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Restoring Solar Thermal On Commercial Buildings

Adveco considers the opportunities for restoring solar thermal systems…

For more than a decade at the start of the 21st Century, the government drove efforts to explore the validity of solar renewables, first solar photovoltaics for generation or electricity and later solar thermal as a means of capturing solar energy onsite for water heating. Purchasing flat plate or evacuated tube systems, proved cost-effective and the technology enjoyed a heyday with many public sector buildings employing one or both options.

Nearly fifteen years on, many of those systems now sit unusable on the roofs of those buildings. The causes are varied, poor initial installation issues and particularly a lack of servicing and maintenance ultimately lead many systems to overheat and fail, even sealed systems. Manufacturer support for evacuated tube systems also waned as key suppliers moved away from the technology. Other sites were prone to vandalism, with stones thrown at panels with devastating consequences.  For many organisations, the costs of protecting an installation or repairing it were too high and they were simply switched off and written off as a loss. 

Solar technology did not die though, and serious consideration should be given to restoring solar thermal back to operational status.  Properly installed and serviced solar thermal systems are proven to have a long operational lifespan with low maintenance demands, especially flat plate collector systems. Those with proven drainback technology employing gravity flow to preserve operational qualities of the solar fluid required to transfer solar energy as heat to the hot water application are notably robust.  A well-designed and balanced hot water system deploying solar thermal as a preheat can offset a minimum of 30% of the annual energy demands for hot water in the UK. For some regions, this percentage is much higher and in the summer months, solar can meet all a system’s heating demands, especially in the case of buildings with lower daily hot water demands such as offices.

The drive for net zero has also helped reinvigorate interest in restoring solar thermal as the commercial sector is challenged to transition from gas to electric water heating. The energy bill shock for many – since grid electricity continues to be substantially more expensive than gas (by a factor of 5.51 at the close of 2023) – has meant technology that can offset electrical energy usage is becoming more attractive. The return on investment (ROI) for solar thermal is once again powerful, with systems able to pay back capital investment in under ten years.

The New Rooftop Battleground

Chillers, heat pumps and solar systems are all vying for valuable rooftop space as public sector organisations look to reduce carbon emissions and embrace high-efficiency heating and cooling. This is especially the case for organisations operating small buildings, or those with high-rise city centre properties. Specifications will often aim to deploy solar photovoltaics (PV) to supply electricity for space heating and water. When retrofitting gas-based hot water systems this is a less efficient route since PV will always offset grid electricity at 136g/KWh, equivalent to 18 kg of CO₂/m²/annum. Compare this to solar thermal which offsets gas emissions at 233g/kWh, or 148 kg of CO₂/m²/annum. This makes solar thermal eight times more effective per m² than PV when addressing carbon emissions from water heating, translating to a smaller panel area for solar thermal on the rooftop. We would always advocate splitting solar water heating (solar thermal) from solar space heating (PV) to gain the greatest efficiencies. A typical office may require, as a rule of thumb, one solar thermal collector per 100 litres of thermal storage capacity. Most commercial-grade applications will typically require six to 20 solar collector panels.

Restoring Solar Thermal

With new high-efficiency, robust flat plate collectors and protective drainback, cylinders and controls to integrate solar thermal with electric top-up there is a real opportunity to restore solar thermal systems which have fallen into disrepair. Most refurbishments where overheating has been the cause of shutdown will require new collector panels and pipework which fortunately is a relatively straightforward replacement as the reinstallation process will have minimal impact on extant plant room appliances. This allows for upgrading existing gas water heating, saving energy and reducing emissions from the existing system.

Alternatively, Adveco can support the transition to full electric water heating with solar thermal through bespoke system design and product supply. For smaller systems and organisations with lower capacity demands, such as offices or GP surgeries, Adveco FUSION offers a pre-defined low-carbon system that is compact, easy to install, resilient and cost-effective. For organisations considering, but not ready to commit to a heat pump-based system, FUSION T is available now with an option that delivers a twin-coil stainless steel tank and mounted ARDENT electric boiler and controls without the heat pump preheat. This iteration allows for solar thermal to be introduced into the lower coil as the system preheat with a small amendment to the controls to optimise top-up heating from the boiler as the pre-heat fluctuates across the year.

With FUSION now supporting capacities up to 750 litres with 24 kW heat output, it is suitable for solar systems designed for small to medium-sized buildings. While most solar thermal systems would be designed to split the preheater and after heater, this single-cylinder FUSION scenario avoids the typical requirements of a 50/50 capacity split between preheat and top-up. Adveco’s smart controls allow the system to ‘cheat’ in favour of the solar thermal delivering a 600-litre solar capacity in a 750-litre tank for an extremely compact option for an all-electric low-carbon emission solar water heating system with a minimal rooftop or façade footprint.

Today, commercial organisations have more choice than ever when introducing sustainability into a new or existing building. In the latter case, reducing the impact of building works and avoiding business disruption can be a critical decision-making factor. Addressing the sustainability of hot water demands is one of the lower-impact projects available to organisations with immediate and definable delivery of carbon savings and, with solar, energy offsetting operational savings. For organisations that previously invested in the technology but have let it lapse, now is the perfect time to reconsider restoring solar thermal systems or adding it to existing applications to bolster efficiency and cut costs and carbon emissions. 

Learn more about Adveco’s solar thermal offerings for commercial water heating applications.