A $2K Solar Space and Water Heating System

We have been working on a very simple solar system that will do space heating and domestic water heating from the same system.  Its a very simple system that takes only regular DIY skills to build.  Nearly all the materials can be picked up at the local Home Depot type store, and the ones that can't have good online sources.

The collector for the new system

I've documented this system better than any other system on Build-It-Solar -- there are over a hundred pages of design and build information that should make it fairly easy to adapt the system to your situation.  There is also a lot of material on how stuff works and on other alternatives for each part of the system -- a bit of a text book on solar space and water heating.

Collector before painting.

We used twinwall polycarbonate glazing.

The system design is based on the $1K Solar Water Heating System that many people have built with good success.  It uses the same drain back collector system, and the same single large, vented to the atmosphere drain back tank.  It also uses the large coil of PEX heat exchanger for domestic water preheat.  The differences are that the collector is larger to provide extra capacity for space heating, the storage is larger, and there is a new system to distribute heat from the tank to a simple radiant floor loop.


The new radiant floor system just takes water from the top of the tank, pumps it through the floor loop, and returns it to the bottom of the tank -- no heat exchangers, no antifreeze -- just a little PEX tubing and a pump.

The new pump for the radiant floor loop.

We used a staple-up floor loop with insulation under.

This is the big coil of PEX that serves as the domestic water preheat heat exchanger.

The system is about as simple as you can get for a full four season, cold climate solar space and water heating system.  Simple is good (I think)  -- for airplanes or solar systems :)

It could (and should) be expanded with more collector area and more tank size to be able to do more space heating.  We would have added more collector area if we had the space for it on our south wall.  We do already have a dedicated solar space heating system, so this new one gets a part of the house not heated by the existing one.

The total cost of materials was a bit over $2000.  The system could be built for as much as $700 less, but we opted for "higher end" choices in the glazing, trim, and controller areas. 
I would estimate that the price for an equivalent commercially installed system would be north of $15,000  -- so the cost saving is significant.  Based on the 3 year payback for the $1K water heating system, I expect the payback for this system to be 3 to 4 years.


I'd very much like to hear any comments on how the writeup could be improved, or on things that are missing or not clear -- you can add a comment here or email me at gary@BuildItSolar.com

All the details on the new space + water heating system...


Gary

Plug in PV

Clarian is planning to come out with PV modules that can literally be plugged into the wall to make your own  grid-tied PV system.

The system consists of one or more 200 watt PV panels, each with a micro grid-tie inverter.  Each system also has a SmartBox for monitoring the system. 
The first 200 watt PV panel/micro inverters plugs into an regular wall plug.  Additional 200 watt panels panels plug into the first panel daisy chain style.    The SmartBox plugs into an AC outlet and (apparently) allows you monitor the system.

You can add several of the 200 watt panels -- each one is 60 by 40 inches.

They also have a 1000 watt unit with a "6 to 8 hour" installation time -- perhaps this needs a connection to the breaker panel, but I could not tell.

This looks like a very nice solution for people who want to get started a PV system without having to hire an installer -- it lets you start for less than $1000, and add to it from time to time.  The projected prices they show are competitive, and the unit is said to qualify for the federal 30% tax credit program.
They expect to have the units "in stores in 2011".


The micro inverter has all the usual safety features for not powering the grid when the grid is down to protect line workers.

The system also provides for monitoring your system from the web, again  similar to the Enphase systems.

While it seems like a very nice development, I do wonder about a few things:

• Will local utilities buy into the system -- normally, the utility would have to install a net meter to insure that you actually get credit for power you generate during times when you send power out to the grid.
• Basically the PV panel connects to the wall outlet via what amounts to an extension cord -- it seems like this might limit mounting possibilities and perhaps not look as neat as some might like (or not).
• PV panels are large and catch a lot of wind -- they need to be mounted carefully, and I could see people being a little too casual about this and losing expensive panels.
• I could also see people spending a couple thousand on this to save 60 KWH a month when the same $2000 spent on conservation and efficiency projects would save 500 KWH a month.

It will be very interesting to see how it all plays out.

The link to their website is: http://www.clarianpower.com/solar.html

Thanks to Gordon for sending in the note on this gadget!

Gary

Evaluating Ordinary Window Screen as a Solar Air Heating Collector Absorber

This is a chance to exercise your Physics brain a bit.

A few people have used a couple layers of ordinary window screen as the absorber for solar air heating collectors.  This is the same stuff you put in windows to keep the bugs out.
Scott and I have been doing some testing of air heating collectors of various types, and to the surprise of some, the collector that uses the two layers of window screen as the absorber has done as well or better (so far) as other more complex absorbers.

The way these collectors work is shown in the diagram -- air enters the collector via the bottom vent and is routed to the glazing side of the screen absorber.  The screen has a little bit of pressure drop and this tends to spread the air evenly over the screen.  As the air works its way through the screen, it is heated, and eventually makes it way out the top vent located at the top back of the collector behind the screen. 

