“Solar thermal vs photovoltaic, what?”
You’ve just managed to wrap your head around the concept of photovoltaic systems. Now all of a sudden you’re hearing about solar thermal and it feels like you’re back at square one.
While both of these systems seek to replace their fossil-fuel counterparts by using solar energy, they are very different from one another.
But don’t stress! This is what we’re here for.
In this article, we’ll discuss both of these solar-based systems by defining them and breaking down their respective components and processes.
In addition to the above, we’ll make the two battle it out to see which system comes out on top in certain areas.
Solar Thermal VS Photovoltaic – An Overview
Have you ever made the mistake of touching your car steering wheel on a sunny day and burning your fingers? If so, you’ve had a first-hand experience with the end result of solar thermal energy.
The steering wheel both absorbs and stores heat from the sun. Solar thermal systems collect and store heat in the same manner.
Solar thermal encapsulates any type of technology that takes sunlight and converts it into heat. That heat can be used for three primary purposes:
- To convert it into electricity.
- To heat water for your home or business.
- And to heat spaces within your house.
There are also two general types of solar heating systems: passive systems and active systems.
This type of heating takes place in a space like a Passive House.
Passive solar space heating happens when the sun shines through the windows of a building and warms the interior. The solar energy is absorbed by the building materials and heats the interior of buildings by natural radiation and convection.
Active solar heating systems have collectors for heating a fluid (air or a liquid) and fans or pumps to move the fluid through the collectors.
Here the fluid is heated and sent to the interior of a building, or to a storage system where the heat is released, and then sent back to the collector to be reheated.
Active solar water heating systems usually have a tank for storing solar-heated water.
A plant utilizes its leaves to absorb and store solar energy for photosynthesis. This process helps generate energy so that it can grow.
Why are we telling you this? Like leaves on a tree, PV systems produce energy from the sun by converting solar rays into usable electrical energy.
This energy can then be used to power a variety of appliances – kettles, cars, heating systems, even entire households.
There are 3 main types of PV systems:
- Grid-tied – This system uses a standard grid-tied inverter and does not have any battery storage. This is perfect for customers who are already on the grid and want to add solar to their house.
- Grid/hybrid – Ideal for customers who are already on the grid but want to have battery back- up in the event of outages, etc.
- Off-grid – This system is for people who want complete energy independence – they is no connected to the public electrical grid.
Solar Thermal VS Photovoltaic – Components
These systems vary in their complexity.
This document from the U.S. Department Of Energy identifies the following components of a basic solar thermal system:
- Solar thermal collector.
- Storage tank.
- Pressure relief valves.
- Piping to move heat transfer fluids from collectors to storage, and to carry cold fluids to the collector.
- Insulation for the piping.
- Valves to isolate, bypass and drain the solar system.
- Air vents.
Solar Thermal Collector
The solar collector is the boiler of the solar thermal system. They are either non-concentrating or concentrating.
Non-concentrating – The collector area (the area that intercepts solar radiation) is the same as the absorber area (the area absorbing the solar energy/radiation). Solar energy systems for heating water or air usually have non-concentrating collectors.
Concentrating – The area intercepting solar radiation is greater, sometimes hundreds of times greater, than the absorber area. The collector focuses or concentrates, solar energy onto an absorber.
Solar thermal power plants use concentrating solar collector systems because they can produce the high-temperature heat needed to generate electricity.
Additionally, there are several types of solar thermal collector technologies. The U.S. Environmental Protection Agency identifies them as follows:
- Unglazed solar collectors
- Transpired solar air collectors
- Flat-plate solar collectors
- Evacuated tube solar collectors
- Concentrating solar systems
In the next section, we’ll touch on how each of these works.
In some solar thermal systems, the heat storage tank or tanks may be the largest component. One or more storage tanks may hold heated water.
PV or solar systems also vary in their complexity.
A basic PV system consists of the following components:
- Solar Panels
- Charge Controller
- Electrical Safety Equipment – fuse box, breaker, switch, sensors, and electrical wires.
The heart and soul of any PV setup.
A single panel is made up of an assembly of photovoltaic cells mounted in a framework for installation.
These panels are grouped together in an array and they work by converting photons from the sunlight into direct current (DC), which then flows into your inverter.
These panels come in 3 forms:
There’s a lot more to these components than you may think. If you’re interested in learning more about solar panels, check out our article – Solar Panels For Home Use (The Ultimate Guide).
The solar charge controller is another essential part of a PV system. It has 2 functions:
- Regulate the power output of your solar panel.
- Properly charge the battery.
There are currently 2 types of solar charge controllers: PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking).
The energy that your PV system generates is stored here.
There are various types of solar batteries. Each of them has pros and cons when it comes to storing your solar energy production.
Solar batteries are specially designed for solar systems and are different from your regular car battery. You might then wonder what the different types of solar batteries are.
There are currently 4 types of batteries fitted for solar energy storage:
- Lead-Acid batteries
- Lithium batteries
- Red-ox flow batteries
- Hydrogen batteries
If you’d like to learn more about these types of batteries, click here.
