Topping up wind generated electricity

Wind power is often chosen either because an electrical mains supply is not available on practical grounds such as with some caravans, houseboats etc. or because it is too expensive to install because of the remote location. It would be unlikely that wind power could provide all the electricity required and therefore additional means of generating electricity may need to be considered. Systems available include photovoltaics, waterpower and conventional small generators, …………………..all these systems have advantages and disadvantages some of which are described below.

Photovoltaics (PV)

Photovoltaic cells (PVs) are a very different technology from solar water heating, and use light to generate electricity. They are particularly well suited to sites where a grid connection would be difficult or expensive or that are only used in the summer. For an independent power supply, solar works well with wind as there is a good balance of both over the year. Solar electricity, like electricity from other renewable energy sources, doesn’t produce carbon dioxide or harm the environment.

Although start-up costs are higher than other renewable technologies, PVs have key advantages:

• there are no moving parts to fix so they are relatively easy to install and maintain
• they can be sited in urban areas and are not restricted in the way that wind and hydro-power systems are
• they can replace other roofing materials, for example tiles. The cells are embedded in a flat, waterproof material to form ‘modules’, which make ideal cladding material for walls and roofs
• they need not take up any additional land space.

It is hoped that efficiency gains will make PVs a very attractive proposition in the next two decades.

Solar panels that produce electricity are expensive to buy and produce only relatively small amounts of electricity. They need to be sited in a good position and may take up a lot of valuable space. However they do have the advantage of producing pollution free energy and the output is greater in the summer, which is often when the wind is not so strong.

Photovoltaic systems use cells to convert solar radiation into electricity. The PV cell consists of one or two layers of a semi conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers, causing electricity to flow. The greater the intensity of the light the greater the flow of electricity.

PV systems generate no climate changing gases, saving approximately 325kg of carbon dioxide per year for each kW peak installed (Kilowatt (kW) peak – PV cells are referred to in terms of the amount of energy they generate in full sun light). PV arrays now come in a variety of shapes and colours, ranging from grey ‘solar tiles’ that look like roof tiles, to panels and transparent cells that you can use on conservatories and glass to provide shading as well as generating electricity. As well as enabling you to generate free electricity they can provide an interesting alternative to conventional roof tiles!

You can use PV systems for a building with a roof or wall that faces within 90 degrees of south, as long as no other buildings or large trees overshadow it. If the roof surface is in shadow for parts of the day, the output of the system decreases. Another consideration is that the roof also be strong enough to hold the significant weight of the panels, especially if the panel is going to be placed on top of existing tiles. A trained and experienced installer should always carry out solar PV installations.

Prices for PV systems vary, depending on the size of the system to be installed, type of PV cell used and the nature of the actual building on which the PV is mounted. The size of the system is dictated by the amount of electricity required to be supplied.

For the average domestic system, costs can be around £4,000- £9,000 per kwp installed with most domestic systems usually between 1.5 and 2 kwp. Solar tiles cost more than conventional panels and panels that are integrated into a roof are more expensive than those that sit on top. If you intend to have major roof repairs carried out it may be worth exploring PV tiles as they can offset the cost of roof tiles.

Grid connected systems require very little maintenance, generally limited to ensuring that the panels are kept relatively clean and that shade from trees has not become a problem. The wiring and components of the system should however be checked regularly by a qualified technician.

Some local authorities in the UK for example require planning permission to allow you to fit a PV system, especially in conservation areas or on listed buildings. Always check with your local authority about planning issues before you have a system installed. Obtaining retrospective planning permission can be difficult and costly!

Water power

Obviously waterpower is only possible where there is a usable source of running water. Construction and installation is expensive and maintenance is relatively high. The energy produced is again pollution free.

