Green Building, Part 4: Renewables

One of the most exciting features of green building technologies are the renewable energy systems. These systems not only enable homeowners to produce energy for their own homes, but can also produce energy to sell back to the grid. In the following section learn about the many unexpected ways in which homes can heat themselves – and in the long-run save money too.

Renewable energy

One of the successes for renewable energy at the domestic level was the Renewable Heat Incentive, a government initiative set up in April 2011. This provided government funding for homeowners installing ground and air source heat pumps, wood fuelled room heaters, stoves & boilers and Solar Thermal water heating. However the consultation document published in 2016 has among other things implemented a budget cap on the initiative and proposes to remove support for solar thermal deployment.

Heat Pumps and Geothermal Energy

Geothermal energy is heat found in the ground. At a depth of just 1.5 – 2 metres temperatures   between 7 – 10 degrees C are available. The apparatus required to extract this heat is a ground loop which comprises of lengths of pipe buried in the ground either in a vertical borehole or a horizontal trench. The pipes form a closed circuit which is filled with a mixture of water & antifreeze.

Inverter heat pumps by Stiebel Eltron

A heat pump circulates the liquid in the pipes. The liquid absorbs the heat from the ground with the aid of an evaporator within the heat pump. The heat pump also has a compressor which moves the refrigerant round the heat pump compressing it to the temperature needed for the heat distribution circuit. The condenser releases the heat to a hot water storage tank to feed the distribution system.

The Energy Saving Trust estimate the installation costs can be anywhere between £11,000 - £15,000 depending on the type of property & location. They also provide a table of estimated savings so that replacing an old electric storage heater might save an average household between £830 and £1,465 a year.

The running costs, at present, are greater than that of mains gas fired central heating especially as electricity is required to power the compressor and pump. However, to put this in context, for every unit of electricity used to pump the heat, 3-4 units of heat are produced. If mains gas is not available, running costs compare favourably with oil, LPG or electric space heating alternatives.

You may want to consider other types of heat pumps which extract heat from air (at temperatures as low as – 20 degrees C) and transfer it to water to boost stored hot water temperatures and to heat swimming pools.

Solar water heating

Solar water heating works along side your conventional water heater to reduce impact on the environment. Almost all of a household’s hot water requirements can be met by solar water heating during the summer months and about 50% the rest of the year. A 2-4m2 area of S.E. to S.W. facing roof receiving direct sunlight for the majority of the day is required to install solar collectors. Expect to pay between £3,000 - £5,000 for a domestic flat plate collector. An evacuated tube system is more expensive as it is more efficient.

As well as a solar collector, a heat transfer panel and a water storage tank are required. Some combination boilers are not suitable for use in conjunction with solar water heating systems. 

It is possible with a certain level of skill to fit a solar water heating system yourself; however, DIY jobs are not eligible for grant funding. The Product and the Installer have to be accredited by MCS Micro generation Certification Service. 

1st April 2010 saw the launch of the Feed-in Tariff – an incentive to encourage the nation to generate electricity from renewable sources in order to help meet the government’s EU target of 15% renewables by 2020. The original scheme was modified by the government in February 2016 and details can be found here


Technologies include Wind Turbines, micro CHP, small Hydro or Anaerobic Digestion and Photovoltaic panels which have the capacity to generate up to 5MW.

Photovoltaic technology employs polycrystalline cells to harness the sun’s energy & convert it to electricity. As a guide, the pay-back time is estimated to be eleven years for a domestic 4kWp installation with a supply and fit price of £5,000 - 8,000. 

The Feed-In Tariffs system means that you can get paid for using the system and generating electricity and feeding it back to the grid. New tariffs have just been introduced the current rate for generation is 4.39p per kWh and selling back to the national grid at 4.85p per kWh.


The contract period will be different for each technology this reflects the life expectancy of the equipment. For Photovoltaic installations the period will be 25 years.

Wind Power

In 2015 11% of UK electricity was provided by wind energy and by the end of the year the Independent newspaper reported that onshore wind energy was for the first time cheaper than from any other source.

