Volkswagon XL1 Concept Car

The XL1 is the latest in VW's 1-litre car strategy.  The aim for the 1-litre strategy is to develop a practical car that will use only one liter of fuel to travel 100 km  -- equivalent to 240 miles per gallon.

This amazing latest version carries two adults in side by side seating. The latest prototype can go 100 km on 0.9 liter of gas -- 260 mpg!

The car accomplishes amazing fuel efficiency through low weight, very low aerodynamic drag, and a very efficient diesel/hybrid power train. 

The low weight is accomplished in part through the use of a carbon fiber composite body.  Advanced materials are used in other areas to reduce weight, and the seating for only two people no-doubt also helps.  The empty weight of the XL1 is 1750 lbs -- and this includes the battery pack for the hybrid power train.

The low aerodynamic drag is accomplished through a combination of a very low drag coefficient and a low frontal area. The XL1 has a frontal area of 1.5 sm and a drag coefficient of 0.186.   Compare this to a VW Golf with a frontal area 2.22 sm and Cd of 0.312.  The drag force is proportional to the product of frontal area and drag coefficient, so the XL1 drag force at any given speed will be about 40% of a Golf.
Much of the frontal area reduction is achieved by reducing the height, which must make for an interesting seating position.

The car is powered by the combination of a 0.8 liter turbo charged diesel engine and a 20 KW ( 27 hp) electric motor.  The The car is a plug in hybrid, and can run on electricity alone for up to 22 miles.  The engine was derived directly from the current TDI VW engine.

All the information above is derived from the VW press release, which I suppose is fluffed up a bit, but even allowing for  some VW optimism, the car is an amazing accomplishment.  It shows the synergistic effect that applying a whole range of technologies to a new design can bring.  Just think of the impact that widespread use of this kind of design could have.

More information:
A fairly detailed desctription of the the XL1 design...

An overview on AutoBlogGreen...

Some nice pictures on AutoBlog...


Gary

Ken's DIY Solar Air Heating Collector -- Aluminum Soffit Absorber

Ken sent in the details for his solar air heating collector.  The collector uses an efficient flow through absorber that is made from vented aluminum soffit material.

Flow through absorber designs like Ken's are very effective at picking up the heat from the absorber, and give high collector efficiencies.

 

This is how the collector works -- cool room air enters at the bottom, flows up and toward the back through the vented soffit absorber, and then out the outlet at the top.  The air flowing through the soffit material efficiently picks up heat from the solar heated soffit material.

This picture of the collector on its side before the glazing is installed shows the vented aluminum soffit material that acts as the absorber.  The air flows through the small vent holes in the soffit material, picking up heat at it goes through.

The picture above shows the collectors metal frame made from stud track material.

See all the construction details on Ken's collector...



Thanks to Ken for sending this in!


Gary

Ken's Large Solar Water Heating System

This is a very nicely done solar water heating system that generally follows the $1K design, but has a lot of excess capacity that can be used for hot tub or space heating purposes.

200 sqft of collector mounted on roof -- a nice look!

 Ken was able to get a set of older, but unused collectors from Craig's list.  The six collectors provide  nearly 200 square feet of collector area, so the system has excess capacity that Ken plans to use for hot tub heating and/or space heating.

 The tank is a very nicely done EPDM rubber lined tank with a capacity of nearly 500 gallons.  The design details on the tank are very nicely done, and it should be a good source of design information if you are building a tank for your system. 

The EPDM lined, non-pressurized nearly 500 gallon tank.

The PEX coil heat exchanger has been recoiled for improved heat transfer.

The 300 ft coil of  PEX heat exchanger recoiled for better efficiency.

All the details on Ken's system...

Thank you Ken for sending this in!


Gary

Sand Bed Heat Storage for Solar Home Heating Systems

Heat storage for solar home space heating systems is normally done with a large water tank.  The water in the tank is heated by the solar collectors, and the heat is then drawn out from the tank when needed to heat the house.

Schematic of a sand bed heat storage system.

 Another alternative that is gaining some followers is to store the heat in a sand bed located directly under the house.  Most commonly the sand bed extends under a large part of the house and is typically a couple feet thick.  The bottom and edges of the sand bed are insulated from the surrounding dirt using rigid foam board insulation.  The house floor slab is often poured directly over the top of the sand.  PEX pipes are run through the sand and water heated by solar collectors is circulated through the coils in the sand bed to heat the sand.
Pretty simple.

