DogStar Solar's Alternative Energy Updates

Sun Strikes It Hot: What’s Happening in the Global Solar Thermal Markets?
August 21, 2011, 5:31 pm
Filed under: Solar Thermal

By Jackie Jones,

August 18, 2011

London — In Europe, almost 50 percent (48 percent in 2007, to be precise) of the total energy consumed is used to produce heat. Almost a third of that goes into high-temperature industrial processes, but over 40% goes into heating and providing hot water for our homes. The remainder is used in commercial/service sectors and low-temperature industrial processes. And almost all this heat is produced from fossil fuels, whether directly or via electricity.

Partly because it needs to be produced near to its place of use, making it less tradable than electricity, heat as a commodity is generally regarded as somehow lower status than electricity. Even more so, it seems, with renewable heat – wood pellets and solar thermal just don’t seem to have the high-tech appeal of shiny PV, nor the majesty of wind turbines. Meanwhile, while the electricity industry still searches for a truly applicable form of energy storage, heat lends itself well to storage on many scales. It shouldn’t be underestimated.

Solar heat has become a surprisingly big player. According to the 2011 report from the IEA solar heating and cooling programme Solar Heat Worldwide (authored by Werner Weiss and Frank Mauthner), the solar thermal collector capacity in operation worldwide at the end of 2009 was 172.4 GWth. Across the 53 countries covered in the report, the annual yield of these water-based collectors was 141,775 GWh, or 510,338 TJ (the relatively small amount of air-based solar thermal is excluded). This corresponds to an oil equivalent of 14.4 million metric tonnes and an annual CO2 saving of 46.1 million metric tonnes.

Though the final numbers for 2010 are not in, capacity was expected to have reached 196 GWth by the end of 2010, producing 162,000 GWh of output. This level of capacity is very close to that of wind power globally (194 GW), which admittedly has a greater yield than solar thermal. However, the contribution made by solar thermal heat far exceeds the capacity and output of solar PV, geothermal power, or any other ‘new’ renewable (though biomass and large hydro contribute more).

While most of the installed capacity is currently used for production of domestic hot water – the simplest solar thermal application – the scale and range of applications is becoming much more diverse. In some European countries solar combi-systems are widely used to provide space heating in addition to hot water, and district heating by solar is also expanding. Plus, the potential for solar process heat (for commercial/industrial uses where hot water is needed) is starting to be exploited. Figure 1 (shown overleaf on page 47) shows the distribution by application in the top 10 markets.

By the end of 2009, some 59 percent of the world’s solar thermal (101.5 GWth), was installed in China, with Europe accounting for 32.5 GWth. The US and Canada had a combined capacity of 15 GWth. Much of this (over 80 percent in the US) is unglazed collectors for pool heating. These three regions together account for 86.4 percent of the global total.

Counting all solar thermal (including the unglazed collectors widely used in the US for pool heating), China, the United States and Germany are world leaders in total installed area/capacity. Turkey has retained its position as world number four. However, if unglazed collectors are removed from the calculation, Turkey and Germany are almost equally placed, behind China.

The remaining installed capacity is made up by various countries including Australia and New Zealand (5.2 GWth), Central and South America (4.7 GWth), the Asian countries of India, South Korea, Taiwan and Thailand (4.6 GWth), Japan (4.3 GWth), the Middle East represented by Israel and Jordan (3.5 GWth) and a handful of African countries (1.1 GWth), namely Namibia, South Africa, Tunisia and Zimbabwe.


When it comes to new installations, 2009 was a year of impressive growth for solar thermal, with an extra 36.5 GWth of new capacity being added. This means that collector installations were up by over 25 percent on the previous year. (If the predictions in the IEA report are correct, at least 23 GWth will have been added in 2010 as well.)

And, 80.6 percent of those 2009 additions (29.40 GWth) were installed in China, with the remaining 10.2 percent installed throughout Europe. The remainder was spread between the US/Canada, Australia/New Zealand and Central/South America (about 2 percent in each of these three regions), with the rest of Asia, the Middle East and Africa making up the remainder.

The report says that Australia reported a 78.5 percent growth in annual installations of glazed water collectors in response to a new financial incentive scheme, while in Mexico, the total number of glazed water collector installation grew by 31.5 percent – mainly due to a broad market campaign for solar water heaters, with low interest rates helping.