Hydropower systems convert potential energy stored in water held at height to kinetic energy (or the energy used in movement) to turn a turbine to produce electricity.
Hydro Electricity can be one of the cheapest methods of providing off-grid renewable electricity, but it is also very site specific. One advantage is that on a good site you may not need batteries or an inverter – the turbines will often produce 240 volts AC and can just be turned on when needed. The ideal situation is one where there is no grid electricity (otherwise the capital cost of a system is generally too high to make it financially viable on a small scale), and a water course with a good flow and a high head. You will have to obtain an abstraction licence in the UK from the Environment Agency.

A good hydro site depends on the ‘head’ of water (the vertical drop) and the flow rate. To estimate the energy in a water source, multiply the flow (in litres per second) by the head (in metres) by 10 (acceleration due to gravity). Divide your answer by 2 to account for losses and inefficiencies, and you will have a rough idea of the potential power generation in watts.

Although it will cost several thousand pounds to install a hydro system, in some situations it will be cheaper than paying the cost of connecting to the grid. The basic equipment for a 1kW battery charging system might cost £5,000 to £6,000, plus installation costs, while a larger system can cost tens of thousands of pounds.

Old watermills, and other low-head sites, are not usually good sites for generating electricity. A large, slow-moving body of water gives a high torque, which is needed by mills for mechanical work, whilst it is easier to generate electricity where there is a fast flow of water that can be channelled to hit the turbine at high pressure. However some old waterwheels have been converted to generate electricity, so it may be worth looking into.

A micro hydro plant is below 100kW. Improvements in small turbine and generator technology mean that micro hydro schemes are an attractive means of producing electricity. Useful power may be produced from even a small stream. The likely range is from a few hundred watts (possibly for use with batteries) for domestic schemes, to a minimum 25kW for commercial schemes.

Hydropower requires the source to be relatively close to the site of power usage, or to a suitable grid connection. Hydro systems can be connected to the main electricity grid, or as a part of a stand-alone (off-grid) power system. In a grid-connected system, any electricity generated in excess of consumption on site can be sold to electricity companies.

In an off-grid hydro system, electricity can be supplied directly to the devices powered, or via a battery bank and inverter set up. Allowances should be made for any seasonal variations in water flow, which can affect the amount of electricity delivered to the system i.e. having a back up power system.

It is possible for single households with a mains connection located near a hydro source to install a micro hydro system. They can go ‘off the grid’ entirely, or stay connected and sell excess electricity to the grid. The capital cost is high, but the prospect of zero or even negative electricity bills may tempt you!

Provided the resource is there, community hydro projects can also be a viable proposition. Potentially, there are great benefits in clubbing together to increase buying power or sharing expertise – although the work involved should not be underestimated.

Energy available in a body of water depends on the amount of water flowing per second, and the height (or head) that the water falls. The scheme’s actual output will depend on how efficiently it converts the power of the water into electrical power (maximum efficiencies of over 90% are possible, but for small systems 50% is more realistic). Hydro electric systems are generally divided into 2 categories, low and high head.

This will depend on the resource available and your energy needs. For houses with no mains connection, but with access to a micro-hydro site, a good hydro system can generate a steady, more reliable electricity supply than other renewable technologies at a lower cost. Total system costs can still be high, but often less than the cost of a grid connection, and with no electricity bills to follow. Note that in off-grid applications the power is used for lighting and electrical appliances, however space and water heating can be supplied when available power exceeds demand.

Hydro costs are very site specific and are related to energy output.

For low head systems (not including the civil works – so assuming there was an existing pond or weir), costs may be in the region of £4,000 per kW installed up to about 10kW, and would drop per kW for larger schemes.

For medium heads, a fixed cost of about £10,000, and then about £2,500 per kW up to around 10kW – so a typical 5kW domestic scheme might cost £20-£25,000. Unit costs drop for larger schemes.

Turbines can have visual impact and produce some noise, but these can be mitigated relatively easily. The main issue is to maintain the river’s ecology by restricting the proportion of the total flow diverted through the turbine.

You will need to talk to the relevant planning authorities to ensure the site and design is acceptable and identify any other permissions required.

