About This Article:
Who else wants a super-modern home?
A whole lot us do.
But while solar hot water may not feel exciting, it is an essential part of a modern solar energy installation. And the reason revolves around one, single word: efficiency.
Curious? ...Read on!
Who else wants a super-modern home?
A whole lot us do.
But while solar hot water may not feel exciting, it is an essential part of a modern solar energy installation. And the reason revolves around one, single word: efficiency.
Curious? ...Read on!
Why Solar Hot Water Matters
You may be aware that solar electric power has become far more efficient over time. Take a look at this impressive looking chart from NREL (the National Renewable Energy Laboratory):
In the chart above, home solar panels are called "Crystalline Si Cells." They are shown in purple - larger image here
Charts like this can be difficult to decipher. But the general trend is clear: solar electric efficiency is on the rise.
In fact, the efficiency of home solar PV cells have now tested at a whopping 26.2%!
Of course, commercially available solar electric panels score a bit lower than this, but high-quality solar manufacturing companies maintain products that can exceed a 20% efficiency as of this writing.
However, You Can Triple That Solar Electric Efficiency Instantly
Impressive as these numbers and trends may be, you can triple the high water mark of solar PV. Simply use a solar thermal collector to replace one small part of your solar electric installation!
Why?
Because believe it or not, solar thermal efficiencies for commercially available products typically run between 75% and 80% (to prove this to yourself, simply download the excel file at this link).
This is clearly a staggering improvement when utilizing roof or ground-mounted space. And the boost it delivers to your solar electric system cannot be overestimated, really.
But how does this technology actually work? And is it truly effective in the chilly, gray winters of Portland's rainy climate?
How Solar Thermal Energy Works
Solar thermal installations can boost the overall efficiency of solar electric systems by using more of the sun's energy to directly heat water in your home (instead of wasting some of that energy by converting it into electricity first). Alternately, solar thermal panels may replace part of the heating performed by a fossil fuel like natural gas.
In the summer months, it is easy to conceptualize how this might work. But what about the the winter months? Clearly there isn't enough solar energy to heat all of the water in your home.
The key is in the assistive approach with which solar thermal is designed.
In fact, it is extremely rare to find a solar hot water system that completely eliminates the need for other energy inputs. Instead, solar thermal generally acts as a booster to other forms of heating. Here's how.
Solar Hot Water: A Quick Overview
When water enters your home, it is nearly always cold.
This cold water is channeled into a hot water tank where energy of some kind is used to heat it to a specified temperature. A thermostat regulates all this, so that the energy source is applied once the temperature drops below a certain degree.
During the summer months, a well-sized, solar thermal system will generally heat this water to the temperature set by the thermostat (there are 2 different ways this can work. More soon).
In the winter (or during an extended period of heavy clouds) the solar energy collectors harvest some energy from the light that impacts them. This smaller amount of energy is applied to the water in your tank, increasing the temperature a bit. The gap is then typically made up by an electric or gas heat source.
With a well-designed, evacuated tube installation, it is possible to capture even brief inputs of energy (when the winter clouds break momentarily, for example). In addition, light clouds can produce a significant amount of useable energy without direct sunlight.
Variables to Consider in Solar Thermal Systems
Direct-Heated Solar Hot Water Systems
Here in Oregon, it is unusual to see a direct-heated thermal solar system. This is the simplest form of solar hot water.
In a direct-heated system, water from your tank would be directly circulated into the solar thermal panels (often called "collectors"). You would then use this water in your household.
A direct-heated system is more efficient at transferring heat to your tank, but there are serious drawbacks; including a lack of resistance to freezing temperatures and the risk of scaling and deposit buildup that can clog solar collectors.
Closed Loop Solar Thermal Systems
It is far more common to find completely closed loop solar thermal systems.
These solar installations are more resistant to any kind of damage from freezing, an important consideration during a cold snap here in the Portland area, for example.
These closed loop systems come in two different styles: the traditional closed loop and the drainback system. Both systems make use of a heat exchanger to heat the water in a hot water tank.
How Do Closed Loop Systems Work?
In contrast to a direct-heated system, these closed-loop systems keep the fluid from your solar collectors completely separate from the potable water in your tank.
A heat exchanger (often a set of copper tubes that run through the interior of a solar hot water tank) puts this hot fluid in a location that can transfer heat into the cold(er) water of the tank.
In the event that the fluid from from your panels is colder than the water in your tank, the circulation of the fluid is paused using a control system, typically consisting of a valve and a thermostat. A small electric pump (often solar PV powered) manages the needed fluid circulation.
Traditional Closed Loop Systems vs. Drainback Systems
In a classic (or traditional) closed loop system, a propylene glycol mixture is used to ensure that the solar thermal fluid does not freeze.
The drawback to these systems is that propylene glycol mixture must be monitored closely and replaced every 2 - 5 years to ensure its proper functioning.
In contrast, most modern solar thermal systems use a high-tech drainback strategy.
These so-called drainback systems allow the solar thermal fluid to drain back out of the solar collectors when temperatures drop to a dangerous level (as the name suggests). The advantage here is that the fluid need not be as closely monitored, need not be replaced nearly as often and can be used to maximize energy transfer, instead of to avoid freezing.
The downside of this approach is the need for a small, extra tank to capture the fluid when it is removed from the collectors, and a slightly more powerful motor to ensure proper fluid circulation. It also requires a professional installation by a highly qualified technician.
This article outlines the 8 essential factors that Synchro recommends you consider when selecting a solar installer to handle this kind of specialized work.
Synchronize Your Design Process
If you get the chance, there is an advantage to working with a company that can design solar thermal and solar electric systems to work well together. Chances are that an increase in total system efficiency is nearly impossible to avoid in many situations.
Also, keep in mind that the actual installation of solar hot water systems requires a completely different set of credentials. A company that can do both solar PV and solar thermal must maintain an incredibly deep understanding of all aspects of the solar contracting process.
In addition to the standard solar electric & contracting requirements that all of us carry in Oregon, these specialized professionals require full plumbing licensure as well. Oregon Plumbing licenses can be identified by the letters "PB" in official contractor searches (this stands for Plumbing Business. For example, our plumbing license number is PB781).
Here at Synchro Solar, we also maintain an optional Solar Thermal License (called an STL). This a specialized designation that requires extensive knowledge of solar energy, in addition to deep knowledge of the plumbing environment. You can see all of our licenses and look up our contracting history at the Oregon.gov website (here at this link).
If you have questions about exploring a solar installation of any kind, with or without a solar thermal component, we would love to hear from you!
You can easily reach us by phone or by using the button below to send us an email.
(503) 208-4076
