Okay, two more parts to go and we should be able to cover the system completely and hopefully inform those a bit who wish to install their own systems.  Part 1: Basics, Part 2: Panel selection, mounting, and orientation.  Part 3: Controls, Inverters, etc…

Once the panels are installed, we need to somehow bring their output together and transfer it to the grid and/or batteries.  We first connect all the panels to a unit called a combiner box.  This unit can be built into the inverter or can be separate.  In our case the unit is separate and installed on the roof near the panels.  All the wires go into this box, combine together and the output is sent down two wires to the charge controller.  There is no charge controller in a grid-tie only system since there are no batteries to charge (the output of the PV panel goes directly into the inverter).

The charge controller is an essential device that does several things.  Most importantly, it takes the power from the panels and charges the batteries properly and efficiently and essentially shuts the panels off once the batteries are full.  Newer charge controllers utilize a method called Maximum Power Point Tracking (MPPT), which is a complicated method of searching out the “sweet spot” in a panels output and charging the batteries optimally.  This feature can add 20-30% to your panel’s rated output under certain conditions (sunny cold days in particular).  The extra money spent on this feature is definitely worth it (we went with the Outback MX60, a reputable industry standard from Arlington, WA).

The batteries.  It used to be that battery banks were these behemoths that required constant maintenance for long-term survival.  This is still true in some circumstances, and most notably with flooded lead-acid batteries.  These are still the most affordable battery in terms of $ / storage capacity.  Recently, another type of battery is making an in-road into the renewable energy market, the AGM (absorbed glass mat) battery.  They are very tolerant to temperature fluctuations, are good deep cycling batteries (meaning you can discharge the battery 80% or more and still recharge it without damaging it), and don’t create hydrogen gas when charging.  They are, however, more expensive, almost twice the cost.  We purchased four AGM batteries for our system (MK 12v/245Ah).

The inverter is next.  This device takes the DC voltage of the batteries and transforms it into the AC power we use in our homes.  It also interfaces with the utility and decides when to sell excess power, shut itself off in the case of a power outage, and can start a backup generator if you have one.  The inverter is rated by wattage, and one must decide how much backup power they need.  We opted for a 3,000-watt unit since our demand is low and our essential needs are small (pump, freezer, refrigerator).  You can get inverters as large as you’d like, and most can be connected together to increase capacity. We went with an Outback Power GTFX 3048 inverter.

The remaining components of the system are primarily disconnect switches, conduit and monitors.  All systems need to have a way to let the owner know what the system is doing.  Since I’m a gauge kind of guy, we opted for extensive monitoring that will allow me to collect data regarding every part of the system.  I think being able to see what is going on allows you to fine tune the operation for increased performance.

Many packages today are coming prepackaged and very easy to install.  My first system required me to source every little part and wire it together on my own and have it inspected by the state.  New systems are being assembled from the parts you request (or your installer) at the distributor’s facility, and they are able to “list” the item as being code compliant, simplifying the inspection process.  We purchased our system made to order like this and found the increase in cost to be negligible in the scheme of things.