The potential advantages of this approach are that its very simple in that there is really no heat distribution system required -- the sand bed directly heats the floor slab.  It also allows quite a bit of storage at a relatively low price.  It allows enough storage that for a very well insulated home, its possible to store up a bit of the winter heat needs in the sand bed in the fall. 

One unique feature of the sand bed storage scheme is that the living space is directly coupled to the heat storage.  This makes the system simple and basically eliminates the need for a heat distribution system, but it also means that there is less control of heat transfer from the heat storage to the living space.

There is not a lot out there on sand bed storage, but I've collected what I could find on this page....

The recent article in Solar Today on sand bed storage got me to thinking and running a few numeric checks, and I have to say I'm a bit skeptical of some of the claims made for sand bed storage in the article.  I've included these thoughts at the link above, and would appreciate your thoughts on them.  If you have experience with a sand bed storage home, I'd love to hear about it.


Gary

Two Combined PV and Solar Heating Systems

Solar electric systems operate at about 15% efficiency -- the remaining 85% is mostly turned into heat, which is wasted on nearly all current PV systems.  The heat is not only wasted, but it causes the PV panels to run hotter, which lowers their efficiency.

There have been a number of attempts to try to harvest the waste heat that PV arrays produce for space or water heating -- here are a couple fairly recent additions.

PVT Solar's Echo System
This system is a combined PV and solar thermal system.  Conventional PV panels are spaced a few inches  above the roof plane leaving a space between the roof and the bottom of the PV panels.  The top and sides of the PV array are closed off so that the only opening for airflow is along the bottom of the PV array.  Fresh air is drawn in under the PV panels along the open bottom edge, and is heated as it progresses up between the hot PV panels and the roof.  Vents through the roof at the top of the array take the heated air into the house and use the heated air to heat domestic water and/or for space heating. 

Heat from the cavity formed under the sealed PV panels is collected and used for space and water heating.

From a thermal point of view, the system is basically an unglazed collector that takes in ambient air and heats it all the way up to temperatures good for space heating (most solar heating systems get a head start by heating room temp air up).  I would think that this system might work well in some climates, but the combination of unglazed collectors and heating all the way from ambient would seem to limit its use in cold climates?  The SRCC report (link below) would seem to confirm this if it is for the same system -- the efficiency curve intercept is 0.24.

The PVT Solar concept  is a very simple, and could certainly be implemented on a DIY basis.   While the thermal performance is likely to be well under a good dedicated thermal collectors, the extra "free" thermal energy would likely be more than the electrical energy the PV array generates.

I would love to hear from anyone who has one of these systems, or know more about them.

More details and links on the PVTSolar system...

Solar Wall PV/T
This is a variation on SolarWall's well know transpired solar air heating collector system.  In this version, PV panels are spaced over Solar Wall's transpired solar thermal collector absorbers.  The SolarWall collectors draw in the heated air behind the PV panels.

The PV panels sit over the standard Solar Wall transpired air heating collectors

It would be interesting to know how the thermal efficiency of this PV version of the Solar Wall compares to a regular Solar Wall.  I would think the addition of the PV panels may reduce the thermal efficiency of the SolarWall because PV panels would not be as efficient an absorber as the SolarWall absorber they are shading?

I did not see any detailed performance numbers on their site.

More details and links on the Solar Wall PV/T product ...

It will be interesting to see whether these products do well.

Gary

Super Insulated Stock Tank

This is a really nice and simple design from Scott for a well insulated stock tank for horses or other livestock.

It is basically a tank within a tank with the space between filled with insulation.

This shows the two tanks Scott used.  The inner tank is a commercially available heated bucket, so with Scott's design there is no need to have a drop in the tank type heater -- the heater is built into the bucket.

Adding insulation between the two tanks -- see the full story for how best to do this.

And, this is the finished tank.

Scott uses a KillAWatt meter to measure tank heater electricity consumption, and has seen a 61% in heater energy consumption.  A drop from about 6.3 KWH per day down to 2.5 KWH per day!

All the details on building Scott's insulated stock tank...

Details on several other DIY solar and insulated stock tank projects...


