It is well known that cave houses provide a noise free and weather proof environment (cool during the summer and warm during the winter). These structures also shield one from man-made Electromagnetic radiation that is present everywhere. Furthermore, since most of the materials used in construction are local, the environmental impact is minimal. Shown below are some cave houses from around the world. Some are simple dwellings with the most basic necessities, while other have running water, electricity and wireless access.
Pakistan was hit by a devastating earthquake in October 2005. Soon afterwords the government of Pakistan formed the Earthquake Reconstruction and Rehabilitation Authority, commonly known as ERRA. ERRA created 11 training centers for reconstruction of private homes destroyed in the earthquake. One of the techniques promoted in this reconstruction effort was the so called "Bhatar" method of construction.
Bhatar consists of reinforced stone masonry where parallel horizontal timber beams are inserted into the stone masonry at regular intervals to ensure coherence of structure. This is a much more economical option than typical construction which requires transport of cement, bricks and steal to remote mountainous regions. The houses constructed in this fashion are not only earthquake resilient but also energy efficient since the stone masonry acts as an insulator to heat and cold.
After the devastating earthquake of 2005 which destroyed nearly half a million rural homes in Pakistan, there was an urgent need to build earthquake resistant homes. Thus came into being PAKSBAB which is the short form of Pakistan Straw Bale and Appropriate Buildings. So far PAKSBAB, from its limited resources, has build 27 homes in northern parts of Pakistan. These homes have been built using indigenous resources and by training the local people in construction of straw bale houses.
A typical straw bale house has an area of 576 square feet and costs $3000 on average. This turns out to be $5.2/square feet which is less than half the cost of brick and mortar houses. A typical home comprises of two rooms, a verandah and a kitchen and requires around 1200 hours of labour. So 6 people working for 8 hours daily can construct a straw bale house in 25 days!
The main advantages of straw bale houses over brick and mortar houses are highlighted below.
1. Energy efficiency, since straw is a good insulator
2. Non toxic products are used (light straw, clay and wood)
3. Cheap materials are used resulting in a cost that is half that of a regular house
4. Resistant to earthquakes
Straw bales required for the construction of these energy efficient and earthquake resilient homes are built using manually operated farm jacks and locally manufactured compression moulds. Furthermore the local industry is being encouraged to supply straw bales and other materials required for these projects. Additional appropriate building methods that PAKSBAB is promoting include passive solar, rainwater catchment, solar lamps, high-efficiency cooking and heating, and the use of natural building materials such as light straw clay, wattle and daub, and cob.
I have been asked this question many time by my friends "Can I Run My Air Conditioner on Solar". The short answer to this question is YES YOU CAN. For the longer version you would have to read rest of the article below.
Lets assume that you have a basic unit that is categorized as 1-ton. Now the way Air Conditioners work is that they draw a lot of current at the start, as much as three times the normal steady state current. So a 1-ton AC might be drawing only 1200 Watts at steady state, it may require as much as 3600 Watts at start up. Now there are two ways to solving this problem. Either you can put up 3600 Watts of Solar Panels on your roof and operate your system only when peak sunshine is available. Or, the better option is to have enough panels to run the AC at steady state and use some batteries to provide the initial peak current or power. These batteries will also provide back up after solar hours and when the electricity from the main grid is not available.
One company providing solar solutions in Pakistan recommends installing 1800 Watts of solar panels and 600 Ampere Hours of batteries. So assuming that we have 6 hours of peak sunshine available the solar panels would be able to run the AC for about 6 hours directly on solar energy (assuming an average power consumption of 1800 Watts). After the solar hours the battery would be charged by the main grid and can provide backup of at around 4 hours (12 V x 600 Ah / 1800 W =4 hours). Also one must not forget that to convert DC voltages to AC voltages you would need an inverter and for controlling the charge and discharge cycles of the batteries a charge controller would be needed. Usually the modern solar inverters have built in charge controllers which somewhat limits the costs.
