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

A Report on Our PV System After One Full Year of Operation

Its been one year since we put in our PV system, so I thought I would do a little report on how its performed, and what living with the system has been like.

The system is ten 215 watt panels and uses the Enphase  micro-inverters with each panel getting its own grid-tied inverter.

Our ten panel, 2150 watt micro-inverter PV system.

In a nutsehll:

• The system has been trouble free -- no repairs or problems.
• The maintenance has been very minimal -- wash the dust off once in a while, brush off the snow, inspect the system for problems.
• Performance has been about 8% above the PVWatts estimate for the year

The system produced 3320 KWH for the year -- about 8% more than PVWatts going in estimate.

Building the mounts and installing the PV panels.

Its interesting (maybe) to note that when we moved into the house our power consumption was up at around 1000 KWH per month -- near the US average.  We pursed a bunch of conservation and efficiency measures which got our usage down to right around 500 KWH per month.  All these changes are spelled out here in our Half Program.  The cost of all the conservation measures was about $1,200 dollars. 

We then added the PV system, which generates about 275 KWH per month, and takes our net consumption down toward 200 KWH per month.  The PV system cost us about $10,000 ($6,500 after rebates).  So, for us, the conservation measures were about ten times more cost effective in saving electricity than the PV system.
The message is do the conservation stuff first -- after you've gotten your consumption down, then think about a PV system to work on the remaining usage.  This approach will save you a ton of money compared to just installing a PV system that is big enough to meet your current usage.

We are still working on conservation, and I think  we can get down to less than 100 KWH a month -- maybe even down to a net zero for the year.  A 100 KWH per month is a lot of electricity if used carefully -- as any off-grider will tell you.

More details on the first year of use experiences...
(Including how solar thermal DIY systems compare to solar PV DIY systems)

Full "how to" on planning and installing our grid-tie system...

Lots more on building your own PV system...


Gary

Would Wide Solar Collectors Work Better With Horizontal "Risers"?

DIYers will often build collectors that are quite wide (20+ ft) for solar space heating.  The usual approach is to run a manifold along the top and bottom of the collector, and then connect the two manifolds with closely spaced risers that have fins attached to capture the sun's heat  and transfer it into the water flowing through the risers.

It has been suggested by Alan Rushforth that it would save material and might also result in a more uniform water distribution to the risers if they were run horizontally instead of vertically.  You end up with a much smaller number of much longer risers (hisers?).   This reduces manifold material, and reduces the number of manifold to riser joints -- these joints are time consuming and expensive, so reducing the number of them would be a good gain.

In order to push this idea along a little further, I did a test by turning my old prototype copper tube/aluminum fin collector on its side so that the risers run horizontally and the manifolds are vertical. 

In a nutshell, the test appears to show that at least for this small collector, the startup process, flow distribution, and drain back all work without problems -- I think it looks promising. 
What do you think?

All the details on the results here...


This idea has been discussed some in the Yahoo Simply Solar group and the Yahoo Solar Heat if you want to see a bit more on it -- these are both good groups for solar heating questions (and answers :).

Gary

Performance Logging for Neil's UK Solar Water Heating System

Neil has been logging the performance of his very nicely done solar water heating system in the UK.

The collectors for Neil's system

As the plots show, the system performs well.  The plots also give a good view of how the tank thermally stratifies during during the day as the heat exchanger removes heat from the tank.

Performance for 1 day -- see link below for more

For:
- More details on performance of Neil's system...

- Construction details on Neil's system ...

- More examples of $1K style solar water heating systems...

- More on DIY solar water heating...

Gary

Yellow Energy Labels for TVs

Starting in 2011 the FTC will require the yellow Energy Guide labels on new TV sets.
These are the same labels you now find in new dish washers, fridges, ...

The new Energy Guide label for TVs

I think this is a great development and will make it much easier for people who want to buy a low energy use and low carbon emissions TV to do so.

We recently went through the TV buying experience and found it to be very hard to get good data on how much power a given TV uses.  TV power consumption varies over a huge range and its large enough to have a significant effect on household power use.  I found the Energy Star label program for TVs to be very unhelpful -- I'd go so far as to say its misleading.  In contrast to the Energy Star labels, these Energy Guide  yellow labels give actual power consumption and should be very helpful.

If you are looking for a new TV, be sure to take energy use into account -- by looking carefully you can find a TV that performs very well and that uses substantially less power.

I'd like to see these Energy Guide labels on anything that uses more than a trivial amount of electricity -- I think that it would make it much easier for people to take energy use into account when buying.
A good next step would be to put them on those 24/7 power sucking TIVO  type units.

Gary