Instantaneous Thermal Efficiency
December 23, 2010, 10:45 am
Filed under: Solar Thermal

Ref: Caleffi iDronics July 2009

The performance of any solar combisystem is implicitly

linked to the performance of its solar collector array.

The best solar combisystems are designed to enhance

collector efficiency. Doing so requires a fundamental

knowledge of what collector efficiency is and how it is

affected by operating conditions imposed by the balance

of the system.

In an “ideal” solar thermal system, none of the heat

produced by the auxiliary heat source would enter the

solar storage tank. This prevents the auxiliary heat source

from increasing the temperature of the storage tank above

what it would be based solely on solar energy input. Such

heating, if allowed to occur, delays the startup of the solar

collection cycle, and thus reduces the energy collected

during that cycle.

All solar tanks rely on temperature stratification to direct

heat added by the auxiliary heat source to the upper portion

of the storage tank. This minimizes heating of the lower

portion of the tank, and thus reduces interference with the solar collection control process.

The instantaneous thermal efficiency of a solar collector

is defined as the ratio of the heat transferred to the

fluid passing through the collector divided by the solar

radiation incident on the gross area of the collector, as

shown in figure 1.

Instantaneous collector efficiency can be measured by

recording the flow rate through the collector along with

simultaneous measurement of the collector’s inlet and

outlet temperature. The intensity of the solar radiation

striking the collector must also be measured. The Formula

can then be used to calculate the instantaneous

thermal efficiency of the collector.

Formula :


c = specific heat of fluid (Btu/lb/ºF)

D = density of fluid (lb/ft3)

f = flow rate (gallons per minute)

Tin = collector inlet temperature (ºF)

Tout = collector outlet temperature (ºF)

I = instantaneous solar radiation intensity (Btu/hr/ft2)

Agross = gross collector area (ft2)

8.01 = a unit conversion factor.

The phrase instantaneous collector efficiency can vary

from moment to moment depending on the operating

conditions. Do not assume that a given set of operating

conditions is “average” or “typical,” and

thus could be used to determine the

collector’s efficiency over a longer period

of time.

Instantaneous collector efficiency is very

dependent on the fluid temperature entering

the collector, as well as the temperature

surrounding it. It also depends on the

intensity of the solar radiation incident

upon the collector. This relationship is

shown in figure 2 for a typical flat plate

and evacuated tube collector.

The thermal efficiency of each collector is

plotted against the inlet fluid parameter. This

parameter combines the effects of inlet fluid

temperature, ambient air temperature and

solar radiation intensity into a single number.

Solar Thermal Heating
December 13, 2010, 7:48 pm
Filed under: Solar Thermal

Solar thermal heating is one of the most cost effective and efficient ways to incorporate the benefits of renewable energy into a building. Because the sun is used to generate heat, the fuel is not only clean, but it is also FREE!  That means lower utility bills! Once any higher initial costs of solar system equipment are recovered through avoided electricity costs, the system will only require expenditures for maintenance. Additionally, if a solar heating system is included in the mortgage of a new home, the cost savings and benefits are immediate. It is important to note that equipment and installation costs are significantly defrayed when utilizing federal, state and local incentives and rebates designed to encourage use of energy efficient and renewable energy technologies.

Solar thermal systems offer a range of applications to reduce energy costs. Solar heating systems are an excellent way to heat swimming pools, a building’s water, and interior space. A typical residential solar water-heating system reduces the need for conventional water heating by about two-thirds. It minimizes the expense of electricity or fossil fuel to heat the water and reduces associated environmental impacts (U.S. Department of Energy).

Solar heating systems are a clean energy technology that not only contribute to the health of the environment, but also protect human health and well-being. They are clean emitting, which means no harmful pollutants such as carbon dioxide, sulfur dioxide, nitrogen oxides, and other wastes are released into the atmosphere. The result is clean air to breathe and a healthy thriving planet for present and future generations.

These benefits all equate to a perfect outcome of lower energy costs, clean environment, improved conditions for human health and welfare, and increased energy security.

Fine-Tuning a Solar Water-Heating System
July 30, 2009, 4:02 pm
Filed under: Solar Thermal

This landlord used data logging to adjust a solar water-heating system for maximum energy savings.

