Once you have assessed and actioned your Building Design, Solar Capture,Thermal Insulation and Air Tightness you will need to consider your renewable energy requirements – whether it is of value to you and, if so, which do you use and how do you incorporate your requirements into your new home.
The majority of our customers incorporate renewable technology in their homes. We have vast experience of new technology and would be pleased to assist and advise on any renewable energy system you may be considering.
The first thing is to understand the most common forms used in homes today – what they do, how effective they are and how many years will they take to pay for themselves (‘Pay Back Period’) and we examine some options below.
Solar Thermal is a very effective means of heating hot water for domestic use. It can be used all year round but, understandably, the best results are in the summer when sunny days are more likely to occur. It is quite possible to survive from May to October using only solar heated water. It works very well for domestic hot water heating and it is possible to use it to assist with space heating.
The technology for this has been perfected over a number of years and is tried and tested. There are a number of registered installers through the UK.
There are two main types used in the UK – evacuated tubers which are best suited to our latitude and flat place collectors which look better but are not quite as efficient. Do remember to size panels according to siting, occupancy and spring/autumn solar gain.
Solar Thermal is at the top of the renewable list and therefore something we highly recommend to all our customers.
Solar Photo Voltaics (PV)
Solar Photo Voltaics are often seen powering road sign lighting, navigation buoy lights and trickle chargers on boats. The remain expensive to make and each silicon based cell converts sunlight directly into low voltage D.C. electricity using semi-conductor technology.
They are usually set out as roof arrays, covering a minimum of 4 square metres. They generate electricity when there is daylight and their output varies depending upon light intensity. The expected life span is 30 years or more (the oldest cell in existence is not that age yet!) and the current pay back period is about the same time. For those customers who wish to use them there are at least two companies who actually produce PV roof slates, tiles and shingles for partial or whole roof covering.
PV cells remain very expensive to make and as there are only a few manufacturers throughout the world, they are expensive to buy, with PV roof tiles being more expensive than frame mounted PV panel arrays.
PV electricity is converted into 240V A.C. using an inverter and any excess may be exported to the national grid. Micro-generation of electricity will become more popular due to the Governments’s introduction of a ‘Feed in Tariff’ where a premium price is paid for micro generated electricity. This is an encouraging move which, when coupled with the inevitable escalation of fossil fuel based energy prices, will see the pay back period for photo voltaic installations come tumbling down. This in turn will result in more and more people turning their homes into micro power stations.
Love them or hate them, Wind Turbines are very emotive machines! Ideally, they should be mounted on masts well above and away from local obstructions in locations with undisturbed air flow and sufficient average wind speed to spin the blames above minimum operating rotation. The generation is mounted at the top of the mast, directly behind the blades.
The resulting electricity output can be significant and can provide a considerable contribution to annual electricity consumption. As with PV panels, any excess power may be sold to the grid.
The pay back period can often be within the Government’s recognised 15 year period.
The selection of a wind turbine to generate electricity will not just be an appraisal of the technology, it will also involve site assessment, visual appreciation, neighbour opinion and planning department reaction. There is a lot of research and development taking place at the moment resulting in different sorts of turbines being invented and investigated. It is possible that we will see cylinder types (similar to the old fashioned push mower), vertical axis turbines and ducted turbines coming onto the market in the near future.
The installation of a wind turbine may be viable as part of an integrated micro-electricity generation system.
The best way to describe a Heat Pumps is to think of it as a fridge working in reverse. Low grade heat is extracted from a source (usually the ground, but could also be a river or even the air) and is circulated to the heat pump by a refrigerant. Once in the heat pump, the heated refrigerant is compressed, raising its temperature and, as it expands, the resultant heat is transferred to a hot water storage vessel or directly to heating the pipes. The refrigerant is returned to the low grade heat source to take in more heat.
Additional heat input is sometimes required in order for the domestic hot water to reach acceptable temperatures. Most heat pumps require electricity to power them. For 1kw of electricity consumed, 3 or 4kw of heat output may be expected. Thus, the C.O.P. (Coefficient of Performance) is 1:3 or 1:4 – beware of higher claims!
The usual method of harvesting low grade heat from the ground is via a pip buried about 1.5/1.8 metres below the ground in the garden. Approximately 50/60 metres would be required for a family dwelling. The alternative is to drill boreholes, although they are more expensive.
The design and sizing of the system is critical as it is only possible to extract so much heat from any given ground area. In extreme cases, If you try to take too much heat from the ground, localised freezing can occur.