In an alternative to this picture, it has been suggested by Laren over at the Yahoo SimplySolar group that the screen is really quite open, and that much of the sun passes right through the screen and ends up getting absorbed instead by the back wall of the collector.  In this view, the screen still helps, in that it does absorb some of the solar, but, perhaps more importantly, it keeps the heated air from migrating back to the cold glazing where heat losses would be high.

I did a little test to measure how much of the incident sunlight 1, 2 and 3 layers of fiberglass and aluminum screen absorb, and some tentative conclusions and some questions come out of this.  So, take a minute to look at the results and see if you have any ideas to contribute on making these absorbers more efficient -- or, maybe you think there is a better option altogether?

The Window Screen as a Solar Absorber Test Stuff...

Gary

New: PV pump for solar DHW, 3 day EV conversion, PV system sizer

Just a few new content items on Build-It-Solar:

TOPSFLO PV powered pump for solar water heating systems:
This is a new and very low cost pump that is intended for circulating water in solar water heating systems.  Its a DC pump and is designed to be driven directly by a small PV panel.

It has a startup head capability of about 9 ft, and a nominal flow rate of about 2 gpm -- good for 60+ sqft of collector area.  It is also good for temperatures up to 200F and has automatic shutdown for higher temperatures.  Its a brushless design and should provide a long life.  But, it is new, so I suppose there is a bit of buyer beware.
http://www.builditsolar.com/Projects/SpaceHeating/Components.htm#TOPSFLO 

Thanks to Rodney for sending in a note on this.


Gas to Electric Car Conversion in 3 Days!
This is an interesting project that took on converting a small gas powered Daihatsu Charade in a weeks time -- they actually managed to do it in 3 days!

They did quite a nice job of documenting the whole thing including a very nice video that gives a good feel for what's involved in a EV conversion.  I suppose its only fair to say that there were as many as 10 of these guys working on the car at once -- it might take one of us a bit more than 3 days.

http://www.builditsolar.com/Projects/Vehicles/vhehicles.htm#3DayEV

PV System Designer
This is a handy calculator to get several alternative actual system definitions based on your available PV panel area, climate, and power range you are interested in. 

It will pick several alternative actual systems based primarily on lowest price.  The definition includes specific PV panels and a specific inverter with prices, but does not include other details that make up the system -- so, there are still a lot of things to add to get to a full system.

http://www.builditsolar.com/Projects/PV/pv.htm#PVPowerCalculator

-------------------------
Getting close to putting up the detailed how-to on our new, simple, solar water + space heating system -- maybe Monday.


Gary Feb 12, 2011

The Peel P-50 -- A Really Small Car

The Peel P-50 is officially certified as the world's smallest car by Guiness.

Passenger capacity 1 (plus one shopping bag).
Doors 1.
Wheels 3.
Displacement 50 cc.
Empty Weight 130 lbs.
Fuel Efficiency 100 mpg.

Described in this CNET article and in the very amusing BBC video...

Judging by the video it might benefit from outriggers and some pollution controls.

Solar Water Heating Using a Unique Master and Slave Collector Design

Gordon has added solar water heating to his very very efficient home.  The system is loosely based on the our $1K solar water heating design, but incorporates some really interesting changes.

The collector uses a large "slave" collector to enclose and improve the efficiency of a smaller "master" collector.  This is design developed by Dinh Khanh some years  back and is explained in detail by William Shurcliff in this chapter of his book on solar innovations...   Basically, the larger slave air heating collector provides a warm environment for the small water heating master collector.  In Gordon's rough test, the slave collector increases the heat output of the master collector by about 50%.  This is the only application of the Khanh design that I know of, and, so far, it looks like it will do well.

The "master" water heating collector is about the top 2/3rds and the "slave" collector
extends over it and all the way to the ground.
The three small panels inside the slave are PV panels to drive the pump.

Gordon's tank and heat exchanger design are also unique.   He used a galvanized metal livestock tank lined with and EPDM liner mounted inside a well insulated wood frame.

The tank with the copper coil heat exchanger about to be installed.

The heat exchanger uses two 75 foot coils of 3/8 inch diameter copper pipe hooked up in parallel.  Using multiple small diameter coils in parallel should increase the heat transfer surface area and efficiency while still keeping the water pressure drop small.

This shows the valving that allows the heat source to be
the electric tank, solar heat, or both.

 The full story on Gordon's solar water heating system with construction details...

Details on the $1K solar water heating system...

If you have not read the story on Gordon's conversion of an old schoolhouse into a VERY low energy consumption and very attractive house, its a good one...

For the full text of the book by Dr. Shurcliff mentioned above, "New Inventions in Low-Cost Solar Heating -- 100 Daring Schemes Tried and Untried" go here...   This book is my all time favorite solar book -- it is a 1979 book and is out of print, but Dr. Shurcliff allowed me to scan it in and make it available as a free download.  The book was written during a period when many creative people were working on solar heating, and the ideas are as fresh, innovative, and interesting now as they were then.

Gary

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