The sun is just one of the essentials that makes life on Earth possible. With a star in our backyard just 151.76 million kilometres away, undergoing constant nuclear fusion reactions and emitting energy on a cosmic scale, it makes sense to look to our sun to energize our world.
As we put more time and money into trying to decarbonize our energy generation, we are expanding the degree we can channel the light and heat we get from the sun into clean energy. Solar panels are just one way we harvest the sun’s power – this article will dive into the different ways we currently harvest the sun’s energy in our homes and buildings.
The 5 types of solar power
According to the National Renewable Energy Laboratory – one of the premier authorities of solar energy and other renewable energies – there are five main ways that we can harness the sun to power and heat our homes.
Solar Photovoltaic Technology – Utilizing solar cells to convert sunlight into electricity.
Passive Solar Technology – Design with the sun in mind, like adding south-facing windows to warm the interior space.
Solar Water Heating – Utilizing the thermal properties of sunlight to provide hot water for your home or business.
Solar Process Heat – Utilizing the thermal properties of the sunlight to heat air, provides space or water heating, on a commercial or industrial scale.
Concentrating Solar Power – Using mirrors and lenses to concentrate the sunlight to generate high temperatures, which can be used to generate electricity.
Solar Photovoltaic
Solar photovoltaic technology is one of the most common today when it comes to harnessing the sun’s energy. Solar Photovoltaic generally comes in the form of solar panels, but the technology seeks to expand beyond this point soon.
Today, the majority of solar panels in both residential and commercial applications are silicon-based, but many different materials are capable of reacting to photons of light from the sun to generate electricity.
The process of how each type of photovoltaic cell generates electricity comes down to the formulation of the cell, which has other impacts on the performance and price of the solar panels available.
Different types of solar cells are as follows:
Monocrystalline solar panels
Monocrystalline solar panels will be the most common solar panel on the market in 2024. Monocrystalline solar panels are often easy to identify, due to the darker colour these panels have.
The creation of monocrystalline panels starts with creating a silicon ingot – a cylindrical formation of silicon. This ingot is created by placing a “seed crystal” of pure silicon into a pool of molten liquid silicon, which is “slowly pulled a rotated upward” to form the ingot. The ingot then is cut thinly, into a shape that is called a “Wafer” among the industry. This creates the type of crystal construction that forms the basis of a solar cell, which are then combined with other solar cells to create a solar panel. On average, it takes between 32 and 96 of these silicon wafers to create each solar panel.
What contributes to the popularity of monocrystalline solar panels is the efficiencies they can easily attain – between 17 and 22%. However, the trade-off for the improved efficiency is a higher price point than polycrystalline panels.
Polycrystalline solar panels
Polycrystalline solar panels (sometimes referred to as multicrystalline solar panels) are another common type of silicon-based solar panel.
Easily distinguished by their blue, square-shaped cells with no space between (unlike the rounded edges of the monocrystalline solar cells), Polycrystalline are common, but way less common compared to monocrystalline.
Polycrystalline solar cells are created from silicon crystals. The main is that the silicon for a monocrystalline solar cell is created from a single silicon crystal, where the polycrystalline solar cell contains many crystals that are melted down and formed into a cube, from which the silicon wafers are cut.
Since production is easier, the resulting solar panels can be manufactured quickly and less expensively than their monocrystalline counterparts. The trade-off is less efficient, with Polycrystalline panels ranging between 15% to 17% generally.
Thin-film solar panels
Thin-film solar panels are an interesting variant of solar panels that is available today. These panels, named after their thin, flexible design, are many, many times thinner and lighter than what’s typical of the other types of current solar photovoltaic cells.
The process of creating one of the many types of thin-film solar panels involve depositing a thin layer of some kind of photovoltaic substance onto a substrate, often glass, plastic or even metal.
Due to these unique traits of these solar panels, the use-case of photovoltaic generation has expanded greatly and is expected to expand further as this technology develops.
These panels have many advantages over traditional silicon panels, including flexibility that enables placement almost anywhere the sun shines. They are also tremendously lightweight, meaning they can be placed on a rooftop without a mounting system in place.
While crystalline solar panels are rigidly defined, there are many different forms of thin film solar panels today, based on what they are made from. Each of these materials creates a different ‘type’ of solar panel, however, they all fall under the thin film solar cell umbrella.
Some different types of “photovoltaic substances” include:
These panels are typically cheaper to make due to requiring less raw materials than their crystalline counterparts, However, these panels are less efficient than those made from crystalline silicon, with an average efficiency of between 10% and 13%.
