Tag Archives: off the grid

Bimodal Solar PV, Grid-tied & Off-grid Combo, Close to Missoula

9 kW array, just outside Missoula, Montana

SBS Solar was really excited to work on this bimodal system.  It is just a few minutes from downtown Missoula, and the customer wanted to be fully self sufficient when the grid was down.  The customer had a slightly higher then average residential load so we sized a 36 module Canadian Solar CS6P 250P for a total of 9 kW system capable of supplying over 10 Mega watt hours annually.
We used eight of the 6 volt Unigy II 1016 amp hour Gel batteries for storage.  At over 400 lbs a piece just getting the batteries in the basement was a feat for four strong guys.  We were concerned about the end nailed stair treads giving it up with the weight we were applying, but thankfully no issues.

6 volt Unigy II 1016 amp hour Gel batteries for storage, at over 400 lbs a piece!

We used the most advanced charge controller on the market (the Xantrex XW MPPT 80 600) capable of converting up to 550 volts DC from the array to battery bank voltages allowing us to use large strings of up to 12 modules in series.  This was a huge benefit on this system allowing us to achieve less then 2% loss running four strings of 10 gauge wire on a 250′ home run instead of 12 strings of 4 gauge with a standard 150 volt max controller with a dramatic cost difference.

Xantrex XW MPPT 80 600 Controller, Two Xantrex XW6048 inverters, Xantrex XW PDP Power Distribution Panel, and SCP System Control Panel

We used two of the Xantrex XW6048 inverters to supply the home, charge the batteries from the generator, and backfeed the utility from the PV Array for a total of 12,000 watts so there is room to grow in the future.  The combiners, disconnects, Xantrex XW PDP Power Distribution Panel, and SCP System Control Panel completed the system.  The Xantrex XW SCP allowed us to program the inverters and charge controllers to perform the complicated tasks of keeping our batteries happy through all temperatures, feeding critical loads during a power outage, and back feeding the power meter when the grid is up and the sun shining.
Our customer shut his power off the first weekend to see how the system would keep up with his usage and was very pleased with the power production.  When using the system off grid to power the critical load panel it only pulls as much juice from the array as is necessary to keep up with the loads and keep the batteries charged that weekend he only used approximately a third of his capacity.
This was a great system for the SBS Solar to complete, as we finished up just before installing the 22.5 kW Xantrex XW system in Hamilton with 5 times the battery capacity.  That post is coming soon!

Maui – Final Phase

We finished the off-the-grid system in Maui in June of 2010 and it seems to be working wonderfully all summer.

All in all, we installed a 5.6 kW solar array, battery bank and inverter system on the island of Maui for an off grid facility. The system powers a main house, two guest houses and a pool house.

We had fun with this project as it is located in such a beautiful part of the world and the local Hawaiians where integrally involved in the installation work. Because the system is beyond the power lines we employed a large battery bank and backup generator fired by propane. This system design varies greatly from grid connected systems where batteries are seldom employed as the power grid serves as “financial” power storage.

Cloud cover and precipitation vary extremely from 12 to 360 inches per year depending upon the microclimate which made the system sizing a bit more challenging. To compensate for this variable we included a 30 kW generator and four inverter/battery chargers which can recharge the batteries in several hours time.

Here is our photo show of the final install, inverter and battery bank, etc… If you want captions, please click on the image below and then on the icon in the lower right w /the four-arrows for full-screen mode.

Dan Bradbord, SBS Solar Guru


Maui Part II – Ready to Install

After five weeks of designing, ordering and coordinating over sea shipments, we are about to depart for the final installation phase of our Maui PV system.  As things move a bit slower in this part of the world we have needed every day to bring the pieces and people together to be at this point.

Several hundred feet of buried conduit are being set this week in advance of the final week push of installation.  A new concrete pad has been poured for the 500 gallon propane tank which will fuel the backup generator.  Project objectives have grown which is typical yet always different.  As we found a place for this tank it was decided to pull the old above ground diesel tanks which died long ago.  It is amazing to see what this rainforest climate can do to steel.  The top portion of the tanks have literally rotted away.  Don’t stand in one place to long or a vine will start growing up your leg.

We will be installing 27 Sharp 235 watt modules, three of which will operate the swimming pool circulation and filtering pump directly.  An Outback power panel including 4 outback inverter/ chargers will be placed in the equipment room along with 24 -2 volt cells to give us a large battery storage system.

Check out the video clips of our initial inspection.


Not a bad place to have to work as long as the vines don’t get ya!

Dan Brandborg
Photovoltaic Energy Specialist
NABCEP Certified

Maui Part I – Aloha from SBS

Missoula to Maui – two trips – 6-weeks – off the grid – this is awesome!

We completed our in depth site analysis of the Maui, Hawaii facility earlier in April.  We shot three video clips of the existing 20 year old PV system which we will soon have on our site. The clips detail the review of this system which is at the end of its useful life, and our suggestions of what to replace it with.

In brief we will be installing a 5.6 kW solar array and expanding the existing mount structure.  The two Trace inverters will be replaced with four Outback inverters and a Outback power panel.  A stationary generator will be installed to maximize the battery charging ability of the above mentioned inverter/chargers and minimize the generator run time.

As the pool filtration pump was found to be consuming one third of the entire facilities electrical power, this AC pump will be replaced with a DC pump powered from its own three module solar array.  This will maximize overall efficiency and greatly reduce the man hours spent in cleaning the pool.

We are scheduled to install this system in the first half of June so we will keep posting as we go.


Dan “the Solar Man” Brandborg

Photovoltaic Energy Specialist

NABCEP Certified