Renewable Technology

Wind Turbine

Renewable energy resources are constantly replenished through the cycles of nature - their supply will never be exhausted. Fossil fuels, on the other hand, are finite resources. They will become increasingly scarce and expensive to extract and supplies will become concentrated in politically volatile areas of the world before reserves are finally exhausted.

A gradual shift towards using renewable energy would mean:

reduced CO2 emissions
secure and stable energy supply for the long term
reduced reliance on expensive fuel imports
investment and employment in our indigenous renewable energy projects, often in rural and underdeveloped areas

Today, renewable energy sources meet about 2% of Irelands total energy consumption. This figure breaks down in roughly equal proportions to heat from wood fuel in the domestic and wood processing sectors and electricity production from hydropower.

In 2002, the share of renewable energy in gross electrical consumption of the countries of the European Union contributed 13.4%. By 2010, it is the objective of the EU to raise this contribution to 22.1%.

EU policy also targets an increase in the contribution of renewables to 12% or Europes total energy by 2010. There are a few different options commonly used in houses recently, the main ones are:

1. Solar Panels

House with Solar Panel

Active Solar Heating is one of the primary ways for buildings to use solar energy. This technology uses solar collectors to transform sunlight into heat to provide space and/or water heating. Solar water heating is the most common application of active solar thermal in Europe. A correctly sized solar water heating system can cover 50-60% of your hot water heating requirement with free solar energy.

A solar thermal system providing space and water heating is generally referred to as a solar combisystem. It is generally sized to cover 30 to 40% of the annual heating requirement of a house in Northern Europe. In Ireland, a solar combisystem using air as a heat transfer medium is gaining in popularity. It has the advantage of combining solar heating and ventilation through the same system. It is particularly suitable for low-energy houses.

By 2005, over 3,000 households used a solar heating system in Ireland, compared to about 5 million households in Europe.

Are there different types of solar panels? Yes there are two types at the moment:

Flat plate collectors are a single plate of glass set over an array of copper/plastic pipes in a shallow box. It uses radiation to transfer heat to the water in the pipes.
Evacuated tube collectors are tubes which come in a set of double walled glass cylinders. Air is removed and replaced with a fluid which then boils, condenses and heats liquid flowing through a loop connected to each tube which is transferred to by water to your cylinder. Evacuated tubes are more efficient than plates.

What size solar panel do I need?

You ll need roughly one square metre per person in the household. Each metre of panel will heat between 30 and 60 litres of water. For plate collector this is 1.2 to 1.5 m per person.

What direction should the panel be faced? Ideally full south but anywhere between SE and SW depending on available unshaded roof space.

Do solar panels work all year round?

Even in dull weather the panels will provide 40% to 60 % of your hot water. The collectors need radiation rather sunlight, in winter they will heat your water to 30-40C whereas in summer this could be 80C

2. Geo-Thermal

Geothermal / Ground Source Heat Pumps

Ground source heat pumps, also known as geothermal heat pumps, are used for space heating and cooling, as well as water heating. They operate on the fact that the earth beneath the surface remains at a constant temperature throughout the year, and that the ground acts as a heat source in winter and a heat sink in summer. They can be used in both residential and commercial or institutional buildings.

How it works

The earth's surface acts as a huge solar collector, absorbing radiation from the sun. In this country the ground maintains a constant temperature between 11oC and 13oC, several metres below the surface. Geothermal Heat Pumps take advantage of this by transferring the heat stored in the earth or in ground water to buildings in winter and the opposite in summer for cooling. Through compression, heat pumps can pump up heat at low temperature and release it at a higher temperature so that it may be used again. A heat pump looks similar and can perform the same functions as a conventional gas or oil boiler, i.e. space heating and sanitary hot water production. For every unit of electricity used to operate the heat pump, up to four units of heat are generated. Therefore for every unit of electricity used to pump the heat, 3-4 units of heat are produced.

Installation in the Home

The system has three main components: a series of pipes in the ground, a heat pump and a heat distribution system. Lengths of plastic pipes are buried in the ground, either in a borehole or a horizontal trench near the building to be heated or cooled. Fluid, normally water with anti-freeze, absorbs or emits heat to the soil, depending on whether the ambient air is colder or warmer than the soil. In winter, the heat pump removes the heat from the fluid, upgrades it to a higher temperature for use in the building, typically in under-floor heating. A distribution system is needed to transfer the heat extracted from the ground by the heat pump. The heat is often in the form of hot water and is distributed around the dwelling by radiators or a low temperature under-floor heating system.

