Possible adaptations of basic systems

There are several possible adaptations that can be made to solar water heating systems based on the price that the end-user is willing to pay for the system as well as on whether or not the systems should be linked to the existing water heating system. The available adaptations are discussed briefly below.

Pumped/active and thermosyphon/passive systems

Passive systems are the normal thermosyphon/convection systems which work on the natural circulation of the water/heating fluid between the collector and the storage tank. They can only work in close-coupled systems where the storage tank is located above the collector area. This height difference makes natural thermosyphoning possible. In homes with large roof areas that allow for the installation of an in-roof storage tank above the collector plate it is possible to install passive systems that are not close-coupled, but these installations are not feasible in small, low-cost houses⁵⁷. Active systems use a pump to circulate the water/heating fluid between the collector and the storage tank. Pumps are used when the solar collector is used in conjunction with a storage tank that is located lower than the collector inside the roof of a house, such as when the collector is linked to a conventional electrical water heater (SEA 2009, pp.7-9). Figure 26 shows the basic configuration of a typical passive close-coupled system. Figure 27 shows a typical active SWH system.

Figure 26 Close-coupled Thermosyphon System (Hagens 2009)

57 As such these installations are not shown in the typology of systems given in Figure 18.

Figure 27 Schematic of a Typical Active SWH System

Direct and indirect systems

In direct systems the fluid flowing through the collector area is

used in the house. Water flows into the storage tank from the inlet through the collector area and back into the top of the storage tank where it is then tapped off for use in the house.

Direct systems (see Figure 19 and where the water is lime free

the pipes overnight or if lime clogs up the circulation system In indirect systems (see Figure

Solar water heating systems can be designed to operate as high or low pressure systems. High pressure systems are more suitable for

water from the system can be more easily mixed with high pressure cold water supplied by municipal lines. High pressure systems are however more expensive than low pressure systems as they need to be constructed

withstand high pressures. In low pressure systems determined by the height of the storage tank

where the water is used, the higher the water pressure will be relatively low heights of roofs

problems when water from the SWH has to be mixed with pressuris

Schematic of a Typical Active SWH System (DeLaune et al. 1995)

fluid flowing through the collector area is the water

Water flows into the storage tank from the inlet through the collector area and back into the top of the storage tank where it is then tapped off for use in the house.

19) can only be safely used in areas where frost does not occur and where the water is lime free, otherwise the system will be damaged when

if lime clogs up the circulation system (SEA 2009, pp.7 Figure 20) water flows into the storage tank and manifold

indirectly heated through conduction by a heat exchanger pipe through which a heating fluid circulates after passing through the collector area. Indirect systems are more durable and can be used in all weather conditions and for all water types (SEA 2009, pp.7

he requirement for extra piping, a manifold and heat exchangers.

systems

Solar water heating systems can be designed to operate as high or low pressure systems. High are more suitable for domestic use in middle- to high income home water from the system can be more easily mixed with high pressure cold water supplied by municipal lines. High pressure systems are however more expensive than low pressure

problems when water from the SWH has to be mixed with pressurised municipal water (DeLaune et al. 1995)

the water that is eventually Water flows into the storage tank from the inlet through the collector area and back into the top of the storage tank where it is then tapped off for use in the house.

can only be safely used in areas where frost does not occur when water freezes in (SEA 2009, pp.7-8).

and manifold where it is heat exchanger pipe through which a heating fluid Indirect systems are more durable and can (SEA 2009, pp.7-8) but they are for extra piping, a manifold and heat exchangers.

Solar water heating systems can be designed to operate as high or low pressure systems. High to high income homes as water from the system can be more easily mixed with high pressure cold water supplied by municipal lines. High pressure systems are however more expensive than low pressure

Electrical backup for solar water heating systems

On completely overcast days solar water heaters are unable to heat water to sufficiently high temperatures (Florad 2010). Electrical or gas backup systems can be installed to ensure that hot water is always available. Conventional electrical heating elements can be installed in the storage tank and activated when back-up heating power is required. The electrical heating element can be installed in the storage tank of a close-coupled system or, if the SWH is linked to an existing conventional geyser, the old element can be retained. In order to ensure that the backup system activates only when required, a timer can be installed but this increases installation costs (Van Gass & Govender 2009). Alternatively demand water heaters can be installed above the hot water taps and switched on when the SWH is unable to heat water.

Solar Water Heaters for Low-Income Contexts

SWHs are probably the least expensive water heating technology on a life cycle cost basis as the source of energy, sunlight, is free (SEA 2009, p.3) but the systems are relatively expensive to buy and install. Additional adaptations that are made to systems lead to further increased costs. The cheapest systems available are close-coupled, direct, low pressure systems (Van Zyl 2009, Bester 2010, Hallet 2010) without electrical backup and these are the focus of the rest of this study as they are the systems which would be most affordable in a low-income housing context. Though an initial reaction to this statement might be that this will lead to the installation of ineffective systems for poor people this is not the case. There is no need for an active system as the target population for this project do not have electrical geysers installed in their homes and there is thus no need to install an active system.

Stellenbosch and most of the coastal areas of the Western Cape, the primary focus area of this research, are frost-free so there is no need for indirect systems⁵⁸ (Wesselink 2009, Hertzog 2009).

The only real compromise is with regard to high vs. low pressure systems. In this case the water usage patterns in the target population, where very few homes have installed showers, somewhat mitigates the negatives of low pressure systems. However, the rationale for this thesis is in part that there is a suppressed demand for hot water in low-income households and one can expect that more of these homes will install showers if they have freely available hot water. At present the cost of pressurised systems (Hallet 2010) outweighs this concern – the approach is taken that low pressure SWHs are already a major improvement on electrical kettles for water heating and that prevailing economic conditions make the installation of more expensive systems impractical. Homes also have the option of adding water mixing valves at a later stage to mitigate this problem (Ndamane 2010). Similarly it is suggested that, if possible, systems should be installed allowing for the future addition of electrical backup.

Incorporating electrical backup from the outset will lead to smaller electricity demand reductions and an opportunity might be missed to encourage behavioural changes to maximise solar energy used for water heating.

58 In areas where the municipal water is prone to causing calcification or corrosion indirect systems may be required but calcification has not been an issue in the Kuyasa or Kwanokuthula rollouts.

The following section will provide an overview of the development of the global solar water heating market in order to illustrate the maturity of the technology and the impact that it has already had in several countries.