More Spark Plugs

Well, if you have been following the saga of the shorting spark plug here and here you'll remember that the high performance spark plugs I got from Enerplus (called Pulstar) shorted and burned out my ignition coil, but the company reimbursed me for the plugs and the coil replacement. My mechanic put stock plugs back into the 2002 Prius, and since then I've been sadly watching as the gas mileage deteriorated by 0.1 mpg per month. And pushing on the steering wheel and saying "come on, come on..." as the car struggled onto the freeway in the morning.

Anyway, I finally broke down a couple weeks ago and bought another set of Pulstar plugs. Enerplus has been working on improving them, and version 2.0 supposedly has a longer lifetime as well as a fix for the occasional high resistance problem that plagued the original plugs I had. Plus they are less expensive.

I recently had the car in for a 75,000 mile checkup and asked my mechanic to put them in again. He looked at me a bit funny and asked if I was sure, but when I told him that the company had made good on their guarantee, he was relieved. I've reset the mileage, hopefully it will get back up to 46 mpg it was before the resistance started creeping up last summer.

System Remodel Coming

My wife and I are in the process of planning a system remodel, or deep energy retrofit, on the house. The idea sprang out of a problem we are having with the cathedral ceiling in the hall that runs the length of the house. The ceiling is cracking along the ridge and on one seam near the north side. According to a structural engineer we had look at the problem, the cracking is happening because the ceiling is spreading. When we moved into the house in 2003, we had the rotting, termite-ridden shake roof removed and replaced with a nice 40 year composite roof. The plywood decking increased the weight of the roof, and since our house was built in the 1970's before they really had the technology of cathedral ceilings down, there is no steel in the ceiling supports. So the weight causes the wood to compress and spread. We had a couple contractors come in last summer and give us bids, and included in the bids was the cost of taking the dry wall off the rest of the ceilings in the house and reinsulating with closed cell foam - a messy job at best - to increase the heat retention in winter. The bids came in around $100K, a lot of money just for some drywall work and insulation.

We decided to think about what more we could do that would move our house closer to our goal of net zero energy. The experience with getting bids on the ceiling showed us that we were about at the limit of what we could do by attacking the problem piecemeal. Most contractors are clueless about how to do good insulation. When we had the kitchen ceiling redone a couple years ago to get rid of leaky can lights, I had to walk the contractor through what he needed to do to get a tight seal, though he is otherwise quite competent and is the most accurate in doing bids that I have found. We decided to work with an architectural firm that has lots of experience with green architecture, Vox Design in downtown Mountain View. Vox is run by Randy Potter and Forrest Linebarger. I know Randy from my time on the Mountain View Sustainability Task Force,  we ended up working with Forrest because he had the most time. We've had four meetings with Forrest since Christmas and are getting close to finalizing the design.

The first order of business before Christmas was to get an "as-built" CAD model of the house, since we had no plans. One Saturday, a guy came over and measured the whole house, checked out all the various kinds of surface (hardwood floor, etc.). Our house has a lot of odd corners here and there, many of the walls don't exactly line up as you might expect, so he had some difficulty getting an accurate plan. This is somewhat of an architectural feature, not a function of sagging over time or anything like that. The house is in a style called "Sea Ranch" after a development along the Mendocino Coast that was built in the 1970's and influenced a lot of the tract architecture in this part of the Peninsula, like the Eichlers did in the 1950's. There are many apartment buildings and townhouses that were built in this style in Mountain View, we owned such a townhouse prior to buying this house, and liked the style so much that we decided to buy another one.

After the "as-built" plans were done, we worked with Forrest to scope the project and define exactly what we wanted. Needless to say, as the planning developed, various odds and ends fell out and a couple of items came in. We have three Hunter ceiling fans that we decided to remove. Ceiling fans are about the worst form of cooling around. They generate more heat than they remove. If you stand right under them, they do generate some cooling but for that they heat up the air around the motor. We never  use them. The ceiling fan electrical connections in the ceiling then are freed up. In the living room and Buddha room, we'll put in light fixtures, since these rooms are dark. In the hall, we'll put in shades that are electrically driven and cover the ridge skylights at night. These skylights radiate lots of heat out of the building on cold winter nights, because they are at the highest point in the house which is where all the warm air collects. And we will  put a skylight in the living room with an electric shade to increase the natural light.