After going through all this technical jargon the question that needs to be answered is "How Much Would This System Cost". The answer to this is around Rs.450,000 including transportation and installation. You might think that this is too high a cost, but think of it this way, even if you are saving Rs.5000 on your electricity bill per month you would have saved enough to offset the cost in about 8 years. And solar panels would last you much longer than 8 years (typically around 25 years).
An entrepreneur in Islamabad has built a solar car that can run at 80 km/hour and has a range of 80 km. The car has solar panels on all its sides and roof which provide the energy to run the car. The car can also be plugged into an electrical socket to charge the batteries when they get discharged and solar energy is not available. According to the the designer all components have been locally manufactured except for the motor which has been imported from overseas (and obviously panels must have been imported as well). The current version of the car is a 2-seater but a 4-seater is also under construction.
The car is registered in Islamabad under the local laws. The company that invented this car, known as Economia, wants to commercialize this car by offering it has an alternate to taxis running on CNG and/or fuel. The company has submitted a proposal to the Government of Pakistan to allow it to start a local taxi system in Islamabad with 30-40 taxi stands in important areas of the city. This is a very encouraging development but it remains to be seen if it is able to taste commercial success.
According to the specs provided on the website the 2-seater version runs on a 2.2 KW motor whereas the 4-seater version runs on two 2.2 kW motors. The operating voltage of the motor and batteries is 48 V. The car is expected to be highly efficient and cost only Rs. 1/km. The price of the different versions range from Rs. 350,000 to Rs. 525,000.
|Voltage of Battery||48 V||48 V|
|Power||2.2 kW x 1||2.2 kW x 2|
|Distance Per Charge||80 km||80 km|
|Charge Time||2-3 hours||2-3 hours|
|Maximum Speed||40-60 km/hr||60-80 km/hr|
|Motor||2.2 kW x 1, 48 V||2.2 kW x 2, 48 V|
|Charger||48 V, 20 A||48 V, 20-40 A|
|Controller||48 V, 90 A x 1||48 V, 70 A x 2|
1. Input of 2.2 KW at 48 Volts means the motor needs 45 Amps to run.
2. If the solar panels on the car are about 500 W (100 W for each side and 100 W for the roof) the car would need to charge for about 4.4 hours in the sunlight to provide 1 hour of drive time. Realistically speaking, the 500 W panels would be producing only half the rated power since they cannot all be aligned to the sun at the same time.
3. Assuming that when the batteries are fully charged they can provide 2.2 KWhr of energy or simply 2.2 KW for one hour. At Rs. 15 per unit the cost for charging the batteries from an electrical outlet comes out to be Rs.33. Now if this car is able to drive for one hour at 60 Km/hour the cost per km would be Rs. 0.55 (this is assuming 100% efficiency which is practically not possible).
Pakistan is blessed with solar and wind energy. We have discussed solar in our previous articles, now let us have a look at wind map of Pakistan. It can be seen from the figure below that unlike solar which is available in most parts of the country wind power is available in only limited corridors along the coast and some northern parts of the country. It is well known that a wind speed of at least 12 miles per hour (5.4 meters per second) is required for the wind turbine to work. If we look at the major cities we can say that wind power is available in the cities of Karachi, Hyderabad, Quetta and Islamabad.
Like solar, wind projects also require a large initial investment. Wind power projects can be divided into two main categories namely on-shore and off-shore. The typical cost for these projects in the developed world, is analyzed by IRENA in a study conducted in 2012. It can be deduced from this study that for on-shore projects the cost is $1.7-$2.45 per Watt. This can be compared to price of solar for Quaid-e-Azam Solar Park Bahawalpur which is around $1.31 per Watt. Off-shore projects require even higher initial investment, with price per Watt ranging from $3.3 to $5.0.
If we look closely at the costs for an on-shore project we see that 64% of the cost goes into the construction of wind turbines. Within this category the major cost is associated with the rotor blades and tower. These two components of the wind turbine account for more than 30% of the total cost. Other major contributor to the total cost is the foundation which accounts for 16% of the total cost. For off-shore projects the rotor blades and tower contribute about 50% to the total cost.
A description of the main components of the Wind Turbine is given below (reproduced from IRENE document).
