We get asked from time to time what is the best way to install a thermocouple on a solar collector during installation. While certain manufacturers include a thermal well in their collector this both solves a problem and causes a problem. The same manufactures that supply thermal wells advocate only installing glycol based systems. The thermal well is installed in or near the top header on one side of the collector. Since the well is only on one side of the collector this can lead to extra line runs on the roof to cross from one side of the array where the solar fluid is exiting the collectors to the other side of the array where the thermal well is located. This is not ideal. Additionally, some manufacturers will install wells that are required to be immersed in the solar fluid. Not bad for a glycol based system that is always wet but on a drainback system this doesn’t work particularly well.
Several of the domestic manufactures have taken the approach of not supplying any wells with the installer then simply using a strap clamp to strap the sensor to the manifold. This has the advantage of allowing you to install the sensor on either side of the collector so no extra wire run. The disadvantage of this approach is that the sensor is then farther away from the collector thus making timely temperature detection more difficult.
One solution to this problem is to simply take advantage of the rubber grommet as the clamp for holding the sensor (see picture).

With this scenario you then are able to install the sensor on either side of the collector as well as get a close temperature indication of what is going on inside the collector.
Another solution is to cut a hole in the back of the collector and through the insulation and then affix the thermocouple to the back side of one of the fins. This has the advantage of getting the temperature reading in the middle of the collector but the disadvantage of voiding most manufacturers warranties.

Solar pool heating systems are one of the most cost efficient uses of solar thermal technology. The cost of heating the average residential pool using a gas or electric heater is approximately $2,000 per year, according to the US Department of Energy. The cost of the average solar pool heating system is between $2,000 and $4,000. Although solar pool heating systems are exempt from federal and most state incentives and rebates, the payback period is usually between one to two years. After the payback period, owners of solar pool heating systems can enjoy their solar heated pool for free!

Solar pool heating systems work much the same way as drainback solar domestic hot water systems. In the collector loop, the pool water is heated in the solar collectors. The pool pump will be turned on and the flow of the pool water will go through the panels when the collector temperature is greater than the measured pool temperature. A pool heating system generally doesn’t include a heat exchanger. When the pool panels are no longer hotter than the pool (or the maximum desired temperature is reached) the flow is no longer directed through the panels. The panels (with the assistance of a vacuum breaker) would then drain the fluid back into the pool. If a certain temperature is required then a back-up heater would be installed after the pool panels prior to the heated water reentering the pool.
If your home already is already utilizing a closed loop solar domestic hot water system, you may be able to integrate a solar pool heating system. A valve would be installed on the glycol mixture’s return line. This valve would be able to divert the heated glycol mixture to a second heat exchanger to heat pool water. A sensor and controller would be required to prioritize the two loads. The domestic hot water system would receive first priority. The heated glycol mixture would be diverted to the pool heating system, the second priority, only after the required temperature of the domestic hot water system had been met.
The above integration of a solar pool heating system into an existing http://www.solarhotusa.com/index.html may not be employed in an open loop system.

All atmospheric solar
storage tanks are constructed of an outer layer to withstand environmental conditions, an inner layer of some type of insulating material to reduce heat loss, and an inner liner to reduce corrosion and extend the life of the tank. However, atmospheric solar storage tanks are constructed of many different types of materials.

Since large capacity tanks are difficult to maneuver through doorways, assembly of some atmospheric tanks is done at the installation site. This may reduce the shipping costs as well.

next – stainless steel tanks

The U.S. solar water heating industry produced a record year of growth in 2008, with a 50% increase in capacity compared to 2007. By the end of 2008, approximately 139 MWTh (MegaWatts Thermal equivalent) was installed, bringing the total installed capacity to about 485 MWTh, according to a report released by the Solar Energy Industries Association.

One of the main reasons for the growth of the solar water heating industry was the extension of the residential and commercial solar investment tax credit. Additionally, the public has become increasingly aware of solar energy options available and more concerned about the overall energy crisis.

Even with the significant growth of the solar water heating industry in 2008, solar energy (solar water heating and photovoltaics combined) accounts for only 1% of the total U.S. energy usage. This small percentage is mainly concentrated in several states, possibly as a result of varying http://www.solarhotusa.com/support.html. The state of Hawaii, with its tax credit of 35% of the cost of a solar hot water installation, accounted for 37% of the total MWTh installed in the U.S. in 2008.

The U.S. currently ranks fourth in the world in installed solar energy capacity (solar water heating and photovoltaics combined). Germany ranks first, with Spain and Japan ranking second and third respectfully.

It is expected that the U.S. solar water heating industry will continue to grow in the coming years as the country confronts the issue of reducing solar energy costs to the same level as that of conventional fossil fuel energy.

