Jack Taylor, general manager Europe, Allume Energy looks at providing solar energy in multi-unit properties.

The risks of climate change now need little introduction. We are already starting to live with the impacts of a changing climate on the environment, communities, businesses and supply chains. A recent Intergovernmental Panel on Climate Change (IPCC) report revealed that our ambition to limit global warming to 1.5°C is now hanging by a thread. With voices challenging whether keeping within the 1.5°C trajectory is even still feasible, each 0.1°C rise above 1.5°C is hugely significant.

Added to the climate emergency has been a cost of energy crisis, with wholesale energy prices increasing rapidly from the second half of 2021 onwards. While monthly gas prices fell by 1.0% between March and April this year - the first time since October 2020 - this has largely been seen as a drop in the ocean compared with a rise of 66.8% between the same two months a year ago.[1]

With over 56% of people using less fuel in their homes because of increases in the cost of living, the need for cheaper, climate friendly energy solutions has never been greater.[2]

Net Zero and the UK’s use of solar

A cornerstone of the UK’s strategy to reach net zero by 2050 is the legally binding requirement under the Paris agreement to meet its “nationally determined contribution” (NDC) - to reduce emissions by 68% by 2030, compared with 1990 levels. With less than 7 years to go, and with the UK’s built environment sector responsible for 25% of the nation’s greenhouse gas emissions[3], it is incumbent upon building owners and developers to accelerate the uptake of renewable energy sources for private, commercial and local authority properties.

While the UK is among the top 12 countries for solar power capacity, only 4.1% of the UK’s 29 million homes now generate electricity from solar power – and the growth in solar energy alternatives has been mostly confined to commercial buildings and to single-family detached properties. This is despite the growth in multi-unit dwellings. In 2021, 5.4 million households resided in flat, maisonette or apartment accommodation - up from 4.9 million households in 2011.[4]

There also appears to be slow uptake in the social housing sector, despite the urgent need to ease the cost of energy crisis. In 2017, the UK government earmarked £1 billion to install solar panels on around 800,000 council properties by 2022, but five years later only 170,237 of those homes had solar panels installed – less than a quarter of the target.[5]

Research undertaken by the Center for Sustainable Systems as part of the University of Michigan in the US, revealed that although apartments are generally significantly smaller in size than houses, those situated in buildings of five or more units still emitted significant amounts of emissions – typically as much as 50% of houses.

The study found that emissions from electricity use for lighting and appliances are likely to be slightly lower in an apartment due to their smaller average size, but will not be dramatically different from a house. The typical electricity consumption of an apartment is 3,000 kWh per year, so based on the carbon intensity of the UK grid, that would cause the emission of 200 kilograms of CO2 each year.

According to the International Energy Agency (IEA), solar is now the cheapest energy source in the world – and the need to switch to a more sustainable source of energy is evident. So why have so few multi-unit properties – both private and local authority-owned - taken advantage of solar systems? Primarily it’s because, until now, options for installing individual solar systems and connecting them up to individual units was a largely unworkable solution for both developers and retro-fits due to cost, footprint and inefficient energy utilisation. Historic technical and ownership barriers are also difficult to navigate, due to the dominant leasehold ownership model of most flats in the UK.

However, a recent solar system installation in Cardiff has demonstrated how these challenges have been cost-effectively and elegantly overcome.

New kid on the block

Earlier this year, Wales & West Housing (WWH) and the Welsh government announced the first installation of Allume Energy’s innovative solar technology to provide clean, affordable electricity to a 24-unit residential block of flats in Cardiff.

With a typical solar PV system, this would normally have entailed the installation of 24 sets of panels, 24 sets of inverters and 24 batteries, taking up valuable physical space and involving greater cost and installation time, as well as far from optimal energy utilisation.

The project has connected 24 flats to lower-cost solar energy at Odet Court, with the potential to meet 55-75% of each flat’s electricity demand. Based on the average usage of 1,800-2,400kWh for a one-bed flat, this could equate to an electricity bill saving of around 50% (£390-530) a year, given current average electricity costs in the UK of 34p/kWh. In fact, data from our monitoring platform throughout April and May 2023 at Odet Court shows that the average bill savings across apartments is 41% - this will vary throughout the year as heating, cooling and other electricity needs vary. The project has been funded by the Welsh government in association with Wales & West Housing as part of the Optimised RetroFit Programme.

