Choosing between solar array options

The following are our informal notes on a variety of options which we considered as we narrowed down which system to install and how to finance the purchase.  Please don't take our word for it; do your own research before making any decisions.

Deciding between bids – overall philosophical question

Is the goal to install the most economical panels or are there other goals (ex. maximizing # of kwHs/$ saved by the nonprofit, doing the most for the environment, preventing the most CO2 from the atmosphere)?  Are there constraints on your options?  (ex.  least effort required of the nonprofit, economic justice criteria, aesthetics)

Reliability - the importance of your inverter
Because solar panels are extremely reliable, the inverters become an important variable in the reliability of the system.  There is substantial variability in reliability between brands of inverters, though not much difference in how much energy is produced.  We were advised by several independent experts and interested lay people to go with a name brand inverter, for example, SMA (the largest producer) and Xantrex.  (Note:  each website describes warranties on their products)

All inverters fail and need to be replaced in about 10 years.  
Current replacement cost:    String inverters are about 20-25c/watt of the installation cost.  Microinverters are about 40-50c/watt of the installation cost.

Microinverters vs. string inverters
Microinverters are better if there will be any shade on any of the panels.  When panels are in series (one inverter per array or array row), shade on one panel decreases the production of the entire array/array row.  If there is no shade on the array, then the advantage of microinverters is less significant. 

Microinverters are better if one goal of the installation is to maximize generation.

Microinverters are better if there is a failure.  For a single string, the failure of one panel brings down the array.  However, we would need to keep an eye on production to look for decreases in power generation which would signify the failure of one panel/microinvertor.  Such failures are less dramatic and therefore easier to miss than the failure of the entire array.

A string inverter has the advantage that one replaces it without having to worry about compatibility with other inverters in the system.  With changes in the technology, there could be a problem replacing one microinverter with a new, compatible unit because the original technology could become obsolete.  They don’t anticipate this would be a problem, but it is theoretically possible.

Maintenance and warranty
The primary maintenance expense is the replacement of the inverter(s) at 10-15 years.  There are unlikely to be other expenses.

On a small array, there is no need to wash each panel quarterly.  Do blow off leaves and pine straw if they clump anywhere on the array, this is most likely to happen at the edge where sliding debris may cluster.  With a large array, quarterly maintenance and measurement makes sense.

Do a visual inspection from time to time to see if anything looks odd – for instance, bees nesting in the inverter box.

Some people install screens around the perimeter of the array to keep squirrels from going underneath and chewing wires.  The need for this is determined by how high the panels are above the roof.  Ask the installer.

A 2-5 year warranty on installation will cover the initial period. If equipment is going to fail, it is likely to be in the first 2 years.  If thermal expansion is going to cause wires to break because they were strung too tight, this will happen after 2 summers.

Solar hot water solar panels have a spotty history of reliability.  When people say they have had trouble with solar, they usually mean solar hot water.  Solar photovoltaic panels have a great track record.