Tower: These are most commonly tapered, tubular steel towers. However, concrete towers, concrete bases with steel upper sections and lattice towers are also used. Tower heights tend to be very site-specific and depend on rotor diameter and the wind speed conditions of the site. Ladders, and frequently elevators in today’s larger turbines, inside the towers allow access for service personnel to the nacelle. As tower height increases, diameter at the base also increases.
Blades: Modern turbines typically use three blades, although other configurations are possible. Turbine blades are typically manufactured from fibreglassreinforced polyester or epoxy resin. However, new materials, such as carbon fibre, are being introduced to provide the high strength-to-weight ratio needed for the ever larger wind turbine blades being developed. It is also possible to manufacture the blades from laminated wood, although this will restrict the size.
Generator: The generator is housed in the nacelle and converts the mechanical energy from the rotor to electrical energy. Typically, generators operate at 690 volt (V) and provide three-phase alternating current (AC). Doubly-fed induction generators are standard, although permanent magnet and asynchronous generators are also used for direct-drive designs.
Transformer: The transformer is often housed inside the tower of the turbine. The medium-voltage output from the generator is stepped up by the transformer to between 10 kV to 35 kV; depending on the requirements of the local grid.
Bottomline: For Pakistani companies interested in indigenous development of small wind turbines (0.2kW - 100 kW) a good point to start is to develop rotor blades and towers which contribute to 30% cost of an on-shore wind power project (this increases to 50% for off-shore projects). The material used could be steel or wood which is easily available in the local market. One can also experiment with lighter materials that increase the efficiency of the system. A small wind power project of 3000 Watts can easily support all the appliances of a typical household in Pakistan (except the heavy loads such as air conditioners or large freezers/refrigerators).
The government of Pakistan has recently launched the Quaid-e-Azam Solar Park in the Cholistan desert near Bahawalpur. The project aims to produce 100 MW of electrical energy by end of 2014 and 1000 MW by end of 2016. This is a small step in the right direction. Countries like India, China and Germany are much ahead in the game with installed solar projects of 2600 MW, 20000 MW and 36000 MW respectively. Let us take a closer look at the price that we will have to pay for the energy produced.
The cost of the 100 MW project is around $131 million, that is the price per Watt is $1.31. That seems to be quite good, lets look closely. We know that 400,000 panels are to be installed in the first phase to produce 100 MW of electrical energy. This means that each Solar Panel would produce 250 W and the cost of each panel would be $327.5 or Rs.32750.
Assuming that there is peak solar energy available for six hours daily, each solar panel would produce 1.5 kWhr of energy each day or 547.5 kWhr of energy per year. This amounts to 13687.5 kWhr of energy over a 25 year period (assuming that the performance of the Solar Panels does not degrade over the 25 year period). Now assuming that each unit of energy (kWhr) is sold at Rs.15 the total energy produced by the Solar Panel over its life period amounts to Rs.205312.5 i.e the revenue earned from selling electricity is 6.27 times the investment (205312.5/32750=6.27).
In other words the investment is recovered in 4 years and you have free electricity for the remaining 21 years. Please note that the above calculations do not include the operational costs, if any. Also, the above analysis assumes that the performance of the Solar Panels does not degrade over its life time.
Final Comment: The location of the proposed project does not seem to be optimum as Bahawalpur is receiving 2000 kWhr per squared meter per year as opposed to vast expanses of Balochistan that receive 2200 kWhr per squared meter per year.
The map below shows the solar energy falling on a horizontal surface of area 1 m2 during one year. It can be seen that areas of Balochistan and Southern Sindh are most gifted while Peshawar, Lahore and Islamabad also have quite favorable conditions. Lets assume that we are installing a Solar System in Karachi where the annual irradiation is around 2000 kWhr/m2. This means that there is an average daily irradiation of around 5.5 kWhr/m2. This means that a Solar Panel of area 1 m2 would receive 5.5 kWhr per day or 1 kW for 5.5 hours daily. If the above Solar Panel has an efficiency of 20% we can produce 200 Watts of electrical energy from it for 5.5 hours each day.
