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Chapter 3

The reduction in the cost of furnaces or boilers due to substantially better thermal envelopes is normally only a small fraction of the additional cost of the better thermal envelope. However, potentially larger cost savings can occur through downsizing or eliminating other components of the heat- ing system, such as ducts to deliver warm air or radiators (Harvey, 2006). High-performance windows eliminate the need for perimeter heating.A very high-performance envelope can reduce the heating load to that which can be met by ventilation airflow alone. High-performance envelopes also lead to a reduction in peak cooling requirements, and hence, in cooling equip- ment sizing costs, and they permit use of a variety of passive and low-energy cooling techniques.

If a fully integrated design takes advantage of all opportunities facilitated by a high-performance envelope, savings in the cost of mechanical systems may offset all or much of the additional cost of the high-performance envelope.

In considering daylighting, the economic benefit for most commercial build- ings is enhanced when sunlight is plentiful because daylighting reduces electricity demand for artificial lighting. This is also when the daily peak in electricity demand tends to occur (Harvey, 2006). Several authors report measurements and simulations with annual electricity savings from 50 to 80%, depending on the hours and the location. Daylighting can lead to reduced cooling loads if solar heat gain is managed and an integrated ther- mal-daylighting design of the building is followed (Tzempelikos et al., 2010). This means that replacing artificial light with just the amount of natural light needed reduces internal heating. Savings in lighting plus cooling energy use of 22 to 86%, respectively, have been reported (Duffie and Beckman, 2006).

Daylighting and passive solar features in buildings can have significant financial benefits not easily addressed in standard lifecycle and payback analysis. They generally add value to the building, and in the case of office buildings, can contribute to enhanced productivity (Nicol et al.,

  • 2006)


      • 3.8.2

        Active solar heating and cooling

Solar drying of crops and timber is common worldwide, either by using natural processes or by concentrating the heat in specially designed storage buildings. However, market data are not available.

Advanced applications—such as solar cooling and air conditioning, industrial applications and desalination/water treatment—are in the early stages of development, with only a few hundred first-generation systems in operation. Considerable cost reductions are expected if R&D efforts are increased over the next few years.

Solar water heating is characterized by a higher first cost investment and low operation and maintenance (O&M) costs. Some solar heating applications require an auxiliary energy source, and then annual loads are met by a combination of different energy sources. Solar thermal

Direct Solar Energy

hot water systems are generally more competitive in sunny regions but this picture changes for space heating due to its usually higher overall heating load. In colder regions, capital costs can be spread over a longer heating season and solar thermal can then become more competitive (IEA, 2007).

The investment costs for solar water heating depend on the complex- ity of the technology used as well as the market conditions in the country of operation (IEA, 2007; Chang et al., 2009; Han et al., 2010). The costs for an installed solar hot-water system vary from as low as USD2005 83/m2 to more than USD2005 1,200/m2, which is equivalent to the USD2005 120 to 1,800/kWp9 used in Annex III and the resulting levelized cost of heat (LCOH) calculations presented here as well as in Chapters 1 and 10. For the costs of the delivered heat, there is an additional geographic variable related to the available solar irra- diation and the number of heating degree days (Mills and Schleich, 2009).

Based on the data and assumptions provided in Annex III, and the methods specified in Annex II, the plot in Figure 3.16 shows the sen- sitivity of the LCOH with respect to investment cost as a function of capacity factor. Research to decrease the cost of solar water-heating systems is mainly oriented towards developing the next generation of low-cost, polymer- based systems for mild climates.The focus includes testing the durability of materials. The work to date includes unpressurized polymer integral collector-storage systems that use a load-side immersed heat exchanger and direct thermosyphon systems.

Over the last decade, for each 50% increase in the installed capacity of solar water heaters, investment costs have fallen by around 20% in Europe (ESTTP, 2008). According to the IEA (2010a), cost reductions in OECD countries will come from the use of cheaper materials, improved manufacturing processes, mass production, and the direct integration into buildings of collectors as multi-functional building components and modular, easy to install systems. Delivered energy costs are anticipated by the IEA to eventually decline by around 70 to 75%. One measure suggested by the IEA to realize those cost reductions are more research, development and demonstration (RD&D) investments. Priority areas for attention include new flat-plate collectors that can be more easily inte- grated into building façades and roofs, especially as multi-functional building components.

Energy costs should fall with ongoing decreases in the costs of indi- vidual system components and with better optimization and design. For example, Furbo et al. (2005) show that better design of solar domestic hot-water storage tanks when combined with an auxiliary energy source can improve the utilization of solar energy by 5 to 35%, thereby permit- ting a smaller collector area for the same solar yield.


1 m² of collector area is converted into 0.7 kWth of installed capacity (see Section 3.4.1).


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