How Many Tanks for a Simple Solar Hot Water System?

I was just asked this question the other day, which reminded me that this is a frequent question that people ask and don’t always understand. There are many manufacturer’s today that are promoting single tank solar hot water systems. Whether or not they are a good idea depends mostly on your situation. To keep this simple, I am only talking about simple residential solar hot water systems.
A single tank system means that the water heater and the solar storage tank are the same tank. On the surface, this sound like a super idea. Most people already have a water heater, so you don’t have to spend the additional money for a separate solar storage tank. This also means that you don’t have to plumb between the tanks, install a valve tree, etc.
However, you need to look at how the system will perform to understand what you are letting go by not having a separate solar storage tank. First, with only one tank, you don’t have as much storage. Typical water heaters are only 40-50 gallons. Whereas, typical solar storage tanks are 80 gallons or more. That means you could have at least half the storage in a single tank system that you would have in a two tank system. How much energy you can store in the solar storage tank depends on the temperature that the tank is in the morning and the temperature of your high limit for the tank. This is what frequently occurs with many solar hot water systems in the summer time in Colorado and around much of the USA. If the tank is 90F in the morning and your high limit is set at 170F, Then that gives you 80 degrees of an 80 gallon tank to store energy. With water, you can easily calculate how much energy that is, known as a BTU (British Thermal Unit).

The equation is: Q=Mass of water x (finish temperature.-start temperature)

Please be aware that this equation is simplified to make this example easy to understand.

First, you need to find the mass of 80 gallons of water, a quick Google search finds 1 gallon of water weighs 8.34 lbs. (pounds)

So, the equation looks like this for the 80 gallon solar storage tank.
Q= 80 x 8.34 x (170 – 90)
Q= 53,376 BTU’s

For the single tank system, you have 40 gallons, with the minimum temp no less than 120F and the high limit the same as for the two tank system, 170F

So, the equation looks like this for the 40 gallon single tank system.
Q= 40 x 8.34 x (170 – 120)
Q= 16,680

Comparing the two amounts of energy that you can store. The two tank system can store 3.2 times the amount of energy of the single tank system.

Second, if you are using flat plate solar collectors, their efficiency drops dramatically at higher temperatures, which will reduce your energy collected by even more. I will go into more detail on this in a future post.

Finally, I do think that the single tank systems can make sense. Mostly, they make sense for applications where there is no room for a second tank. If the option is ‘no solar system’ or a single tank system. Then, the single tank system will perform much better than no solar system. As with everything solar thermal, always consider the application.

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Advantages of Maintaining your Solar Energy Products

In the solar world, there isn’t much regular maintenance needed for most systems that harness the sun’s power. What you do need to be cautious of, is who you allow to service the equipment. First, I always recommend that you go to the installing company. If that is not an option, you will need to be certain that the company you choose has experience with your type of system. For solar thermal systems, this is much more important than solar electric systems. This is because solar thermal systems tend to be more complex and also less understood by many contractors that claim to ‘know’ these systems. Frequently, I have seen that because a solar system installs one type of new domestic hot water system, they feel that they know all systems. This is like saying that you sell Toyota cars, so therefore can fix all vehicles, old and new!

When selecting a company to service your equipment, be sure to ask them if they are familiar with that equipment. How long have they been in the solar industry? and do they have liability insurance. When I get service calls from potential clients, I can frequently tell what kind of system they have from them answering only a few questions.

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Tornado Catastrophes and Nuclear Power Prove Solar is Right

Distributed generation is the term that is becoming more popular in the rest of the world. It is the use of small power plants in many locations as opposed to huge power plants in few locations far apart. We have the technology, we just need the will.

The recent natural catastrophes (Fukushima and the Tornadoes in the Southern USA), which seem to be happening with much more frequency. Show yet another reason why we need to let these large power plants go the way of the dinosaur and move into the future.

With centralized power plants, we are constantly one disaster away from shutting down a portion of our economy. With a decentralized system, much like the internet, it is difficult to completely shut down the electric grid. Solar and wind systems can be a vital part of that decentralized energy. The remainder of our power, our base power, can easily be handled by natural gas powered turbines that can startup and slow down easily to adapt to power needs and the variability of power generated from the wind and the sun.

Recent natural gas findings in the US have the natural gas industry considering exporting. It would make more sense to use that cheap energy here at home to supplement what the alternative energy technologies do not make.

Our current financial crisis is yet another reason. Funding for these behemoth power plants, is risky and difficult. Funding for smaller projects such as solar or wind are much less risky and come with a fixed power cost.

Switching over to a distributed generation for our power grid will keep the US ahead of the energy curve and is the most solid path we could choose into the future. The cards are all laid out, all we need to do is play our hand and move into the future.

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Solar Thermal Systems, Drainback Vs. Closed Loop, a guide

A drainback or a closed loop solar thermal system is still a huge debate in the solar thermal industry. I have always maintained that each system is right for the right application. Drainback or Closed Loop systems are just different ways to ensure that the solar system does not freeze. A closed loop system uses Propylene Glycol mixed with water (typically about 50%) to keep the solar system from freezing. A drainback system simply drains back all of the fluid in the solar system to a collection tank when the system is not running. With the fluid out of the collectors and exposed piping, there is nothing to freeze.

For the bigger systems (commercial and industrial), a drainback system rarely makes sense. Drainback systems make the most sense for small residential to large residential (or light commercial) systems. The best benefit of a drainback solar thermal system is that it can simply shut down when the system has no place to put the heat (ie, the solar storage tank has been charged and can take no more heat). Of course, this is assuming that the collectors can also handle stagnation conditions, many cannot, especially evacuated tube collectors. Since the drainback system can handle staganation, this makes them ideal for applications where the system may be oversized during some periods of the year (like a heating system in Colorado). The drainback system also is a simpler system to maintain, with only water as the fluid (though you can added propylene glycol for added safety). The downsides of drainback systems; A large pump is required to overcome push fluid all of the way up and into the collectors, so the pump uses more power than a closed loop system. The plumbing and installation of the collectors is critical and any mistakes can destroy the whole system by freezing. This makes the systems typically more difficult to install and usually only installed by solar contractors with more experience.

