We will continue to update this section from time to time, if you have any related question, you may submit here.
Insolation is the spot measure of solar radiation that finally reaches that particular surface of the earth. Also known as Incident Solar Energy. The popular expression of Insolation is kilowatt-hours per square metre per day (kWh/m2/day). Since it is a measure of the solar energy incident on a given area over a specific period of time therefore also measured by the amount of solar energy received per square centimetre per minute.
Insolation Data of Few Cities:
| City / Month | kWh/m2/day |
|---|---|
| ISLAMABAD | |
| January | 2.82 |
| February | 3.31 |
| March | 4.76 |
| April | 5.83 |
| May | 7.09 |
| June | 7.29 |
| July | 6.67 |
| August | 5.71 |
| September | 5.44 |
| October | 4.61 |
| November | 3.44 |
| December | 2.57 |
| Annual Average | 4.962 |
| LAHORE | |
| January | 2.78 |
| February | 3.92 |
| March | 5.12 |
| April | 6.1 |
| May | 7.13 |
| June | 6.91 |
| July | 6.31 |
| August | 5.69 |
| September | 5.43 |
| October | 4.78 |
| November | 3.74 |
| December | 3.02 |
| Annual Average | 5.078 |
| KARACHI | |
| January | 4.07 |
| February | 4.95 |
| March | 5.97 |
| April | 6.24 |
| May | 6.62 |
| June | 5.8 |
| July | 4.9 |
| August | 4.74 |
| September | 5.42 |
| October | 5.3 |
| November | 4.3 |
| December | 3.81 |
| Annual Average | 5.177 |
| PESHAWAR | |
| January | 2.68 |
| February | 3.29 |
| March | 4.68 |
| April | 5.71 |
| May | 6.77 |
| June | 7.21 |
| July | 6.98 |
| August | 6.15 |
| September | 5.45 |
| October | 4.56 |
| November | 3.29 |
| December | 2.53 |
| Annual Average | 4.942 |
| QUETTA | |
| January | 3.47 |
| February | 4.24 |
| March | 5.62 |
| April | 6.6 |
| May | 7.53 |
| June | 7.89 |
| July | 7.56 |
| August | 7.19 |
| September | 6.52 |
| October | 5.56 |
| November | 4.08 |
| December | 3.35 |
| Annual Average | 5.801 |
| FAISALABAD | |
| January | 2.83 |
| February | 3.89 |
| March | 5.22 |
| April | 6.02 |
| May | 7.01 |
| June | 6.92 |
| July | 6.62 |
| August | 5.91 |
| September | 5.57 |
| October | 4.82 |
| November | 3.7 |
| December | 3.04 |
| Annual Average | 5.129 |
| NOWSHERA | |
| January | 2.67 |
| February | 3.29 |
| March | 4.7 |
| April | 5.77 |
| May | 6.9 |
| June | 7.33 |
| July | 7 |
| August | 6.13 |
| September | 5.55 |
| October | 4.6 |
| November | 3.32 |
| December | 2.5 |
| Annual Average | 4.98 |
| HYDERABAD | |
| January | 4.08 |
| February | 4.88 |
| March | 5.94 |
| April | 6.24 |
| May | 6.96 |
| June | 6.48 |
| July | 5.87 |
| August | 5.73 |
| September | 5.97 |
| October | 5.21 |
| November | 4.21 |
| December | 3.79 |
| Annual Average | 5.447 |
| MULTAN | |
| January | 3.27 |
| February | 4.1 |
| March | 5.41 |
| April | 6.02 |
| May | 6.89 |
| June | 7.04 |
| July | 6.85 |
| August | 6.47 |
| September | 5.79 |
| October | 5.01 |
| November | 3.86 |
| December | 3.25 |
| Annual Average | 5.33 |
| ABBOTABAD | |
| January | 2.62 |
| February | 3.08 |
| March | 4.43 |
| April | 5.64 |
| May | 7.01 |
| June | 7.18 |
| July | 6.51 |
| August | 5.74 |
| September | 5.21 |
| October | 4.54 |
| November | 3.38 |
| December | 2.39 |
| Annual Average | 4.811 |
| MARDAN | |
| January | 2.59 |
| February | 3.24 |
| March | 4.6 |
| April | 5.78 |
| May | 7.05 |
| June | 7.4 |
| July | 7.07 |
| August | 6.21 |
| September | 5.56 |
| October | 4.54 |
| November | 3.3 |
| December | 2.43 |
| Annual Average | 4.981 |
| GUJRANWALA | |
| January | 2.6 |
| February | 3.76 |
| March | 5.05 |
| April | 6.01 |
| May | 7.13 |
| June | 6.99 |
| July | 6.47 |
| August | 5.88 |
| September | 5.57 |
| October | 4.75 |
| November | 3.65 |
| December | 2.9 |
| Annual Average | 5.063 |
| GUJRAT | |
| January | 2.59 |
| February | 3.63 |
| March | 4.95 |
| April | 6.01 |
| May | 7.18 |
| June | 7.09 |
| July | 6.61 |
| August | 5.9 |
| September | 5.56 |
| October | 4.67 |
| November | 3.59 |
| December | 2.82 |
| Annual Average | 5.05 |
It depends how much it cost you at present without having it. This might be different in cases where if you have a single source of electricity at the moment or already making use of standby/backup source like diesel Genset etc. If you are making use of diesel generator for 4 hours daily, and now you generate same amount of electricity from a Solar system, you can recover the cost of Solar system in just one year to one-and-a-half year depending upon your Capex (initial capital expense). The normal payback period for a WAPDA user varies between 5 to 8 years.
