Welcome back to our IDEMA project blog series . Last time, we introduced the three step Renewable Energy Assessment Framework and the outcomes of step 1, identifying suitable technologies. So, today, we’re going to talk about step 2 and how we applied it to IDEMA.

 Understanding Energy Demands

While step 1 of our framework is about identifying renewable energy technologies that could be suitable for a site, step 2 explores those technologies further to determine which ones (or combination of) best meet the demands of a proposed development. 

Currently, London local authorities require developments to be net-zero carbon. To achieve this, developments are encouraged to not only follow the energy hierarchy and reduce their energy demands, but also to generate part of their energy needs through using onsite renewables.  We believe that first step (reducing energy demands) is by far the most important and effective way to achieve net-zero carbon. This is why our IDEMA project partners MillsPower and L&B worked endlessly to design a building that consumed the least amount of energy.  After ensuring our IDEMA houses were as energy efficient as possible, the next step was to understand the total energy requirements. This is essential for any development, to ensure that energy demands are met 24/7, 365 days a year. 

For each IDEMA home to be self-sufficient, we needed to generate 8,016 kWh per year per home.  However, we’d set ourselves a bolder challenge: to not only be self-sufficient but to generate surplus energy, in order to meet a target of £3,000 of revenue per home.  With these goals in mind, we needed to ensure that the technologies we had identified as suitable in step 1 - solar, air source heat pumps and potentially anaerobic digesters - not only met, but actually exceeded demands.

Assessing Our Shortlist Against Our Energy Needs

As step 1 of our assessment framework identified Solar Photovoltaics (PV) as a potential suitable technology, we turned our attention here first, looking at both solar panels (generating electricity) and solar thermal (generating heat). 

Our analysis demonstrated that even when maximising roof space with solar panels, electricity generation would be deficient between November and February, due to limited sunlight. In fact, a solar panel system of about 150 m2 (almost 3 IDEMA homes) would be required to fully power a single IDEMA home in December. 

The situation would be further complicated if we were to introduce solar thermals to generate heat. In this instance, the electricity provided by solar panels would be even lower as the solar thermal panels would compete with solar panels for roof space. The provision of solar thermals would also typically require a backup heating system, such as a gas boiler, negating our desire to become fully self-sufficient and net-zero carbon. For this reason, and even though solar thermal technologies met the site condition’s assessment in step 1, undertaking step 2 demonstrated that they would not be suitable for our IDEMA development, showing the value of a multi-step assessment framework.

Next therefore, we explored the potential of Air Source Heat Pumps (ASHP), one of the other technologies which had met our criteria in step 1.  Our modelling showed that ASHP could meet the heating demands of the development throughout the year, without having to provide a backup system or compromising on roof space.  Although on its own, it was unlikely to generate excess energy.

While it is possible to store the energy generated for use in the winter months, we decided to explore other technologies, in addition to the ASHP and the solar panels, as the goal of IDEMA was to generate surplus energy. So, we undertook some analysis to determine the suitability of anaerobic digester (AD) technologies, the final technology that we’d identified in step 1 and that warranted further investigation. Here, we found that the food generated from the total IDEMA development (11 homes) would produce less than 20% of the energy needed for a single IDEMA home. Was the problem that our 11 homes simply didn’t produce enough food waste?  To test this theory, we upscaled the catchment area to include 708 residents and a combination of restaurants, bars and schools, producing 410kg of food waste per day – the maximum amount required for the assessed plant. Even then, the generated energy only met 55% of the electricity demands of the 11 IDEMA homes. If the electricity is sold at 6p/kWh, then only £2,206 worth of revenue can be made - equating to an estimated payback period of 61 years.  Our conclusion was that for smaller scale developments, AD technologies do not appear to be suitable.  We do however believe they’re worth considering at a larger, community scale.

We still wanted to achieve our energy surplus target, so we also assessed the potential of Micro Combined Heat and Power (Micro-CHP). This technology can run on biomethane fuel, a renewable source, and generates both heat and electricity. The technology on its own is not suitable for meeting peak demands of the development, however through its provision, alongside other technologies, surplus energy could be generated.

Less is more

Through our modelling it became clear that in order to both meet the demands of the development and generate revenue through surplus energy exports, a combination of four renewable energy technologies would be needed. So, we modelled a number of scenarios to understand which combination would be the most financially viable and sustainable. The three scenarios are presented in the following table:

Option A was our initial configuration, where maximum energy is generated from the use of solar PVs, an ASHP and a micro-CHP, which runs continuously. However, as both the ASHP and the micro-CHP produce heat, this results in surplus wasted energy. In fact, approximately 9,600 kWh of heat would be lost per year with this option – enough to heat 16 IDEMA homes. This heat loss didn’t fit with our sustainability ambition, despite the surplus electricity being generated. So, we developed Option B, removing the ASHP. However, even with removing this technology, a lot of heat is still being wasted from the continuous operation of the micro-CHP (6,200 kWh/year).

This then brought us to Option C, where we removed the ASHP and set the micro-CHP unit to run only when heat is needed. Although this option results in less surplus energy than the others, it avoids heat loss, it has reduced capital costs and interestingly enough, it actually results in the most revenue.

How can that be? Well, in today’s market conditions, more money is made by avoiding energy imports from the grid, rather than selling energy to the grid. So even though less energy is exported in this option, the reduced capital costs from removing the heat pump and reduced maintenance costs of the micro-CHP, mean the revenue is highest, and the payback period is also the lowest.  

This analysis demonstrates that when it comes to renewable energy technologies, less really can be ‘more’. Achieving net-zero carbon is beneficial and desirable as we think about the broader challenges facing our cities today, but targeting energy surplus isn’t always the right approach. Financially speaking, you can generate more money for yourself by using less renewable energy technologies and reducing your energy imports. So, although our goal was to generate surplus energy, our research has demonstrated there are actually limited benefits from this.

Now, our focus isn’t only on what’s financially viable. We also looked at the lifecycle impact of renewable energy technologies. Stay tuned for our next blog to find out about the final step in our assessment framework.

If you are embarking on a development and would like to better understand our framework or to learn more about our work, we’d love to hear from you.  Drop us a line at [email protected]