Dissecting our System

Our Roof Panels
These are the photovoltaic panels that produce all of our power. The panels on the left are BP275f 75-watt panels produced by BP Solar, the panels on the right are S-100 100 watt panels produced by Solec. Between the two installations we get a maximum rated power output of 1200 watts. The best output I've seen on a cold day with fresh snowfall (which increases output by reflecting light onto the panels) is 47.4 amps. The panels are rated to produce 38-39 amps in full sun.

The increase is due to a number of factors. Panels are rated for output at sea level and 70 degrees F temperature. Our 9000' altitude increases the output of the panels because the sun is stronger (less air to filter it), also, the panels will operate more efficiently in cold temperatures and will pick up additional solar energy from the reflection of light off of snow. I have seen ground mounted panel installations where crushed white gravel is spread in front of the panels to increase light reflection. A little added reflection is a good idea but too much, as with mirrors or metal reflectors, can damage the panels.

The power produced by the panels is sent to this unit, an Infinity 6 power center made by Bobier Electronics. I'm not even sure if they are available any more. The PV power enters through the breakers on the upper left side of the unit and passes through an automatic switch (located inside the Infinity) that is controlled by the Omnimeter in the center of the unit.

The Omnimeter is a multifunction computer control and metering unit that can handle up to 100 amps of DC input. It senses the voltage of the battery, compares it to the voltage coming from the panels and when the panel voltage exceeds the battery voltage it closes the switch and allows power to flow into the system from the panels. At least that was supposed to be how it worked. Over time that has proven not to be the case and I've made some modifications that have improved the functionality and power output of my system..

One of the things the Omnimeter does do well is to act as a system monitor. The Omnimeter provides digital readouts of the conditions at four points in the system, the PV input, the DC output (the breakers on the upper right), the inverter, and the batteries. It is easily programmed to show the capacity of the battery bank (in our case 1500 amp hours) and will reset its readout when it determines the battery bank is full. It is extremely useful to have a way to determine the power consumption/production of the various parts of your system and the unit works well in that regard..

The Infinity 6 also provides breakers for 24 volt DC output, which in our case is used to operate our DC well pump and DC pressure pump. This makes it extremely easy to monitor the power consumption of our pumps. I know, for example, the normal power consumption of the well pump and if I check the meter and see the consumption is abnormal (either too much or too little) I know there is a problem with the well pump and can fix it. The pump has operated flawlessly for the last 4 years but on the rare occasions when the line has frozen I've been able to notice it by the increased power consumption of the pump trying to pump against the ice plug in the line. Without the power readout I wouldn't know there was a problem until we ran out of water.

The power produced by the panels is stored in these batteries. They are sealed Dynasty AGM lead acid batteries connected through a buss bar. Each battery is rated at 100 amp hours capacity at 12 volts DC. To get them to 24 volts DC 2 of the batteries are connected in series, i.e. the positive terminal of one battery is connected to the negative terminal of the adjacent battery. A series connection increases the voltage output of the interconnected batteries while keeping the amp hour capacity the same. This basically creates a single 24 volt 100 amp hour capacity battery out of 2 12-volt batteries.

The description of this battery system, and what happened with my original battery bank can be seen on my battery page. The 12 pairs of batteries in this bank give me a storage capacity of 1200 amphours at 24 volts DC.

When connecting batteries together or to an inverter or control panel it is imperative that you not scrimp on the cables. All the cables in our system that connect the batteries to each other and to the buss bar are 1/0 welding cable and the connections to the inverter/control panel are 4/0 welding cable. Series cables must all be the same length though the parallel cables need not be. Also, the distance between the batteries and the inverter should be the absolute minimum you can manage. The longer the cable the higher the voltage losses. The cables in our system that connect the batteries to the inverter are each 5 feet long.

Our AC "house power" is provided by this Trace 4024 inverter/charger. Rather than being connected directly to the batteries it is connected to the large breaker in the Infinity 6 control panel. Though I had some initial troubles with the 4024 (and considerable trouble with Trace technical support) the unit has now run without a problem for the last few years of continuous service. Though I haven't needed to contact them lately, I have also heard that Trace's technical support has undergone a much needed overhaul, kudos to them for that. (UPDATE: My latest experience with Trace's technical support was light years better than my earlier experiences. They have done a great job of getting their tech support up to snuff and willing to explain and listen, two qualities they were lacking in the past.

The inverter also has a built-in battery charger which allows the battery bank to be recharged from any AC source, such as the grid or a generator. Trace has also included a remote start option that allows the unit to control a generator automatically, starting it and stopping it as needed. However, in a well designed system this should not be necessary. We find that we run our generator only during extended stormy or cloudy periods, which don't happen often here in Colorado (especially this year).

The 4024 is marketed as a "sine wave" inverter, which means that it "mimics" the sinusoidal waveform of grid power fairly well. It is actually (in Trace's words) a "stepped approximation of a sine wave", rather than a "true" sine wave, though you will often see it marketed as a "true" sine wave. At the time we installed our system it was the only inverter on the market that produced anything like sine wave AC power and we installed it because of the electronics and motors we would be running with it. Motors prefer sine wave to the "modified" sine/square wave output of previous inverters.

Now, however, there are more choices for sine wave inverters with far better output and more of a "true" sine wave. One such is the Xantrex ProSine series of inverters, the largest of which is 3000 watts with a superior battery charger built in. Xantrex bought Statpower, who first built the Prosine series, and I'm not entirely sure they are still pushing them as hard, since they represent competition for the Trace series. But they are still good inverters and better than the Trace and I've not heard of any plans to stop making them. Another good inverter, new in the last couple of years, is the Outback sine wave inverters. These are highly rated inverters that can be bought standalone or as part of an integrated with also includes the highly rated MX60 MPPT charge controller. If I had it to do over again, or had the money to afford it now, I'd get myself an Outback system in a heartbeat.

All Contents 1997-2006
Wagonmaker Press
Thomas W. Elliot