Diesel and petrol generators

As long as the supply of fuel is maintained this form of generation should be available at any time. Both diesel and petrol generators are readily available both new and second hand. The diesel used to run such plant has a lower tax than diesel used for transport. They are however noisy and usually use fossil fuels which pollute the atmosphere.

Biomass

Energy from biomass is produced from organic matter of recent origin. It does not include fossil fuels, which have taken millions of years to evolve. The CO2 released during the generation of energy from biomass is balanced by that absorbed during the fuel’s production. We call this a carbon neutral process.

Biomass is often called ‘bioenergy’ or ‘biofuels’. These biofuels are produced from organic materials, either directly from plants or indirectly from industrial, commercial, domestic or agricultural products. Biofuels fall into two main categories:

• Woody biomass includes forest products, untreated wood products, energy crops, short rotation coppice (SRC) e.g. willow, miscanthus (elephant grass).

• Non-woody biomass includes animal wastes, industrial and biodegradable municipal products from food processing and high-energy crops e.g. rape, sugar cane, maize.

For small-scale domestic applications of biomass the fuel usually takes the form of wood pellets, wood chips and wood logs.

There are two main methods of using biomass to heat a domestic property:

Stand-alone stoves providing space heating for a room.

• Can be fuelled by logs or pellets but only pellets are suitable for automatic feed
• Generally 6-12 kW in output
• Some models can be fitted with a back boiler to provide water heating.

Boilers connected to central heating and hot water systems.

• Suitable for pellets, logs or chips
• Generally larger than 15 kW.

Stoves can achieve efficiencies of more than 80%. They are normally used to provide background heating whilst adding aesthetic value, as they are designed to be located in the living area of the house itself. Although many wood burning stoves act as space heaters only, the higher output versions may be fitted with an integral back boiler to provide domestic hot water and, if required, central heating via radiators.

There are many domestic scale log, wood-chip and wood pellet burning central heating boilers available. Log boilers require manual loading and may be unsuitable for some situations, whilst automatic pellet and wood-chip systems can be more expensive. Many boilers will dual-fire both wood chips and pellets, although the wood chip boilers will require larger hoppers to provide the same time interval between refueling.

Boilers can be designed with an integral hot water energy storage tank or accumulator tank that stores water up to 90 Deg C,enabling the supply of heat to be further decoupled from the combustion of the fuel. This is particularly helpful with log boilers where systems operate at full load and the matching of demand with load is performed by the accumulator.

You should consider the following issues if you are considering a biomass boiler or stove. An accredited installer will be able to provide more detailed advice regarding suitability.

Fuel: It is important that you have storage space for the fuel, appropriate access to the boiler for loading and a local fuel supplier.

Flue: The vent material must be specifically designed for wood fuel appliances and there must be sufficient air movement for proper operation of the stove. Chimneys can be fitted with a lined flue.

Regulations: The installation must comply with all safety and building regulations (see Part J of the Building Regulations).

Smokeless zone: Wood can only be burnt on exempted appliances, under the Clean Air Act. This mainly applies to domestic appliances.

Planning: If the building is listed, or in an area of outstanding natural beauty (AONB), then you will need to check with your Local Authority Planning Department before a flue is fitted.

Capital costs: This generally depends on the type and size of system you choose but installation and commissioning costs tend to be fairly fixed. Stand alone room heaters generally cost £1500 – £3000 installed. The cost for boilers varies depending on the fuel choice; a typical 20kW (average size required for a three bed semi detached house) pellet boiler would cost around £5000 installed, including the cost of the flue and commissioning. A manual log feed system of the same size would be slightly cheaper.

Running costs: Unlike other forms or renewable energy biomass systems require you to pay for the fuel. Fuel costs are generally dependant on the distance from your fuel supplier; if you have a supplier near by this will reduce the costs of the fuel considerably. As a general rule the running costs will be more favourable if you live in an off gas area.

