Thursday, 24 June 2010

Solar electric panels

Solar electric panels turn light into electricity. They are commonly called "photovoltaic" (PV) panels because they generate a voltage from the energy in light. As daylight is abundant, PV panels offer a truly universal opportunity for clean energy. Although they will only ever be part of the solution, given that the sun regularly sets, they are an important part: tried, tested and reliable

Electricity from your roof
At the heart of a PV panel is a junction of two semiconductors, one positively charged and one negatively charged. The light that enters the panel bounces free electrons across the junction, creating an electric current. Using some smart electronics, this low voltage direct current is transformed into high voltage alternating current - the stuff we use every day in our homes

Despite the complexity of the technology, PV panels are very simple to use. Once they are installed on yur roof and plugged in, you can usually forget about them. There are no noisy moving parts wearing ut, no fuel or waste to lug around. Maintenance is minimal and the panels should last for decades (well beyond the 25 year warranty) as the solid state technology does not degrade.


Solar power and domestic needs
One of the few disadvantages of solar power is its poor match to our actual use of electricity at home. The sun is at its highest in the middle of the day when we need very little electricity, and absent altogether on winter evenings when the lights, television and ketle are all on. Happily this does not mean that PV panel owners have to go to bed at dusk - they simple switch to mains electricity instead. Most PV systems are fully intergrated with the national grid and owners are paid for the surplus they export.

System components
Almost any roof or wall can generate electricity with a PV panel attached, but a pitched roof facing due south is best. South-east and south-west facing roofs are also suitable. You will get a decent output from a PV panel even under cloudy skies but direct sunlight pushes this output up to three- or four-fold. Ideally you want a site free from shadow-casting obstructions, but don't be put off if there is a little shading. Your roof must of course be strong enough to support the panels.

Tuesday, 22 June 2010

Electricity

Electricity is fantastically convenient and clean at the point of use, yet it is the dirtiest of all the fuels we see in our homes because so much energy is wasted in the power station. Out of sight and out of mind, power stations relentlessly spew carbon dioxide and toxic particles into the air. Greening up your electricity use is therefore a top domestic priority.

National electricity generation
Most of the electricity produced in Britain is generated in coal (37%), gas (35%) and nuclear (19%) power stations. Only 4% comes from 'renewable' sources, and much of this is from burning the gas that comes off landfill waste dumps. The supply of truely sustainable electricity, such as wood, wind and solar power, is increasing.

Coal and gas power stations ae the single biggest source of caron dioxide emissions in the UK. Modern gas-fired power stations are the most efficient of the fossil-fuel stations, but half the energy in the gas is still lost up the power station chimney as heat rather than converted to electricty. Nuclear power stations have low carbon emissions but create an ever-growing stockpile of radioactive waste that will remain toxic for thousands of years (long after all current civilisations have disappeared). Whatever the pros and cons may be of fossil fuels and nuclear power, neither can be considered green.

Greener electricity
There are three ways  you can reduce the environmental impact of your electricity consumption: use less, make your own and switch to a renewable supplier. The first of these is by far the most important. As we will never be able to meet our current national demand for electricity using renewable power alone, a truly green future for electricty is only possible if we can radically reduce demand as well as increasing renewable supply. If you can also boost this supply by installing some renewable power of your own, so much the better.

Reduce demand
Everyone can take steps to reduce their ue of electricity. If you use electricity for heating and hot water, consider whether you could switch to a different fuel. It is far more efficient to burn gas in a boiler to heat your home than to burn it in a distant power station and then use the electricity generated for the same purpose

Make your own
Most households in Britain could generate some or all of their own electricity. If you have a sunny roof or wall, solar power is within your reach. If you have an unobstructed view of the prevailing wind, a wind turbine is definitely wirth considering. If a river runs through your back garden, a water turbine is a possibility.

Friday, 18 June 2010

Walls

The walls of your home do many different jobs at once. They support the roof and the floors, keep the heat in and keep the rain, cold and noise out. You will have to act fast if the roof is falling down, but millions of people survive with poorly insulated walls simply by turning the heating up. Getting your walls to work properly in every respect is therefore a top priority for greening up your home.