1. The above map is for energy collected by a horizontal surface. A suitably tilted surface or a tracking one can obtain significantly more energy.
2. The received energy not only depends upon the relative position of the Sun and Earth but also on the atmospheric conditions such as cloud cover during different seasons.
It is quite well known fact that installing a solar system at your home requires a large initial investment. But it is also known that solar panels have a typical life period of 25 years. Other equipment used in a solar system such as batteries, charge controllers and inverters have a shorter life span and may need to be replaced every 2-4 years. In this article we try to calculate the payback time of a simple solar system that uses all its energy in real time converting DC voltage produced by the solar panel to AC voltage through an inverter.
Let us assume that our load requirement is 500 W and we have 5 solar panels of 100 W each. We next assume that we have an inverter also rated at 500 W. Let us further assume that the solar panels receives peak sunshine for 6 hours daily (this is called Peak Sun Hours and is quite complicated to explain in this brief article). Therefore the total energy produced during a 24 hour period is
500 W x 6 hr = 3000 Whr = 3 kWhr
In one month the solar panel would produce
3 kWhr x 30 = 90 kWhr or 90 units of energy
Now assuming that a unit of energy is sold to you at Rs. 15 (including all the taxes and surcharges) the total savings per month are
90 units x Rs. 15/unit = Rs. 1350
Now let us look at the investment we made in the solar system. Solar panels are widely available in the local market for Rs.100/watt. This results in Rs. 50,000 investment in solar panels. An additional Rs. 10,000 are spent in the inverter. So the total cost of the solar system is Rs. 60,000.
So the payback time of this solar system is
60,000 / 1350 = 45 months or 3.75 years
This is highly encouraging because all your investment is recovered in less than 4 years and you have 21 years of free energy from your solar system.
1. The above analysis is also valid for grid tied systems where the energy is sold to the grid during the off peak hours (day time) and bought from the grid during peak hours (evening, night time).
2. A real system would also need some batteries to provide backup when there is a power shut down and solar energy is also not available.
3. Although solar system is expected to have 25 years of life, it will not operate at 100% throughout this life period e.g. it might be operating at only 80% after 20 years.
Solar Irradiance refers to Solar Energy falling on to the Earth on a unit area. Since this Solar Energy is limited to certain wavelengths (or frequencies) therefore it is usually given as a function of wavelength and the has the units of Watts/m2/wavelength. This is shown in the figure below for a unit area perpendicular to the solar rays and lying outside the Earth's atmosphere. This is referred to as AM0 since there is zero atmosphere, as opposed to AM1.5 which is on the Earth's surface.
So roughly speaking we can say that most of the Solar Energy lies between the 0 to 4 micrometer (NREL gives the AM0 spectrum from 280 to 4000 nanometer). A device that can capture all of this energy would be very useful and this is the aim of all modern Solar Cell manufacturers. The total Solar Power available on a surface of unit area can be easily calculated by integrating the above given Solar Irradiance curve from 0 to infinity and this gives us a magic number of 1367W/m2 (the value of the dotted curve at 4000 nanometer).
But all of this power does not reach the Earth's surface. Some of it is absorbed on the way. The total Solar Power available on the Earth's surface is equal to 1000W/m2 i.e. a reduction of 27% from that outside the Earth's atmosphere. The magic number of 1367W/m2 might be important for satellites using Solar Panels for their energy requirements and orbiting the Earth outside its atmosphere.
The Solar Spectra can also be calculated by using the theory of Black Body Radiation. According to this the Solar Spectra can be well estimated by a Black Body radiating at a temperature of 5960K (blue curve).
1. The Irradiance of 1000W/m2 is under ideal conditions (bright sunny day, at zero altitude and solar rays perpendicular to the capturing surface) but even this is not available to a Solar Home since the Solar Panels only have 15%-20% efficiency. So a 1m2 Solar Panel might only give you 150W-200W under ideal conditions. But do not get depressed yet as new research findings promise Solar Cells with efficiencies as high as 45%.