The Energy Harvest

Renewable Energy Systems in Church Property

“Sustainable development … meets the needs of the present without compromising the ability of future generations to meet their own needs.” (Our Common Future—Brundtland Commission, 1987)

In recent years the rise of interest in renewable energy has been startling. Although there remain those who are unconcerned about wasting energy, and there are those who are devoted to the green agenda, probably the majority of us want to take reasonable steps to reduce our carbon footprint, if someone shows us the way.

Knowing what to do is half the battle. There are always people who say, for example, we shouldn’t buy energy-saving light bulbs because they contain mercury, a toxic contaminant in landfill. However, the nature of human progress is to take two steps forward and one back. There are almost always unwanted side-effects to every constructive change we make. It is therefore important that the impacts of each change are assessed in the round.

When it comes to energy, it is not possible to harvest it without damaging the earth in some way. Wind turbines, for example, are thought of by some to be ugly. Their manufacture and construction cause damage and use materials. Similarly all of the options for the Severn Barrage will cause damage in various ways, including the ecological effects. The damage caused by renewable energy systems must be balanced against that caused by the burning of fossil fuels. This balancing act is made more difficult by the diverse nature of the effects to be balanced — it is like comparing apples with bananas. However, by pooling the necessary expertise, research bodies in the industry have come up with reasonable judgements, which are constantly under review. (They favour energy-saving light bulbs, for example.)

Saving Energy — the First Step

Because energy harvesting always causes damage, the starting point for reducing our carbon footprint is always to reduce consumption. And the starting point for reducing consumption is to reduce waste. Reducing waste will reduce consumption without affecting our level of activity or comfort. It is saving energy with no strings attached.

The first way to reduce waste is to change our behaviour, in particular our habits. And the changes that will have most effect are those to do with the most power-hungry systems. A poorly-insulated building will consume a large amount of energy for space heating (i.e. heating the inside of the building as opposed to the hot water), so in this case that would be the first thing to look at. With buildings insulated to current standards it is also worth considering hot water and lighting. The application of common sense to reduce waste in this way requires no further mention here.

On a more fundamental note, with poorly-insulated church buildings the question of whether to use them at all during the coldest part of the season could be asked. Those who operate the heating systems will have a feel for how much energy it takes to bring the church to an acceptable temperature.  Alternative venues could be considered.

Secondly we can reduce the heat loss of the building. Roof, walls, floor and windows all leak heat, and gaps allow warm air out and cold air in, sometimes causing uncomfortable draughts. Insulation technology is constantly advancing, and tried-and-tested techniques and materials are available. Application of 50mm (2 inches) of advanced insulation can make a major difference, which a qualified energy assessor could quantify in terms of increased temperature or lower energy consumption.
For best results insulation must be designed to fit the use of the building. Placement of insulation can make a difference between a quick-heat building (with low heated thermal mass) and a constant-warmth building (with the opposite). A quick-heat design would generally be better for a building that is only occasionally used (say once a week).

Most draughts are, in effect, uncontrolled ventilation, and can account for over 20% of heat loss. When renovating a building it’s worth considering how to seal gaps which result in uncomfortable draughts, and introduce controlled ventilation to provide the fresh air that is needed. Note that some draughts are caused not by gaps but by convection of cold air downwards from cold windows; this typically happens in very cold weather when the air inside the building is warm.

Having looked at reducing our consumption of energy, we can now turn to harvesting it in a more sustainable way. Fossil fuels and the systems which use them are still the norm. Therefore it takes more effort to specify something different. A few options are given below, but before diving in it is worth mentioning finance. Substantial grants are sometimes available for certain technologies in certain circumstances, but the situation changes from time to time. For this reason it is beyond the scope of this article. Suffice it to say that finance will almost always be a key consideration in any decision-making process concerning renewable energy.

Photovoltaic Cells (Solar Panels or Tiles for Generating Electricity)

Solar panels come in two varieties: photovoltaic (PV), which generate electricity, and thermal, which generate heat.

