mechanical handling equipment
Stage 2: Harness green energy
Green energy can be defined in terms of the generating of power from a range of low-carbon renewable sources close to or at the point of use. The primary aim of adopting green energy is to achieve a shift from carbon-intensive energy sources principally based on coal or oil, either directly or indirectly via the production of grid-based electricity. The main forms of renewable green energy sources include:
biomass (wood chip or other waste), wind, solar thermal, solar
photo-• voltaics;
recovered process waste energy, such as heat from refrigeration plants
•
or air compressors;
recovered kinetic energy;
• air, ground or water thermal-exchange units.
•
In addition, low-carbon alternatives such as natural gas and bio-diesel could be included although there are substantial additional sustaina-bility issues associated with these fuels, which have been discussed elsewhere.
The suitability and potential applicability of the four sources of power on the energy mix for an individual warehouse depends upon a wide range of operational, cost, environmental and market factors. Principal amongst these are:
the operational pattern of energy demand versus the generating
char-• acteristics of the alternative green energy supply;
the cost and scalability of each green energy technology;
•
the relative generating efficiency and life cycle emissions levels of
• alternative technologies;
the rate of technology maturity and innovation;
• regulatory and market conditions affecting price, demand and supply
•
conditions.
Demand for energy within the warehouse in the form of either electricity or heat is not constant. It is dictated by hourly and weekly throughput patterns as well as longer seasonal weather changes over the year. Further local variation in generating periods due to local weather conditions, the proximity and orientation of buildings or levels of associated activity adds further complexity. This creates issues of managing total energy demand against short-term fixed generating capacity, the availability and cost of sourcing variable additional short-term external energy supplies, and the disposal or sale of surplus green energy or a means of storing that surplus energy. Consequently, local generation of green energy is likely to provide only a partial solution. Studies looking at these demands and generating patterns suggest that 44 per cent of onsite renewable energy will be exported (sold) whilst only 38 per cent of demand can be satisfied by green energy (UK GBC, 2007).
Like most transformational processes the economics of power gener-ation are subject to economies of scale and a balance between capital costs, fuel input costs versus lifetime operating costs and not just the greenhouse emissions and energy conversion rates. A review of each technology goes beyond the scope of this analysis but some studies suggest a 10-fold cost per kg-CO2 benefit of using offsite renewable versus onsite generating (see Figure 8.3), highlighting the need for companies to proceed with caution in this area. On the other hand, recovered process energy systems or solar thermal systems for pre-heating water appear to lend themselves effectively to local site applications on an energy conversion, cost and operational basis. Similarly ground source heat pumps need only ‘100 kWh to turn 200 kWh of environmental or waste heat into 300 kWh useful heat’ (Gazeley, 2004: 137).
0 2 4 6 8 10 12 14
Capital cost of small-scale wind Capital cost of solar PV Capital cost of biomass CHP Capital cost of large-scale wind
£ per kg CO2
12.5
14.78
1.15
1.02
Figure 8.3 Comparison in estimated cost of on and offsite renewables Source: Adapted from UK Green Building Council (2007: 48).
Technologies such as solar photovoltaics are still a maturing technology where current payback periods are still calculated in periods of 15–20 years, which is far longer than the current rate of technology improvement.
The use of combination technologies such as self-cleaning transparent film technologies in conjunction with solar photovoltaic laminates such as ETFE roof-light panels may prove more cost and energy efficient, even in the medium term. These are reported as having 50 to 200 times less embodied energy, with a trial 33,900 m2 distribution centre installation generating 80 MWh of power and saving 32 tonnes of CO2 (Gazeley, 2008). By comparison, small wind generators with an estimated five-year payback may offer better short-term alternatives although these may convert only 30 per cent of the wind energy into electricity. By comparison, whilst a 600 kW wind turbine would have a capital cost of £400,000 and generate 1.5 gigawatts, a solar photovoltaic array would require an investment of £10 million and a roof space of 20,000 m2 (UK GBC, 2007).
In contrast, combined power and heat (CHP) systems using biomass are capable of achieving viability in the scale of generating low life cycle emissions at acceptable costs. However, studies do suggest that CHP systems require extended operating periods of 14 hours per day as well as proximity to other domestic and commercial users to achieve overall viability (UK GBC, 2007).
The final factor affecting the growth of green energy comes from regulation of developments and the regulatory regime within the wider energy market. In the UK many local authorities are adopting the ‘Merton rule’, which follows the London Borough of Merton’s requirement in its planning regulations that all developments are required to generate 10 per cent of their generated energy needs from renewables. The true value of this policy needs to be set in the context of the factors high-lighted earlier, as well as broader UK renewable energy policy. The UK encourages new small capacity generators not via preferential ‘feed’ tariffs for micro-generators, as in the rest of Europe, but Renewable Obligation Certificates (ROCs) to the major power generators. Here the commercial generators and energy retailers are required by the regulator to make up an increasing percentage of their energy capacity from renewables sourced from either large or small generators that qualify for Renewable Obligation status. In cost terms, sourcing electrical energy from the retail market rather than local micro-generation may therefore in the medium term offer a more cost-effective and low-risk route than engaging with onsite micro-power generation.
This cautious approach, even when linked to reducing energy intensity, has been shown by several studies to be insufficient to achieve an overall reduction in energy intensity of warehouse operations. To go to the next stage of sustainability and approach zero emissions, companies
need to incorporate many of the previously-mentioned features within their buildings and operations and then go beyond current building standards (UK Green Building Council, 2007; Reed and Wilkinson, 2005;
Papadopoulos, Stylianou and Oxizidis, 2006). The next section high-lights the advantages to be gained by designing sustainability, energy management and green energy generation into the next generation of buildings.