These are actually minor points, though, the major point is that we plan to take off the dry wall and reinsulate the entire upstairs including all the ceilings, and about 80% of the downstairs outer walls, and fix the spreading problem by putting steel in the hall ceiling. The only exceptions are the master bedroom and bath, where we will live during the work, and the kitchen, which we had reinsulated a couple years ago. This will be a messy job, requiring scaffolding through the entire house. All the furniture must come out, and we must essentially move out into the back bedroom. Because the house will be much tighter, we need to install a Heat Recovery Ventilation  (HRV) system. This takes outside air, runs it through a heat exchanger in which the inside air either heats or cools the incoming air depending on the season, and vents the fresh outside air into the building and the stale inside air out. The ventilation ensures that the inside air is always fresh and the heat recovery function ensures that heating or cooling energy isn't wasted.

Other work includes plans to add a geothermal heat pump which will require drilling two wells in the front yard. Geothermal heat pumps are the most efficient HVAC systems around, and will give us some air conditioning in case we get more hot, muggy weeks as the climate changes, like the one we had last August. We will replace our wood pellet stove in the living room with a gas-fired fire place, 88% efficient. I really wanted a new wood pellet stove that was more automated, but Santa Clara County  no longer allows wood burning appliances to be installed due to problems with severe air pollution in winter during inversions. This fireplace will work when the electricity is out (but not of course the gas) and though it will not get us to full net zero energy, we  will buy carbon offsets for it. Yes, I know,  they are like indulgences during the Middle Ages but we still have a gas cooking stove which we don't plan to replace because cooking with gas is much nicer than with electricity. Maybe some day they'll have biogas or someone will come out with a wood stove that doesn't let off any air pollution.

We will also replace our gas backup tank water heater with an on-demand electric water heater to supplement the solar. We decided on an electric backup because we can install solar PV to offset the electricity. We decided on an on-demand heater rather than use the second heat exchanger in the solar tank or an electric coil because any heater that was connected to the solar tank would not take full advantage of solar energy. If you set the tank temperature to 120F, then the electricity will always come on to keep the temperature at that point, even if it is in the middle of the night. With an on-demand heater, the solar collector has an opportunity to add energy during the day, and the on-demand heater only comes on to top off the temperature to 120F when there is demand. So it should use much less electricity, though it will probably be more expensive initially. And it will require that we install a 200 amp electric service from the grid, but we were planning on doing that anyway, since we wanted the extra capacity for the geothermal and maybe another electric car - someday, when our budget recovers from this project.

Finally, we plan on adding more solar PV so that we can offset the geothermal heat pump, the electric hot water heater, and also generate some solar to offset the gas (in addition to the offsets bought from PG&E). Right now, we're looking at a 4 kw system total, but it may go up since there is now no downside to installing as much solar capacity as your pocktbook and roof resource allows. Starting next year, PG&E will pay you back for any extra power you generate above what you use (YAAH!). Over the last 6 years, we've consistently given PG&E something like $70-180 a year back because we've generated more power than we've used, primarily because we've done a lot to reduce our consumption (our solar PV system is actually not very large). This year we gave back much less because of the plug-in hybrid car and the new solar thermal hot water system, which uses a pump.

We're now at the point where we have a preliminary budget (around $200K - expensive!) and are beginning to work on plans to move the furniture out. Forrest is going to start the design of the geothermal system, and we still need to make a few additional decisions. It's going to be pretty disruptive but when we're done, the house will be a lot tighter, more like modern houses, and we should have around 90% of the carbon footprint eliminated (100% if you include offsets).  Stay tuned!

The Electric Car Resurrection I: Some Background

If 2003 was the year when GM killed the electric car, then 2010 is shaping up to be the year when it is resurrected. Nissan is currently firming up plans to sell the Leaf by year's end. GM is on track to release the Volt (not an all electric but close). Tesla has had their Roadster out for a couple years now, and recently I actually spotted one on 237 while driving to work in the morning. Then there are the smaller players, like the Fisker Karma, a plug-in hybrid like the Volt but more expensive, and the Chinese manufacturer BYD that is backed by Warren Buffet. Is the electric car now about to go mainstream and solve our problems with Mideast oil, carbon generation, and pollution?

After seeing the documentary film "Who Killed the Electric Car?" in 2006, I decided to look into what it would take to get an electric car. At that time,  there were exactly zero commercially available electric cars, not even at the $109,000 price of the Tesla. So the only alternative was to convert an existing ICE powered vehicle to electric. I spent about two years researching what that would take.

