Thursday, May 08, 2008

Another Grid Power Failure

And another test of my off-grid solar electric system:

With each grid power failure I learn new things, and Wednesday’s power failure was no exception. This power failure occurred early in the afternoon while I was at work. It was a gloomy day, and batteries were not fully charged at the time of the failure, making it necessary to switch the system on manually. This would have been easy for me to do, had I been home at the time, but not so easy for a family member. The simple system I once had is now an automated system with several components and switches. Explaining over the phone how to switch the system on is not as simple as it was in the past. It went something like this:

Me: Flip the Inverter toggle switch on.
Family Member: Which one is the inverter?
Me: The black box that says Exeltech on it.
Family Member: Where is the on/off switch?
Me: It is under the Kill-A-Watt meter.
Family Member: Which one is the Kill-A-Watt meter?
Me: It’s the grey thing that’s plugged in to the inverter.
Family Member: I don’t see a switch under the Kill-A-Watt meter.
Me: The switch isn’t on the Kill-A-Watt meter, it’s on the front of the Inverter.
Family Member: OK. I’ve switched it on and I see a green light.
Me: That’s what you should see. The system is now on.

From this experience I’ve learned that I need to better educate family members so they’ll be prepared for the next grid power failure. To help with this, I’ve created a visual aid. The name of each device is listed next to its picture, along with a brief description. Basic operating instructions are also provided. The challenge is to provide enough information, but not too much. Too much information could be confusing.

First of all, family members need to understand the system configuration. There are two common system configurations:

Configuration #1: In the event of a grid-power failure, the inverter switches on, and the loads are automatically switched from grid power to battery power.

Configuration #2: Loads are powered by battery power until battery voltage drops to a preset level. Loads are then automatically switched to grid power.

My system is wired for Configuration #2. The system doesn’t automatically switch on when a power failure occurs; it switches on when batteries are fully charged. The refrigerator, freezer, and anything else plugged into the system’s AC outlet will automatically switch to grid power when the inverter switches off, but a grid power failure does not automatically switch the loads to battery power.

Because it is sometimes necessary to switch the system on manually, it must also be switched off manually, and users also need to know when to do that. Users need to monitor battery voltage, and must avoid letting battery voltage drop too far. This can be a little tricky too, since battery voltage is influenced by the size of the load. And so, without supplying too much information, I need to set a low-battery-voltage limit for them to follow.

To complicate things just a little, I’ve also provided information about the back-up battery bank, and how to switch it into the circuit. As with the main battery bank, battery voltage must be monitored and voltage must not be allowed to fall below a predetermined low-voltage limit.

Wednesday’s grid power failure was brief, about 2 hours, but it was a valuable learning experience. With the visual aid I’ve created, and a little instruction, we’re better prepared for the next power failure. We’ve been having a lot of storms lately, so we may not have to wait long to find out.

John

1 comment:

Damon said...

Power here in suburban London is pretty reliable, and I often tell people that adding a UPS would *lower* the reliability of a computer system in most cases, since the UPS will fail more often than the grid. I can't remember the last outage in the 15+ years that I've been here.

So, like you, I've made no especial effort to have my system automatically switch to battery (and a lower LVD threshold) when/if the grid fails.

Maybe when I do my rejig for the Lithium battery set I'll do exactly that: a simple detection that the grid is on, and in its absence move the LVD threshold down.

Rgds

Damon