Air source heat pumps are popular where thee is insufficient ground to buy the pipes. However, their seasonal performance can not match that of ground source types.
A typical heat pump unit with hot water storage requires very little maintenance (just like a fridge). Some heat pumps with minor modification and additional equipment may also be used for cooling in the Summer. Heat pumps are a good bet for our customers as the technology is tried and tested. The pay back period is relatively short and they work best when combined with underfloor heating. Another benefit for our customers is that we have access to Swedish heat pumps!
Combined Heat and Power
Combined Heat and Power is potentially likely to be the fastest growing ‘low carbon’ energy source, replacing gas boilers in large numbers, within the next decade or so.
In simple terms a CHP unit consists of an engine (various types are available) that powers a generator to make electricity, whilst at the same time producing waste heat that may be used for heating. The idea is to reduce reliance on mains electricity and to use the waste heat for space and water heating.
The major manufacturers are due to release ‘Micro CHP’ into the UK market very soon. For a number of reasons, Micro CHP units that use a stirling engine are not suitable for a low energy home but those based upon fuel cell technology are likely to be.
We recommend that our customers research this technology thoroughly. A possible scenario would be to initially install a high efficiency gas fired condensing boiler with a view to changing to a fuel cell powered Micro CHP as and when the technology has been full tested and is proven.
Biomass is, in essence, a fancy word for ‘wood burning’. It includes other plant and animal material that is either burnt or digested. In reality, we are talking about sophisticated, high efficiency wood stoves and boilers.
Wood is a renewable resource that is, in effect, stored solar energy. As trees grow and the wood is formed, CO2 is absorbed from the atmosphere and oxygen is expired. So, wood as a ‘green’ fuel is good! If the dried wood is burned at high temperatures, the stored solar energy is converted to heat, whilst very little CO2 is emitted. The right burning equipment is required and now that there are automatic feed boilers on the market, they have the capacity to do just that.
Wood pellets are the best, but wood chips, or even logs, are used. Wood pellets are common in Sweden, the USA and Europe but, as yet, there are only a few importers and suppliers in the UK, although their numbers are gradually increasing. At present, wood fuel costs are roughly the same as oil and gas but the boilers are twice the price.
The Forestry Commission is getting very excited about Biomass heating, probably because the market for small round timber for paper making has collapsed and they foresee selling wood for burning as very lucrative proposition. They also see woodland being ‘managed’ better because there will be demand for thinnings and coppiced wood.
Many people believe that, for a number of reasons, electricity is the fuel of the future. At the point of use it is at least 100% efficient (rising to 300-400% for heat pumps).
Currently, our national power stations release staggering quantities of CO2 into our atmosphere – they waste all the heat produced in the generating process as cooling water via towers, rivers and the sea. In general, power stations are only 37% efficient at converting raw fuel to electricity resulting in electricity being a very environmentally bad energy source. The standard assessment procedure used to calculate the carbon emission of any new home includes fuel factoring – needless to say, electricity has a poor rating.
However, if you produce the electricity at the point of use from, for example, a combined source (such as PV, Wind Turbine & Micro Chip) and the waste heat from generation is usefully used for home space heating, it suddenly becomes very ‘Green’. The Government is aware of this and is struggling to produce a coherent energy policy for our future. Just how do we maintain 21st century living using available, affordable and environmentally friendly fuels?
North Sea gas is running out and replacement foreign supplies are not secure – oil is available but only for a limited time and supplies and subject to uncontrollable world events. Reserves are also becoming more and more difficult to extract. In the short term, coal fired generation will have to fill the energy gap but that in turn increases the amount of CO2 pumped into the atmosphere. So, at a National level, that really only leaves ‘renewable’s’ and nuclear as long term future options.
Some of the greenest environmentalists have publicly stated that as a nation we may be cornered into expanding our stock of nuclear power stations (which currently stands at just one) because they are non pollutors and the resultant electricity conversion is 100% when used. The only problems are ‘where do you store the spent fuel rods? and ‘don’t they become possible terrorist targets?’
Renewable energy will not be an answer to national demand unless and until individuals either voluntarily decide or are economically encouraged to use them.
Renewable energies can seriously harm your wallet without necessarily helping your comfort or the future of the plant. Before spending a fortune on something you don’t fully understand but you maybe being sold to use as ‘the answer’, ‘eco friendly’ or ‘better than the rest’, do remember that the best use of renewable energy technologies is achieved when they form part of a holistic approach to minimising energy and use and not just as a stand alone and bolt-on adjunct.