Domestic Hot Water » Solar thermal

Savings

Typical gas systems provide thermal efficiencies in the range of 76-79 per cent; while average conventional electrical devices offer thermal efficiencies of 97-99 per cent. Solar water heaters are characterized by the so-called “energy factor”. Commercial solar water heaters can provide energy factor in the range of 0.8-4.8. Solar hot water systems offer strong potential for environmental protection and mitigating effects of green house gases. For example, the Solar Initiative that funded over 300 residential and commercial projects in California has an expected savings of about 18 TJ/year for gas customers and 312,000 kWh/year for electricity customers. It is estimated that conventional fuel such as gas or electricity could be cut up to 50 per cent under optimal conditions (IEA, 2007).

Energy and cost savings

Payback period due to the use of solar thermal systems is highly dependant on the quantity of hot water produced, conventional fuel used for water heating and local energy prices. Payback period is generally less when the amount of hot water required is large and the energy cost is high as well. High capital costs of solar thermal systems are not justified when the amount of hot water required is generally very low and can be easily and cheaply produced by alternate means using gas and electricity. Solar thermal systems are becoming more popular in cold and temperature climates due to the high requirement of domestic hot water and increasing fuel prices. Their usage in residential buildings in hot climates is highly restricted by the high capital cost combined with less hot water requirement which makes a very long pay back time.

The following example shows energy and cost savings in tropical countries by replacing existing water heaters with SWHs. It is estimated that a typical household in Guatemala with SWH installed can save Euro 21 annually. It assumes water usage for 3 showers for a typical Guatemalan household per day. At present most of the households used inline in-line electric shower heaters, which typically require 6 kW of power. Assuming that a solar water heater can provide for half of the energy needs for these showers, a household could save 410 kWh of energy per year (Al-Beaini et al., 2007).

Annual household energy savings from solar water heater use in Guatemala

Description	Typical Guatemalan Household (without Solar Water Heater)	Typical Guatemalan Household (with Solar Water Heater)
Estimated average shower length (minutes per day)	7.5	7.5
Average kW usage from shower head’	6	6
Estimated average heated showers per day	3	3
Average in-line showers per day*	3	1.5
Total minutes of in-line heater use per day	22.5	11.25
Total daily kWh used in showering	2.25	1.13
Total annual kWh used in showering	821.25	410.63
Total annual kWh reduced by solar water heater use	-	410.63
Annual Savings (in Guatemalan Quetzales)°	-	205.31
Annual Savings (in US dollars)	-	$27.38 (Euro 21)

‘assumes that a solar water heater will offset half the use of in-line heater; *based on average power of commonly available in-line water heaters; °the Appropriate Infrastructure Development Group (AIDG) estimates that electricity in urban areas of Guatemala averages 0.5 Quetzales per kWh; °assumes exchange rate of 7.5 Quetzales per U.S. dollar

Costs

The cost of the solar thermal system varies depending on the type of solar collector and storage system. Flat plate collectors typically cost less than the more sophisticated evacuated tube collectors. In cold climates solar thermal systems is often supplemented by an auxiliary heating system. It is estimated that solar hot water system cost between € 800 - € 1,300 per m² (SEAI, 2010) in Europe and approximately € 3,000 – € 4,500 per whole solar thermal system package in the USA. More elaborate data on regional cost estimates for different parts of the world is unavailable.

Environmental

Haralambopoulos and Spilanis (1997) calculated the potential of solar hot water systems to substitute fuels (i.e., lignite/oil) used in electricity production to provide for hot water distribution in six solar zones in Greece, and consequent amounts of pollutants avoided. Their results are presented in the table below.

Overall amounts of avoided pollutants by electricity production through lignite / oil and fuel saved due to solar hot water production in Greece

Pollutant	Quantity (ktonns/yr)
Nox	0.9
CO₂	687.1
Particulates	0.7
SO2	6.3
Lignite	601.8
Oil	90.3

Haralambopoulos and Spilanis (1997)

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Domestic Hot Water » Solar thermal

Savings

Annual household energy savings from solar water heater use in Guatemala

Costs

Environmental

Overall amounts of avoided pollutants by electricity production through lignite / oil and fuel saved due to solar hot water production in Greece

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Domestic Hot Water » Solar thermal

Savings

Annual household energy savings from solar water heater use in Guatemala

Costs

Environmental

Overall amounts of avoided pollutants by electricity production through lignite / oil and fuel saved due to solar hot water production in Greece

Select an Option

Select available Technology

We recommend reading our essential documents on buildings: