Hands On Solar

I've been busy tinkering with almost all aspects of my solar thermal system for the last couple of months but have been very poor with my documentation.  A lot has happened and hopefully I'm on the road to having a smooth running system. 

As I had documented already, I was having some problems with the WEL.  The problems seemed mainly with the sensors, both the roof collector sensor and the in-tank sensors.  I eventually concluded that it was a due to the lack of waterproofedness of the sensors.  The longest-lasting solution tried to date was using some of the 2-part plumber's putty at the sensor/wire interface.  Once that sensor failed, I tried a succession of other ideas such as some silicone-in-a-tube and simple crimping with connectors that had electrolytic gel in them.  Neither of those solutions lasted more than a few days.  Around this time, the Taco pump failed and I started to look into the values the sensors were reporting to the pump and found that those sensors were starting to fail as well. 



Some investigation revealed that the Taco-supplied sensors appear to be sourced from Tekmar (Tekmar Universal Sensor 071).  This became apparent when I discovered that the Tekmar temperature:resistance profile reported in ther Sensor Catalog Page (page 3) was exactly the same as what Taco was reporting in their Solar Control Pump Instruction Manual (page 6).   A call to Tekmar technical support revealed that these sensors are definitely not designed for immersion duty but that they were coming out with a version of this sensor that was designed for direct burial in July.  Supposedly this sensor would be should work in an immersion enivronment, but the representative wouldn't go so far as to state that it was designed for that application.  This sensor has a retail price of $42 but can be found online for about $20.  The Tekmar technical information above revealed that these sensors can appropriately be classified as "10K thermistors" which is apparently a pretty common class of sensors. 

I figured with this information, there must be some supplier of a 10K thermistor that is designed for immersion....  (to be continued)

I had a chance to actually sit down by the pumps yesterday evening as the sun was setting to witness what was actually happening with the pumps.  As the sun came and went yesterday, I had episodic problems with the no-flow situation previously described.  As always, unplugging the pump and "resetting" the system always resolved the problem.  Unforunately, I can't babysit the pumps all day along.  I need to definitively figure out what the problem is and either find a way to adjust the pump behavior or find a way of automatically resetting the system when I'm not around to reset it manually.

My observations are pretty much what I suspected.  As the pump speed decreases stepwise due to the decreasing amount of thermal energy on the roof, everything seems to be fine until what appears to be the slowest speed setting.  Once the pump steps down to that speed setting, the power of the pump is insufficient to maintain the column of water up to the collectors and drainback begins.  What follows from here is speculation but it seems most logical to me that at a certain point, drainback occurs until the equilibrium point whereby the level of water in the pipe above the pump should be at the level of the water in the tank -- let's say 18" above the pump impeller for argument's sake.  All this time, the pump is continuing to run at its slow speed thinking that is all that is required to keep the delta T at its setpoint.  At this point, however, instead of circulating fluid, I suspect that the pump is frothing up the water in the pipe and agitating it enough to get air entrained into the fluid and eventual create an airlock around the impeller.  Since fluid is no longer flowing up through the collectors, assuming there is still some thermal energy to collect on the roof, the collector temperature rises again and increases the delta T.  The pump controller then stepwise increases the pump speed to try to bring the delta T back down to its setpoint.  The lack of fluid flow ends up letting the delta T rise such that the pump controller eventually tries to run the pump at full speed.  The pump stays at full speed until the sun goes down or the delta T falls spontaneously.  By this time, however, the pump has gotten extremely hot as the circulating fluid acts as both the lubricant and the coolant for the pump.  This is the basis of my concern that something may have gotten cooked in the pump as a result of one too many overtemperature episodes.  Even if air entrainment was not an issue, I'm not sure that the pump would be able to get the fluid back up to the collectors with its stepwise increase in pump speed uintil it got to full speed anyways.