By Richard Reis, P.E.
Reis houseThe author pointed the collectors about 20 degrees east of south because of the building alignment. This slightly lowers the solar potential and means that most energy is gathered in the morning. PHOTO COURTESY RICHARD REIS, P.E.
Back in the 1980s, during the Carter administration, I installed a solar water-heating system in my house. That drain-back system still operates dependably and has paid for itself many times over.
After I bought a five-unit apartment building, it made sense to upgrade its plumbing to incorporate solar water heating. Each apartment had its own electric meter, so the tenants paid the bills for running their own lights and appliances. But the building had a house meter too, and as landlord, I was paying the utility bill for the washer, dryer, hall lights — and for a water heater that served all five apartments.
I studied the utility loads and determined most of the electrical energy from the house meter went to heat water. The solar system would be designed to displace most of that electrical demand. I solicited proposals from the few solar contractors in my area and selected one that offered a competitive and complete job, including design, permitting (no small feat in Montgomery County, Md.), materials, installation and warranty.
The contractor installed the system in March 2004. We pointed the collectors about 20 degrees east of south because of the building alignment. This slightly lowers the solar potential and means that most energy is gathered in the morning.

We went with a conventional, modern double- circuit system, with four flat-plate collectors, a pump, two storage tanks with built-in heat exchangers, a controller, a pressure gauge, a pressure tank and a bypass valve, with a glycol-water heat-transfer fluid in the closed primary circuit. The pump runs when the fluid temperature at the collectors exceeds the temperature at the bottom of a storage tank. We kept the original, conventional electric water heater. The solar system preheats water in the storage tanks, which is then fed to that original heater, which now functions as the backup water heater. When the temperature in the backup heater falls below its set point, its electric circuit kicks on. The hotter the water from the solar system, the less electricity the backup heater consumes. An anti-scald valve keeps outflow to showers and sinks safely below 120˚F (50˚C).

The following items were noted during initial commissioning:
• The contractor promptly resolved piping and venting problems.

• The backup water heater had been set to heat water to 130˚F (56˚C). We reduced that to 120˚F (50˚C).

• We reduced hot water use by replacing the apartments’ conventional sink aerators and shower nozzles with low-flow models, 1.5 and 2 gallons (5.7 and 7.6 liters) per minute, respectively.

• To improve appearance and extend life, we covered the black foam pipe insulation with white plastic.

• Because it cast shadows over the collectors, we removed an invasive mulberry tree. We planted new trees where they wouldn’t shade the solar system.

We installed an OnSet data logger ( to evaluate performance. I would use the data to help plan system improvements. The device records when the solar pump turns on and off, and it graphs both the temperature near the top of the storage tank and the electric current used by the backup heater. Since the backup heater presents a simple resistive load, multiplying current by line voltage yields power used. Integrating power over time for each day yields daily backup energy demand. The solar controller and pump also draw power, but it’s a negligible amount compared to what’s needed by the backup heater.

Chart 1Chart 1
Chart 2Chart 2

Chart 1, above, shows the performance of the system over several days in April 2008. On the days when the sun was shining, April 15 to 18, the solar pump ran, the storage tank temperature rose and the backup heater demanded little current. Chart 2 shows energy demand was lowest on those days. By contrast, April 13 and 20 were overcast. The pump ran less frequently, the storage tank temperature stayed lower, and the backup heater current and energy demand were higher. Energy use was high on April 14 because the two previous days were mostly overcast. Residents took their morning showers before sunrise, so the backup heater did the work.

Chart 1 shows that the storage tank temperature follows a consistent pattern on sunny days:
• Morning showers lower the tank temperature. [A]

• The solar pump turns on and the tank temperature rises. [B]

• Even when no water is drawn, the tank’s temperature drops slowly, indicating a low and constant rate of heat loss. [C]

