Solar Water Heating: Pumping Out Lots of Energy for Low Cost

Tue, Mar 3, 2009

Energy Types

Are you looking into solar to green up your energy use? Thinking about solar electric (PV)? If so, you might be overlooking another powerful solar energy application – solar water heating.

Solar hot water or solar thermal is nothing new. The first commercial solar water heater was patented in 1891 – sixty-two years before the invention of the solar cell. By 1909, solar heating systems evolved into something very like what we use today, with separate collection and hot water storage components.

Solar water heating was tremendously popular in the early part of the 20th century, especially in California and Florida. An estimated 8 million households heated their water with the sun in these areas, until aggressive marketing by utility companies resulted in most of these systems being replaced with electric and gas heaters.

Today, solar water heating is making a comeback, especially amongst savvy home and business owners looking to get the biggest return for their renewable energy dollars. Solar thermal doesn’t have the allure of photovoltaics (PV). It won’t light up your store or make your computers run – and it rarely makes front page news. What it will do is pump out loads more energy per dollar invested.

The Solar Workhorse

The cost for a solar panel is roughly the same whether you’re looking at solar thermal or PV. The balance of the system, including parts and labor, works out to about the same, too. But that’s where the similarities end.

Solar thermal collectors average about 40 sq.ft., versus 15 for a PV collector. That’s almost 21/2 times the sun exposure – which translates to a heck of a lot more energy per dollar over the life of the panel. In addition, solar thermal beats PV when it comes to panel efficiency. The hot water panel will capture over 50% of the solar energy that strikes it. A fairly efficient solar electric panel will only convert about 15% to usable energy. It all boils down to this: the solar water heating system delivers somewhere around 10 times the usable energy you would get from a similarly priced solar electric system. That’s significantly more energy, and it makes solar thermal hands down the most cost effective solar heating system on the market.

Solar hot water is an energy workhorse that will pay for itself in an average of seven years from the date of installation. After that, it’ll keep pumping out free energy as long as the sun shines. And the higher the price of fossil fuel, the more the savings.

Does it Work in the Winter?

In a word, yes. Solar thermal works whenever the sun is shining – even when temperatures dip into the single digits or lower.

To understand why it works, it’s necessary to describe a little about how it works. Without going into detail (there is more than one type of solar thermal collector), the basic idea is this: You have a layer of glass covering a black absorbent surface. Sunlight travels through the glass to heat the absorber plate or tube, thus heating it up. The heat is contained by the glass and picked up by water or antifreeze solution running through tubes in the collector. The heated water is then pumped to a storage tank (you can use a solar powered pump if you want) where it remains until needed. A well-insulated hot water storage tank can keep you supplied with warm water well after the sun goes down.

It’s simple in concept, but don’t let that fool you. Solar thermal collectors have been known to produce 300+F degrees water even on a very cold winter day in Wisconsin, where winter temperatures routinely stay below 20F degrees for weeks on end. (Because it’s a closed system the water has no way to vaporize into steam, which is why you can get superheated water.)

The limiting factor in winter is not temperature, but day length. Shorter winter days and lower sun angles mean less solar energy captured during the dark part of the year. However, if your solar panels are well placed your system will still provide some heat during the cold months. If you can plan most of your hot water use to take place during the afternoon and early evening you could still see significant savings even during the shortest days.

Looking at it from a yearly perspective makes the most sense. Depending on your climate and hot water needs, a solar water heating system could save you up to 85% of your current heating costs.

Keep in mind, too, that you don’t have to depend on the sun for 100% of your heating needs. Most solar thermal installations are hybrid systems, using natural gas or electric as a back-up energy source. That way, you enjoy substantial savings when the sun is shining, without worrying about running out of heat when it’s not. And, in the event of disruption to your gas or electric supply, you won’t be completely without hot water.

Is Solar Thermal for You?

Can you benefit from solar water heating? First off, let’s address the obvious. The more hot water you use, the faster your payback will be on a solar thermal system. The typical solar thermal system results in 50-80% savings in monthly water heating bills. If your business uses lots of hot water, such as a hotel or restaurant, you’re likely to benefit significantly.

But what if you aren’t a big consumer of hot water? If you own a tax consulting company or a real estate office and only use hot water for washing hands and the occasional coffee mug, don’t write off solar hot water just yet. It also has space heating applications. If you already have a hot water heating system, solar thermal may be a good choice for you, depending on your system type. It’s also possible to set up a water to air heat exchanger for your forced air system. Contact a solar thermal installer in your area for information and advice specific to your situation.

And remember, all the mechanics won’t do a bit of good if you don’t have access to sunlight. Thermal panels can be located 200 yards or more away from your building and still perform cost-effectively, but they do need adequate sun exposure. At least six hours a day of sun is a good rule of thumb. An evaluation by a qualified certified solar site assessor, known as a site assessment, will reveal exactly how much sunlight you have to work with. Roof-mounting is the most popular choice for solar panels of any type, but they can also be mounted on the ground or on the side of your building.

Grants & Incentives

Now is a great time for your business to invest in solar water heating. Concerns about dwindling energy supplies and global warming are fueling all kinds of renewable energy incentives, from tax cuts to grants, guaranteed loans and even outright cash rebates. In a February 24, 2009 speech to Congress, President Obama expressed his commitment to “double this nation’s supply of renewable energy in the next three years.” That translates into billions of dollars of federal funds in the form of grants, loans and tax credits being made available to businesses as well as homeowners eager to benefit from renewable energy technology.

On the federal level, solar thermal systems qualify for the same 30% federal tax credit as solar electric systems. The U.S. Departments of Energy and Agriculture both offer renewable energy grants and loans. Many state and local governments offer loan and grant money, tax credits and exemptions, and/or cash back for investing in renewables, too. Even some power companies are jumping on the bandwagon with grants and other incentives of their own. No matter what size solar installation you’re considering, you’re sure to find resources out there to help make it affordable and even more profitable.

What About PV?

Even if you’re not concerned about the environment, solar hot water is worth looking into from a cost savings standpoint. As stated above, solar water heating is ten times more efficient than solar electric. Most solar thermal systems represent 50-80% savings in monthly energy bill savings. And, the typical pay-back time averages 7 years. In fact, it’s sometimes possible to buy the installation on a loan, and save more each month on your energy bill than you spend on your loan payment. Now that’s a no-brainer investment!

But does that mean we should forget about PV?
Absolutely not! The advantage of solar electric is that it’s unlimited. When your system is producing more power than you need, you just send your excess to the grid. Many if not most power companies these days will buy excess electricity from privately owned solar or wind electric systems.

Once you’re using all the hot water you can use, PV is the sensible next step. It will let you operate your business on an even cleaner, greener basis. But if you’re just starting out in solar, and if your situation warrants it, you can’t do better than to sink your money into that renewable energy workhorse – solar hot water.


Bob Ramlow, Solar Water Heating, Copyright 2006 New Society Publishers (available from www.newsociety.com)

U. S. Department of Energy, A Consumer’s Guide to Energy Efficiency and Renewable Energy

DSIRE (Database of State Incentives for Renewables and Efficiency)

By Anne Michelsen

Anne Michelsen is a freelance copywriter who promotes Green and renewable energy businesses using direct response marketing techniques. She is also co-owner of a solar installation company, Marathon Renewable Energy. She can be contacted through her website, www.GreenInkCopywriting.com.

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