Payback: This will depend on the fuel being replaced and the type of wood fuel being used but will be more favourable in off gas grid areas.

Producing energy from biomass has both environmental and economic advantages. It is most cost-effective when a local fuel source is used, which results in local investment and employment. Furthermore, biomass can contribute to waste management by harnessing energy from products that are often disposed of at landfill sites.

Solar water heating

Solar water heating systems gather energy radiated by the sun and convert it into useful heat in the form of hot water. This technology is well developed with a large choice of equipment to suit many applications. Solar water heating systems work alongside your conventional water heater to provide hot water.

It can provide almost all of your hot water during the summer months and about 50% year round. It will reduce your impact on the environment – the average domestic system can reduce carbon dioxide emissions by 0.25-0.5 tonne per year, depending on the fuel replaced.

• The system which best suits your needs depends on a range of factors, including:
• Amount of south facing roof space.
• Existing water heating system (e.g. some gas combi boilers may not be suitable).
• The budget you have for the project.

A competent professional installer should assess your situation and discuss with you the best configuration to meet your needs.

Solar water heating can be used for domestic water heating and also for larger scale applications such as swimming pools. A solar water heating system for domestic hot water comprises three main components: solar panels; hot water cylinder; and a plumbing system.

Solar panels are fitted to your roof and retain heat from the sun’s rays and transfer this heat to a fluid. A hot water cylinder stores the hot water that is heated during the day and supplies it for use later. The plumbing system is made up of simple piping and sometimes a pump, which moves the fluid around the system.

Preferably you will need 2-4m² of southeast to southwest facing roof space that receives minimal shading during the main part of day.

Space to locate an additional water cylinder if required.

Costs vary due to a range of factors. The typical installation costs for flat plate collectors is £2,000 – £3,000 while evacuated tube systems will cost £3,500 – £4,500.

Alternatively you can fit or build the system yourself. It can work out cheaper but will take longer and you’ll need a certain level of skill. However, you should bear in mind that DIY jobs are not eligible for grant funding.

Solar hot water systems generally come with a 10-year warranty and require very little maintenance. A yearly check by the householder and a more detailed check by a professional installer every 3-5 years should be sufficient (although you should consult your system supplier for exact maintenance

requirements).

Over 44,000 solar water heating panels have been installed in the UK to date. Solar panels contain water which is heated by the sun, and this then usually goes through a coil in a hot water cylinder, transferring the heat to the water there. You need to have a conventional water heating system as well, such as a gas or oil fired boiler, or perhaps a back-boiler on a wood stove, to top up the heat from the panels when necessary and provide hot water and space heating in the winter. (If wood comes from sustainably managed forests, it is potentially a renewable fuel and is carbon neutral as it absorbs the same amount of carbon dioxide when growing as it gives off when burnt. It is important that wood is well seasoned and burnt efficiently, or it will give off harmful dioxins.) In most cases solar water heating panels will not provide space heating because there is insufficient sun in the winter, when you need heating most.

If your boiler needs replacing, a condensing boiler is most efficient and you can find out further details in the UK from your local Energy Efficiency Advice Centre (Freephone 0800 512 012). Condensing boilers are more expensive but the savings on fuel should compensate for the extra cost within a few years – and from then on you’re saving money and fuel!

You can add solar panels to most existing hot water systems, though you will usually have to add an additional hot water cylinder or change your existing one to a twin coil cylinder. It can be more difficult to use solar water heating with a ‘combi’ boiler because they are designed to take cold mains pressure water, and solar systems tend to supply hot or warm, low pressure water. Check with the boiler manufacturer or with a solar engineer to see if your boiler is suitable. Solar water heating is often ideal for swimming pools – contact CAT’s free information service Email: info@cat.org.uk for further details.

Ideally solar panels should be placed somewhere south facing and free of shade, and they can be mounted on the roof or at ground level. You may need a pump to circulate the water round and some regulating equipment.