My first stop was Electroautomotive, a company in nearby Felton that has been doing conversions and offering conversion kits since the energy crisis of the '70's. I attended a one day workshop on conversions held by Electroautomotive in Silicon Valley. I found out that the technology for hobbist conversions basically had also changed little since the 1970's. They were recommending a 80 volt DC system with flooded lead acid batteries. My 2002 Prius has a 274 volt NiMH battery pack and AC traction system. The range for one of their conversions varied depending on the weight of the coverted vehicle. For maximum range, they were recommeding using a 10 year old Geo Metro, since the weight is under 1500 lbs, or a light weight pickup truck, also preferably 10 years old, and then filling the back with batteries. Cost would probably have run around $8K-$12K depending on batteries and components, and, of course, I would have had to do the conversion work myself, no small problem since I am by and large hopeless with tools more complicated than a screwdriver.

The problem with converting a 10 year old car to electric is ... you end up with a 10 year old car (dents, cracked plastic from aging, no airbags or antilock breaks, stained upholstery) that goes maybe 100 miles if you are lucky. I looked into converting a new car, but there were only three cars on the market that were at or under 1500 lbs - the Toyota Yaris, the Honda Fit, and the Chevy Aveo. These are tiny cars with very little room for batteries. Given the minimum amount of room, the range would probably have been less than 100 miles.

Then there are the batteries. Lead acid batteries only last around 3 years when used as traction batteries in electric cars. Even though they are cheap (maybe around $800 for a full set) and they are up to 99% recycled, they are still heavy and having to swap out the batteries every 3 years is a major inconvenience. Flooded batteries were recommended for automotive traction applications because they have the best power output, but they are notoriously fickle and require checking periodically to be sure the plates aren't drying out. Sealed batteries require less maintenance but they don't provide enough range.

While I might have been able to live with having an expensive 10 year old car, the range was the show stopper. I wanted at least 120 miles so I could comfortably drive up to San Francisco and back without recharging (not of course that I do such a drive often, but I at least wanted to be able to do it in principle). So the next thing I looked into was lithium batteries. In principle, I would have been able to get the range I wanted, but the cost would have been prohibitive, around $20,000 just for the batteries. At the time, there was only one company that was selling prismatic lithium ion batteries appropriately large enough for such applications, Thunder Sky in China. Lithium ion batteries require a different kind of charging system and are much more sensitive to overcharging and extreme draw down than lead acid batteries.

I then turned to the local Electric Autombile Association and attended one of their meetings to find out whether anyone had experience with lithium batteries. The meeting was interesting, the featured speaker described an electric motorcycle for racing in which he attempted to clinch the world land speed record for 2 wheeled vehicles (I think he succeeded in the interim). His strategy was to essentially draw down the lithium batteries so fast that they were essentially ruined after one run, then to swap them out for the next. Not a strategy that would work for my vehicle, however.

After asking around, I got some warnings about Thunder Sky batteries, that the quality was variable. Someone said they had bought a bunch and some had turned out to run down after only a few charge/discharge cycles. Left unsaid, however, was whether the battery chemistry was safe for vehicular applications. I don't know what chemistry Thunder Sky used, but the battery chemistry used for laptop and cell phone batteries is completely inappropriate for vehicular applications without lots of additional engineering. Tesla, for example, spent years designing an explosion control cabinet to contain any of the thousands of laptop battery cells they use in the Roadster from igniting the others should a cell catch on fire. If Thunder Sky used the same chemistry as used in laptop batteries, an electric car with those batteries would have been a dangerous hazard should an accident occur.

I also finally got real about my ability to do the conversion work. Realistically, even if I got a membership at Tech Shop, there was no way I would have the time nor the motiviation to pursue the project to completion. I asked around at the Electric Automobile Association whether anybody knew of a place that would do a conversion. There was a guy there who said he would do one, we took up an email correspondence but it turned up he was really interested in selling electric scooters and the correspondence was just talk. I searched the Internet a bit. The Internet search turned up one guy in LA who had been doing conversions, but he had since stopped. There were some conversions for sale in San Francisco, a Toyota Yaris if I recall correctly, but the range was under 100 miles.

In the spring of 2008, I was just about to give up in despair when A123 Systems announced their L5 modules for turning a 2004-2008 Prius into a plug-in hybrid. And that is the subject for another post.

