Solar powered air conditioning: the facts
As environmental issues continue to grab the headlines commercial end-users have finally realised the importance of publicising their green credentials, with corporate responsibility becoming a competitive issue. This new environmental agenda is driving companies to not only focus on the way they run their businesses but also to look at the buildings that they work in. Since energy efficient climate control equipment can make a big difference to an annual carbon output it is important for end-users to purchase the right selection of building services equipment, guided by their building services consultant.
In order to answer environmental concerns the HVAC industry has been working hard to improve the efficiency of traditional climate control as well as moving to alternative solutions such as heat pump systems. These developments mean that solar power has now finally emerged as a viable way of powering, or partially powering, an air conditioning system, and it is this development that has excited many in the building services industry. But what is it all about, and what will it mean to building services consultants?
The solar cells that make all this possible are also referred to as photovoltaic cells. Cells, either in banks or individually, use the photovoltaic (PV) effect of semiconductors to generate electricity directly from sunlight. It is the same technology which powers those little solar pocket calculators, but until recently their use in many manufacturing sectors has been limited because of high costs. PV technology has also been used to power devices in remote applications like roadside emergency telephones and even orbiting satellites and spacecraft. Now thanks to a recent reduction in manufacturing costs the range of cost-effective uses for solar power is growing. Around the world it is being used more and more for a great range of tasks: from the illumination of road signs, to generating residential electricity. Its popularity has been boosted by schemes where excess generated electricity can be sold back to the national grid.
Sanyo Air Conditioners’ new technology offers the first standard solar air conditioning solution available to the UK market. Sanyo has combined its expertise in high performance solar power PV cells with its heat pumps, to produce highly efficient air conditioning systems. The key to the technology is a power inverter, which allows the solar power to be harnessed to any air conditioning system, to offer high efficiencies of up to COP at 7.0 for part load.
How does it all work? Sanyo’s model sees the photons in the sunlight hitting the solar panel cells and being absorbed by the silicon, which is a semi-conducting material. Negatively charged electrons are then knocked loose from their atoms, which in turn facilitates flow through the material to produce electricity. This electricity enters the inverter as direct current (DC) electricity. The inverter then turns this DC electricity into 240-volt AC (alternating current) electricity, which is essential for air conditioning. The AC power enters the utility panel and is distributed to the air conditioning system. When the air conditioning is not being used, the electricity can be diverted to power other facilities, or flow into the national grid.
Along with the inverter, the other important technological elements are the PV cells themselves. Sanyo’s HIT (Heterojunction with Intrinsic Thin layer) technology features a thin amorphous layer on top of high-quality monocrystalline silicon wafers. This makes them the most advanced and energy efficient available. They boast a cell efficiency of up to 20%, the world’s highest level of conversion efficiency in mass production, and excellent performance in low light levels, which makes them ideally suited to temperate climates.
Solar power, as a means for generating electricity for air conditioning should be seriously considered by building services consultants and their clients. Currently the technology is available for a number of specific projects in the UK but will be widely available next year. As the technology develops further it will surely become more widespread, and could even become the de facto power supply for air conditioning systems. Quite apart from being the environmentally-responsible thing to do, it helps end-users establish their green credentials, illustrating to the general public that they are forward thinking and willing to invest in the right technology for this century’s environmental challenges.
The good news is that many large businesses have buildings which would be excellent sites for solar powered air conditioning. The reason for this is that they tend to have sufficient roof space to accommodate the necessary banks of PV cells. This means that PV cells do not need to be laid beside the buildings they serve, taking up large areas of land, as is the case in some places. This is a major advantage, and improves overall building efficiency.
If cost or budget space is an issue, it is possible to apply for grants which will fund PV procurement and installation costs. One such scheme is the DTI’s low carbon buildings programme, where grants for the installation of microgeneration technologies are available to private businesses.
Even though solar cannot yet provide enough energy to run air conditioning systems single-handedly, it can provide a useful chunk of the necessary electrical power, and as the technology continues to evolve this proportion will grow. The point is that it can make a difference now to air conditioning power usage while giving a huge boost to businesses’ green credentials.
Solar powered air conditioning can not only benefit the end-user economically, since the amount of electricity required from the grid is reduced, but its environmental benefits are clear also. It is a significant addition to the overall air conditioning industry drive for high levels of unit and system efficiency, and solar power should be adopted universally, as soon as possible.