Outback Solar System

The primary backup power system for my house is a battery-based grid-connected but not grid-interactive solar power system with the following specs:

Plus a whole host of other bits and pieces!

Panel Orientation

As shown above, the panels are on two faces of the roof. One half face south, the other half west. I have precious little space on the south face, although I could have mounted the second set below the first. However, that lower portion of the roof gets shaded by trees fairly quickly in winter.

Fortunately, I have since found that there is little harm in using the arrangement I chose. I get less power in the morning hours, but then the lower row would have been shaded by the peak of the roof anyway. During the midday hours I am seeing total wattages consistently falling between the STC and PTC ratings, so I can't complain there. In the late afternoon the west-facing panels continue to produce power well after the south array stops.

24-March-2012: Cool, upgrades! Today I added six KD185 panels to the system. Using the same charge controller - I'm hardly taxing it, with the new panels I *might* hit 40A on a good day! I went with the slightly larger panels because the total cost was considerably cheaper than getting another eight 135W panels. I had to have help getting them on the roof, though! The 135s were just barely small / light enough to handle alone, but not these! Especially not on the steep pitch of my roof.

Second set of panels

So here are the new panels. They live at the north end of the roof, facing west. They actually will get sun longer than any of the first sets, so should extend my runtime somewhat. Yes, there is a shadow on the panels from an antenna mast. Nothing is perfect! It isn't there very long, and isn't affecting power production too adversely. This is the best spot I have now, so it'll have to do!

To Grid-Tie or Not To Grid-Tie

My system is not "grid-tied" in the way most people mean. It is connected to the grid in that the inverter has a 120VAC power input that can be fed from a generator or the grid. However it will not backfeed power into the grid ("grid interactive").

From a functional standpoint, it would be desirable to be grid-interactive. The system could then produce as much power as possible the entire time the sun is up, and any excess is fed back to the grid. I wouldn't have to cycle the battery bank, and I wouldn't have to change any wiring in the house - the power produced would feed any devices that happened to be running at the time.

But there are downsides.

My primary objection is as a tinkerer / experimenter. I like being able to do whatever I want with my systems. On a whim, I can tear the entire thing apart and reconfigure it, add to it, rearrange. When you go grid-tied though, you have to have the system inspected. Any changes may mean reinspection. The power company gets a say in what happens inside my home! No thanks...

It is also not financially cost-effective, at least in my area. While I would most likely be producing excess power during the day, due to the way my power company has configured their rates any savings I might see would be wiped out by the extra monthly fee they impose for the privilege. Other areas of the country have much better rate structures for grid-tie, but here power is too cheap.

Inverter and Loads

So my system has its own breaker panel, with dedicated circuits to run various parts of the house. The AC "grid" connection is actually wired to a plug, so I can also use the generator during a power outage to run loads and recharge the batteries if necessary. (There is also a dedicated generator circuit, the generator plugs into it outside and there are outlets inside so I don't have to run extension cords.)

Inside componentsMy normal daily loads for the system are primarily my home network - computers, switches, etc. There are also a few lights on it so things don't go dark in an outage. If need be, I can easily and quickly plug the fridge, furnace, or just about anything else in. Gotta keep the essentials happy though, for my computers this has become a massive UPS!

This image shows the charge controller, batteries, inverter and breaker panel. It wan't complete at the time I took the picture so things were a bit messy. I need to get some new shots sometime...

Counting Costs

In a nutshell, there is NO cost benefit to the system I have installed! Fortunately, I didn't install it for that reason.

I have spent roughly $8,000 on the primary solar system as it stands today. This doesn't count labor, as I installed everything myself, nor does it count any other panels and hardware I have. If I could have perfect weather every single day of the year, based on current generation numbers I could produce a theoretical total of around 1,642 kWh per year. At current rates for power in my area - $0.09/kWh - that's a whopping $148 per year!

Assuming nothing ever requires repair or replacement, it would take over 50 years to financially break even. I can guarantee the batteries won't last that long - if I'm lucky I'd need 5 sets, possibly 10. I also won't have 365 perfectly sunny days every year. It's possible the doom-and-gloomers are right, and power rates will skyrocket soon, but they would have to get very high indeed for this sort of system to be cost-effective!