• Other hot water use, such as late-night washing, also draws down the temperature. [D]
After measurement, the following issues were noted and corrected when feasible:
• The solar storage tanks lose heat (and energy) even when no water is drawn. These mechanisms may be at work:
– Conductive loss from the storage tanks. To reduce this loss we added insulation blankets. These recovered their cost in less than one year.
– Nighttime thermosiphon circulation may draw heat-transfer fluid from the hot storage tanks to the cooler collectors.
Further measurements will determine if this is occurring. If so, the addition of a one-way valve may resolve the issue.
• The factory set the controller to shut off the solar pump when the storage tank temperature exceeded 140˚F (62˚C). This set point was raised to prevent much higher stagnation temperatures in the collector plates, which might lead to degradation of the glycol mixture.
In addition:
• I reinforced the lightning protection by grounding the glycol pipes directly to the cold water supply line with heavy copper wire.
• Pipes and collector racks should be raised from the roof surface to permit rainwater and debris to flow freely to the gutters. We missed that issue, but it would be critical in a colder climate to prevent formation of ice dams.
The solar water heater, with the later improvements, has reduced the building’s electric draw from about 800 kWh to less than 300 kWh per month. After a state grant and the 30 percent federal tax credit, this system will pay for itself via energy savings in four years.
Solar Water-Heating Economics
The economics of solar water heating work out to an attractive 51-month payback when measured by the avoided cost of electrical energy. Here’s the analysis:
1. The economic analysis of any capital investment starts with the cost of the proposed system, including components (collectors, storage tank, pumps, pipes, etc.), plus the cost of installation. To get a measure of those costs, I considered 10 web sites estimating the costs of complete and installed systems. The average cost was $7,360.
2. The total water-heating load can be computed in million British Thermal Units* (MBtu);
• The amount of hot water used per person (gallons/day): 33
• The number of people in the building: 8
• Days per year: 365
• Weight of 1 gallon of water: 8.33 pounds
• Required temperature: 120˚F
• Average temperature of incoming water: 58˚F
• Required temperature increase: 62˚F (120˚F – 58˚F)
Energy required: 24.88 MBtu per year
3. The amount of energy provided by a solar hot water system depends on the solar fraction — the ratio of solar heating to total heating required. I estimate this as 0.7— within the U.S. Department of Energy’s range for solar fraction. Thus the solar water-heating system displaces 17.42 MBtu per year.
4. For electric draw, convert the solar heat to annual kilowatt-hours, considering the efficiency of the water heater and the cost of electrical energy in kilowatt-hours.
• Kilowatt-hour per MBtu: 293
• Annual heater output required: 5,105 kWh
• Electric heater efficiency: 90 percent
• Annual heater input: 5,672 kWh
• Annual solar controller and pump usage: 244 kWh
• Annual net solar energy: 5,428 kWh
• Cost: $0.16 per kilowatt-hour (retail cost of electricity)
• Annual cost avoided: $869
Simple payback in years: 8.5 years
5. Consider government benefits:
• Federal solar tax credit: 30 percent
• Maryland solar grant: 20 percent (maximum of $3,000)
• Total grants: 50 percent
• Net cost: $3,680
Payback: 4.25 years, or 51 months. Payback times are longer when solar displaces natural gas water heating.

Photovoltaic Comparison:
The solar hot-water system displaces 5,428 kWh annually. To produce this much electricity would require about a 4-kilowatt photovoltaic system, costing about $30,000 — about four times the cost of the solar water-heating system without government benefits.
*A Btu is the heat required to raise 1 pound of water 1˚F.
About the author: Rich Reis, P.E., is principal engineer of Conservation Engineering ( He can be reached at rreis[at]verizon[dot]net.

Got Solar ?
April 8, 2009, 7:23 pm
Filed under: Solar Thermal

Solar 2008 Year In Review   !!!!!!!!



Solar energy is the cleanest, most abundant, renewable energy source available. And the U.S. has some of the richest solar resources shining across the nation. Today’s technology allows us to capture this power in several ways giving the public and commercial entities flexible ways to employ both the heat and light of the sun.

The greatest challenge the U.S. solar market faces is scaling up production and distribution of solar energy technology to drive the price down to be on par with traditional fossil fuel sources.

Solar energy can be produced on a distributed basis, called distributed generation, with equipment located on rooftops or on ground-mounted fixtures close to where the energy is used. Large-scale concentrating solar power systems can also produce energy at a central power plant.

There are four ways we harness solar energy: photovoltaics (converting light to electricity), heating and cooling systems (solar thermal), concentrating solar power (utility scale), and lighting. Active solar energy systems employ devices that convert the sun’s heat or light to another form of energy we use. Passive solar refers to special siting, design or building materials that take advantage of the sun’s position and availability to provide direct heating or lighting. Passive solar also considers the need for shading devices to protect buildings from excessive heat from the sun.