Bob's Solar Project

One year!

Bob — Sat, 12 Aug 2006 14:17:00 +0000

One year ago today, Rick brought the battery box he had made to my house. We placed it in the basement, connected the ventilation ducts, put the batteries in the box, and wired them up. I consider this the official starting date of my solar system, although I had been running it in a crippled fashion (bad batteries) for over a month. The new batteries enabled me to take full advantage of the shingles on the roof.

So what does it look like a year later? Since August 12, 2005, the charge controller has recorded 1726 kilowatt-hours of solar energy harvested, an average of 4.7 kwh per day. The maximum yield was on June 24, 2006: 10.5 kwh for the day. The minimum was zero, which happened four days last winter when snow covered the roof all day. Here is a chart showing the daily solar yield.

It should be recalled that on some days the charge controller went into float mode, meaning that the batteries were fully charged. More solar energy was available but I had no place to put it. We still haven't connected a dump load to make use of this extra energy, and the possibility of selling back to the grid looks like it will be too much trouble and expense for too little benefit (either to me or the planet).

Of course, there were many days, especially in the winter, when the solar energy was insufficient for my household needs. This chart show the average daily kwh's from solar (from the charge controller's log) and the grid (by reading my electric meter weekly):

The grid totals for July and August of this year are slightly higher because of the heat wave in late July/early August. While I don't use air conditioning, I had to run the dehumidifier almost non-stop during those two weeks to prevent mold, and I was running electric fans as well. The high temperatures also seemed to reduce the efficiency of the solar shingles, as expected. While many of those hot days had abundant sunshine, the roof never produced more than 8.7 kwh on any one day, even though I had plenty of demand for it. For comparison, there were days of similar length and sunshine in May that produced over 10 kwh. I was afraid that maybe one of my shingle strings had become disconnected, but I checked this with my voltmeter and found that all are still working properly.

While the financial savings so far are very minimal compared to the cost of the system, I have enjoyed being relatively blackout-proof--sometimes when I didn't even know it! I know I was able to watch a World Cup game when the grid power was out, and there were two other times when neighbors asked me if my power was out and I said I had no idea. We haven't had any lengthy blackouts like in 2003, yet, but I'm pretty well prepared if we do.

What's next? I'm currently looking into ways to use solar to heat my house. I have had the shrubs on my south wall removed, opening up lots of area for solar collectors. The simplest approach would be to install a solar air heater or two, but I'm considering something more elaborate, perhaps involving thermal storage. I'll post updates here as they happen.

In the News

Bob — Tue, 25 Apr 2006 15:03:00 +0000

I'm quoted in today's Detroit News about my solar power project. I'll be presenting a talk about the project this Saturday at the Festival of Sustainable Living taking place at the Oakland Steiner School in Rochester Hills this Saturday from 12 to 1 PM.

There's also an article I wrote about my project in this month's local Sierra Club newsletter, but it's not available online.

Late winter update

Bob — Sun, 12 Mar 2006 15:37:00 +0000

It has been a very warm and sunny winter here in Michigan. Whether it's just a statistical outlier or the onset of global warming, I don't know. But aside from the month between Thanksgiving and Christmas, there hasn't been very much cold weather, and even less snow. February and early March have been spectacularly sunny, and my solar numbers reflect that.

Here's a chart showing the average daily kilowatt-hours generated by my roof, by month.

Several things to note:

The July and early August numbers were hampered bad batteries. My first set of batteries was unable to hold a charge, so the solar power had to be used as it was produced--additional sunshine was wasted (and not recorded by the charge controller).
I do not have a "dump load" connected, and haven't since the system started operating. This means that once the batteries are fully charged and the sun is still shining, no more solar power is produced (basically, the charge controller opens the switch on the wires from the roof to protect the batteries from overcharging). Net metering should solve this problem.
I have been experimenting with the HBX mode settings on the inverter. HBX allows the system to automatically switch to grid power when the batteries get low, and then back to solar once the batteries have recovered. The Outback inverter lets me define "low" and "recovered" in terms of voltages. If I set these too low, the batteries will discharge too much, shortening their lifespans. If I set them too high, the batteries charge too quickly and the additional solar power available goes to waste (as above). I adjusted the settings higher back in December, hoping to protect the batteries by keeping them in a nearly fully-charged condition most of the time. This also provides me with plenty of backup power in case of a blackout. In February, however, I was caught by surprise by the string of sunny days, and on many of those days I lost quick a bit of potential solar power. I have now lowered the voltage settings to close to where I had them in the summer. Again, net metering should resolve this concern. I'll be able to maintain the batteries at close to full charge most of the time, prolonging their lives and staying prepared for a blackout.
My 1988-model natural gas furnace was not working well this winter, and got much worse in February. It had a high-wattage fan motor (500-600 watts). In mid-February I replaced it with a new Carrier high-efficiency two-stage furnace. It has a DC fan motor which only uses 80 watts in the low stage (although it runs a higher percentage of the time, so the savings aren't quite that dramatic). In any case, the furnace situation makes it difficult to make much sense out of my energy usage this winter. In December, I had an inefficient old furnace using lots of watts in the cold weather. January was warmer, and I spent the last eleven days in Mexico. When I got back, the furnace was hardly working at all, so I was using electric space heaters a lot (big electricity hogs). Finally, since mid-February I've been enjoying my new furnace. It should save substantially on both electricity and gas use compared to previous winters.

