Power from Above

Solar panels on warehouses

Proponents of solar power have, for years, been pushing the case for exploiting otherwise unused warehouse and commercial roof space. It’s appealing at first sight but quite a few factors have to be taken into account, Ruari McCallion learns.

The drive for renewable and zero-carbon energy is accelerating and being driven by multiple pressures.

First there is the drive to reduce carbon footprints generally, which is especially burdensome for manufacturing and logistics sectors because their businesses tend to be carbon-intensive or, at least, more intensive than financial services, for example.

Consumer pressure comes a strong second…

Consumers increasingly want not only to be told that the goods they are buying have a low environmental impact; they want to see the evidence.

Third, the cost of energy – which has rocketed since the most recent armed conflicts – has given a degree of urgency to the situation. Security of energy supply has become crucial; businesses simply cannot afford unscheduled interruptions. Demand will continue to increase, relentlessly. Automation will drive up energy consumption in commercial buildings and electrification of transportation will increase pressures on the electricity grid, across Europe.

The soaring cost of conventional oil and gas-powered energy generation has made alternative energy sources more commercially realistic.

Do look up

Wind turbines have become an established means of generating electricity, and a familiar site on commercial premises. It is being argued with increasing enthusiasm that logistics operations should raise their sights even higher. The area that is still very largely unexploited for zero-carbon power is warehouse rooftops.

Warehouses have very large roofs, which should, in theory, be ideal locations for capturing power from the sun and generating photovoltaic (PV) power – which is what solar PV* panels do. It is estimated¹ that up to 25% of Europe’s electricity needs could be met by rooftop solar PV. In the UK, less than one per cent of appropriate commercial rooftops have solar panels installed. If the full potential was exploited, up to 500 GW of power could be generated. The current installed capacity is 14 GW.

¹Source: Electron Green

(*Just to note – solar PV and solar thermal are not the same thing. Solar PV generates electricity; solar thermal heats – or pre-heats – water.)

Check suitability

But not all buildings are suitable for solar PV; they are heavy, after all.

Bill is a respected authority on solar power internationally. He invented the Carbon Neutral Protocol and persuaded a range of global interests, including NGOs, carbon traders, academics and politicians, to come together and create one of the first international voluntary standards for carbon. Electron Green now works with partners including Mileway (a pan-European logistics platform owned by Blackstone) and GLP, which acquired Gazely Construction, the eco-friendly warehouse developers. So, if he says that not all premises are suitable, it’s worth listening.

“Building owners in the UK and Europe need to conduct structural checks on buildings before installing solar panels. Generally, buildings constructed from around 2000 onwards are likely to be suitable. But even these may have insufficient structural capacity, because of potential ‘value engineering’, mezzanine insertions or other post-construction additions.”

Cutting tax

Is it worth investing the time, trouble and capital in installing solar PV? It depends on several factors. One immediate attraction in many countries across Europe is that electricity generated ‘behind the meter’ – i.e., not supplied from the grid – is not subject to VAT, IVA, green levies or carbon taxes.

However, the attraction of ‘behind the meter’ generation will depend on how grid electricity is charged. In the UK, the common structure is a relatively low standing charge with a high – and fluctuating – unit cost. At a typical 25p per unit charge for commercial supply, solar can offer significant savings. At the other extreme is Spain, which often has high standing charges, but low unit costs (as little as six cents per kWh), which means that solar offers no advantage. This goes a long way toward explaining why the roofs of buildings in one of the sunniest countries in Europe are not covered with solar panels.

Light and power

Solar panels are rated by the amount of power they can produce in ideal conditions. Around five square metres of panels will produce around 1100-1200 kWh/yr in central France, southern Germany, Austria, Hungary and Slovakia. In southern England, it could produce about 1000 kWh/yr. Northern Scotland and most of Scandinavia would get around 700-800 kWh/yr from the same installation.

Countries in higher latitudes, such as the UK and Scandinavian nations, have less powerful and less usable sunlight; in general, the further north you go, the less attractive solar becomes. In the depths of December – as this article is being written – northern Finland, Sweden and Norway have no usable sunlight at all for a few days. Northern Scotland has less than six hours, which means that the proposed Spaceport in Sutherland is unlikely to be solar powered.

That doesn’t mean that solar power should be dismissed out of hand in higher latitudes. Across Europe, GLP has 700 megawatts (MW) of installed solar capacity, which makes a big contribution to its drive to reduce carbon emissions. The business case, in practice, depends on the cost of grid electricity, even on a single building.

Thomas Leach Colour, a printing firm based in Oxfordshire, England, has just had 117 rooftop solar panels installed by Electron Green over 280 m² of its roof space. The 58.7 kWp (peak power rating) panels, which provide electricity at a fixed rate, are expected to save Thomas Leach £2,900 in the first year alone and up to £400,000 over their lifetime. Grid-supplied electricity use will be cut by 45% and the company will save up to 357 tonnes of carbon over 25 years. Installation costs were borne by Electron Green; Thomas Leach pays for the electricity supplied from the panels, at a lower cost than grid electricity.

Panels in Spain, southern Italy and Greece are likely to offer higher production levels, and Turkey and the Middle East even more. But, in the case of North Africa and the Middle East, it should also be borne in mind that – paradoxically – efficiency of solar panels declines when temperatures go above 40⁰C. It doesn’t bring efficiency down to the level of the dark northern climes but it’s not a one-way street. It may be, in the future, that new solar panel materials will both improve effectiveness and enable a wider range of peak performance across a broader band of temperatures and light.

Watch this video to see how easy it can be to go solar.

Match need to supply

Potential users must also consider what their power needs are. Offices and low-demand equipment – including heating, ventilation and air conditioning – could get a lot of their needs supplied by solar PV, as could constant energy-intensive use, like in printing, cold storage or data centres. However, it would be unlikely to be very useful in applications where demand fluctuates significantly, such as fast-charging a fleet of electric vehicles, unless there was also some energy storage capability to ‘buffer’ the solar generation against the demand. (Energy storage is an important consideration if a site is to be self-sufficient and separate from the grid.)

The on-site power network should be right-sized and right-purposed. There will be some needs that can only be supplied by the grid. A windy area that has a lot of darkness – as in the northern locations – would be leaning more heavily on wind as an adjunct to grid power.

There is no single answer to the burning question: is it right for me? It depends. But there are lots of resources to help you get a better idea of whether your building will pay back your investment and how fast (see box). It isn’t just about power: it’s also about carbon footprint and ESG (environmental, social and governance) performance. Price pressures, volatile supply and legislative pressure to improve EPC (energy performance certificate) ratings of buildings mean that the possibilities are well worth investigating, to help determine best approaches.

With thanks to Electron Green for its help in preparing this article. www.electrongreen.com

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