Recalculating Solar Hot Water Performance

My previous post on the carbon reduction cost performance of my solar hot water system was unduly pessimistic. I now have the December gas bill and it looks as if the reduction is about 10% for a half year of use, or an estimated 20% for a full year, which is what I had originally figured it would be. That considerably improves the carbon reduction cost performance. Here's what the new chart looks like:

As you can see, the per kg. carbon reduction cost for my high end system is really around $27 per kg rather than $67 as in the last post. For the low end thermosyphon system, the performance is even better, around $9 per kg.

Furthermore, the state of California recently announced a subsidy of up to $1500 for solar hot water systems, on top of the 30% federal tax rebate. The last two bars show the per kg carbon reduction cost for the low end thermosyphon system and my high end system taking into account the subsidy. The subsidy still doesn't make a solar hot water system competitive with a gas fired tank hot water heater, but it helps. Figuring that at gas fired tank system costs maybe $1500 installed, it would still take around 15 years of gas savings, assuming the price of gas stays constant, to make up for the difference between the $3300 subsidized, after tax rebate cost of the low end thermosyphon system. The high end system would take longer.

Of course, if you have an electric hot water heater, the savings could be considerably better, since electricity costs more per joule of energy delivered to the water.

Update on Spark Plugs

You'll recall in this post, I described how the high performance Pulsestar spark plugs from Enerpulse blew out the ignition coil on my 2002 Prius. I sent in the coil and the plugs to Enerpulse and requested they make good on their guarantee that their plugs would not harm your engine by reimbursing me for the cost of the plugs and the repair. To my surprise, I received a very nice letter from Enerpulse apologizing for the damage and a check reimbursing me for the cost of the repairs and the plugs.

It seems that some instances of their older plugs occasionally had a problem with resistance growing over time, and if the resistance becomes high enough, it causes the plug to wear down fast and eventually misfire, which can then cause damage to the coil. This explains the rapid deterioration in mileage and performance I was seeing over the summer, followed by the catastrophic failure.

They also offered a 10% discount on their new G3 version of the Pulstar plugs. These have improved lifetime and better performance. I am tempted, since the torque and pickup on the 2002 Prius is terrible, but after one bad experience with the product I am not sure whether it makes sense to try it again. I still have a set of their original plugs in my 2008 Prius, so far, they seem to be performing fine.

Solar Hot Water Part VII: Retrospective

This post is about  "lessons learned" in the process of building our solar hot water system, discussing problems and some speculations about what might help to solve them.

As mentioned in the last post, a minor problem with using the system is that the gas-fired tank tends to cool off when the gas is turned off in the summer. In the long run, we plan to get rid of the gas-fired tank backup and put in a modulating on-demand electric hot water heater. My original plan was to couple the second heat exchanger in the tank with a geothermal heat pump or high efficiency gas boiler, but neither of these options is ideal. Geothermal heat pumps won't put out more than 140F and you need the heat transfer fluid substantially hotter to get good heating when the water flow is heavy, like when you are doing laundry and taking a shower at the same time. A gas boiler wouldn't allow the tank to derive optimal heating from the sun. If the thermostat is set at 120F (recommended for domestic hot water), then the gas boiler will come on when the water drops below that temperature and the solar collector won't come on. Same is true for solar tanks with a backup electric heater coil inside the tank. The solar tank can't preheat the water. An on-demand electric hot water heater should allow the solar tank to heat up as hot as the sun can get it, and just add enough energy to bring the domestic hot water up to 120F in the winter. In addition, we can add some solar PV to our roof to offset the electricity used to  run the on-demand heater. That should make our domestic hot water supply completely carbon neutral.

Aside from the aformentioned problem with an installer that did not know what he was doing, the primary problem with the system, though, is price. It is simply very expensive for the amount of carbon reduction achieved. Below is a graph comparing the cost per kilogram of eliminated carbon to two other alternatives: the same system but with a glass-lined tank instead of a stainless steel tank, and a cheaper thermosyphon system which a friend who lives in the same town had installed:

I used the estimated figure on gas eliminated from the Performance blog and included the federal tax rebate of 30% off installed system cost. I did not include the cost of the closet modifications for the thermosyphon system, because the storage tank is integrated into the collector so no change would have been needed in the closet. Note that the estimate here on cost per kilo carbon removed for our solar hot water system is too low, it does not include the winter when the solar thermal collector is contributing little.

