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Living Offgrid Affordably #16:ZZT-ZZT, The Power Inside

9/7/2012 12:55:43 PM

Tags: solar power, living offgrid, alternative energy, Jeff Chaney

Jeff with his one kilowatt array After building and installing the array last time in “Power Us Up, Scotty”, we are ready to bring the power where we need it, inside the building.

The “service entrance” (picture in previous article) was located 6 feet from the northwest corner of the building, to place it underneath the first short flight of steps and landing. I had chosen to house the battery bank and peripheral equipment (to be detailed with photos in a future article) under the stairs because of limited space in this small building. This action did not conform to code, it did not allow ample room or access to the hardware. The biggest detriment was the fact that the stair treads must be removed to inspect and water the batteries. Very cumbersome. When the main house is built, I will include a “power room”.

I installed a reducer at the building end of the underground pipe, to convert the 6 inch pipe to 2 ½ inch. The smaller pipe rose about 2 feet above ground, to enter the building. The joint between pipe and wall was caulked.

Having a limited budget at the time, I chose a Xantrex C-30, 30 amp charge controller. Consisting of two modules with a total output of 14.2 amps, the array would mate to the C-30 just fine, with room to expand later.

The 1/0 (one ought) power lines were connected to a junction block. #6 wire was used for the short run from the junction block to a disconnect, from the disconnect to the C-30, then finally to the battery bank.

I had decided to use a combination of batteries for head-to-head testing purposes. This is highly not recommended! Lower performance and battery life will result. In spite of this knowledge, I am known to conduct some unorthodox experiments. I used four Optima yellow top and four Deka marine 12 volt deep cycle batteries, all wired in parallel to maintain 12 volts and multiply storage amp/hours. The Optima’s contain gel electrolyte, the Deka’s flooded lead acid. These should not be used together, but I wanted to compare them. The main reason not to combine them is that they have different charging requirements. The best charge voltage for one type is not best for the other type. As a result, one type will suffer and not yield a full lifetime.

As a compromise, I set the field adjustable bulk and float charge voltages as follows: bulk voltage - 14.4 volts, float voltage - 13.3. These voltages match the requirements for the lead acid batteries, but are not ideal for the gel cells.

Even though my test was lacking some accuracy, the results were not unexpected. With 8 years of use, the lead acid batteries had to be replaced at 4 year intervals. The gel cell batteries were replaced at the end of the 8 year cycle, yielding twice the life of the lead acid type. At twice the initial cost, the gel cells lasted twice as long. The other main factors were that the gel cells did not have quite as many amp/hours of storage capacity, nor did they receive optimum charge voltages. On the plus side, they did not require watering. The final conclusion was that either type would do a fine job, and at a comparable cost.

Large industrial batteries are available, and well suited, to this application. However, they come with two huge disadvantages. One, they are very heavy and require machinery (a forklift) to handle them, and shipping costs are high. Two, they represent a large initial expense. But, when you consider that they will last for up to twenty years, they can be very cost effective in some situations.

Art 16 Battery Meter The next, but most important by far, component installed was a shunt from which the battery meter could monitor system performance. I chose a Trimetric 2020 meter from Bogart Engineering, shunt included, that is very simple to use and program. I consider this meter the absolute minimum monitoring device one should use. Other, more sophisticated meters are available that will log and store more data, if the budget allows.

THE most critical exercise in offgrid living is battery bank health and state-of-charge, which must be tracked very closely. Meter cost is negligible compared to battery bank replacement expense. The shunt is wired into the negative main battery bank cable. All charge entering and all loads exiting the bank must route through this shunt to yield accurate results. In the early days, we viewed the meter thirty-plus times daily. Ten years later, it is still checked several times every day. The battery meter truly is your lifeline.

Power was then run to a conventional Square D breaker box, whose breakers were d/c rated. This would be the “12 volt” or “d/c” breaker box. I wanted to utilize d/c throughout the building as much as possible, since d/c is more efficient than a/c, especially for loads having long run times. The Novacool refrigerator and all lighting would be d/c powered.

From this breaker box, the building was wired with 12 volt d/c using standard 12/2 wire, as opposed to conventional14/2, to minimize line loss. Standard switches and outlets were placed throughout the building.

Art 16 Switched Outlets All outlets were switched, plus we utilized switched surge strips in the entertainment center and home office, to help eliminate “phantom loads”. Any appliance that uses a remote control draws power all the time, even when turned off. If it has a digital clock, it draws power continuously. These constant power draws quickly add up to a lot of unnecessary usage. Practically every building can realize reduced usage by at least 10% by eliminating “phantom loads”. Stereo systems, televisions, numerous clocks on myriad appliances, coffee makers, and anything that employs a timer, are “phantom loads”. A stereo will lose the preset stations, a small price to pay, but a t.v seems unaffected. Future articles will examine this in detail.

We have power to spare in the summer months, but in winter need to save all the power we can to avoid generator use. What we can not avoid is to reuse and recycle any and everything when possible.

All photos by Jeff & Kathy Chaney

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