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LAST UPDATED: 17 NOVEMBER 2020
Introduction to Solar Power: The Difference Between Photovoltaic and Thermal
Thinking about investing in solar for your home or business? Whether you’re motivated by economics, energy independence, or environmentalism, there’s never been a better time to go solar. Solar, you might’ve heard, is more affordable now than ever. If you’re new to solar, or just looking for a bit of a refresher, this article will help you understand the basics of solar power and how you can harness it.
Our planet receives plenty of energy from the sun in the forms of light and heat. Every hour the sun beams more energy onto Earth than the entirety of humanity uses in a year. Solar power is using this energy to heat and power our homes. This energy can be harnessed through two types of technology: solar thermal (heating water and/or air) or photovoltaics (PV), also known as solar electric (converting light to electricity). Solar power is an important source of renewable energy and its abundance makes it a very appealing source of energy for your home or business. Harnessing the power of the sun will increase your energy security through reliance on a local, inexhaustible, energy source that enhances sustainability, reduces pollution, mitigates the effects of climate change, and insulates you from rising utility costs. The easiest way to make use of solar energy is to install a solar thermal or PV system on your property. SUNSHINE TO HEAT: THE BASICS OF SOLAR THERMALSolar thermal systems convert sunlight into thermal energy (heat) through the use of solar thermal collectors. At its most basic a solar thermal system consists of three parts:
Solar thermal collectors are the workhorses of your system, converting sunlight into heat. Multiple collectors can be connected together to create a solar thermal array and increase the amount of heat your system produces. For residential applications there are two varieties of collector: flat plates and evacuated tubes. A flat plate collector is made up of a metal case with a glass plate on one side through which a fluid is circulated to absorb the sun’s heat. Evacuated tube collectors comprise a metal frame that holds between 20 and 30 glass tubes that absorb and transfer the sun’s heat to a circulating fluid. The tubes are vacuum sealed to insulate them from the ambient air temperature. We generally recommend evacuated tube collectors for cold climates however each has its pros and cons. Regardless of which you choose, a heat transfer fluid circulates through the collector, collecting the heat and transporting it to where it can be used or stored. The second component of a solar thermal system is something to store the heat collected by the panels until it’s needed. This is usually a solar tank containing an internal heating coil to transfer the solar heat from the heat transfer fluid into water stored in the tank. In this way the heat collected by the panels get trapped in the water held in the solar tank until it’s needed. The water in the tank can then be used just like hot water produced by a conventional electric or gas hot water tank, the difference being that this water was heated for free and in an environmentally friendly manner. Last but not least, there’s the pump station and heat transfer fluid. This is what transports the heat from where it’s captured, the solar thermal collectors, to where it’s stored, the solar tank. The heat transfer fluid of choice is water mixed with enough non-toxic anti-freeze to ensure it doesn’t freeze during the winter. Standard plumbing fixtures, either copper piping or PEX tubing, contain the heat transfer fluid on its journey from the solar thermal collectors to the solar tank and a pump station is used to circulate the heat transfer fluid between the collectors and tank. Simple Solar’s FREEDOM WON systems come with a fully automated pump station specially designed for solar thermal systems. There are plenty of manufacturers of solar thermal collector and solar tanks, but Simple Solar are the only ones who manufacture the FREEDOM WON! SUNSHINE TO ELECTRICITY: THE BASICS OF PVPV systems convert sunlight into electricity through the use of PV panels. PV systems come in two types, grid-tied and off-grid. Grid-tied systems are connected to the electricity grid whereas off-grid systems are not. Grid-tied systems can feed excess electricity you generate into the grid, for which you may be paid by your utility company, and you can take electricity from the grid when you don’t generate enough. Off-grid systems require batteries to store the electricity that you generate and a backup generator is usually a good idea. Grid-tied systems can also be combined with batteries. This adds a significant element of complexity and cost to a system but further reduces your reliance on grid electricity and allows for an emergency backup if the grid goes down.
A basic PV system consists of three parts:
PV panels are what most people envision when they think of solar power. They’re rectangular panes that convert sunlight into electricity via the photovoltaic effect. The electrical output of a PV panel is given in watts and PV panels are generally grouped together into an array of connected panels. This means that so long as you have the space and the budget, a PV system can scale up to provide as much electricity as you require. To determine how much electricity an array generates you simply add the wattage of all the panels in the array together. For example, a 6.0 kW system could be made up of 24 250 watt modules or 20 300 watt modules. The mounting hardware for PV panels is called racking. These metal struts and fasteners allows you to mount your panels pretty much anywhere you can image. Inverters convert the DC electricity generated by your PV panels into usable AC electricity. Inverters come in two types, string inverters and micro-inverters. String inverters are generally found combined with a charge controller for battery connected systems. For grid-tied systems, micro-inverters, which connect directly to the PV panels, are cheaper, safer, and easier to install. WHICH SYSTEM IS RIGHT FOR YOU?
Combining solar thermal and PV is the most efficient way to generate all the energy you need. This combined system consists of five evacuated tube collectors for heating and 13 PV panels for electricity.
If your goal is to be completely energy independent then it’s most effective to get both a PV and thermal system. Using PV for heating is inefficient and requires three times the roof space of a comparable thermal system to generate the same amount of heat; the conversion rate from solar energy to heat energy is about 70 % whereas the conversion rate to electricity is only about 20 %. However, a thermal system is unable to provide the electricity necessary to run your appliances. A combination of both systems can meet all your heating and electrical needs. If your goal is to reduce your monthly energy bills or greenhouse gas emissions then geographic location should be taken into consideration. In colder locations, places where the winter temperature is below freezing, an average of 70% of a household's energy use goes towards heating, making a thermal system a better choice. In warm climates, where heating is not as important, a PV system is likely the better choice. Factors such as building insulation and efficiency of already installed water heaters and furnaces should be taken into consideration as well. For example, if you’re using an electric hot water heater than a solar thermal system will reduce your electricity bills by such an extent that the system will pay for itself within three years, assuming average hot water consumption and electricity pricing. Are you ready to go solar? Browse our FREEDOM WON and PV kits or if you’ve got a project in mind send us a the details and we’ll send you a quote. |
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