Payback and Maintenance

The initial capital costs of installing a Geothermal Heat Pump system is usually higher than other conventional central heating systems. However, under the Greener Homes Scheme, there are now grants available which will reduce initial costs significantly. A large proportion of the outlay will be for the purchase and installation of the ground collector. The system is among the most energy efficient and cost effective heating and cooling systems available. Typically, four units of heat are generated for every unit of electricity used by the heat pump to deliver it, and the payback is typically about 8- 10 years. The life expectancy of the system is around 20 years. Once installed a heat pump requires very little maintenance and anyone installing a heat pump should speak with their installer regarding a maintenance agreement.

Air to Water Heat pumps

An Air to water heat pump works in similar to a geothermal unit except it absorbs low temperture energy.

3. Heat Recovery Ventilation

Over the last decade there has been a huge emphasis on increasing the thermal efficiency in buildings, in particular private houses. We now have draught free, well insulated buildings. This has brought with it a whole set of new problems - poor air quality.

The most effective way to combat this is to mechanically ventilate the building. A balanced ventilation system is one that brings in an equal amount of air to that which is being extracted from the building. Ideally, the fresh air being brought into the building should be 'warmed' and filtered. Air vents, as used in most buildings ARE NOT a solution.

A heat recovery ventilator (HRV), sometimes called an air-to-air heat exchanger is different than conventional vents and fans. With standard ventilation, air circulates through static, open vents or is expelled by fans, such as those used in bathrooms, kitchens, and attics.

When room air escapes or is expelled, the energy that was used to heat or cool it is wasted. An HRV can save 75 percent or more of that wasted energy. As it pushes out stale air, it pulls in fresh air, and with little or no mixing of the two air streams it transfers the heat from the outgoing air to the incoming supply. The fresh air arrives pre-heated and, with some units, pre-humidified or dehumidified.

Heat Recovery Ventilation Unit

Whole house HRVs provide fresh air to all rooms. They often require routing ductwork to several places: to rooms where you want to exhaust stale air, particularly bathrooms, laundry rooms, and kitchens; to the outdoors; and often to the central heating and air-conditioning systems return air supply.

Though whole house systems are installed primarily in new houses, they can be retrofitted into some houses that have good access for ductwork, particularly those with unfinished basements. To simplify installation, some systems can take advantage of existing ductwork - they're piped into the return-air system.

4. Pellet Boilers

Wood Pellet Stove

Wood Pellet Stoves are a new and very popular way as a means to provide heat. Pellet Stoves use wood pellets as its primary heat source. These wood pellets are tightly compacted and dense which causes it to be burned very efficiently and powerfully. Pellets usually come from the byproduct of sawmills and are very easily transportable due to their size (about half and inch) and their weight. These days, the prices of stove burning sources such as fossil fuels, chopped wood, natural gas and electric gas are gradually going up and wood pellets are a very cheap and easy to manufacture resource and has a very low pollution rate. It is now possible to get boilers which are also capable of burning grain i.e wheat as well wood pellets

5. DISTRICT HEATING SYSTEMS (NORMALLY FOR HOUSING SCHEMES APARTMENTS OR COMMERIAL UNITS)

District heating is the use of a centralized boiler installation to provide heat for a number of buildings. This can use a heat only boiler, or the heat from a combined heat and power (CHP) plant.

Boilers that burn wood fuels such as wood chips and pellets tend to be physically larger and more expensive than equivalent gas or oil boilers. This is partly as a result of the physical requirements for a high temperature combustion environment and transporting the solid fuel. As boilers get larger however the disparity with gas and oil boilers becomes comparatively smaller, and so wood fuel becomes more economically attractive, especially for installations of the scale of a few hundred kW.

District heating makes use of these cost advantages, as well as the administrative benefits of using a single boiler installation to provide heat to a number of buildings. These might be a number of individual houses, blocks of social housing, local council offices, a school, etc.

Combined Heat Power (CHP) Unit

District heating is much more common in some European countries than in the UK. In Denmark for instance district heating provides around 60% of heating. However there are now a number of successful district heating schemes in the UK, both using fossil fuels and biomass.

A typical district heating installation consists of a highly insulated "heat main" of flow and return pipes distributing hot water (or steam) past all buildings which might be connected. A junction point allows easy connection to each building, from which hot water can be taken from the main to a heat exchanger (heat substation) within each building. The heating circuit within the building is thus isolated from the heat main. Temperature measurement of the flow and return lines, plus a flow meter (together forming a heat meter), allow the actual heat usage within each building, or even apartment, to be separately measured, and delivered heat billed for accordingly. Remote meter reading by modem, secure web interface or drive-by are all possible, as are remote diagnostics to ensure reliable operation.