Closed loop systems are much more flexible and easily adapted to large commercial and industrial applications. They also can be used for residential systems. With closed loop solar thermal systems, the biggest issue is around stagnation. Stagnation occurs when the solar system doesn’t have anywhere to put the heat that is being collected from the sun. This is when the flat plate systems can get over 340F and the evacuated tubes as much as 400F. At these temperatures there are several issues. The first is that the propylene glycol becomes more acidic the longer the fluid is at the higher temperatures. The second has to do with the fluid boiling. This is more of an engineering problem. The system has to be designed to accommodate boiling or it will overpressurize and release fluid (also known as a ‘blow-down), which can be dangerous. See my post about glycol (Glycol in Solar Thermal Systems….) In general, with glycol systems they should only be used in applications where the solar fraction is low. No higher than 50% is preferred, especially in commercial systems. The more consistent the year round load on the system, the better it will perform, and the less the system has the possibility of needing frequent maintenance to change out the fluid.

To recap; Use the right system for the right application. Closed loop solar thermal systems are best suited for applications that have a consistent year-round load. Drainback solar thermal systems are best suited for systems that must have a higher solar fraction and or have a load that is not constant. If you want to read more about me or my company follow this link

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Solar Thermal and Ground Source Heat Pumps can work together

This week I was having lunch with one of my product vendors. Jeff Morrow at Solar Heat Exchange Manufacturing. He was nice enough to buy me lunch, and he also told me about some new developments using ground source heat pumps tied into solar thermal systems. Traditionally, I didn’t think this was a great idea. However, seeing what was done, I think this could be a fantastic development. It also helped that John Sigenthaler in his February 1, 2011 article for PmEngineer (Well Grounded Solar) was promoting the concept. Basically, the solar system is used to either heat a solar storage tank for domestic hot water or to heat the return loop of the GSHP (isolated from the solar system by a heat exchanger. This way, whenever the solar system is not able to heat the solar storage tank, it can heat up the ground loop. Sigenthaler pointed out that this does blend well with the solar output. In the late winter season (say around March), the ground source heat pump ground loop is at it’s lowest temperature, and could be even using backup heating (possible resistance electric!). This is the time of year when the solar system is starting to put out more of its heat then in the winter. That heat can be used to feed the return to the ground of the ground source heat pump ground loop. This way, the solar system can directly boost the output of the ground loop when it needs it most, Pretty cool.
Feel free to contact me at our company website Simply Efficient Solar and Wind

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Solar in Colorado, not dead yet!

Xcel has come to an agreement with the solar industry and is reinstating the system this coming Wednesday (March 23rd, 2011).  For the small program (which is where most of the companies were doing most of their business) the rebate amount has been reduced to $1.75 (initially, and it will continue to go down over time) and the REC (Renewable Energy Credit) payment has been changed from an upfront payment to a performance based payment.  To get more details, follow the link to COSEIA’s website (Xcel Energy article).

What does this mean to the solar industry? I can only put out directly what it has meant for Simply Efficient and speculate on where the solar industry of Colorado will go today. I am hopeful that this shake-up will allow for some serious weeding out of companies that are not committed to working in Colorado. A thinning of the number of companies is inevitable and needed, and hard to ignore any longer. As the rebate levels drop, I expect to see the largest players, the ones from out of state, close shop and move to more promising territories. Without the up-front payment, I have trouble seeing the leasing programs remain feasible. The bigger in state players (Namaste, Bella, SolSource) will be forced to grow into other more favorable solar states (if they haven’t already) and severally cut down their size in Colorado or close their doors. The smaller companies will also have to shrink and or close. The longtime established thermal companies will go on as they have all along before all of the Amendment 37 excitement came around.

Overall, these changes in the solar industry will leave Colorado with a few solar companies. The companies that do stay here, will ultimately have to be the stronger companies, so they should be here for the long-haul.

I’ve been in the solar industry for 12 years now. When I started there were only a handful of companies, most of them only did solar thermal systems. We will all have to wait and see what the consumer’s want and do our best to give it to them.

Daimon Vilppu

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Why Do We Fund Nuclear Research?

What is happening in Japan is an immense tragedy, and my heart goes out to everyone over there.  What is happening with the nuclear reactor is concerning and also one of my biggest reasons for not supporting Nuclear Energy as a green technology.

When I was in college, in engineering.  I thought nuclear power made sense.  It held such promise as a non-polluting energy source.  Of course there were issues, but the engineers could figure out a solution.

It wasn’t long after originally holding those beliefs that I decided that nuclear power was not as good as it looked.  Today I tell people that the sun is about as close as I would want a nuclear reactor to be (93 million miles away).  In the US, we haven’t brought online a nuclear reactor since 1996.  And I’m OK with that.  Yet we continue to fund research for nuclear power at very high levels. Look at the chart below. Nuclear Energy funding has dwarfed all other technologies. Today, we could easily spend that money on solar electricity directly, not just research.

Today the numbers are getting closer together and more equal.  But Solar still continues to be funded at levels lower than any other technology.  Unless we have some real solutions to the dangers of nuclear reactors (like we are seeing today) and also the danger as well as the expense of disposing of the nuclear waste.  It is unlikely that I will become a supporter of Nuclear Energy.  Definitely never as a ‘green’ technology.

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