The European Member States have to work out a Renewables Action Plan this year, outlining how it will reach its 2020 target
by Werner Weiss and Peter Biermayr
London, UK [RenewableEnergyWorld.com]

The European Union and its Member States have committed themselves to achieving a 20% share of renewable energy in Europe’s final energy consumption by 2020. As only three renewable sources (biomass, geothermal and solar) generate heat, it is crucial to clarify how these different sectors can contribute to the renewable energy target. A new study being released this autumn – Study of the Potential of Solar Thermal in Europe, which has come from two Austrian bodies (AEE – Institute for Sustainable Technologies and Vienna University of Technology) examines the growth that can come from solar.

Obviously, solar thermal systems will be needed to provide a substantial share of the low temperature heat: deep geothermal sources are limited to a few locations in Europe, and shallow geothermal is considered within this study as an energy efficiency technology; biomass will be used for transport fuels, electricity generation and medium-to-high temperature applications.

In order to provide the European Union and its Member States with substantiated information on the solar thermal contribution to the 20% renewable energy target and its long-term potential, detailed surveys were conducted using a representative sample of five European countries – Austria, Denmark Germany, Poland and Spain. The information gathered was then extrapolated to cover the 27 EU countries. The study examined both the technical and economic potential of solar thermal technologies, for different applications, including low-temperature industrial heat requirements and cooling.

In order to determine the potential contribution solar thermal could make to the overall heat demand in the selected reference countries, a model was developed for the future demand – taking into account energy efficiency measures. Using this model as a base, future heating and cooling demand was calculated for 2020, for 2030 and 2050. The model includes three scenarios and focuses on the following segments:
* space heating of residential buildings
* hot water preparation in the residential sector
* space heating in the service sector
* industrial low temperature heat (up to 250°C)
* air conditioning and cooling in the residential and service sectors

The three scenarios are a ‘Business As Usual scenario’ (BAU); an ‘Advanced Market Deployment scenario’ (AMD), which includes financial and political support mechanisms such as subsidies and obligations, moderate energy efficiency measures and improved research activities; and a ‘Full R&D and Policy scenario’ (RDP), which includes substantial financial and political support mechanisms, energy efficiency measures and research activities.

Contribution of Solar Thermal to the EU 20% Renewable Energy target

Assuming there is a 9% reduction of the overall final energy demand due to energy efficiency measures by 2020 (compared with 2006), then solar thermal would make up 6.3% of the European Union’s 20% renewable energy target under the RDP scenario, and 2.4% under the less ambitious AMD scenario. The share of renewables in 2005 (to the EU-27’s total energy consumption of 13,609 TWh) was 8.5%. To reach 20%, an increase of 11.5 percentage points in renewable energies is required across the EU-27 countries by 2020. The contribution of solar thermal to that increase would be 12% according to the RDP scenario, 4.5% according to the AMD scenario and 2.9% in the BAU scenario.

To reach the goals of the RDP scenario, a 26% average annual growth rate of the European solar thermal market is needed up to 2020. (By comparison, the average annual market growth in Europe between 2000 and 2007 was 12.4%.) A 15% average annual growth rate is required to reach the goals of the AMD scenario and a 7% growth rate for the BAU scenario. The resulting total collector area by 2020 would be between 97 million m2 (BAU) and 388 million m2 (RDP). These collector areas correspond to total installed capacities of 67.9 GWth and 271.6 GWth, respectively.

Economic Effects

According to the RDP scenario the effect on employment would be considerable. In total, the solar thermal sector would encompass 470,000 full-time jobs in 2020, in the European Union domestic market alone. €214 billion would be required in the solar thermal sector to reach the 2020 goals of the RDP scenario. This includes production, engineering, trade and installation of solar thermal systems from 2006 to 2020.

Solar thermal contribution to the energy supply and CO2 reduction

The solar yield in the RDP scenario is 155 TWh in 2020. This corresponds to an oil equivalent of 22 billion metric tons. Taking this oil equivalent into account the annual contribution to the CO2 reduction by solar thermal systems is 69 million metric tons.

Technology Innovation

Stepping up solar on this scale will require innovation. In order to use the potential much larger roof and facade areas will be needed for the installation of solar collectors.

Large-scale solar renovation of buildings will make use of prefabricated elements, with solar providing space heating, cooling and hot water. Combisystems will play an essential part, and a key issue is the development of thermal energy storage.

