[RE-wrenches] Off-Grid Sizing Case

[Allan Sindelar]

Mark,

You haven't provided enough information for the questions you're asking. You
have said nothing about the customer's load profile.

 

Did you install a Tri-Metric in the system? CAH will allow you to estimate
daily consumption. Otherwise, get the customer to provide a load analysis,
and compare it to the you did with him/her when you designed the system.

 

Part of the likely problem is that neither gennie or array will charge
sufficiently. You didn't say what the charge amps is with the gennie, but I
suspect it's surprisingly low, meaning a small degradation in charge
efficiency substantially increases charging time. The combination of a cheap
portable generator and DR inverter(s) is particularly prone to poor
charging, as the DRs grab the peak of the gennie's waveform, and cheaper
gennies provide adequate RMS voltage but poor peak voltage. Check you peak
voltage on the gennie under load - it needs to be 164V for full DC output.
Low peak voltage often results in very low DC charging current. This is
covered in more detail in the sidebar on page 100 of the June/July 09 HP
article on generators.

 

There are no cheap solutions for your customer. For a no-cost solution, take
4 L16s out of the system, run one string. The cheapest charging solution is
a good-sized 5,000-6,500 W) 120/240V inverter-generator, such as Honda or
Yamaha. Don't run the inverters at max charge rate (70A on a DR2424 X 2
inverters is a C/5 rate, too hot for those L16s). Otherwise add lots of
array.

 

We set C40s to 1.600 bulk, .900 float. The C40 only absorbs for two hours;
this could also contribute.

 

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 <http://www.positiveenergysolar.com/> 

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Mark Frye
Sent: Thursday, December 03, 2009 10:23 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] Off-Grid Sizing Case

 

Folks, 

I have a customer with a 3 year old system  in northern CA: 

8 - Deka 370AH, 6V, 2x4 banks - 740Ah @ 24V 
2 - DR2424 120/240V series 
4 - EC-120-GL 
1 - C40 CC 
1 - 5000W, old portable gas gen 

The problem is increased gen runtime probally due to chronic undercharging. 

Based on estimated consumption in the home, I think he needs about 2X the PV
to meet the energy production needs in the summer (5 kWH/day)(30% DOD/day).
But in order to get C10 charging during the summer he would need 5X the PV?

Money is and issue. So what should I recommend: 

1 - Increase PV 4X to 5X, add MPPT controller to get to a PV based system
with gen support 
2 - Get a 3K to 5K propane gen and and run as a gen based system with PV
support 
3 -? 
  
Mark Frye 
Berkeley Solar Electric Systems 
303 Redbud Way 
Nevada City,  CA 95959 
(530) 401-8024 
 <http://www.berkeleysolar.com> www.berkeleysolar.com  

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