Passive Solar
Passive Solar Technology is a less specific technology, and more a set of design principles that can be used to harness the sun’s heat to heat or even cool a space. The key word here is “passive”.
When designed thoughtfully, a building can maintain comfortable temperatures through just how it absorbs heat and how that heat can be redispersed through the space. Passive solar works use certain constructions, like carefully considered window placements (called “apertures”), and large blocks of brick, concrete, stone or some other material called a thermal mass, as well as ways to distribute the accumulated heat to where it is needed, through conduction, convection, and radiation.
Passive solar heating and passive solar cooling are two sides of the same coin. With solar cooling, these systems use shading and natural ventilation to store cool air or redistribute warm air
Solar Water Heating
Solar water heating is channelling the sun’s heat to cover the hot water needs of your home (we will touch on solar water heating for larger buildings shortly). Using natural sunlight for your hot water needs can be a cost-effective, renewable investment worth considering, especially if the weather is favourable for the system year-round.
Solar water heating systems come in two varieties: active systems feature mechanisms like pumps and controls to circulate the water, while passive systems do not have these mechanisms and rely on phenomenon like thermodynamics and gravity.
Active systems heat either water (in a system called “Direct circulation systems”) or a non-freezing fluid (in an “Indirect circulation systems”) which is then used to warm the water. These systems often are the most efficient systems, but due to the pumps and controls required, are more expensive. In Canada, where our winters are very cold, an indirect circulation system is recommended, as winter will render the system useless otherwise and potentially cause damage.
Passive solar water heating systems aren’t as efficient as their active systems, but can be cheaper, require less maintenance, and are more reliable. However, they can be harder to operate or maintain in areas which see below-freezing winters, so your mileage may vary here.
Solar Process Heating
Solar Process heating is the advanced application of some of the previous concepts, like solar passive heating and solar water heating, but scaled up to be viable for commercial or industrial buildings.
For example, solar process space heating requires having a “transpired collector” on a south-facing wall to accumulate heat throughout the day in the form of hot air, which can then be released into the ventilation system when the thermostat is turned up.
Water heating on a much larger scale than what can be found in a residential home also falls under the “Solar Process Heating” umbrella. These systems have most of the same components compared to a residential solar water heating system: solar collectors to collect industrial levels of thermal energy, a heat exchanger, a pump, and any amount of large storage tanks to store the heated water.
While space heating is easy to understand and implement in a solar passive system, space cooling on a larger scale can be more expensive and complicated. Space cooling can be accomplished using thermally activated cooling systems (TACS). There are two main ways that we see thermally activated cooling in buildings today:
- Solar absorption systems – use thermal energy to evaporate a refrigerant.
- Solar desiccant systems – Provide cooling by “drying” the air.
Solar Thermal
The sun can get pretty hot. While photovoltaic generation is the most common form of electricity derived from the sun, thermal energy can also be harnessed to generate electricity, called Concentrated Solar Power (CSP).
Since the majority of these solar thermal projects are intended to generate much more energy, these systems employ the use of lenses or mirrors to concentrate the sunlight to temperatures – between 150 and 1500 degrees Celsius. From there, the thermal energy can turn a generator, and thus create electricity.
Right now, there’s only one solar thermal generator site in Canada – a small, 1 MW site in Medicine Hat, AB called the Medicine Hat ISCC Project CSP Project which came online in 2014.
Most of what differentiates these systems is how the sunlight is concentrated. These methods are described below.
Linear Concentrator Systems
These systems use a “linear” receiver – a straight tube filled with a fluid that the thermal energy of the sun heats up. These systems use mirrors that are rectangular yet curved, which the receiver runs along.
There are two main forms of this system:
- Parabolic Troughs describe the shape of the reflector, which each have a receiver fixed overtop each trough.
- Linear Fresnel reflectors feature several mirrors, either curved or flat, which are installed on trackers that reflect towards a fixed receiver tube, which may or may not have another parabolic mirror to further redirect the light onto the receiver.
Dish/Engine Systems
These systems utilize a concave dish, lined with mirrors, to focus the sun’s rays on a central thermal receiver, which can then convert the thermal energy into a usable form.
Power Tower Systems
One of the more land-intensive forms of solar generation, Power Tower Systems feature a large field of Mirrors on trackers called “heliostats” that concentrate sunlight towards the receiver which is located at the top of a central tower.
Concentrating solar towers use the second-most land In terms of median land use per unit of electricity, and so they are not hugely viable here, but have proved successful in desert locations like Nevada.
Comparing energy rates and renewable energy options
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