Micro Inverters vs String Inverters

Over the past several years, Micro Inverters have been pushed over the market as something that is the ultimate answer for solar installations.
At American Made Solar and Wind (Mardel Souza Inc), we have refused to make installations with micro inverters for several years for several reasons.
Here is a list of the reasons we try to stay away from Micro Inverters in general:

a)Temperature exposure:
As with all electrical components, microinverters will work better under cooler temperatures. To illustrate this better, you need to look at your laptop or your computer. How many fans and heat elimination devices do you see? Look at the transformer down the street: All the metal and oil are to keep the transformer working under the coolest possible condition.
With this said, the concept of microinverters fails to provide a good point of installation. The recommended point is under the panels, in the rail system. That is in the roof. Even the solar panels experience efficiency loss under higher temperatures. Actually the voltage is lower in a hot summer day in Texas than in a cold day. All electrical components should work better when they approach to absolute zero (kelvin). Even Canada has high temperatures during some months of the year. Life expectancy of such devices is lowered by such temperatures. A full study of this can be seen in this article:
http://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0131279

b) Newer panels with high wattage.
As of today, the major companies to buy microinverters only manufactures microinverters for 250watts or lower, which in contrast with the newer panels that are rated 300w>>> the use of older modules is encouraged. Its been our policy to install only newer modules. We try not to keep inventory. Higher wattage in a module means less reails and less labor. Lower cost.

c) Guarantees.
When we install a system, we count on the system to be working for more than 25 years. We have been on business for 11 years and we expect to be in business for much longer than that. By law, all Solar Installations should have a 5 year minimum guarantee. If the life expectancy is yet to bee seen. Although they might be backed up by 10 or higher years of guarantee, I have been on this business long enough to know better. I have seen companies that claim that no microinverter has failed, but companies like Enphase which is publicly own is yet to be profitable. The micro inverters are exposed to the elements. In the coast and some other unfriendly environments, I have seen NEMA4 equipment deteriorate faster than intended. Until I see companies like Enphase making profit, I will continue my skepticism. http://newsroom.enphase.com/releasedetail.cfm?ReleaseID=982485

d)Shades
Microinverters claim that their strong suit is shade and individual control of the solar panels. To a certain extent it is true. However, the new inverters from companies like KACO have different controls over different strings. That means if a string is exposed to shadows or a different roof, the inverter will not allow circular currents and losses from such shades.

Going back to our microinverters, I did call three major suppliers of microinverters and requested information on guarantees and technical data. My impression is that all the big companies are betting on selling microinverters today while they fix all major issues and issue guarantees (if they are claimed) tomorrow. Back in 2012 it was rumored that what some microinverter companies wanted was just to sell the idea to bigger companies like SMA and KACO. Now that SMA and Kaco offer microinverters, I guess the real challenge is to make such companies profitable and their product as good as the string inverters.

I found this article interesting and non-biased, but I think its outdated. String inverters have more control over individual panels this days.
https://www.energysage.com/solar/101/microinverters-power-optimizers-advantages-disadvantages

Alejandro Peña
Mardel Souza Inc
September 16,2016
alexpena@ausasolar.com

Solar Collector issues When disconnected

Its been a while without blogging.  But we are back.

This week a potential customer called us with a very unusual problem.
The family installed a solar water heater from a solar company who is not in business anymore. Sadly this is a common practice we see all over the country, but we generally try to help the person, as means to make the industry in general look better.

Anyway, our techs arrived to the property. The solar water heater was leaking profusely.
It was properly connected. It had sensors and an expansion tank (very unusual as most plumbers do not install it in Texas).  The pressure relief valve was working.

The techs asked if any unusual activity in the house was done. The customer told our techs “We were on vacation and the water company disconnect the water for a bit…”

Disconnecting the water from an open loop solar water heater is like having a fry pan in the stove for days without anything on it, only much more worse.

If the water heater is not fed with continuous water , the system will prevent overheating by expelling the water through the relief valve. Normally, cold water will replace the hot water and the relief valve will close.  If no cold water is available, the heat will increase the pressure inside until it bursts the tank open.

When your installer installs a solar water heater, its convenient to place a sign for the water company to let them know not to disconnect the water from the property, or the water heater will be damaged.

This is the reason we prefer to installed closed loop systems.

I didnt find anything on this issue online, but please post if you find any links on similar problems.