Long-Term Potential – Beyond Domestic Hot Water

In 2050, the solar thermal contribution to the European Union’s (EU-27) low temperature heat demand ranges from 47% (RDP scenario) to 8% (BAU scenario).
The corresponding annual solar yields are 1552 TWh (RDP) and 391 TWh (BAU). The collector area needed to reach these goals is between 8 m2 (RDP) and 2 m2 (BAU) per inhabitant in the EU-27. The resulting total collector area is between 3.88 billion m2 (RDP) and 970 million m2 (BAU).

If solar thermal is to contribute significantly to the long-term heating and cooling demand in EU-27 countries then the primary focus in central and northern Europe must be on systems for space heating (solar combisystems) and in the Mediterranean area on systems providing space heating, hot water and air conditioning (solar combi+ systems).

If the focus remains solely on solar thermal systems for domestic hot water preparation, then the solar thermal contribution to the long-term final energy demand will be limited. By 2030 the full potential for these applications will have been reached and the market would be reduced mainly to the replacement of old systems. Another important segment with considerable potential is low-temperature process heat for industry, (up to 250°C).

With upscaled R&D and market/political support, solar heat can make a valuable contribution to Europe’s energy future. It’s the right moment – in fact, without the renewable heat sector, the 2020 targets will not be reached.

Werner Weiss is at AEE – Institute for Sustainable Technologies, Gleisdorf, Austria. Peter Biermayr is with Vienna University of Technology Energy Economics Group, Austria.

The full version of the Solar Thermal Potential in Europe study is available: http://www.estif.org/.

This study was prepared in the framework of the EU-funded project RESTMAC, TREN/05/FP6EN/S07.58365/020185. The Solar Thermal partner in the RESTMAC project is ESTIF, European Solar Thermal Industry Federation.

In a previous blog we posted a video that showed how to “get the air out” of your glycol solar heating system when you it. An astute customer realized that since he was planning to mix his glycol with his water he could reduce the number of times he needed to cycle the charging pump by starting with straight water. After he has charged the system with straight water (which doesn’t foam nearly as much as a water/glycol mixture) he can then finish the charge by switching to a bucket of straight glycol. He needs to pay attention to his ratios as well as checking his concentration after he is finished but this process greatly reduces the times he needs to cycle his system to get the air out. By eliminating the issue of foaming in the bucket the charging time is greatly reduced.

Thanks Jason.

When trying to diagnose a system it is frequently important to determine whether the pumps are working in your solar heating system. The first (and least accurate) method most contractors go with is feeling the pump to see whether they are vibrating. This can be misleading because vibration from nearby mechanical equipment can cause you to assume the pump is spinning when it might not be. A very easy and accurate way to determine whether the pump is spinning is to remove the bleed screw from the top of the pump (see video). When you remove the bleed screw (not available on Taco pumps) you will see an inner slot on the end of the shaft. You can only see this when the pump is not spinning. Since the slot is directly connected to the shaft and impeller, if the slot is rotating you know the pump motor is spinning. Turn the power off and you should see the slot.

By removing the bleed screw and accessing the head of the pump you can also spin the shaft freely with a slotted screwdriver. You should be able to feel if the shaft is binding in any way.

This is the time of the year when the calls start rolling in. “I have a single tank solar water heating system and the water heater has stopped working.” This is not a service call you should need to run out on.

Using a standard electric water heater for both your solar storage as well as providing your back-up heating has many advantages including; reduced floor space, ability to use standard tanks, less standby losses from the tank, better heat recovery, and less cost. But now we come to the rub. Electric water heaters have a thermostatic breaker built into the top element. When the thermostat senses temperatures over 170° F it automatically trips this safety breaker. This breaker is designed as extra protection in case you have a run-away element in your tank to keep the system from getting too hot.

Frequently a solar water heating system will supply 100% of your hot water needs during May through September. If at any time during that period the top of your tank exceeded 170° F the tanks thermostatic breaker will trip. As the cooler and cloudier weather sets in the back up element is no longer able to kick in and you receive a service call. Fortunately, the fix for this problem is simple and within the reach of even the least proficient home-owner.

Simply remove the cover plate over the upper element, depress the red button with the eraser of a pencil and voila you are back and running again. (see picture)

Water Heater Reset Button

So next time you get this call don’t fret and think about the little red dot.

When installing a pressurized solar heating system an issue that the installer must be concerned about is getting the air out of the system.  If the installer leaves too much air in the propylene glycol/water solution they can have all kinds of problems including: pump cavitation, vapor lock, air lock, unwanted system noise, decrease in efficiency, overheating and premature system discharge.  None of these conditions are desirable.  The question then is how do you insure that you adequately purge the air from the system.  The process isn’t difficult although you can’t take any shortcuts and achieve consistent results.

