When I started writing this morning, my intention was to present a slightly more technical, close-up look at what solar PV and solar thermal systems are and how they function. The idea was to split solar down the middle, to give a description of solar PV and solar thermal and finish with a section describing how the SunPump fits in and what it offers. However, after I got started I realised that you can’t just divide solar into ‘PV’ and ‘thermal’ anymore. There is now a legitimate third category – the hybrid. Hybrids are solar thermal or PV panels that integrate a separate, ‘non-solar’ system into their design. It’s exciting to think that, after decades of solar PV and solar thermal panels developing and evolving, a whole new frontier of hybrid systems has been opened up. Before we get into this new world of solar hybrids, however, lets take a look at the existing, traditional solar systems that are out there.
Solar PV: Solar’s Poster Boy
When most people think of solar panels, they think of solar PV. We all know the blueish-black panels to see – they’re an increasingly common sight these days. We all know that PV panels generate electricity, but how does this process actually work?
As the video explains, the heart of solar PV systems is made of silicon (or rather two different types of silicon layered one on top of the other). When Type-N and Type-P silicon are layered together, a weak electric field is created. Essentially one layer of silicon is positively charged and the other is negatively charged. When photons from sunlight hits the silicon layers, electrons are ‘knocked free’ from their respective layers. This process creates a flow of electrons from one type of silicon to the other. Which is to say, this process creates electricity. This electricity is then collected by thin metal plates or ‘fingers’ in the panel. From there, the electricity can be sent to an external circuit and can then be used to power any electrical system. It’s an ingenious design, but it’s limited by poor efficiency (i.e. the amount of solar energy hitting the panels compared to the amount of electricity the panels generate). At the moment, commercial PV panels run at roughly 15% efficiency, meaning solar PV can just about compete with non-renewable sources of electricity. If efficiency can go up to something approaching 50% (which is possible in laboratory conditions today), we would probably be looking a revolution in the energy sector.
Solar Thermal: The Efficiency King
Traditional solar thermal panels operate on a more basic, simple design. In a solar thermal system, the panels have a liquid running through them – usually a glycol/water mixture. The panels are exposed to sunlight (there’s no silicon or electrons needed here) and the liquid is heated. This heated liquid is then piped down into a water tank, where the heat is transferred into the water. What happens next is up to the how the solar thermal system is designed; some systems will heat hot water for taps and facets, while others will go one step further and provide enough energy to heat an entire home. What’s great about solar thermal systems is that they are much more efficient than solar PV. 70-80% efficient solar thermal systems are quite common, meaning that your panels get much more energy per square foot compared to solar PV. The main drawback of solar thermal is the same problem that has – until very recently – plagued all types of solar panels: the panels only collect energy when the sun is shining. At night, when solar thermal systems are arguably needed most, the panels aren’t collecting anything and the system’s efficiency drops dramatically.
SunPump, Hybrids and the evolution of Solar Thermal
This is where the SunPump comes in. The SunPump takes the efficiency of solar thermal and integrates an air-source heat pump directly into the panels. Heat pumps move heat from one place to another, rather than directly creating heat. It’s basically the same technology that keeps the inside of your refrigerator cold, only working in reverse. Because heat pumps move heat around rather than directly create heat, they are highly efficient. More importantly, heat pumps can extract a surprising amount of heat from the air even in very low temperatures. What this means is that the heat pump can operate efficiently at night. With a SunPump, you have solar thermal power heating your home and domestic hot water by day, while at night you have a highly efficient air-source heat pump keeping your home and hot water at the temperature you require. This allows a SunPump to operate as a primary heat source, meaning that you don’t need any other heating system in order to keep your home heated 24 hours a day, 365 days a year. It’s a huge step forward for solar thermal heating, allowing a renewable and highly efficient system to compete with (and beat) oil and gas burning systems for the first time. You can learn more about how the SunPump works here.