Taking all of that into account, here is a chart comparing my average daily solar and grid usage since August:

And in the lemonade-out-of-lemons category: Last year, there were only three trees which could cast shadows on my solar shingles. This would only happen in the early morning or the dead of winter, but still they were cutting into my solar power. For better or worse (actually both), all three trees were emerald ashes, and had been infected by the emerald ash borer. As you can see from this picture from April 2005, the trees were already dead:

As a safety measure, the city came through the neighborhood in December and cut down all the ash trees. So now, it's all sun, all the time.

And yes, that second photo was taken today, March 12, 2006, technically still winter in Michigan. I was wearing shorts and a T-shirt when I took it. Sixty-three degrees! (It feels warmer than that.)

Inverter for sale?--grid-tie possibilities

Bob — Fri, 10 Mar 2006 19:20:00 +0000

Last year, as we were assembling my solar system, the Michigan legislature and eleven electrical utility companies (including DTE) reached a net-metering agreement for Michigan. Also last year, Outback Power Systems introduced net-metering compatible battery-based inverters--in other words inverters with all of the capabilities of mine PLUS the ability to sell back to the grid. Figuring my timing was just a bit off and happy with my system, I didn't think about it too much. Until recently.

I looked up the details of the Michigan net metering agreement, which can be found on page 237 of a lengthy PDF file from DTE (Standard Rider No. 16). I also called Outback to see if the new inverters are interchangeable with my current FX2548. They said that they were; furthermore, they can upgrade my FX2548 in about ten days for $350. A better option, if I can find a buyer, would be to buy one of the new inverters and sell my old one. The current price for an FX2348 is $1493, while the grid-tie-capable version is only a few dollars more. So, if I can sell my current inverter for $1300 or so, both the buyer and I can save a couple hundred bucks.

So--any readers out there planning an off-grid system who might need an almost new 48V, 2500W inverter? If you're nearby, stop over and I'll throw in a bunch of wire and other goodies you may need for your project!

(Note: I'm not sure if the FX2348 is the same inverter as I have. Mine was listed as an FX2548--either they modified the design to a slightly lower power output, or they determined that the 2500W rated output was a bit optimistic. I don't think I've ever pushed mine to anything close to 2500W.)

2005 solar summary

Bob — Mon, 02 Jan 2006 14:43:00 +0000

Predictably, December was by far the worst month so far for my solar shingles. Lots of snow, shortest days of the year, low sun angle, and almost constant overcast brought the average kilowatt-hours per day down to 0.8. In August and September, the average was 6 kw-h per day. Combined with the increased demand from the furnace and the lights and TV being on more often, I went from about 99% of my electricity coming from solar in August and September down to only about 8% (the rest comes from the grid).

The first big snow was on Thanksgiving. I finally ran out and bought a roof rake, which I used for the first time that day. I have to use a ladder to be able to reach the top-most shingles. Raking the snow off of the solar shingles takes about 15 minutes, and I did it about five times in December. There were three days in December when the roof remained covered with snow all day--those were the only days without any solar power generated.

Here's the daily kw-h outputs from the time we first turned the system on through the end of the year:

The data come from the MX-60 charge controller. Some of the numbers for the summer month are below the actual solar power available, since on several days the batteries were fully charged while the sun continued to shine, and the system remained in float mode, unable to use most of the power available. This coming summer I intend to have the dehumidifier hooked up as a dump load, which should mean that I'll be using almost all of the available sunshine. In the long run, replacing my inverter with a grid-tie model is still an option, especially if grid prices skyrocket.

Back in August I haphazardly began reading my electrical meter to see how much grid power I'm using (the monthly power bills, which frequently use estimated readings, don't provide nearly enough detail to track my power use). For the last couple of months I have been more organized, checking the meter every Saturday. The chart below shows my weekly power use, both solar and grid. Until the start of November, the grid numbers are approximate. The dates are the Saturdays that I took the meter readings, and the totals are for the week ending that day. (I couldn't figure out how to get Excel to make the bars wider.) I should also note that the solar numbers are from the charge controller, and therefore ignore the inefficiencies of the charge controller, batteries, or inverter. Unfortunately, the FX2548 inverter does not track its performance the way the charge controller does.

Hopefully December will go down as the worst month of my first solar year--January and February will certainly be the biggest challengers. I'll continue to track the performance and post summaries here.

Finally, they read my meter

Bob — Sat, 19 Nov 2005 23:01:00 +0000

I've been wanting to brag about my electric bills, but the last two months DTE used estimated meter readings, based apparently on last year's bills. Last Tuesday, however, they actually came and read my meter. The result? For the 88 days between August 19 and November 15, I used 106 kwh of grid power. For the same period, my solar shingles produced 441 kwh, or about 80% of my total electicity used. The 106 kwh was well under the minimum of 2 kwh per day that DTE charges just for being connected (I could have used an additional 70 kwh with no additional charge). Because they had used estimate readings to overcharge me for two months, my electric bill this month shows a CREDIT of $34.71.