There are two main types of commercial solar water heating panel available – flat plate and evacuated tubes. Although evacuated tubes are more efficient they are also more expensive and if you spend too much on installing a system you may not necessarily get your money back within its lifetime. (Though it would still have environmental benefits). You can compensate for the lower efficiency of flat plate collectors by installing a larger surface area.

The cost of a flat plate system, including installation, for an ‘average’ house ranges from about £2,000 to £4,000. Evacuated tube systems usually cost from £3,500 to £5,500. However the price will depend on the particular situation – whether you need scaffolding, for example. There are lots of solar water heating installers around, so it is always worth getting several quotes to compare prices. Beware of companies trying to pressure people into buying a system on the spot by offering special ‘discounts’, which in actual fact may not offer a real saving. DIY panels can be installed for anything from around £500 upwards.

Ground source heat pumps (GSHP)

Ground source heat pumps (GSHP) transfer heat from the ground into a building to provide space heating and, in some cases, pre-heating domestic hot water. For every unit of electricity used to pump the heat, 3-4 units of heat are produced. As well as ground source heat pumps, air source and water source heat pumps are also possible.

There are three important elements to a GSHP:

Ground loop – comprises lengths of pipe buried in the ground, either in a borehole or a horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe absorbing heat from the ground.

Heat pump – although we may not know it heat pumps are very familiar to us – fridges and air conditioners are both examples. A heat pump has three main components:

1. Evaporator – (e.g. the squiggly thing in the cold part of your fridge) takes the heat from the water in the ground loo.

1. Compressor – (this is what makes the noise in a fridge) moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit. Condenser, (the hot thing at the back of your fridge) gives up heat to a hot water tank that feeds the distribution system.

1. Heat distribution system – consists of under floor heating or radiators for space heating and in some cases water storage for hot water supply.

Three options are available for the ground loop: borehole, straight horizontal and spiral horizontal (or ‘slinky’). Each has different characteristics allowing you to choose the most suitable for your property. Horizontal trenches can cost less than boreholes, but require greater land area. For slinky coil, a trench of about 10m length will provide for about 1kW of heating load.

The installed cost of a typical 8kW system varies between £6,400-£9,600 plus the cost of the distribution system. Note that costs are dependent on property and location so the cost for a system for your home may differ.

The efficiency of a GSHP system is measured by the Coefficient of Performance (CoP). This is the ratio of the number of units of heat output for each unit of electricity input used to drive the compressor and pump for the ground loop. Typical CoPs range between 2.5-4. The higher end of this range is for underfloor heating, because it works at a lower temperature (30-35oC) than radiators.

Based on current fuel prices, assuming a CoP of 3-4, a GSHP can be a cheaper form of space heating than oil, LPG and electric storage heaters. It is however more expensive than mains gas. If grid electricity is used for the compressor and pump, then an economy 7 tariff usually gives the lowest running costs.

You should consider the following issues if you are considering a ground source heat pump. An accredited installer will be able to provide more detailed advice regarding suitability.

The type of heat distribution system. GSHPs can be combined with radiators but under floor heating is better as it works at a lower temperature.

Is there space available for a trench or borehole to accommodate a ground loop?

• Is the ground material suitable for digging a trench or borehole?
• What fuel is being replaced? If it is electricity, oil, LPG or any other conventional fossil fuel the payback will be more favourable. This makes heat pumps a good option for off gas grid areas.
• Do you want to be 100% renewable? If so, purchase green electricity, or install solar PV or some other form of renewable electricity generating system to power the compressor and pump.
• Do you require a back up heating system?
• Is there also a cooling requirement?
• Is the system for a new building development? Combining the installation with other building works can reduce costs.
• Can you incorporate insulation measures? Including wall, floor and loft insulation will reduce your heat demand.

This is an extract from the OneToRemember Wind Power Guide. Get the full guide free by clicking here>>