Monday, February 21, 2011

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

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


Sunday, February 20, 2011

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:

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


Tuesday, February 15, 2011

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...


Saturday, February 12, 2011

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. 

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.

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.

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

Gary Feb 12, 2011

Monday, February 7, 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.

/* Start Analytics ---------------- */ /* End Analytics ---------------- */