The million dollar solar question

BY BOB “hot rod” ROHR
contributing writer

A loud buzz in our industry right now centers around solar thermal. Every trade show and Expo I attend presents another handful of “players” entering the solar thermal business. Designers, installers, homeowners, and yes, even politicians are seeing the future of solar thermal. Many of us who deal in hydronics and radiant systems understand the use of low temperature fluids to provide a portion of our domestic hot water, warm our homes, provide pool or spa heat and maybe melt some snow or ice. It is a very small step for hydronic-knowledgeable designers or contractors to transition into the solar thermal business. All you need are some collectors (a heat source), storage, a pump and controller. Looks a lot like a hydronic heating system except the boiler, per say, is on the roof or the ground outside the building.

Many contractors have embraced the technology, attended the seminars and have multiple system installations under their belt. The solar thermal focus currently, with a weak residential housing market, seems to be commercial and industrial systems. Driving around your service area, you should be able to pick out the prime solar domestic hot water sdhw candidates. Look for businesses with large domestic hot water loads. Hotels, carwashes, laundromats, fast food or any restaurants are the usual suspects.

I encourage you to look deeper into your surroundings to find commercial and industrial potential. Food processing uses a large amount of dhw. One manufacturer I met recently at the annual Colorado Solar Energy Industries Assoc. (coseia) event has his sights set not only on food processing but one big name player with hundreds of plants across the country. He has studied their operations and unique hot water needs and pitches his products and services directly to their plants. Yet another supplier I know has packages for a specific brand of fast food restaurants.

I returned just this week from a military base that is installing 1,900 square feet of collectors for a large housing application in the deep South. Big money, our money really, is being spent to upgrade mechanical systems and add alternative energy components to government projects.

But what keeps tugging at me is the imbalance of solar radiation available from summer to winter. In many Southern and Sunbelt areas, the summertime incoming water temperatures rise, and the amount of radiation available may even triple. What you may find when you run the calculations is the sdhw load may be covered early in the day in a sunny summer condition. Now what? You have designed a system to provide a solar fraction on a yearly basis. Summertime conditions may provide more dhw than you can possibly use. The million-dollar question is: How do you deal with the excess energy you will harvest?

The reality is “you get the most amount of solar energy when you need it the least.” Here are some websites that help you determine the solar radiation available at your location throughout the year:

• http://eosweb.larc.nasa.gov/cgi-bin/sse/sse.cgi?+s01#s01
• http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/

So, a missing component might be a means to use solar thermal energy to condition or cool spaces. Air conditioning, if you will. Turns out the technology to accomplish this has been used for many years here in the US of A. Recall the refrigerator in a recreational vehicle. Fired by a propane LP flame, the unit cools your food. And maybe, more importantly, your beer. Large-scale refrigeration units can be found powered by district steam in cities that create and distribute energy this way.

So the next logical step would be to design residential and light commercial cooling equipment to be powered by solar thermal collectors. Currently, these systems seem to favor the evacuated tube type of collectors for higher temperatures required to drive the absorption cycle.

As we wish, these products are starting to become available. Japan has been manufacturing and installing absorption chillers and some data indicates as much as 40% of their commercial air conditioning equipment is powered by absorption cycle equipment.

While small residential systems, solar thermal-powered ones are starting to show up in the market, look at other options that are currently available, too. If you attended the ahr show in Orlando recently you may have noticed a small direct current powered residential split system air conditioning unit powered by photovoltaic panels. Solar Panels Plus was displaying an 18,000 btu system. This could be a good option for off-gridders looking to keep their cool. A bank of deep cycle batteries provides the power after the sun goes down. The battery bank can be sized to provide cooling after the solar drops off. Solar Panels Plus out of Virginia has been developing this product and testing it for several years now.

Yet another interesting approach was a system that used a Sterling engine powered by a parabolic dish. The Sterling spun a generator to supply electricity.

It is interesting to see this technology, discovered many, many years ago, getting another look.

Stay cool and keep your eyes open for new and exciting solar-powered cooling products.

Bob “hot rod” Rohr has been a plumbing, radiant heat and solar contractor and installer for 30 years. A long-time RPA member, and columnist for Phc News and Mechanical Business magazine. Bob has joined Caleffi North America as manager of Training and Education.