1. After installing the solar panels in the sun make sure that you cover the panels.  You want to charge the system when the panels are cold and the sun is not on them.  You can either charge in the morning, evening or cover the panels when installing and charge it whenever you get around to it.
2. Determine the pressure that you will be charging the system to.  This should be 15 psi + 5 psi for every 10 feet (story) that the top of the collectors are above the pressure gauge, i.e. A system that has the panels installed on top of the second story and the tank is the in garage would charge to 15 + (2 x 5) = 25 psi
3. Make sure that the expansion tank is charged to the number determined in step 2 above.
   

Note:   A pressurized glycol system should have at a minimum the following components: a fill port, a check valve, and a drain port.  The closer the fill port and drain port are located to each other (with check valve or ball valve in between) the easier it will be to purge air from the system.
4.  Pre-mix your glycol to the appropriate ratio for your location in a bucket.
5.  Using three hoses connect 1 – from the bucket to the supply of the transfer pump, 2- from the transfer pump to the charge port of your solar system, and 3 – from the drain of your solar system back to the bucket.
6. Prime the pump
7. Open the valves to both the charge and drain port and turn the pump on.  You should see the fluid level in the bucket diminish as the pump pushes glycol from the bucket through the supply piping, collectors, return piping and finally back into the bucket.  After you start to see the fluid pump around you will want to let the pump run for another minute or so before you turn the pump off.  **** Caution – The hose ends in the bucket should always remain below the fluid level during the whole charging procedure.  Close the fill and drain valve.
8.  Wait until the foam in the bucket completely dissipates (this should take 4 –5 minutes).
9.  Repeat step #7 as many as 4 or five times until you no longer see bubbles or foam entering the bucket as the pump is running.  Once you confirm that the system is running with no foam or bubbles entering the bucket after running for a minute then CLOSE THE DRAIN VALVE.
10.  Keep the tranfer pump running until the desired system pressure (determined in step #2) is reached on the system pressure gauge.  Once the desired pressure is reached then close the fill valve.
11.  Disconnect the hoses to the solar fill valve and drain valve.

You are now ready to turn on your solar heating system.

Although you have done an excellent job eliminating the air as you charged the system you haven’t got it all.  The mixture of propylene glycol and water contains some air in solution.  As the solution heats up the air in solution is squeezed out of solution.  This additional air will accumulate in your system as your system repeatedly heats up and cools down.  Once this air has left solution it will not re-enter the solution and will travel around your system accumulating in local high points.  If your system has a place to capture and release this air then after a few weeks of running you will have a solution that has no (or a negligable amount) air trapped in the system.  With all of the air ultimately eliminated you now have a system that will operate quietly, efficiently and much more reliably.

As the solar water heating business expands to the traditional trades (plumbing and HVAC) we get questions about system payback more and more.  The contractors want to understand that the systems they install will rapidly pay for themselves.  While this is an excellent question it comes laced with many pitfalls.

We can quickly go down the road of answering this question for our own satisfaction although I don’t recommend it in general.  According to “More evidence of Rational Market Values for Home Energy Efficiency” by the Appraisal Journal a home will increase in value $20 for every $1 reduction in annual energy bill.  An average solar water heating system will save a family of 4 approximately $400 per year on their energy bill.  That would mean that if a homeowner installs a system they she see an appreciation in the value of their home of $8,000.  Interestingly, that is also about the national average installed cost of a 64 ft^2 80 gallon tank freeze protected system.  You add to that the current tax incentives which include as a minimum 30% tax credit from the federal government and you now have a system that costs less than it adds in value to your home.  With this stunning fact it would seem that every homeowner that is about to sell there home should add a system simply by the pure economics.  I make the last statement a little tongue in cheek because I understand that some homeowners are concerned about the aesthetics of an installation (I am sure to discuss that later in a future post).

When it comes down to it, the economics of solar water heating are such that a homeowner get shift there assets from their bank to their home and in return get a huge chunk of cash from the government and start saving money immediately on their utility bills.  This should be a no-brainer economically.  Although the logic is clear I don’t recommend sharing this with those that question the value of solar water heating (or more likely solar energy in general).  People’s prejudices, party affiliations and biases are such that rare is the person that will listen to logic.  I would recommend to focus the selling of systems to people that are already convinced of the value of energy efficiency they can be seen all around us.  They are the people that drive hybrids, purchase high SEER air conditioning, bicycle to work, use compact fluorescent lamps, or install programmable thermostats.  The people that are ready are all around us so we need to stop focusing on the people that won’t be convinced no matter what the logic.

Another article that might be interesting is: http://www.pmmag.com/Articles/Column/BNP_GUID_9-5-2006_A_10000000000000620715