Solar Hot Water & System Size Details

July 3rd 2012

Using the sun to heat water is a very similar concept. We saw that a flat black plate in the sun can get pretty toasty. In practice, flat panel collectors can hang onto about 60% of the incident solar energy, transferring this to the water.

Heat paths via radiation through the glass on the front, convection of air within the panel, and conduction through the back and mounting frame all contribute to loss. For radiative loss, radiation from the black panel is intercepted by the glass (thermal IR is not transmitted by glass), warming it up.

This can then radiate both skyward and back to the absorber. A second piece of glass (double-pane) can cut down radiation losses, by returning approximately half of what would otherwise have been lost off the front panel. Some fancy units evacuate air to minimize convective loss, and the backs can be insulated to reduce loss. Given all these thermal leaks, holding on to 60% of the incident energy is pretty impressive.

Let’s assume your household requires 300 liters of hot water each day—the equivalent of four “long” 10 minute showers at a healthy flow of 8 liters per minute. This, by the way, is far more than I believe is really necessary for a household—even if it is typical.

If the water comes in at 10°C, and is heated to 60°C, then we need to supply 15,000 kcal of energy—following the definition of the kilocalorie.

Considering 60% efficiency and allowing for some daily loss in storage, we need to provide 30,000 kcal of solar input each day, amounting to 35 kWh of energy.

As it turns out, tilting a panel to 54° in St. Louis gives at least 3.5 hours of full-sun-equivalent (1000 W/m²) even in December, so that we need 10 m² of panels (a bedroom’s size).

Two New Testing Labs Could Mean Big Boost For Solar Thermal Sector

March 1st 2011

With only five solar thermal testing laboratories currently accredited by the Solar Rating and Certification Corp. (SRCC), the backlog of products awaiting certification is staggering. In turn, delays have rippled throughout the entire solar thermal supply chain, stalling project development.

However, two universities are seeking to change that. Raleigh, N.C.-based North Carolina State University (NCSU) and West Haven, Conn.-based University of New Haven (UNH) are both in the process of developing accredited solar thermal testing facilities, which would bring the total number of accredited labs to seven.

NCSU's initiative will involve the expansion of its North Carolina Solar Center, which already serves as a solar thermal testing facility but is in the process of becoming an SRCC-accredited lab. The project received a $100,000 grant from the North Carolina Department of Commerce's Green Business Fund in 2009, and the initiative was launched shortly thereafter.

UNH began developing its Solar Testing and Training Laboratory last fall, after being approved for a $500,000 grant from the U.S. Department of Energy and a $100,000 grant from the Connecticut Clean Energy Fund. But before the lab can officially begin testing, it must undergo a lengthy and involved accreditation process, Tommy Cleveland, solar testing and training laboratory manager at UNH, tells Solar Industry.

"We're basically starting the whole [project] from scratch, so we're utilizing engineering students here to design all of the equipment and test systems that will be necessary to actually conduct the SRCC OG-100 tests," he explains.

In the first phase of the project, senior engineering students at UNH will design and validate the automated testing systems that will be used at the facility. Then, once the lab is accredited, students will perform fee-for-service testing of solar thermal products. According to Cleveland, UNH expects to begin validating the student-designed equipment this April and to finish the SRCC accreditation process by this time next year.

There is no doubt that the need for new testing facilities is pressing. Solar development is heavily dependent upon financial incentives such as the federal investment tax credit, and in order for projects to receive these benefits, the products used must be SRCC-certified, Cleveland notes.

"I believe that right now, there is up to a 36-month backlog - definitely between a 12- and 36-month backlog - between getting a new thermal product to market and being eligible for the 30% federal tax credit," he says.

In fact, the current shortage of accredited testing facilities is crippling the entire solar thermal supply chain. For instance, some installers are waiting for manufacturers to introduce new collectors to the market, but because of the certification backlog, there is "no end in sight as far as when that's actually going to happen," Cleveland adds.

Despite the perpetual waiting game that has permeated every link in the supply chain, Cleveland is optimistic that the addition of UNH's new testing facility, in combination with the accreditation of North Carolina State University's lab, will go far toward removing these barriers to development.

"Hopefully, it makes a significant dent in the backlog," he says. "As more and more people become aware of proven technology within solar thermal, then I think more and more people will sign on and get solar thermal systems installed."

Solar Thermal System Design Part 1

Jan 21st 2011

Solar Thermal Industry Set To Boom

Jan 4th 2011

The rapidly growing photovoltaic industry has spawned thousands of jobs for people who design, make, and install rooftop solar arrays for homes and businesses. But the smaller solar thermal business is also set to boom in the United States, according to a new government report [PDF].

Solar thermal products come in all sizes -- from rooftop panels that absorb the sun's rays to heat swimming pools and provide hot water for homes to huge mirror arrays that heat liquids to create steam to drive electricity-generating turbines at solar power plants.

Employment in the solar thermal collector industry jumped 22 percent in 2009 from the previous year, said the report from the U.S. Energy Information Administration. The number of solar thermal companies increased by 19 percent.

It's still a small industry, with revenues in 2009 reaching $96.7 million, a 19 percent spike from the previous year. At the same time, total shipments of solar thermal products fell nearly 19 percent.

That's because swimming pool products accounted for 73 percent of the industry in '09. But that's poised to change, as developers are set to break ground on several large-scale solar thermal power plants in the desert Southwest this year.

Those projects will deploy tens of thousands of mirrors, solar troughs, and other components. California alone in recent months has licensed solar thermal plants that would generate more than 4,000 megawatts of electricity -- that will heat a whole lotta swimming pools.

German solar manufacturer Schott, for example, has built a solar thermal component factory in Arizona to supply projects in the Southwest, and other manufacturing facilities are planned for the region.

The seeds of the coming boom can be found in the report's 2009 numbers.

While Big Solar accounted for only about eight percent of the industry's shipments that year, it brought in a quarter of the revenue, a 435 percent spike from the previous year.

Although 57 percent of solar thermal imports -- China was the No. 1 supplier -- were for the pool industry, components for solar thermal farms are likely to be manufactured domestically given their bulk.

In other words, the hot jobs will be found here. 

New York unveils solar hot water system incentive program