Many church buildings are east-west oriented, which means they have south-facing roofs.  These provide suitable platforms for solar PV (photovoltaic) panels, provided they are not shaded by trees, other buildings, etc. The electricity generated has to pass through an inverter, an electronic box of tricks that converts it from DC to the AC suitable for running mains appliances. The power is produced during the daytime and mostly in the summer months, and it doesn’t just work on Sundays, so what happens to the power when the church doesn’t need it? The answer is that usually it is fed back into the National Grid. The latter will happily accept it for free, but to receive payment for it an export meter has to be installed, and an agreement made with a supply company to buy the electricity at a given tariff. A system like this does not normally make financial sense unless the power is sold back to an energy supply company.

An area of 10 square metres could be expected to yield around 1000 kW-hours (units) of electricity a year. Some of that will displace electricity that would have been bought, but generally most of it will be passed to the Grid. Whichever way the electricity goes, around 600 kg of CO₂ will be saved.
Solar PV is a well-established technology, and systems are generally reliable and require next to no maintenance.

Solar Thermal (Solar Panels to Heat Water)

Solar thermal is also a well-established and advancing technology, and is very much more efficient than solar PV. That means that much more energy will be harvested for the same area of panel.
In this case the energy is produced in the form of hot liquid (of a type that won’t freeze in winter), which is typically used in turn to heat water. A system installed on the roof of a house can typically provide all the required hot water in the summer and even about 10% in winter.

However the hot water produced cannot be sold to the Grid(!), nor can it be stored for long. Moreover, it is produced mainly in the summer. So this technology comes into its own when hot water is required every day. Thus installing it on the south-facing roof of a church will not be appropriate unless there are daily activities which require sufficient hot water to make it worthwhile.

Wind Turbines

A wind turbine is often the first device that people will think of when considering renewable energy. A building-mounted turbine makes a statement — it is visible, you can see it working, and it holds a certain fascination with many (me included). Devices suitable for building-mounting can generate up to 1500 watts, the “peak power”, which is delivered in a strong breeze of 30 m.p.h. These conditions may occur only a few times a year for a few hours, and for the rest of the time the output will be much lower, if not zero. Estimates for annual energy output in kWh (i.e. units of electricity) are based on the average wind speed for the area, the height of the turbine hub above ground level, and the roughness of the terrain. Approximate figures for average wind speed are available on the Internet. The terrain to the south-west, where the prevailing wind comes from, is crucial to the performance of a turbine. The sea is the best surface by far, as it causes little air turbulence and does not reduce wind speed. Flat, treeless areas are next best, followed by an undulating landscape. Trees and buildings are bad news, especially if they approach or exceed the height of the turbine. The south-west corner of a church tower, in a suitable landscape, could be a good location.

As with solar PV, wind turbines require an inverter, and excess power can be exported to the Grid. A 1500-watt turbine in a reasonably-favourable site could be expected to yield 2000 kWh (units) a year, and save 1200 kg of CO₂.

Free-standing wind turbines (in a huge range of sizes) are well established. However there is much less experience in mounting them on buildings. The turbine could weigh as much as 50kg, and is on top of a pole several metres above its top support, so installation must be carried out by experts. Factors such as noise and shadow flicker (the effect of the turning blades passing in front of the sun) need to be considered. Long-term reliability of some models is also still unproven; this is especially the case where there are nearby obstacles, as it is thought that the resulting air turbulence may shorten turbine life.

Heat Pumps

Heat pumps take energy from the surroundings and pump it indoors. In effect they are refrigerators acting in reverse, and as such the technology is very well established and correspondingly reliable. There are several types, depending on the source of energy. The two most common types are air-source and ground-source. Air source pumps require a heat exchanger outside which will emit some noise. Grants aside, they are the cheaper option. Ground-source pumps, on the other hand, require either a borehole or a long trench 1–2 metres deep to bury a heat-exchanging pipe. (A stream or a body of water can also be used as the heat source.) Groundwork makes this option more expensive, but grants are more likely to be available.

