Deconstructing a Solar Power System

A widow has asked me to dismantle her 4 year old 10kw PV system. It isn’t that she didn’t like solar power, but she has to sell the house now and mortgage inspectors are brutally thorough and her husband had overlooked the business of permits when he installed the system. In the process of going through Tom’s system I am finding some things of interest. Here are the good, the bad and the ugly.

First of all, his original installation featured 200 amps of solar power and 180 amps of charge controllers. You should know that a 200 amp solar system will rarely crank out that much, but sometimes it does. You should also know what you have in terms of gear. The first MPPT charge controllers were 60 amp controllers and, by golly, that’d better be all you run through them. One still works. The first one that went bad was replaced with a Flex Max 60. Still a 60 amp controller, but it just limits the output and won’t hurt itself. After the second original charge controller smoked, he finally heeded what I’d told him about underspec’d charge controllers and overdid it, buying two of the FM80 units. That’ll darn sure handle it, but another FM60 would have worked because of the current limiting feature. It may be that he just bought the FM80s and put the FM60 in reserve for the day when the final Brand X controller expires. Anyway, read the manual (RTFM) and sometimes you can save money by not buying too small and sometimes by not buying too large.

Now here is something I like. He made his own cables and with 2 cable ties and a strip of inner tube rubber made what effectively serves as boots. You can still easily get to the bolts, but if you drop a tool, you are less likely to short anything out.

These Trojan T105s are only two years old, but the water was never checked. Ever…until it was observed that the system just wasn’t performing up to snuff. Normally, if you dry out a set of batteries, you get fuming acid toward the end, and even early on you can get some really corroded terminals. Lots of people use Vaseline or ordinary grease on terminals to help with this, but Tom used an anti-corrosion electrical grease, and boy does that stuff work! These terminals are all bare copper and there was not a hint of corrosion on any of the 16 batteries. I don’t have a brand for this, but will be checking on it. No more axle grease for my batteries!

I have harped on keeping the batteries watered on many occasions, but that is not the only battery maintenance you need to do. By the way, when the batteries were topped up with MANY gallons of distilled water, the cells were all active and they regained 50% capacity. That’s says a lot for Trojans. I suspect a good desulphation charge will do wonders for these batteries. Worth a try, anyway. But back to the other battery maintenance chore. You have to snug up the bolts to make sure they stay tight and resistance stays low. What happens when there is resistance? Power is wasted in the form of heat. Fire up the a/c and the dryer and you’ll find out just how much heat. Near the top left of the next photo you can see what a T105 terminal is supposed to look like. Then there are two that were a bit loose.

Neither end of this cable was tight and two batteries ended up with melted terminals. I would recommend that 3 of the batteries in this system not be returned to service because of hot terminal damage. They just can’t be expected to tighten, now. Proceed at own risk.

All of the nuts had washers under them, but none were lock washers. Lock washers serve two purposes, they can keep the nut from backing off, but they also provide a little spring tension. What I like best for batteries is the Belleville washer. This is dished and provides great contact pressure without over-tightening the nuts.

I don’t mean to trash Tom’s system, but it is always good to pay attention to what you should and should not do and observe the results of both. Looking at my photo of a ruined $150 battery is a lot less heartbreaking than have it happen to yours!

It just breaks my heart to turn off a working system! –Neal