Warm, green and cosy
Walls with no insulation throw heat away with abandon. Installing insulation can be a major task, given the area you have to cover, but you will definitely feel the results: warm walls make for a green, cosy house. Remember that it is only your exposed external walls that you have to fix, as you can assume that walls adjoining other properties will gain as much heat as they lose

As well as cutting your heating bills by up to a third, insulated walls improve the comfort of your home, prevent condensation forming on your walls and keep the heat out on hot summer days. If however there are any existing problems with your walls,  such as damp, you should address these first or you may make matters worse.


Cavity wall insulation
Many houses built in the twentieth century have double-skin walls with a cavity betwen the two layers. The aim of the cavity is to prevent moisture getting through the wall and into the house. It is also an ideal place to retrofit insulation by blowing it in through holes drilled in the outer wall. The insulation is typically made of polystyrene beads or fragments of mineral fibre which fill up all the nooks and crannies inside the cavity but prevent moisture from tracking across the inner wall

Cavity wall insulation requires professional installation, but this is usually staightforward and takes less than a day. Once the insulation has been blown in to the walls, the holes are made good and the building is left with no significant changes to its appereance

Solid wall insulation
Most houses built before 1930 have solid walls waith no cavity. You can only improve these walls by adding insulation to the inside or the outside. Covering entire walls with a new layer of insulation and a new finish is a big and messy business, so it is worth undertaking with other renovation tasks.

The simpliest way of adding insulation to a solid wall is to stick it on the interior face. Use plasterboard which is designed specifically for this purpose with a layer of high performance insulation already attached. The thicker the insulation layer, the more energy you will conserve. You can do better still by building a new wall in front of the existing one with timber or metal uprights (studs). You can then pack the gaps between the studs with 100mm of insulation or much more. Internal insulation must include a barrier (a polythene sheet uner the plasterboard) to stop water vapour getting into the wall where it could condense on the masonary behind the insulation. This barrier is included in insulated plasterboard products.

The depth you choose will partly depend on how much of your room you are willing to lose (only the exterior walls need insulating, remember) and how many window sills and architectural details you have to work around. If you do not want to lose any of your room space, you could still install thermal wallpaper. This thick lining paper will not do much to cut your heat losses but it will give you warm, condensation-free walls

Tuesday, 15 June 2010

Underfloor heating

Despite the best efforts of designers to produce attractive radiators, our homes undoubtedly look better without them. The popularity of underfloor heating is primarily driven by our desire to liberate our walls from these imposing lumps of metal. By turning the entire floor into one big radiator, underfloor heating puts the heating system in its place: in touch but out of sight

Water vs. electricity
Most underfloor heating systems use hot water supplied by a boiler or other heat source. The water is pumped around all the floors of your house in exactly the same way that it is pumped to radiators.

Some underfloor heating systems use electicity to provide the heat instead. These are easier to install than wet systems, but are not at all eco-friendly. Electricity is the dirtiest and most inefficent domestic fuel because so much energy is lost in the power station. It should only be used for heating as a last resort. Electrical systems are also much more expensive to run.

Efficient and effective
Because radiators are relatively small, the temperature of the water that flows through them has to be kept quite high in order that enough heat can be released into the rooms of your house to keep them warm. As underfloor heating uses a much larger surface area to emit heat, it can run at a lower temperature. As modern condensing boilers run more efficiently at lower temperatures, this difference makes underfloor heating a greener choice. But only just: don't rip up your radiators and install underfloor heating for this reson only.

Underfloor heating is also more effective in delivering heat to where it is needed. Radiators create currents of air that take the heat to the top of the room, where we need it least, and create draughts of cold air at floor level. Underfloor heating is more comfortable because it radiates heat gently across the whole room. There are no hot and cold spots and no currents of dry, dusty air. Rooms with warm surfaces and stable air do not require the high air temperatures of radiator-supplied rooms: you may be able to turn down your thermostat, save energy and still be more comfortable 

Not for everyone
Small lumps of metal heat up very quickly; concrete or timber floors do not. The big disadvantage of underfloor heating is its sluggishness. If your home is cold and you want to heat it up rapidly, underfloor heating will not do the job. Underfloor heating works best with well-insulated, energy-efficient homes that do not lose heat quickly and stay at a fairly stable temperature across the day. It is therefore most suited to constantly occupied homes.

