The operating principle of solar energy generation is fairly simple, at least according to Carmichael Browns, a commercial solar panel supplier and installer. Daylight hits the photovoltaic cells in the panels, which convert it to clean DC electricity. Solid-state semiconductors within the PV cells then absorb the light’s energy upon exposure and transfer the energy to electrons. The absorbed additional energy allows electrons to flow in the form of an electrical current through the semiconductor material. Subsequently, conductive metal contacts/grid-like lines on the solar cells collect the current generated in the semiconductor.
An inverter (the only other major piece of hardware required) converts the electricity from DC to AC for use in a plant. This inverter will operate automatically to optimise system output, making correct sizing highly important. Typically, AC electricity travels directly to the plant’s fuse or distribution board via a meter.
According to Joju Solar, a designer and installer of low-carbon electricity technologies, the inverter is a critical component in good solar system design and, aside from DC-AC conversion, performs additional functions. For instance, components called maximum power point trackers (MPPTs) within the inverter ensure the highest possible electricity production at all times, despite constantly changing environmental conditions (light intensity, temperature and colour). Also, the inverter matches the phase of the generated electricity to the phase of the grid.
String inverters are fairly standard because they take input from a daisy-chain of solar panels called a string. Depending on the size of the system, multiple strings might feed one or multiple inverters. However, the performance of a string is only as good as the weakest link in the chain, which means avoiding shade is very important. One shaded panel could reduce the performance of all panels.
Joju Solar is brand-agnostic, selecting inverters to optimise overall system output, which in the UK means an inverter approximately 10% smaller than the size of the array. Straying too far from this ratio can adversely affect overall electricity generation.
An alternative approach to string inverters is the use of small optimiser units on the rear of the panels to increase overall system yield. Optimisers not only help mitigate the effects of shading and dirt, but also give a small increase in performance by dealing with module mismatch. A 275W installed, for example, can actually be anywhere between 270 and 275W, reports Joju Solar. For a string inverter approach, performance would see a limitation caused by the worst module (270W). With optimisers, however, 275W panels perform as 275W panels, giving an overall increase in yield of 1% or so.
So what about maintenance? One of the main benefits of solar systems is that they do not require much care. There are no moving parts and many panel types offer self-cleaning mechanisms to some extent. According to Carmichael Browns, solar panels operate best with a slight pitched angle, not just for sunlight exposure, but also to support water run-off. Panels can also function on flat roots but may require more regular cleaning.
Cleaning a commercial solar PV system is a simple task and no different from commercial window cleaning. Carmichael Browns says this activity should take place at least bi-annually and around spring if possible.
The inverter is a more active part of the overall solar system and one that will require slightly more attention. Here, the use of monitoring systems will keep the system owner informed regarding performance and identify any faults that might occur. Particularly on larger systems, Carmichael Browns recommends an annual or bi-annual visit from one of its engineers to check the electrical connections and ensure the system is functioning at maximum capacity.
Among manufacturing plants to install solar panels recently is PP Control & Automation, a Walsall-based provider of strategic outsourcing solutions to machinery builders. The company appointed Centreco, an installer of commercial solar energy systems, to fit 108 panels to its frame-supported, 5° inclined steel roof in late 2021.
Electricity generated by panels at PP C&A is for direct use on site. The company is a manufacturing business that only functions during the day. With no plans to operate outside of daylight hours, the business opted against the use of battery storage.
“The system is set up for a small amount export to the grid on days we are not working, such as Sundays,” says Knight. “Depending on our daily usage and the amount of electricity generated by the panels there is also a point when we have to import electricity. The panels cover 22% of all our electricity use. When it runs out, the system automatically draws energy from the grid.”
At PP C&A, the 108 panels wire down to a DC-AC inverter and into the company’s main electrical cabinet, which contains an individual breaker for the inverter. A smart meter tracks how much energy the panels generate and how much CO2 it is saving; presently around 30 tons of CO2 annually.
“The inverter records all voltages and how much electricity we are creating daily, weekly and monthly,” says Knight. “It also sends alerts if there is an issue with the supply. Centreco monitors everything remotely as part of system, which helps us drive improvements in terms of how many kilowatts we purchase from the grid. The life of the system is 25 years and it’s obviously still under warranty at present.”
Knight reveals that the only maintenance required is cleaning and cutting back any overhanging trees.
“I would recommend that more plants take a look at solar panels,” he concludes. “We began this project just before energy price hikes arrived, but we still estimated payback in two years. Imagine how quick it would be at today’s electricity prices.”
BOX: BATTERY STORAGE
Solarsense, which designs, supplies, installs and maintains solar panels – including the Tesvolt range – says that integrating a commercial solar panel system with a battery storage solution instead of exporting it back to the grid means plants can benefit from even higher savings. Storing energy on-site reduces dependency on the National Grid, protecting the plant from potential ‘brown-outs’ and energy rationing, and allowing it to remain operational when competitors cannot.
Solarsense can install battery units on-site as a means to store and discharge electricity at specific times, operate independently from the grid, and offer back-up power when needed. In most cases, batteries integrate with commercial solar panels as a means to capitalise on energy savings. However, they are also suitable for installation as stand-alone systems, independent of a renewable energy source, to store cheaper energy from the grid during lower cost periods, and discharge at peak times to avoid demand charges and peak-time energy costs.