Our system has a cost per kilo approximately that of the new refrigerator and I think it is for the same reason. I exchanged email with a friend who was surprised by the high price per kilo carbon reduction achieved for the refrigerator (which you can also see here). Normally replacing a fridge that is 10 or more years old by a new one is a fairly cost effective. I'm not sure how old the fridge was since it was there when we moved into the house, but on reflection, I think I know what the problem was. The new fridge was exactly the same model as the old, except updated with energy saving features. In our kitchen, the fridge is built-in, so we either had to get the same model or spend money on getting the space modified to take a different model. But the original fridge and now the new one are both high end models, and therefore very expensive.  It is a Lexus fridge, even though, we would have been happy with something a little less high end. Similarly, the solar hot water system is a high end system, and the cost reflects it.

That explains why the carbon reduction cost for our system is about three times as much as for the thermosyphon system, but it doesn't explain why even the thermosyphon system is expensive, at almost $20 per kilo carbon removed. At that price, even with the subsidy, it is not an affordable option for most homeowners. A high end gas-fired tank costs around $700 new, and a low end gas on-demand hot water heater costs about the same. An on-demand gas hot water heater can also result in substantial carbon reduction, though it won't be possible to completely eliminate carbon of course (it would for an electric on-demand heater though, by offsetting with solar PV). The thermosyphon system is around 10x the cost for an on-demand gas system, and our indirect solar system is more than 20x. Prior the WWII, many houses in California had solar hot water systems, and today, there are cities in China where solar provides hot water for over 90% of the homes. Why is solar hot water so expensive, the energy from the sun is free, it should be cheaper in the long run for a solar hot water system?

Well,  one problem is that natural gas (or, as I prefer to call it fossil gas) is just too cheap and likely to stay that way. Fossil gas releases only half the amount of carbon per therm of energy generated from coal, and something like a third less than oil so in some quarters it rates as a "clean" fuel. In addition, recent discoveries of gas deposits in shale across wide swaths of the Northeast and Mid Atlantic states promise that fossil gas will stay cheap for some time to come. On the one hand, that's good news because if fossil gas becomes cheaper than coal, switching electricity generation to fossil gas from  coal in states like Illinois where most of the electricity is generated by coal could result in substantial greenhouse gas reductions. On the other hand, unlike solar and wind, fossil gas is still putting fossil carbon  into the atmosphere. So to the extent that cheap fossil gas prolongs our dependence on energy technologies that dump fossil carbon into the atmosphere, it is doing us a disservice.

The other problem is that the technology itself is actually quite expensive and difficult to integrate into an existing building. It requires extensive plumbing on your roof and a backup system. Integrating with the most common type of backup system requires fussy yearly action to turn the pilot off and on, and results in suboptimal performance when the gas is off in the summer. Adding a backup system that works better costs more money. Compare this with grid tie solar PV, the kind most homeowners get these days, where the backup comes from the grid and so there is really no periodic maintenance needed or any kind of additional hardware. While solar PV requires structures on the roof (and, indeed, can result in roof leaks if not properly installed) and high voltage DC lines which are not trivial to get right, there is not as much dependence on the exact configuration of the existing structure except for proper solar exposure. A solar hot water system is more like the traditional off grid solar PV system, where the homeowner must install a large bank of batteries to store electricity for times when the sun isn't shining. Non-grid tie systems usually cost double or more what grid tie systems do, and the batteries also require monitoring and occasional replacement.

Since technology is what Silicon Valley is all about, you would think a budding entrepreneur would be studying this problem for the next great startup, but, as far as I can tell, there are no startups looking at how to reduce the cost on solar hot water. The economics seem pretty simple to me: get the cost down around where the payback time (sorry, unfortunately that's what most people look at) is around 3-5 years. Say, maybe the installed cost is 2x an on-demand gas heater, and you don't need a half inch gas main installed for it. Anybody up for the challenge?

Solar Hot Water Part VI: Performance

Last summer after the system came up, I turned off the gas hot water heater. The gas hot water heater has a pilot and pilots are just about the most energy wasting thing around. I was seeing temperatures on the solar tank of around 150F-160F in July, and it never rains in summer in California (like the old song says) so I figured we were good without the backup.


The results were mixed. Most of the time, we had plenty of hot water with the temperature being fine. With the shower on the top setting, it was not as hot as with the gas heater on (when you really need to turn the setting down to make it tolerable), but it was adequate for a nice hot shower after a long bike ride. Sometimes, though, the water was just lukewarm. This seemed to happen most often when we didn't use hot water for a number of days (like we showered at the gym) or when we went away for vacation. A couple times we had cloudy weather and the tank temperature dropped to 130F, which is I would have expected, but it didn't affect the domestic hot water temperature unless we didn't use much hot water.