Underfloor heating can also exacerbate overheating problems. If you have rooms with a lot of glazing that heat up quickly when the sun comes out, you will be in trouble if your floors continue to emit heat long after the heating system has been switched off. Such problems can be avoided by reducing the risk of overheating with good shading.

Floor finishes
Underfloor heating can be used with any floor finish, but solid floors of stone or tile are best. Underfloor heating can be laid beneath timber floors as long as the timber is dry. Existing floorboards in centrally heated houses will be suitable, but new timber floors should be given time to acclimatise to the building first. Avoid fitted carpets as these act as insulation and slow down the heat flow to the room. On ground floors insulation must be laid first or you will simply heat the ground.

Monday, 14 June 2010

The right house for a heat pump

Heat pumps are best suited to well insulated, energy-efficient homes. Unlike boilers, they cannot produce a huge surge of energy to heat up a house quickly but prefer to chug away in the background, providing a regular output of heat to keep the building at a stable temperature. If you live in a house that cools quickly and is often unoccupied during the day, a heat pump will not be your best option.

Heat pumps become less efficient as the difference between their source and output temperatures increases. Consequently they are ideal for underfloor heating which operates at a lower temperature than radiators. To enable the heat pump to work efficiently, radiator systems may have to be upgraded with bigger radiators which emit more heat

Ground Works
The ground works for a heat pump can be substantial. Depending on the space available, you can either dig long trenches for the pipework in your garden, at about 2m deep, or put the pipes down a 75-100m borehole. Get a survey done first to ensure that the ground is suitable. The trench option is easier and cheaper but may seriously mess up your garden during installation.

Some heat pumps do not need ground works: air source heat pumps extract heat from the ambient external air or, in some models, from the exhaust of a mechanical ventilation system. Unlike the ground which stays at a stable temperature all year, the air gets very cold just when you want to extract the most heat from it, so the efficiency of air source heat pumps can be very poor. They should only be considered for small properties with very low energy demands.

It is also possible to draw heat from water such as a flowing river. This can be a good heat source because the extracted heat is rapidly replaced.

Thursday, 10 June 2010

Heat pumps

Heat pumps pump heat. It's as simple as that. They extract energy from one place, which gets cooler, and pump it to another place, making it warmer. These clever machines make it possible to take free heat from the environment and put it exactly where you want it.

Technology
A fridge removes energy from he cold interior, cooling it down further, and releases it out the back, creating a stream of warm air. 'Ground source heat pumps' work in exactly the same way but their purpose is to provide warmth rather than to cool things down. They extract energy from the ground, where the temperature is a steady 10 degrees celcius, and transfer it to the inside of your house. The sun beats down on the ground all year, so there is no shortage of energy stored in the earth. Heat pumps do not store heat, they just move it from one place to another.
Three independent loops of fluid are needed to perform the heat pump's task. The first is a loop of anti-freeze that runs underneath your lawn and absorbs heat from the ground. The last is the loop of hot water that emits this heat into your home through underfloor heating or radiators. In between is the loop of refrigerant inside the heat pump that shifts the energy from a relatively cool fluid to a warm fluid, it cannot work by the natural flow of energy. Instead, the refrigerant is repeatedly evaporated, compressed and condensed to pump the heat in the 'wrong' direction

Quite a lot of electrical energy is needed to power the refrigerant cycle, especially the compresser. This means that heat pumps are not necessay cheap to run or 100% green, despite the fact that they are extracting spare solar heat from the ground. Electricity is the most expensive domestic fuel and has the highest carbon emissions because so much  energy is wasted in the power station. Electricity has aout 2.5 times the carbon emissions of natural gas (the cleanest fossil fuel) and costs about three times as much. However the heat energy provided by a groud source heat pump is typically three to five times greater than the electrical energy needed to run it, so heat pumps are still good eco-choices compared to gas, oil or direct electric heating.