The innovative solar + battery system will annually produce and store 50,248kWh of green solar energy for the direct benefit of residents. Each flat will equally share the energy produced, resulting in 2,094kWh per unit. The generative capacity translates into savings in the following way. For any type of solar PV system, when the solar energy is delivered to the home, it is either consumed on-site or exported back to the grid if more solar PV is delivered to the home than can be used by it. A typical solar PV system in the UK will consume on average 40% of the solar energy that has been produced and export 60% back to the grid.

For example, if a home consumes 2,000kWh per year and has 2,000kWh of solar delivered to it, it will consume 800kWh and export 1,200kWh. So, even though over the course of the year the solar generated is the same amount as the home’s energy needs, it will only reduce its grid energy usage by 40%. When multiple flats are connected to solar PV via SolShare, however, the solar PV is directed to the flats when they are using energy. This optimisation increases the average solar consumption from 40% to almost 50%.

The site at Odet Court also includes batteries, which increase consumption even further. Allume estimates the consumption to increase to 55-75% depending on each flat’s energy usage. If 55-75% of 2,094kWh of solar is consumed, each flat will consume 1,152-1,570kWh. If we take the extremes of top-end energy users (2,400kWh) consuming the lower amount of solar (1,152kWh) and lower-end energy users (1,800kWh) consuming the higher amount (1,570kWh), the grid energy reduction will likely range from 50-85% for the flats once the data is reviewed in a few months’ time.

Not only has SolShare significantly reduced the amount of hardware and footprint required, it has also reduced installation costs as compared to a typical solar system. Its ‘dynamic sharing’ capacity also delivers an improved solar utilisation of over 25%. Importantly, SolShare is suitable for retrofit projects as well as new builds, as it does not require any changes to the existing supply and metering infrastructure.

A real asset

SolShare is a potential gamechanger for asset managers looking to upgrade existing housing stock, and also for property developers, due to its ability to improve EPC band ratings and increase SAP points much more affordably than existing solutions.

On average, SolShare increases SAP scores in each flat by 5 to 15 points at a rough cost of £2K to £4K per flat. For asset owners needing to upgrade existing housing stock, this is far more cost-efficient than alternative solutions; adding wall insulation for example, can cost £10-15k per flat for the same increase in SAP points.

What is more, SolShare is sometimes the only way property developers can gain the desired EPC ratings for new build flats. Following the release of SAP 10.2, solar PV must be directly connected to flats. SolShare is the world’s only technology for connecting multiple flats to a single rooftop PV array, qualifying for up to 15 SAP points per flat.

Existing solar PV specialist can easily be trained to install SolShare, making installing systems across the country is easy. In the next two months over 600 flats in the UK will be connected to solar PV by SolShare.

Climate Change Minister Julie James said: “This is an exciting first of its kind project for Wales and exactly the type of thinking we need to see within the housing sector. The decarbonisation of homes plays a big part in our journey towards a Net Zero Wales by 2050 and I look forward to following this innovative project as works progress. At a time when costs are rising, improving the energy efficiency of homes will not only help us to deal with the climate emergency but also help families through the cost of living crisis. It’s another important step in our journey towards a stronger, greener, fairer Wales.”

Joanna Davoile, executive director (Assets) at Wales & West Housing said: “At a time when many people are facing difficult choices of whether to heat their homes or feed themselves and their families, it is only right that we explore ways to make our homes more energy efficient for our residents where possible. In recent years we have been trialling different methods of retrofitting older homes with energy-saving technologies but one of the main challenges has been how to fit PV panels and battery systems to our apartment homes so that everyone living in the schemes could equally benefit. The SolShare system seems to be a much fairer solution as the energy generated by the building can be shared equally to help our residents to keep their electricity costs down rather than going back to the grid. We are excited to see how the technology used in the SolShare system will work for our residents.”

[1] Cost of living insights: Energy; 2 June 2023; Office for National Statistics

[2] As above

[3] Green Building Council

[4] Office for national statistics; Housing, England and Wales: Census 2021

[5] Microgeneration Scheme Certificate