The problem is that the gas-fired tank cools down if the hot water is not used for a couple days. Since there is a lot of water in the gas-fired tank, it takes a while for the hot water in the solar tank to draw through, even though the solar water is really hot. By and large, this wasn't much of a problem; it being summer, an occasional lukewarm shower wasn't an issue. I kept the gas-fired tank off until the end of October then relit it. At that point, the temperature in the solar tank was getting down below 130F.

Below you can see a comparison of our gas usage for July through November in 2008 and 2009:

As you can see, the usage was reduced from July through October, but it shot up in November. That's because we had a cold snap in the beginning of December (the November bill includes a couple weeks into December) this year, and November was generally much colder than last year. One of the difficulties of using year over year comparisons of energy usage is this kind of variability due to changes in the weather, etc. In fact, the increase in November completely overwhelmed the savings for July through October. July through November 2008 was 98 therms while the same period this year was 97 therms, just one therm less, or around 1%. If you look at the period from July through October, not counting the time when space heating was generating most of our gas demand, the reduction in gas usage is around 71%.

From last summer's data, I now know we use about 1 therm a month for cooking. In 2004, I discovered that our forced air furnace had a pilot light (yeech!) and I started turning it off in summer. I can therefore use the summer gas use from 2004 through 2009 prior to installation of the solar hot water system to estimate how much  gas we used for hot water heating. That gas will be completely eliminated in the summer 6 months (essentially April through September) with solar hot water. For the other 6 months, estimating usage is more difficult, because the solar acts as a preheater for the gas heater. So the amount of gas eliminated won't be the same as for the summer; on the other hand, it also won't be zero. To be conservative, we can say that it is, in fact, zero; that is, that the gas tank is responsible for all the hot water heating.

The average gas use in the summer months just for hot water heating is 6.32 therms per month. The average annual monthly use for 2004-2008 is 36.5 therms per month. Figuring 6 months of 6.32 therms reduction  and 6 months of 0 therm reduction, the percent savings comes out to 8.65%. So, say, around 10% reduction since we were on the conservative side about the winter use (yes, I know this is a fudge factor but it is the best I can do with the data I have). Anyway, I think I will need some more data for at least another year before I can really say what the reduction is like. There are also some ways to collect data that require measuring the hot water heater output, which I may decide to collect in the end.

The other interesting issue is the effect of the various insulation treatments I've tried. Below is a graph showing the temperature in the morning and evening in July before I installed the radiant barrier insulation:

I didn't use any sophisticated monitoring device for recording these temperatures, I just wrote them down on paper. That's why there are so many holes in the recording, some days I forgot, others we were on vacation. In general the temperature is running around 160F

Below is a chart of the morning and evening temperatures with the tank completely covered in radiant barrier insulation:

The gap between morning and evening is slightly smaller, and the average temperature of the tank drops over the month. The dates here are getting into fall, when the days are shorter and there is less sun on the collector.

Below is a graph of the morning and evening temperatures after putting on the R-13 fiberglass batt blanket:

The temperatures now are a lot lower because the time period is into December when the sun is at the lowest point, but the gap between the morning and evening temperature has narrowed considerably.

Insulation was highly effective in reducing heat loss from the tank. The temperature drop in degrees F per hour was 0.68 for no insulation - noticeably *above* what Superstor advertises. For radiant barrier only, the drop was 0.54, average of two sets of measurements, one shown above and one taken just before the batt was installed in December. For radiant barrier plus batt, the drop was 0.23. The temperature outside  the tank had little impact, the measurements in September and December for the radiant barrier insulation were close (0.57 in September and 0.52 in December). This might possibly be due to the fact that the tank closet itself has 6" of closed cell foam on the top and around 3-6" on the walls, keeping the tank enclosure toasty.

In fact, the insulation was so effective in cutting heat loss from the tank that I am now a bit worried it might overheat in the summer and cook the glycol. We shall see. I've signed up for a maintenance contract to have them come and check the glycol once a year to make sure it isn't acidic, at least for a couple years until I feel comfortable with the system. And, as a practical matter, the Schueco system is specifically designed to purge if the collector reaches stagnation temperature, to avoid cooking the glycol. So I think the system should be OK, and the extra insulation will sure help in the winter. Why can't Superstor put that extra insulation on the tank in the first place? It can't really be a question of cost. And I wonder, since it has about cut the heat loss in half, whether it would have allowed me to get by with one instead of two Schueco panels? Something for a pleasant evening of calculation in the near future.