Generating electricity by burning fossil fuel in large power stations is grossly inefficient. More than 60% of the energy that the fossil fuel produces is lost at the power station through the generation of heat which cannot be stored or transported and has to be dispersed through cooling towers. A further 3.5% is lost in transmission..

If it is not practicable for individuals to install their own wind turbine on their property it is possible for most of us to buy ‘green energy’ from members of the Energy Savings Trust’s accreditation scheme. At the moment the tariff for buying green electricity will cost a consumer typically £3-£10 per quarter more. There are two types of green tariffs:

Renewable tariff – for every unit of electricity used by the customer, the supplier buys a unit of electricity from a renewable source.

Eco funds – the extra payment goes into a fund to help finance new renewable energy projects.

Timber Energy/Biomass

Biomass heating is a process where organic matter undergoes combustion to release heat into the atmosphere. The production of energy from biomass is split into three distinct categories – solid biomass, biogas and liquid bio fuels. Where small-scale domestic heating applications are concerned, the biomass fuel usually takes the form of wood pellets, chips or logs.

The environmental benefits of biomass heating are twofold – firstly biomass heating is classed as low carbon; as the carbon released during the generation of energy is balanced by that absorbed by trees during their growth. On the understanding the wood is taken from regenerative forests, biomass heating is highly sustainable. Secondly, recycling these waste products avoids disposing of them at landfill sites, helping the UK’s growing waste management problem.

Biomass heating appliances can be seen as a direct replacement to the conventional boiler, but the most economically viable installations are in non-mains-gas areas. Biomass heating appliances that replace oil appliances can reap significant savings, especially because as the demand for wood pellets rises the prices of pellets will continue to fall.

REHAU's RAUTHERMEX pre-insulated PE-Xa pipe is ideal for large district heating and biomass systems over long distances

Wood-fired (Biomass) central heating has been popular in North America and parts of Europe for more than 20 years.

Wood pellets are the most efficient form of wood fuel, because of their low water content (6%) and their manageable size. Pellets can be made from any form of waste wood from the forestry and joinery industries. This includes scrap timber and sawdust and even straw can be used. The pellets are formed in a process which applies heat and pressure. The pellet fed stove or boiler performs at 95% efficiency compared with the traditional log burning stove which operates at only 30-65% efficiency.

Compared with fossil fuel & log burning heating appliances pellet burning appliances are much lower maintenance. Pellet boilers may require refuelling as little as once a week and the small quantity of ash produced will only require emptying every two or the months.

On the negative side, pellet-burning boilers are much larger than solid fuel, gas or oil boilers and therefore may require a special boiler room, ideally, a space of around 1800sq metres. The Energy Savings Trust estimates that including installation a biomass pellet stove will cost around £4,300 while an automatically fed pellet boiler £9,000 and £21,000.

At present, running costs compare favourably only with that of high priced oil, but as pellets become more readily available in the UK and mains gas and electricity prices increase, wood pellet heating may become an attractive and financially viable alternative fuel choice

As yet, wood pellet stoves have not been approved for use in smokeless zones, although, smoke is only briefly visible during start-up.

Carbon dioxide however, is emitted during wood pellet combustion; but because wood is a renewable resource and trees absorb carbon dioxide released in the atmosphere, this may go some way to help redeem this material as an acceptable  greener alternative fuel.

Waterless and Low Water Using Sanitary Fittings

The Waterwise organisation states that 30% of water usage in a household is from toilets and with over 45 million toilets in UK homes they use an estimated two billion litres of fresh water every day.  So a simple and effective way of managing water consumption is to install efficient toilets.

Since January 2001 new WC installations have had to have a maximum flush of six litres. Older toilets will have a flush which uses 7.5 or 9 litres.

Dual flush valves have the ability to save more water by offering a choice of a 6 litre or a 2 litre flush.  Many manufacturers now have dual flush models in their ranges.

Earth/composting toilets use no water but are perhaps best suited for installations in rural areas which may not be connected to mains sewers, as they need space for the storage containers.

Also see:

Part 1: Materials

Part 2: Conserving Energy

Part 3: Electricity and Energy Efficient Boilers