Thanks very much to Scott for sending this in!

Gary

Effect of Partial Snow Cover on PV Panel Output

This is a quick test to see how much a thin layer of snow covering a part of a PV panel effects the output.

In other words, should you bother to clean off the PV panels when they are only partly covered by a light snow?

We had a snowstorm yesterday that covered all the panels with about an inch of snow.  By mid morning today, the tops had cleared off, but the bottoms still had the inch of snow.

I was curious how much this affected the output, so I cleared off 5 of the panels and left the other 5 with the snow on them.  Like this:

Half of panels cleared, half with partial snow cover.

  The effect of power output is shown below:

The effect is pretty dramatic, the panels that were cleared of snow are producing nearly ten times as much power as the uncleared panels.

So, I guess the moral is -- get out there and clean off those panels!

All the details on this test here...

All the details on the PV system here...

Gary


Note - the reason that the panel report above does not show the 5 cleared panels on the left and the 5 snow covered panels on the right is that apparently the panel map I turned into Enphase had some panels in the wrong position -- have to send them a new map.

Effect of Partial Snow Cover on PV Panel Output

This is a quick test to see how much a thin layer of snow covering a part of a PV panel effects the output.

In other words, should you bother to get out there and clean off the PV panels when they are only partly covered by a light snow?

We had a snowstorm yesterday that covered all the panels with about an inch of snow.  By mid morning today, the tops had cleared off, but the bottoms still had the inch of snow.

I was curious how much this affected the output, so I cleared off 5 of the panels and left the other 5 with the snow on them.  Like this:

Half of panels cleared, half with partial snow cover.

  The effect of power output is shown below:

The effect is pretty dramatic, the panels that were cleared of snow are producing nearly ten times as much power as the uncleared panels. 

While its certainly true that only a small amount of shading can cut a PV panels output considerably, I was a bit surprised by this in that snow lets a lot of light through.

So, I guess the moral is -- get out there and clean off those panels!

All the details on this test here...

All the details on the PV system here...

Gary


Note - the reason that the panel report above does not show the 5 cleared panels on the left and the 5 snow covered panels on the right is that apparently the panel map I turned into Enphase had some panels in the wrong position -- have to send them a new map.

Tom's New/Old Wind Turbine AND Other Solar Projects!

For those who have been following Tom Sullivan's wind turbine project, Tom has made a major change.

He has replaced his Breezy wind turbine with this beautiful, restored 1930's Jacobs wind turbine.  Tom replaced the Breezy because it was not proving to be a good match for the wind speeds at his site.  The Jacobs starts up at much lower speeds, and is doing quite well. 
 
For Tom's more detailed explanation on the replacement...

For more details on the Jacobs conversion on Tom's site...  (very interesting)


If you have not seen the story on Tom's self built 140 ft tilt up tower and the original turbine installation, its an amazing DIY project...



Tom got involved in renewable energy projects several years ago when he built a large solar air heating collector for his hanger.   He has since done several very well designed and built solar projects for heating his home, domestic hot water, and hot tub.   He wrote up several of these projects for Build-It-Solar, and there is much to learn from them

Tom's projects on Build-It-Solar...

He got so involved in solar projects that he has started a business to make aluminum heat absorber  fins for solar water heating collectors.  Tom's fins are very well made and efficient, and they save the labor of making your own fins for collectors.   Tom has a new website that provides details on a number of solar projects that he and his customers/friends have done as well as ordering info on the fins.

This just goes to show how solar can suck you in!

Tom's website ...


Gary  November 23, 2010

The Dual-Flush Toilet Project Update

A while back, we replaced all of our toilets with dual-flush units in order to save some water.


We used WaterRidge dual-flush toilets purchased from our local Costco.  At the time, dual-flush toilets commanded some very high prices, and finding them at Costco for less than $200 seemed like quite find.

Our fist WaterRidge dual-flush toilet.

They have steadily been coming down in price, and the last time I was in Costco, they were selling the same model for $60 -- Amazing!  So, if you have been holding off, now is the time.

Anyway, we have replaced all the toilets in the house with the new dual flush WaterRidge units, and the oldest one has been in service for about 3 years.  No problems of any kind with any of them.

All the details on the install, and our experiences to date on the dual flush toilets...

Gary