Although there is no fixed or definite rule for such cost estimates since the make, functions, quality and origin of products available for a solar home system have a wide range, however in rough guesstimate – one may make up his mind for a Chinese origin product ranging from Rs.150000 to 225000 per kW, whereas a western origin system may be available at around Rs.300000 to 500000 per kW. A lot more than just prices of individual products matters here since there are other factors too that constitute the price of a solution.
We have noticed that people who have UPS installed at their homes first think about adding Solar Panels to charge their UPS batteries then we found those very people going one step ahead since most of them are not satisfied with this makeshift arrangement and want to go another step by replacing the UPS with a Solar inverter.
Let us highlight some facts that might help in saving you time and money:
- UPS Inverters have a built-in battery charger.
- When you add a solar charger, this means now you have two chargers – charging the same batteries.
- There is no coordination or control in this dual system to control the source of charging.
- Normally what people do – they switch-off WAPDA in sun hours and get charge from the sun.
- So you need an attentive human mechanism to manage this source switching and checking battery status.
- This bothersome arrangement is not workable in most cases.
- Consequently, battery gets fully discharged time and again – means added cost and trouble.
- A solar inverter system that offers control of charging source and at the same time have more sophisticated charging technique that depends upon monitoring the charged status of battery results in extended life of your asset whereas save you from nuisance.
- The electricity bill is reduced considerably because of control on battery charging source.
In addition to above, a 1kWp Solar System will save you around Rs.30000/= in yearly bills (say assuming an average IESCO bill @ Rs. 16/unit) if solar energy is fully utilized and will pay it back in almost 5 years, that makes a case “why to replace” if one can afford the initial cost.
Actually, there is no fixed answer for this very common question since the sun is not fixed and changes its position (means angle to our ground plane) constantly. Naturally, we have to adjust the tilt angle as per our requirement in view of sun’s known moving path/direction. If we are not using a tracker for our Panels then we shall look at our consumption pattern and optimize the fixed angle accordingly. If our load is more in summer then a lower angle will be better say between (4° to 15°), if our load is more in winter then a higher angle (say from 38° to 55°) might be better and if we need a round year optimization then we may be looking to fix our panels at around 25° to 35°.
The other important factor in selecting the angle is the availability of mounting space and its cost economics.
The required area depends on following factors:
- The wattage & size of the Solar Panel being installed
- Number of rows facing the sun
- Tilt angle at which Solar Panels are installed
We do a quick guess usually as below:
- For a single row installation, the approximate area we assume is between 78-90 Square Feet per kWp.
- For multi row installation, approximation is around 100-150 Square Feet per kWp depending upon the Tilt angle – more the tilt angle, more the area.
In everyday technical terms, the only slight difference is the efficiency of two types, for instance we have both types of Solar Panels in 60 cells assembly per module with exactly the same physical size (i.e., 1650mm x 992mm), in Mono series the highest model is of 270Wp while the highest model in Poly series is 260Wp, however if we take a 250Wp model of any type – there is no technical or practical difference.
The difference will only matter if you deploy highest power model in a mega scale project where thousands of Solar Panels are installed, say if you have to build a 10MWp plant using our highest model from two types, you will need 37037 numbers of Mono and 38462 numbers of Poly type. In this case the difference is significant – 1425 more panels are required in case of Poly type, this will translate in to increased area for installation, that much extra mounting, cabling etc., hence eventually the cost of project even using the less expensive type (Poly) may result in more overall cost.
There is another but almost insignificant difference in two types that is of temperature coefficient which goes in favour of Poly type.
A pulse-width-modulating (PWM) type of charge controller sends spikes of energy to the battery when the battery requires charging (this is done when the energy pulse is ON) and then monitors the charged status of battery (when the pulse is OFF) in order to decide whether to continue charging in next cycle or to disconnect charging. PWM charge controllers are mostly designed on complex algorithms that control the amount of charge and monitors battery status in various practical conditions. The only advantage of using PWM charge controllers in our view is the low initial cost.
