vmp and Vbatt to justify MPPT, and a
tropical climate seldom takes advantage of the higher Vmp of cool/cold
modules that temperate winters provide. Larry, this is just my opinion, and
I respect yours, given that you work in the hottest year-round climate in
the mainland US there in southern Arizona, don't you? (You must get tired of
people making bad jokes and then asking where's your sense of Yuma, I
'spect.)

The SB series uses an adjustable analog boost that is limited to a fairly
narrow range. Even ancient Arco M52L Quad-Lams, with a Vmp around 44V,
exceeded this adjustment range on 24 in-24 out - I tried this years ago.

I have no challenge to Blue Sky's support - I have even called Rick on his
cell phone on a Sunday and gotten answers I have needed. He knows his stuff,
has never refused to help, and has occasionally sent us products to try and
givefeedback on.

But we have just seen enough failures on units 4-10 years old where
installation errors couldn't be blamed and lightning protection was in
place. I have never seen a single failure among the few SB2000 or SB3024i
units we've installed or sold. The 3048 has shown the highest failure rate,
although certainly not higher than other well-regarded units. But the
failures have always required sending the units in for service, and my guess
is that that would be practically impossible in Senegal.

Thank you for catching my mistake.

Allan

Allan Sindelar

Allan at positiveenergysolar.com

NABCEP Certified Photovoltaic Installer

EE98J Journeyman Electrician

Positive Energy, Inc.

3201 Calle Marie

Santa Fe, New Mexico 87507

505 424-1112

www.positiveenergysolar.com

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Larry
Crutcher, Starlight Solar
Sent: Tuesday, June 30, 2009 12:45 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Solar Boost Controller in Senegal

Allan,

MPPT technology is for harvesting the most power possible from any voltage
being produced above the battery voltage, not the difference between Voc and
Vmp. Because of this, nearly every battery charging system will benefit
from MPPT chargers. The climate does not matter for properly designed
systems. In a hot climate (like Yuma ;) ) you want a much higher operating
voltage from the PV panels. There will still be a big advantage from MPPT.
There are very few situations where I would recommend a non-MPPT controller
anymore.

Concerning Blue Sky charge controller failures, I have sold and installed
over 1000 BSE products at our retail store over the years and they have the
LOWEST failure of any controllers we have sold. And, the customer service is
second to no one else. I understand and agree with your opinion to have
serviceable equipment in remote locations.  The most reliable equipment
should be considered first. I also believe that a project like the one Walt
is dealing with should have included spare equipment as part of sale, and,
of course, it should have been designed right. 

I had a Phocos MPPT 100/20 in a test setup for 10 months when it failed. I
can't even begin to talk about Outback problems unless I take my comments to
the RE-bitching list. The BSE 3048 would be a good replacement controller
because it has the same footprint as the SB50 and will handle the high Voc.

Kindest Regards,

Larry Crutcher

Starlight Solar

(928) 941-1660

Renewable Energy Products, Service and Installation

Mailing Address (NO SHIPPING):

11881 S Fortuna Rd.

#210

Yuma, AZ 85367

Shipping and retail store (NO MAIL):

2998 Shari Ave 

Yuma, AZ 85365

On Jun 30, 2009, at 12:01 PM, Allan Sindelar wrote:

Walt,

I would also offer that in a hot climate, MPPT in general is only useful in
a case where odd cell counts take the Vmp away from 24V nominal specs. That
is, MPPT was originally developed to harvest the voltage headroom between
Voc and Vmp, which was greatest in cold ambient temperatures. There is
little benefit to MPPT in a tropical climate, unless it's being used
(incorrectly in this case) to adapt a particular module with odd cell count.

Walt, I would suggest that you consider pursuing replacing the Sharps with
any 12Vnom or 24Vnom module commonly in use there, and then either keep the
SB50 because it's already there, or replace it with the most reliable
non-MPPT PWM controller you can bring in or find in country. This maximizes
the likelihood that the system can be kept in operation even if the SB50s
fail (and experience says that some will in time) and the locals can't get
service or replacement product. It seems to me that the SB50 is an
unnecessarily complex component for this application, and a standard PWM
replacement controller will match poorly and inefficiently to the Sharps.

FYI, I called Earthwalk and spoke with "Joey" there. I copied him on Rick's
email, and got a read response. So Earthwalk is aware of this situation,
although Joey was a computer tech, not one of the "solar experts". If they
have integrity, they'll contact you and start making arrangements to get
this resolved. Perhaps they can wire you the funds to purchase compatible
modules locally?

I have copied Joey on this message as well.

Allan Sindelar

Allan at positiveenergysolar.com

NABCEP Certified Photovoltaic Installer

EE98J Journeyman Electrician

Positive Energy, Inc.

3201 Calle Marie

Santa Fe, New Mexico 87507

505 424-1112

www.positiveenergysolar.com

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