New report questions the effectiveness of renewables in rural areas

With the government offering incentives including the Green Deal and the Renewable Heat Incentive (RHI), many existing oil users may be tempted to replace their existing installations with renewable technology. However, a new report commissioned by OFTEC has questioned the technical and financial benefits of switching from oil to biomass, heat pumps and solar thermal.

The research was undertaken by an independent energy consultant and exposes some of the downsides of renewables in off-gas main areas. In particular the report examined the high installation costs of renewables and questioned whether they would produce the expected carbon and fuel cost savings when compared with oil heating.

 Wood pellet boilers

A wood pellet biomass boiler takes up considerably more space than a high efficiency condensing oil boiler. Unless an existing outbuilding can be used a separate biomass boiler room is usually needed as well as an adjacent store that can hold several tonnes of fuel. Whereas oil tanks can be situated a significant distance from the boiler, automatic feed biomass boilers must be positioned next to their fuel store. Good vehicle access is also required to enable the wood pellet to be blown into the store. For distances over five metres the pellets have to be tipped instead, which requires a specially designed fuel store at additional cost.

Quotes were obtained for replacing an existing oil boiler with an automatic biomass boiler and fuel storage system, which came to £16,300. In contrast OFTEC estimates the cost of replacing an existing oil boiler with a high efficiency condensing one at around £3000 for a typical four-bedroom home. The report also queried the environmental credentials of biomass, referring to a 2011 Friends of the Earth report which posed the question of whether biomass is really carbon neutral, and also referred to pollution concerns from particulates produced when burning woody biomass.

Heat pumps

The report also looked at whether heat pumps would be a good choice for rural households currently on oil. The Energy Savings Trust (EST) estimates a typical ground source heat pump installation could cost up to £17,000 and an air source heat pump installation up to £10,000. Aside from the fact that both types of heat pump require considerable space, neither are a straight swap for an oil boiler due to the lower temperatures they produce. Significantly larger radiators with three or four times greater surface area are needed, or replacement with an under floor heating system.

Heat pumps can offer an advantage over oil boilers is in terms of operating efficiency, but for this to happen they must operate at their highest coefficient of performance (COP) or efficiency rating. However, DECC noted in a report published last year that these efficiency ratings are not always being achieved and it went as far as to suggest that some heat pumps are operating at significantly reduced efficiencies. A field trial of 83 heat pump installations monitored by the EST during 2009-10 found that both ground source and air source heat pumps were operating below their optimal COP.

If a heat pump system is not running efficiently, the costs rise dramatically due to higher electricity consumption. Looking at findings in the DECC report and EST study, OFTEC’s independent consultant calculated that for a four-bedroom home, a typical oil boiler would cost £1468 per annum to run. Using the same efficiency levels monitored in the EST study a ground source heat pump would cost £1355 to run, and an air source heat pump would cost £1779 to run. Although the ground source heat pump would save the householder £113 per year, it has much higher installation costs than a simple oil boiler replacement. If poor COP efficiencies are the reality, then the high costs of heat pumps are hard to justify.

Solar thermal

If a suitable roof is available then solar thermal offers another renewable alternative and can be installed in conjunction with an existing oil boiler. According to the EST a solar thermal system typically costs £4800, which covers everything, including the solar thermal store. The oil boiler and solar system are usually both connected to the thermal store, with the solar thermal providing the majority of heat for the domestic hot water with the oil boiler topping it up if needed. In summer solar thermal can produce up to 90% of hot water requirements, but only 5-10% in winter due to low sunshine hours.

The advantage of solar thermal is that it is compatible with most existing oil boilers. However, 90% of heating oil consumption is used for space heating, with only 10% used to generate domestic hot water. If a solar system provides 50% of annual hot water then the cost savings would be in the region of £88 per annum, which makes it difficult for many households to justify the installation expense.

For the two million oil users in the UK and Ireland, switching to a different fuel could end up costing more. Oil’s current rival – LPG – costs customers around 50% more to heat their homes each year than oil. The latest independent figures show that using an oil condensing boiler to heat a three bedroom home costs around £1355 compared to £2020 with an LPG condensing boiler.

Oil is a tried and trusted technology, and offers a reliable and cost effective source of heating. For most, upgrading to a condensing boiler and improving their insulation is a more cost effective option than the uncertainties of going down the renewable route.