There is a dark cloud hanging over solar energy. Despite frequent government pushes for wider adoption of renewable power sources, progress in recent years has been relatively slow. Here, Steve Hughes, managing director of power quality expert REO UK, explains, there may be a way to part the clouds in solar energy.
Since the mid-1990s, the UK has seen a gradual increase in the amount of renewable energy sources used to generate electricity. However, in spite of two decades of growth and countless incentives and schemes, we are still trailing behind the target of producing 20 per cent of the UKs electricity generation from renewable sources, with current estimates being 15 per cent.
Until 2011, only a small amount of this electricity came from solar energy. Since then, the falling price of photovoltaic (PV) panels and the introduction of feed-in tariffs has driven a surge in sales. Recent government figures showed that UK solar capacity has increased by 62 percent from February 2015-16, with previous findings also indicating a recurring trend of capacity greatly increasing in April.
What we can deduct from these findings is that, while widespread renewable uptake has been poor in relation to the electrical capacities of other energy sources, the UK is taking steps in the right direction. With further plans to power four million homes with solar energy by 2020, the future is looking bright for renewable energy.
It is understandable why so many businesses and consumers alike are switching to solar. Once initial installation costs of PV panels are out of the way, solar energy offers a unique approach to generating both electricity and money - by feeding excess energy back into the grid - while also meeting green guidelines.
Making the most of the sun
Unfortunately, one of the biggest factors preventing a full conversion to renewable energy is its reliability. Due to its dependence on a suitable quantity of radiation, solar power is particularly prone to fluctuations. This inconsistency creates a range of problems for both electricians and end users.
Yet for all the intermittency surrounding solar energy, the bigger issue is that we are unable to take full advantage of the electricity it generates. Once the power is available, it has to be used immediately or it is wasted. This is not due to the power itself, but rather the lack of any viable storage solutions for generated loads.
Currently, the solar energy sector lacks the infrastructure to offer a long-term and reliable source of power. Without a means of storing this electricity, we are at the mercy of nature, whereas using traditional energy sources we have control over the steady (and steadily decreasing) supply.
This lack of affordable storage undermines the use of solar. While installing PV panels allows a business to operate independently of the grid during the day, at night it becomes reliant on electricity from the grid once more. This may mean the business ends up using less traditional energy overall, but it still leaves a dependency on traditional methods of electricity generation.
Obviously, this is not an ideal or sustainable approach. Fortunately, technology is developing in such a way that it seems the storage of renewable energy will soon be a reality. The rising popularity of Original Equipment Manufacturers (OEMs) revealing plans for home batteries, a trend popularised in 2015 by Teslas Powerwall, shows that the industry is working to develop a solution. While the idea of home batteries isnt necessarily a new one, the revitalised interest is likely to drive the price down to a more affordable amount in the foreseeable future.
However, what happens next? Renewable energy sounds very attractive in concept, as a seemingly benevolent method of maintaining our electrical consumption without harming the planet. However, aside from their intermittency and the lack of storage, renewable energies are plagued with a host of power quality issues that have detrimental effects on our electrical infrastructure.
These detrimental effects pose the biggest challenge in switching to renewable energy. While some of the issues may only increase energy consumption, others can cause damage to components on the electrical grid itself.
From solar to terrestrial
Before we can tackle power quality issues, it is important we understand what solar power actually is. The initially generated voltage is in low voltage direct current (DC) form, which means it needs to be converted to an alternating current (AC) voltage before it is able to enter the electrical grid. This is achieved using either single-phase or three-phase inverters, depending on the power requirement and the application.
However, this conversion creates a number of power quality problems. Modern inverters convert energy from DC to AC quickly and efficiently but, due to the speed of switching semiconductors, this results in high-frequencies entering the system. These high frequencies may sound harmless but they cause electromagnetic (EM) noise in systems.
EM noise causes interference in electronic components, including the switch-mode power supplies (SMPS) and inverter drives that also frequently generate this noise. The interference, if left unresolved, can quickly degrade and damage electrical components. To prevent this from occurring it is important that protective measures are put into place to minimise EM frequencies.
While it is not possible to eliminate EM noise from a system, it can be kept under control by installing electromagnetic compatibility (EMC) filters. These are low-pass filters that are designed to attenuate high frequencies of EM noise without disrupting the flow of mains frequency power.
Filtered frequencies are reflected back to the original sources to keep products operating effectively. To facilitate this, EMC filters should be capable of handling the resulting power dissipation without a negative impact on performance. Companies can do this by using larger capacitors and inductors.
Keeping EM noise at an acceptable level allows businesses to safely comply with the relevant standards on EM immunity, such as EN 61000 legislative standards. However, filters are not a one-size-fits-all product and only the right filter for the application can guarantee compliance. Engineers should thoroughly test filters before committing to use them in systems, ensuring that the right frequencies are attenuated.
We recommend engineers should work alongside power quality specialists to find the ideal solution with minimal problems. Once any EM issues are resolved and the solar energy can be safely converted to DC voltage, this electricity must be fed into the main electrical grid through a connecting inverter. This sounds straightforward but it also raises further concerns.
Keeping safe on the grid
Ironically, one of the core selling points for the uptake of solar energy generation contributes to the delay in adoption. The financial incentive for the installation of PV panels is that excess energy is fed back into the main electrical grid, resulting in businesses being paid for the power they help to generate.
However, to do this, companies requires a connection to the power grid. This grid interconnect point of parallel inverters causes another power quality problem - harmonic resonance. This is a common problem in non-linear electronic systems.
Due to the way in which harmonic currents manifest in electrical systems, they result in expensive heat losses and increased energy consumption. Yet even more costly is that, over time, these currents accelerate component wear and ultimately lead to failures. In the power grid, these failures culminate in unstable loads, blackouts or power surges.
This risk is exacerbated by the already present threat of power surges that accompanies renewable energy. Whether it is solar or wind farms, it only takes a storm to cause problems for the electrical output. We know that heavy winds push wind turbines to capacity, but the effect on PV panels is slightly less clear.
Despite its title, solar energy is drawn from radiation that is not necessarily exclusive to the sun. In the case of a storm, lightning can create dangerous situations. If a bolt strikes close enough from the panels, they soak up a sudden rush of radiation, which can cause a surge. Likewise, flashes between clouds can have the same effect.
Of course, this can be subdued with effective grounding of infrastructure. But in order to get rid of the underlying harmonic resonance, it is essential that companies incorporate harmonic current filters into systems.
These filters cause a substantial reduction in the harmonics present in a system, resulting in a total harmonic distortion (THD) drop of more than 50 per cent in some cases. Our REOWAVE passive, for example, has been able to drive down THD to as little as five percent due to its special circuit design and its location in systems. It is these considerations that help businesses efficiently make the most of solar power.
As it stands, technology is only advanced enough to allow PV panels to harness 0.001 per cent of the energy produced by the sun. In the future, this figure will be substantially higher, which will drive the use of solar power and the need for high power quality. It is only by ensuring that infrastructure is capable of meeting this demand that we can enjoy all that the sun has to offer.