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DayCreek Journal

February 3 , 2004

Solar Electric System Comparison

The verdict is still out as to what plan the utility company may approve, but it appears as if the non-net-metering approach will be the best of three bad options. (See January, 44 Journal.) If this is true, a configuration to include a battery bank might be a better choice. This way some of the excess solar power can be stored in batteries instead of giving it away to the local utility for free. Or, maybe the best option is to do nothing and wait a few years until the house is finished and then rethink things. Of course, who knows if any rebate or tax incentives will be in place. No matter how you look at it, it's a tough call.

Here's a summary of the options:

Option 1. Grid-Intertie Only

Click on the above image for a full-size diagram.


This option takes the electricity generated by the solar PV array and directly puts it onto the grid. Whatever my electric load is at the time of production will be supplied by the solar array, but any excess power will go to the local utility cooperative at no charge to them. (At least someone else on the grid will be getting renewable energy instead of non-renewable energy, albeit small. The kicker to this is that the local utility is not buying the power from me, but selling to someone else.)

From a hardware configuration standpoint, this is the simplest and least expensive option. Two Sunnyboy Inverters will be used to convert the 285VDC to 240VAC. Because the PV array will be in series, the DC voltage is much higher. This keeps the wire size small, making it less expensive to run power from the panels to the house.

Option 2. Grid-Intertie with Battery Backup

Click on the above image for a full-size diagram.


Battery backup allows for critical loads to continue to run in the event of a power outage and also stores some of the excess power generated by the PV array that can be used during the night and cloudy periods.

Outback Inverters are well respected in the industry and they have just released a UL listed inverter that is made for grid-intertie with battery backup. Their MX60 controller allows for somewhat higher DC input voltages compared to other controllers which will keep the wire size down somewhat, but not as good as the Sunnyboy inverter.

The Outback configuration also allows for an easy bypass of the inverter in the event of a system failure.

Option 3. Wait and Do Nothing
Frankly, this has been a time consuming exercise so far and I haven't even lifted a tool yet. I have plenty of other things to do like finish the house!

Pro's and Con's

Option Pro's Con's
Grid-Intertie
  • Least expensive option
  • Easiest to install
  • Sunnyboy has a great reputation
  • Highest efficiency
  • No battery backup
  • If the grid goes down, so does the house
  • Going off the grid at some point in the future would require a new inverter and a rewiring of the PV panels.
Grid-Intertie with Battery Backup
  • Some excess power used to charge batteries instead of losing it to the grid.
  • If the grid goes down, power remains on in the house.
  • Same inverter can be used for off-grid configuration, PV panels require no rewiring.
  • Efficiency of system is lower
  • System cost ~$2,500 more.
  • Batteries last about 10 years, then need to be replaced.
Do Nothing
(For Now)
  • Makes my life a heck of a lot easier. (Path of least resistance.)
  • Least costly approach. (short term)
  • Price of PV's continue to slowly drop. More watts per dollar in the years ahead.
  • Does nothing to help the environment.
  • Probably will lose out on a rebate worth up to $8k. (Hard to say what will be available later down the road regarding rebates, funding, etc.)

Installing renewable energy systems is not cheap. If you were to install a system to save money on your electric bills at today's rates, the PV system will definitely take a long time to pay for itself. But one of my original goals was to invest in today's dollars to offset our costs once we are retired.

You can bet that utility costs will continue to rise. As a matter for fact, we're just a few months away from another electric rate hike and you know it will continue to climb in the years ahead. But solar PV will not cover all of our electricity needs and a combination of a wind turbine and an electric generator would be required to keep the electricity flowing 365 days out of the year.

With the current rebate program I am required to keep the system tied to the grid for two years. After the two year period, I would be free to use the system either on or off the grid.

If our plans were to continue to stay grid-intertied the first option would be a no-brainer, but at this point you can only assume that the base rate fee of $21 that we pay per month will only go up. Without buying one kilowatt from the electric utility we pay $250/year for the privilege of being connected to the grid. Over a ten-year period, the money that goes to the grid connection could be used to buy a new set of batteries.

Then there's the environment. Renewable energy certainly is cleaner than the fossil burning and nuclear power plants, but there's a price to pay for the manufacturing of silicon solar cells, inverters, copper wire, etc.

Maybe the best option is to conserve as much as possible. The rule to investing in renewable energy is to CONSERVE FIRST and it certainly makes the most sense. But it sure would be nice to be free from the grid someday. At least it's something to dream about.

Still thinking...