On site renewables - how do the technologies compare?

Yesterday I chaired a discussion for on-site renewable energy at Ecobuild, where  it was my role to introduce the many technologies available. So what are the main technologies and what are the key issues they face?

Photovoltaics (or solar power) is in principle the simplest technology. We can calculate with accuracy what size system can be deployed and how much power it will generate. From this it is reasonably simple to create a financial model on cost CO₂ savings. There are often complications that are overlooked on solar projects that can increase cost or reduce return, such as lights on roofs or the length of cables. In addition, the planning system has become more uncertain for ground mounted systems: a government drive to put solar back on roofs with changing incentives means that solar farms over 5 MegaWatts are unlikely from now on. Consequently I think we will see a lot of 4.99MW schemes, submitted under Feed in Tariffs (FiTs). Although photovoltaics are a simple technology, the returns are lower than others.

Biomass heat scheme offer good returns and are relatively simple, but underperformance is common

On-site wind is more complex; estimating yield is a more difficult task as there are many factors, and the planning process is more expensive and much more uncertain. Having said that, particularly on the <500kiloWatt scale there is a sweet-spot, due to the FiT bands, that offers a good return.  Due to the inherent risks with wind power it is common for sites to partner with third party developers to take the risk and design in return for share of the returns.

Biomass heat has exploded in the UK since the Renewable Heat Incentive (RHI) was launched, which accounts for 95% of applications. The reasons for this are two-fold: it offers sufficient financial return for third party developers, and it is relatively easy to retrofit to existing heating systems. WSP have advised on these investments. They do offer good returns and are relatively simple, but, as DECC research shows, underperformance is common and careful analysis required. Pipe heat losses can be underestimated and boiler efficiency overestimated. Connecting to existing systems also has inherent risks. 

Anaerobic digestion allows the production of biogas from a wide range of biological wastes for heat or electrical generation. Although there are incentives and the opportunity for good returns, securing feedstock over a long period is challenging. The financing and the quantities of feedstock required mean anaerobic digestion is better suited to larger developments.

Although I believe all new developments should use heat pumps as they will produce the lowest CO₂ overall when heating buildings as the National Grid decarbonises, we haven’t advised on any retrofit projects of heat pumps. We are in good company. According to Ofgem  there are  under 350 non-domestic RHI heat pump applications to date, compared to nearly 11,000 biomass. They are also more difficult to retrofit to existing systems and can be expensive.

GasCombined Heat and Power (CHP) can offer significant cost savings for sites where there is a consistent heat and power demand, such as hospitals. However, they will increase CO₂ emissions over their lifetime compared with gas boilers.

There are more technologies, for example solar hot water, Biomass CHP and hydro, however the most exciting technology in the sector we are currently working on is power storage. This gives the opportunity to make renewable energy much more useful and valuable, storing it when not needed and discharging when it is. It is a fast moving market in technology and regulations but it is at least now happening, and we are overseeing a trial system for a supermarket client.

Barny Evans is principal consultant, renenwables and energy efficiency, at WSP