We had two very dark, rainy days this week, which were the lowest kwh my system has had so far-about 0.4 kwh each day. Today was sunny, so I got 4.1 kwh. Nothing like the 9+ I was getting in August, but still not bad for a short day with the sun at low angles.

Here's a chart showing about 4.5 months of solar production:

Solar Decathlon

Bob — Fri, 14 Oct 2005 19:23:00 +0000

Solar Decathlon 2005 is on the Mall in Washington right now! Here are the entries:

Cal Poly San Luis Obispo:

Concordia University (Montreal):

University of Colorado:

Cornell University:

Designed to be produced as manufactured housing, with a target cost between $50,000 and $100,000.

Crowder College:

Florida International University:

Universidad Politecnica de Madrid:

University of Maryland:

University of Massachusetts, Dartmouth:

House will be donated to Habitat for Humanity after competition.

University of Michigan:

University of Missouri, Rolla:

New York Institute of Technology:

Uses a hydrogen fuel cell instead of batteries.

Pittsburgh Synergy:

Universidad de Puerto Rico:

Rhode Island School of Design:

University of Texas:

Virginia Tech:

Washington State University:

There's a lot more about these houses here, including links to the web sites for each house/project. I've been hoping that the U of M would win this, but the competition looks fierce (and I'm afraid they finish dead last in the sketches provided for the overview, although Pittsburgh's is pretty lame as well--photos of models always look tacky). From a purely aesthetic viewpoint, I like the Concordia, Cornell, Madrid, Massachusetts, Missouri-Rolla and Puerto Rico designs best. While the need to transport the houses is a positive in terms of possible conversion to mass production, it does have the downside that it prevents any use of earth sheltering. A few of the houses are intended to be hooked up to ground-source heat pumps once they reach their permanent locations.

System summary

Bob — Sat, 07 Oct 2006 20:21:00 +0000

At some point, I'll turn this blog around so that it reads like a proper story--not told backwards. For now, however, I'll just place this simple summary at the top and postdate it so it will stay there. (It is actually 10/7/05 as I write this.) This way newcomers, like those who come to the October 8 solar tour, can quickly access the basics of the project.

Here are the main elements of the solar-electric system in my house:

84 Unisolar SHR-17 shingles (1428 watts), 12 series strings of 7 shingles each
Outback MX60 maximum power point tracking charge controller
Outback FX2548 2500 watt, 48 volt inverter
8 Rolls-Surrette S-530 deep-cycle solar batteries (530 AH)

Here is a photo of the shingles on the roof:

Here's a photo of the power panels, inverter, and charge controller in the basement:

Links to the major equipment suppliers and other useful sources of information are on the left. Details about this project and how it was done are in the archives, also on the left.

Solar Tour October 8

Bob — Sat, 08 Oct 2005 17:00:00 +0000

The Washtenaw County solar tour will be this Saturday from 10 to 4. My house is on it. Please come!

Solar Tour

Bob — Tue, 27 Sep 2005 03:11:00 +0000

The Washtenaw County solar tour will happen on October 8, and my house will be on it! Please come!

There will be other tours around Michigan on October 1 and October 8.

Simplified battery watering

Bob — Tue, 27 Sep 2005 02:55:00 +0000

I ordered the Flowrite Profill battery watering system last week. It arrived on Saturday, and I was able to connect it up in about 20 minutes:

Special caps replace the original battery caps. Each cap has a float which cuts off the flow of water when the cell is full. The manifold distributes the water to the three cells in each battery.

The battery manifolds are connected together with rubber tubing. Each manifold has three connectors. The unused connectors are capped off.

A hand pump is connected to the manifolds with a simple connector, and the other end goes in the bottle of distilled water. When the pumping gets hard, the batteries are full.

Six weeks, six kilowatt-hours

Bob — Tue, 27 Sep 2005 02:50:00 +0000

Even last year, after substantial conservation efforts, I was still using about seven kilowatt-hours of grid power a day. Now, with the sun providing most of my electricity, I'm down to one kilowatt-hour--per week!

August 14:

(01347)

September 25, six weeks later:

(01353)

Shingle wiring

Bob — Mon, 12 Sep 2005 19:38:00 +0000

I finally got around to making a schematic of how the shingles were wired together in the attic. Here it is:

Click here for larger version.

Solar Tour

Bob — Tue, 06 Sep 2005 17:44:00 +0000

The solar tour is officially scheduled for October 8, and my house will be on it. Unfortunately, that is the day of a U of M home game (vs. Minnesota at 1 PM), which will make it more difficult for people to get around town. My house and several other sites are on the north side of town, away from most of the traffic, so please come if you can! I'll post more details when I get them.

Winverter software

Bob — Fri, 02 Sep 2005 18:44:00 +0000

I've got the Winverter software working on my computer now. When connected to the RS232 port on the Outback Mate, Winverter presents a graphical representation of what's happening with the charge controller and inverter. Here's a screen shot:

Winverter is available from RightHand Engineering for Outback and Xantrex equipment.