So the question becomes what are the possible remedies for this situation?  Perhaps moving the pump lower in relation to the water level in the tank will allow enough water on top of the impeller even during drainback to prevent air entrainment and an air lock.  A fancy system that I've thought of would be to read the flowmeter and collector/tank sensor readings and determine when the system was in its chaotic state and then have a trigger to cut the power to the pump for 30 seconds or so before restoring power to the pump and letting it automatically reset itself, much as I do manually when I'm around.  I will take some pictures and send to Mr. Sweet at Taco shortly.

Solar Renewable Energy Certificates (SRECs) or Solar Renewable Energy Credits are a form of Renewable Energy Certificate or Green tag. SRECs are available in states where a Renewable Portfolio Standard (RPS) exists with a specific allocation for solar energy. SREC programs provide a means for SRECs to be created on behalf of a solar panel owner and sold to state electric suppliers to meet the solar RPS requirement. Electric suppliers are required to use the SREC program to show compliance with this part of the State’s Renewable Portfolio Standard.

The SREC is separate from the value of the electricity itself and permits the owner or purchaser to claim the benefits of the clean energy production by effectively subsidizing the cost of the installed system. SRECs are designed to provide individuals and corporations with an economic incentive to investing in solar electric systems which improve the electric distribution grid. They represent the renewable attributes from a solar facility, bundled in minimum denominations of one megawatt hour (MWh) of production. The additional income received from selling the solar certificates increases the economic value of an investment. Instead of up-front subsidies from the state, solar system owners can recover their investment by selling certificates to utilities.

Lots of information abou RECs are in a wiki.  The solar RECs are discussed in another wiki.

For my purposes, SRECs are about getting some financial compensation for the green electricity I have been producing.  I've known about these certificates for a couple of years now, but have not really looked into them.  Boy have I shortchanged myself.  Turns out that you can get credit for something like 15 years worth of RECs by assigning them to a utility or a broker. The Maryland Department of Energy has put together a little handout that describes in very rough terms what is required to obtain these certificates and how to turn them into cash payments.  They also list several aggregators and wholesalers that will help you navigate the process in exchange for 35-45% of the proceeds.  One of my neighbors and father of one of my daughter's good friend at school is a principal at a renewable energy firm.  We had discussed having him sell my SRECs on a couple of occasions over the last couple of years but I have simply not been diligent enough to follow up.  Turns out his company is one of the ones listed in the Department of Energy's handout.

I ended up speaking with a couple of these aggregators and the story is pretty much the same.  They help you with all the paperwork required to certify and register your renewable energy system with the state and then get your SRECs sold.  It sounded like most of them would sell 15 years worth of SRECs for a lump sum and then give you 55-65% of the proceeds while keeping the rest for their trouble.  I also found out that each SREC currently sells for about $360 but that there is some sort of declining sliding scale over time for their value.  I also got a little bit of information about how these SRECs are actually generated and transacted -- enough to make me think that I should pursue doing this on my own and keep 100% of the proceeds....

From their website (http://mht.maryland.gov/):

The Maryland Historical Trust (Trust) is a state agency dedicated to preserving and interpreting the legacy of Maryland’s past.  Through research, conservation and education, the Trust assists the people of Maryland in understanding their historical and cultural heritage.  The Trust is an agency of the Maryland Department of Planning and serves as Maryland’s State Historic Preservation Office (SHPO) pursuant to the National Historic Preservation Act of 1966.

Apparently, a relatively new requirement for the solar grants is to have a review by the Maryland Historical Trust to get their blessing that these newfangled solar things are not put onto houses of historical importance.  Anyone that looked at my house would know right away that it holds no historical significance!

I had opened up a line of communication with Jonathan Sager at the Maryland Historical Trust to verify that my application was received and at least in-process as Mr. Cohen at the Department of Energy informed me that this was the last hurdle my application had to face before being approved.  I was a bit surprised by the defensive e-mail reply I initially received, but understood that I had to wait for him to return from out of town before getting a status update.

His reply today seemed to indicated that they had not been asked to review my address before this, but in the next sentence gave my property the Historical Trust's blessing.  I was pleasantly surprised how efficiently this was handled.

So now it is back to Mr. Cohen at the Department of Energy.