The heat pump itself is perhaps twice the size of the equivalent gas boiler, and is about as noisy as a fridge-freezer. These systems work best with underfloor heating, in rooms kept at a relatively constant temperature. For rooms only used occasionally, requiring a “quick heat” capability, it would be better for the heat pump to run radiators instead. Heat pumps don’t work so efficiently at the higher temperatures normally used for radiators, but this effect can be overcome by fitting oversized radiators (and in fact these are inherently safer with young children and the elderly as they are not so hot).

The concept of taking energy from the ground at 10°C or the air at 0°C and converting it to the warmth of 40°C in a heating system is hard to grasp, but it can be thought of as pumping heat up a hill from a cold place to a warm place. In the process the cold place gets colder and the warm place warmer. It turns out that it takes only 1kW of electricity in driving the pump to push 4kW of heat up the hill. In other words, using the same amount of energy, a heat pump will produce about four times as much heat as ordinary electric heaters would (and up to eight times as much useful heat as storage heaters would).

Heat pumps can be switched on and off at will, or controlled by timers. If used to replace an electric heating system there should be a very significant reduction in running costs for the same indoor temperature. However, if used to replace a gas boiler, running costs should be carefully investigated; this is because while gas consumption will be much lower, electricity consumption will be higher, and electricity costs more per unit of energy than gas. CO₂ emissions (as a result of the power drawn from the Grid) will be about half what they would be for the equivalent mains gas boiler, and lower still in comparison with bottled gas or oil.

Biomass

Biomass is wood or woody material for burning. For small-scale use it is normally in the form of logs, wood pellets or wood chips. The CO₂ produced in burning biomass was absorbed from the atmosphere during its lifetime, so the net CO₂ emissions are zero (ignoring processing and transportation).

Biomass boilers are available to run radiators and heat water just like a gas boiler. The most automated biomass boilers run on wood chips or pellets. Systems can be completely automatic, and draw the fuel in from a large hopper which can store a year’s supply. Ash is removed automatically and only needs emptying when the boiler is serviced, once or twice a year. Thus they require as little attention as an oil central heating boiler. To reduce the capital cost the fuel feed system need not be included, in which case the fuel would have to be manually loaded into a hopper, typically once a day when the system is run. Pellets are available in the UK, although the number of producers is limited. Pellet quality is crucial to performance. Wood chips can be purchased, or they can be made to order, given the right equipment.

Log boilers have to be manually fed, although they can hold enough fuel for 13 hours. To light them you normally add paper and then just press a button — within a few minutes the logs are burning and already producing heat. Like the other types of biomass boilers, they are more efficient than log-burning stoves.

The more advanced biomass boilers as described above are not yet the norm, and the working together of boilers, fuel and fuel supply chain is not so seamless as with the established fossil fuel technologies. Problems are therefore more likely than with, say, an oil boiler.

Oil prices fluctuate wildly while biomass prices tend to be more stable; but when oil is at about $50 a barrel, biomass prices (for a given amount of heat) tend to compare favourably. There may not be a price advantage over mains gas. Although there is currently a plentiful supply of biomass in the UK, it is not an unlimited resource and is therefore more appropriate as a replacement for oil, electricity or bottled gas in rural areas.

Conclusions

Whilst not all technologies and systems have been mentioned, a flavour has been given of those most applicable to church buildings. Cutting energy consumption is the starting point, beginning with reducing waste. There are pitfalls to all new ideas, and progress is often two steps forward and one back. Therefore, when using new ideas to save or generate energy, extra care should be taken at every stage, from investigation to installation and commissioning. However, the benefits in terms of reduced carbon footprint and, in the long term, reduced costs, are there to be harvested.

The Church has been around for much longer than most organisations. Ought she not therefore be among the forerunners at taking the long view?

“Time is tight: we must act now. Scientists say that, even if we cut greenhouse gas emissions dramatically now, there would be no immediate noticeable change in the effects of climate change. Greenhouse gases remain in the atmosphere for decades. Large bodies of ice and water can take hundreds of years to respond to changes in temperature. Some scientists believe it may already be too late to stop the Greenland ice sheet from melting: this would cause a sea-level rise of 7 metres, though this might take several centuries. Things may well get worse before they get better. But we cannot afford just to sit back and do nothing.” (Feeling the Heat—a Tearfund report linked from the Energy Saving Trust website)

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