Solar Water Heating Systems Compared With Heat Pumps
Considering that water heating accounts for somewhere between 30% and 50% of the electric power cost for the normal household, it’s wise to look at ways to decrease this particular expense. The hot water in most houses is stored in a hot water tank, with an electric resistance element which usually uses between 3kW and 4kW of electric power.
Two methods are generally used to assume the task of providing hot water. Solar Water Heating (SWH), which makes use of solar collectors or solar panels ordinarily mounted on the roof of the building, is a well-proven technology in which radiant warmth from the sun is used to directly heat the water. Heat pumps are electrically-driven units which convert the ambient air temperature into heat, typically utilizing about 1/3 of the electrical power of a comparable resistance element.
There are a number of factors which influence the choice between a solar water heating system and a heat pump system for residential water heating. Here are a few of the pluses and minuses of each kind of installation.
Solar Water Heating: Pros
1. SWH is a well-proven technology
2. SWH systems are capable of providing very high water temperatures
3. ESKOM subsidises SWH systems (terms and conditions apply)
4. SWH systems typically give you a reduction of around 15% on your electric power expenses.
Solar Water Heating: Cons
1. You may find big solar panels on your roof unattractive. However, they do act as an advertisement of your eco-friendly credentials!
2. Solar water heating installations are less effective when it’s rainy or overcast, and don’t work during the night. This results in the water temperature varying dependant upon the weather conditions. A back-up electric heating element ordinarily attends to this issue, but when it is operating, you are no longer conserving energy.
3. The collector panels need to be oriented correctly so that they can gather as much solar radiation as they can.
4. Water filled solar panels are heavy. Your roof may need structural reinforcement before you can place solar collectors on it.
5. SWH installations will typically have a higher up-front cost compared to an equivalent heat pump installation.
6. The payback period of 6-8 years is normally longer compared to that of a heat pump system.
7. The glass tubes are vunerable to damage from freezing, over-pressurization and being struck by hard objects.
8. The temperature generated in solar panels can’t easily be controlled. Electrical geysers aren’t designed to tolerate the pressure that could build up when water is heated by the sun. If you don’t swap your hot water tank with one suitable for solar heating, there is a serious danger of the hot water tank bursting in the roof.
Heat pumps: Pros
1. The up-front expenditures are generally lower than those of an equivalent SWH system.
2. The payback period of 2-4 years is usually quicker than the investment recovery time for a SWH installation.
3. Heat pumps operate day and night, rain and shine. Note that the heat pump only operates when it is necessary to replenish the hot water in the hot water tank.
4. Heat pumps generally offer a reduction in water heating expense of at least 67%. Since water heating generally is the reason for 30% – 50% of your electric power cost, this amounts to a saving of between 20% and 33% on your electricity bill.
5. Heat pumps are easier to install (and to retro-fit to an existing hot water cylinder.) However, the services of a manufacturer-certified installer are required for warranty and insurance reasons.
6. Heat pump systems normally work at a lower pressure than solar water heating systems. This reduces the danger of geysers bursting. It also means that a heat pump can easily be retrofitted to an existing electric geyser system.
7. Modern heat pump installations provide you with a remote control panel which permits you to set the water temperatures without crawling around in the roof.
8. Heat pumps are generally mechanically uncomplicated and reliable.
Heat pumps: Cons
1. Heat pumps become less economical as the air temperature drops below freezing.
2. The maximum water temperature is about 65 degrees. Since any temperature above 52 degrees carries the risk of scalding, this should be sufficient for most household uses.
3. A heat pump utilizes a fan, which usually tends to make a small amount of noise. This ought to be taken into account when the location of the unit is selected.
4. Heat pumps don’t function with no electrical energy, eg. during power outages. Nevertheless, a small device draws less power than a kettle, and can easily be run off-grid by a solar electric or wind turbine system.
5. Heat pumps, like air conditioners and refrigerators, may use greenhouse gases.
Despite the fact that heat pumps were first explained in 1852 by Lord Kelvin, they have been slow to gain popularity in South Africa. ESKOM at this time offers a subsidy for commercial heat pump installations, but they do not give a subsidy for residential systems. However, the installed price of a heat pump system is usually less than the fitted price of a subsidised solar water heating system.
Heat Sense supplies and installs heat pump systems in Johannesburg, South Africa. You can find out more about how to save energy and money at our website,
http://solarwaterjohannesburg.co.za
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