Inverters for solar panels are perhaps the most essential part of your system. They allow your solar panels to power your electronic devices by converting DC (Direct Current) electricity into clean AC (Alternating Current).
There are three types of inverters:
- Micro-inverters (Grid-tie)
- String inverters (Grid-tie)
- Hybrid inverters (Off-grid)
If you’d like to learn more about these types of inverters, click here.
Solar Thermal VS Photovoltaic – The Process
Unglazed Solar Collector
- Sunlight: Sunlight makes contact with the dark material of the collector, which heats up.
- Circulation: Cool fluid (water) or air circulates through the collector, absorbing heat.
Transpired Solar Collector
- Sunlight: Sunlight hits the dark perforated metal cladding, which heats up.
- Circulation: A circulation fan pulls air through the perforations behind the metal cladding, heating the air, which is then pulled into the building for distribution.
Flat-Plate Solar Collector
- Sunlight: Sunlight travels through the glass and hits the dark material inside the collector, which heats up.
- Heat reflection: A clear glass or plastic casing traps heat that would otherwise radiate out.
- Circulation: Coldwater or another fluid circulates through the collector, absorbing heat.
Evacuated Tube Solar Collector
- Sunlight: Sunlight hits a dark cylinder, heating it up
- Heat reflection: A clear glass or plastic casing traps in heat
- Convection: A copper tube running through each cylinder absorbs the cylinder’s stored heat, causing the fluid inside the tube to heat up and rise to the top of the cylinder.
- Circulation: Coldwater circulates through the tops of the cylinders, absorbing heat.
Concentrating Solar Collector
- Sunlight: Sunlight hits a reflective material (i.e., a mirrored surface), usually in the shape of a trough (shown here) or a dish.
- Solar reflection: The reflective material redirects the sunlight onto a single point (for a dish) or a pipe (for a trough).
- Circulation: Coldwater or a special heat transfer fluid circulates through the pipe, absorbing heat.
Below is a step-by-step process of how a standard PV system operates:
- The sun’s rays make contact with the solar panel and an electric field is created.
- The solar electricity generated flows from the silicon cells to the edge of the panel, and into the conductive wire.
- The conductive wire delivers the electricity to an inverter. Inside the inverter, the electricity is converted from DC to AC which is used to power buildings, vans, and motorboats.
- Once the electricity has been converted to AC, another wire transports the electricity to a breaker box which distributes the electricity throughout the building as required.
Solar Thermal VS Photovoltaic – Applications
Here are some of the main uses of solar thermal energy:
- Space heating
- Air conditioning
- Water heating
- Distillation and desalination
Here are some of the main uses of solar thermal energy:
- Home appliances
- Heating & cooling systems
- Water pumping
- General electrical power
Honestly, the list of uses with photovoltaic energy is endless.
Solar Thermal VS Photovoltaic – A Showdown
Time for these two technologies to duke it out.
In this section, we’re going to compare factors such as:
- Savings potential
- Space requirements
There’s no point in going the renewable energy route if the systems aren’t able to produce results. For this reason, it’s important that these systems are as efficient as possible.
Solar thermal can have an efficiency level of up to 70% in the collection of heat from the sun. On the other hand, PV systems have an efficiency of between 15% – 20%.
However, the University of Michigan’s Center For Sustainable Systems notes that researchers have already developed PV cells with efficiencies of around 50%. It’s safe to say that the best is yet to come.
The winner: Solar Thermal
These renewable energy systems are rather pricey -your wallet is certainly going to feel the impact of that initial upfront investment. As such, you want a solar system that both pays for itself and saves you money in the long run.
Photovoltaic systems come with a number of incentives that can save you money, both in the short and long term. These include:
- Net-metering credits
- Federal tax credits
Solar thermal systems don’t seem to qualify for the above incentives because, unlike PV systems, their primary function isn’t to generate electricity.
The winner: Photovoltaic Panels
While going solar is great, it can be tough to accommodate systems that require a fair amount of space.
One of the main reasons to select solar thermal is to save on space. Their higher level of efficiency means that they require less in the way of components to do their job.
So a home that’s pressed for space will likely be better suited to a solar thermal setup.
The winner: Solar Thermal
On a smaller scale, domestic PV systems are more versatile than thermal systems. This is because they can power many different applications – household appliances, transportation, heating systems, etc.
In contrast, domestic thermal systems are predominantly used for space and water heating.
The winner: Photovoltaics
Which Solar Technology Is Right For You?
Like with any important decision, you need to ask yourself some important questions and evaluate your needs.
- Is space an issue?
- What are your energy needs? Are you looking to power multiple applications or are you just needing to power your water and space heating systems?
- What is your budget?
- Would you like to benefit from solar incentives?
The previous section gave you some insight into the advantages of each system. Now it’s up to you to evaluate those advantages as well as the answers to the above sections and make the final decision.
Both solar thermal and PV systems are wonderful examples of green tech. What’s more, knowing about both types of systems and having access to them can only benefit you and our planet in the long run.
The more renewable energy producing options that we have access to, the better. So, while this article may seem like it’s pitting the two forms of tech up against one another, it’s not.
Instead, its purpose is to educate you on yet another fantastic method of renewable energy production.