How to decide on which solar system to use?
Solar energy has become a necessity in the modern world. The everyday use of solar energy has become endless. The application is now seen in everyday uses such as water heating, underfloor heating and even pool heating. Did you know that on average water heating takes up to 27% of your household energy use? There is a big saving on your electricity bill to be made.
Solar energy can also be used to slow down the effects of global warming. The 2nd biggest contributor to global warming is water heating at 16% next to transport at 34%. This gives us a good idea what all of us can contribute to the fight against global warming. It has become law in the year 2010 that all new houses that are built and are more than 300 square metres or more than R750000, will have a solar water heater installed. This is not always enforced, but with the increase of electricity bills, it has become an issue of cost. The time has come to ask the question - not if we can afford to do this but, can we afford not to do this?
Solar water heating works on the basis of the sun radiating energy and the energy is absorbed by the collectors and then transferred to the water by means of heat exchangers. The solar panel will assist or replace the element in some situations. The heat is then stored in a holding cylinder which will supply all the necessary point of hot water.
In South Africa, on the Highveld, we have approximately 5.1 kW per square metre per day’s worth of radiation. This is all wasted energy if not utilized properly. South Africa is in a very high radiation part of the world and this must be kept in mind when deciding on the right system for your house. Some systems we have in South Africa today were designed in countries with lower radiation than us. If these systems are used it might cause your system to overheat due to the extra radiation.
Remember there is no such thing as a perfect product rather just the best application for the task at hand. Before deciding on which solar system is the right fit for you one must consider the risks, benefits and limiting factors involved with solar system installations.
Riks and benefits with Solar Water Heating
One of the biggest problems with a solar system is that the energy from the sun can be difficult to control. Solar systems that are oversized tend to overheat and if the system is undersized the system will not deliver enough hot water. It is more dangerous for a system to overheat as this might cause water to turn into steam, causing an explosion. With overheating it will also lead to rising maintenance costs and will reduce the saving that was supposed to be had.
It is better running the system cooler as we can sometimes put auxiliary heating onto the system, let’s look at an example:
On a conventional water heater , the power to the element is cut with the help of a thermostat. If a hot water cylinder reaches its temperature of 60 degrees celcius, the thermostat will cut off the electricity and the system will stagnate.
In a solar water heater, if the system reaches 60 degrees at 9am in the morning, the system would continue to gather heat at between 3 to 5 degrees. If one works on an average of 4 degrees and we still have 8 hours of sunlight left, the system has the potential of reaching around 92 degrees celcius. The system will then be too hot and will run the risk of opening the TP valve and discharging the hot water. Then the system will cool down and all the hot water would be lost.
Except for the hot water that is lost, the purpose of saving energy and saving costs is defeated. Measures must be taken to ensure that this does not happen by installing the proper tempering and safety valves.
As there are risks in solar water heaters there are also benefits. Solar water heaters reduce carbon emissions and that makes them more environmentally friendly. There is a small carbon footprint because of the production and transport of these units. We can also generate limited hot water in isolated and rural areas, as we can do this without the expense of expensive cables that need to be installed. Let’s look at the differences between conventional heating versus solar heating:
1) Conventional heaters are mostly hidden inside the roof and are not seen from the outside. Solar systems are exposed on the roof and the panel is mostly visible.
2) Conventional heaters have a high running cost. Solar heaters have a lower running cost
3) Conventional heaters need electricity to heat water. Solar heaters can still produce hot water without electricity
4) Conventional heaters have high carbon footprint. Solar geysers have a low carbon footprint.
5) Conventional heaters will run at a lower temperature which will increase the life expectancy. Solar heaters run at a higher temperature that will decrease the life expentancy.
6) Conventional heaters can be installed irrespective of orientation and obstruction. Solar heaters’ installation limited to orientation and obstruction.
7) Conventional heaters can produce hot water without sun. Solar heaters need the sun to produce hot water. Luckily there is an abundance in South Africa.
8) Conventional heaters have a high operating cost. Solar heaters have a lower operating cost.
9) Conventional heaters have on grid supply. Solar geysers are off the grid.
Limiting factors when installing a solar system
When deciding on a solar system, one must first consider some limiting factors before making a final decision:
Geographical area - Are you situated in an area that can get especially cold in the winter? If this is the case you run the risk of having your collectors cracking as the water inside might freeze and expand. It might then be better to go for an indirect jacketed system which will have a food-grade glycol mixture in the jacketed system. This glycol mixture acts as an anti-freeze and will withstand more extreme temperatures.
Aesthetical factor - Although solar water heating systems have many benefits, one can argue that they are not the most easthetically pleasing as they are installed on top of your roof. Some estates and body corporates might disapprove of this. One can however opt for a more aesthetically pleasing option and that is to have a pump assisted system where the cylinder itself is inside of the roof and the collectors outside on the roof. The pump will still circulate the water through the collector and from the collector back into tht storage cylinder.
High and low radiation - Depending if your area has high or low radiation it will affect which collectors you need to decide on. The greatest advantage of black plate panel connectors is that the panel does not absorb enough energy so the stagnation point of the panel is not that high. This means the system can be left for a few days without the system overheating and discharging out of the T&P valve.
In low radiation areas one might opt to rather go for EVT tubes for the collector. They are very efficient in absorbing the UV rays to transfer the heat to the water. The one advantage of these manifolds is that in high radiation areas, the inserts of the tubes can be removed and the tube reinserted, this will cause the manifold to be less effective and reduce the effectiveness of the manifol which in turn prevents overheating.
Availability of public services - If you are situated in a rural area where there is not regularly available public services such as electricity it might be good to rather opt for a thermo syphoning low pressure unit. These units are very popular in rural areas because of their low cost in maintenance and their high life expectancy. These systems are usually identified by a cistern tank that is mounted on top of the hot water cylinder and the EVT tubes that plug into the bottom of the hot water cylinder. The cold water is heated by the EVT tubes and fills the hot water cylinder with hot water. As the pressure comes into the geyser it is reduced by the cistern tank.
In conclusion
Although solar offers alot of benefits one should first consider the limiting factors before deciding on the right system for you. The good news is that there is pretty much a solution for every situation or environment. If you are considering to install solar or to get a free no obligation assessment and quotation please do not hesitate to get hold of us by clicking here…