The limitation of PWM is that we need to arrange the charging Solar Array voltage in the closest possible proximity of battery or battery bank voltage, because when two sources of energies are connected together – the powerful one (i.e., battery) has the potential to pull down the voltage of Solar Panel to its level (say 12V) and this way the output power from Solar Panel will be lost by a proportional magnitude of the difference in two voltages.
Maximum-Power-Point-Tracking (MPPT) is thus invented to overcome the voltage mismatching issue which was resulting in loss of solar power, this type of charge controller by design assures the battery (or battery bank) voltage and adjusts the current supply accordingly to deliver almost all harvested power by the Solar Array. This technique also brings the advantage and flexibility of deploying Solar Array of higher voltages like 150Vdc to charge even a very lower 12Vdc battery/bank efficiently.
In monetary terms, let us compare the difference of energy yield using PWM and MPPT charge controllers from a 1kWp Solar Array.
- Say the overall efficiency of PWM is around 70%
- That of MPPT is around 95%
- Site energy potential as 1860 kWh per year per kWp
- kWh Units realized by PWM charge controllers would be 1302
- kWh Units realized by MPPT charge controllers would be 1767
- If we assume Rs.16/kWh unit of electricity then Rs.7440 loss per year in using PWM
The purpose of a charge controller is to protect the expensive asset (battery section) in a Solar system; though you can connect a Solar Panel output directly to the battery but that will cost in two ways – loss of energy harvesting & early replacement of battery part.
Technically speaking, every kind of battery, because of its internal structure and characteristics, specifies some precise sum of voltage and current while being charged (or discharged) – there are design limits. A Solar Panel is a unidirectional source of energy which generates and supply DC electric power at its given voltage and current rating while battery is a bidirectional energy device which can accept and deliver energy. An intermediate device is required to manage the transfer of energy from one source (Solar Panel here) to the other source (the battery) in order to protect the design limits of battery (or battery bank) and ensure energy transfer efficiency.
Charge controller is a device that regulates the supply of current and/or voltage to a battery or battery bank, also known as charge regulator because of its regulating function.
When the load side circuit is physically isolated from supply, the transfer of energy takes place by “induction” process utilizing transformer at the output of inverters. Galvanic Isolation offers better protection mechanism.
No. All inverters are not capable of powering every type of load, we have defined four classes of solar inverters in view of the “powering capability” of inverter, obviously the ‘price tag’ or ‘price range’ depends on the class of inverter, hereunder our stipulated classes are:
| Inverter Class | Electrical Load Powering Capability |
|---|---|
| Class 1 | Capable of powering continuous duty balanced or unbalanced electrical loads of all types in 3-phase configurations. |
| Class 2 | Can safely run the continuous duty electrical loads of Inductive nature (like air conditioner, motors), Resistive load (like heaters) in addition to Class 3 load. |
| Class 3 | Capable of supporting low surge inductive loads (like ‘inverter based air conditioner’, photocopiers, computer printers, capacitor controlled motors etc.) in addition to Class 4 load. |
| Class 4 | To run all basic electrical loads including fans, lights, TV, LEDs, CCTV, computers, monitors etc. |
Any thing connected in a circuit that consumes electricity to perform its designed function is an “electrical load” in its very practical understanding. Since there are many functions associated with electricity like generation of heat, motion, movement, and illumination or else, accordingly thus there are types of electrical loads like resistive load, inductive load, capacitive load and/or a combination load.
A short and easy to understand definition of PV is found here, that says:
Photovoltaics is the process of converting sunlight directly into electricity using solar cells.
An appropriate definition we found here says:
“Renewable energy: Any energy resource that is naturally regenerated over a short time scale and derived directly from the sun (such as thermal, photochemical, and photoelectric), indirectly from the sun (such as wind, hydropower, and photosynthetic energy stored in biomass), or from other natural movements and mechanisms of the environment (such as geothermal and tidal energy). Renewable energy does not include energy resources derived from fossil fuels, waste products from fossil sources, or waste products from inorganic sources.”
The application requirement matters here before anything else, we are listing few application scenarios from where you may draw a parallel to your application that may help you reach some conclusion:
| Inverter Type | Application Scenarios |
|---|---|
| Off-Grid / Solar | Solar Water Pumps (when no battery or grid is involved, naturally the inverter output varies as the sunshine varies). |
| Off-Grid / General | UPS, On-Board Power Supplies, Home Battery Inverters works when Grid fails etc. (Solar is used to charge the battery only) |
| Off-Grid / Hybrid | A true off-grid system where the load may also be served by mixing the solar and battery energy sources as and when available, a bankable and standalone Solar Power Systems which will work without Grid. |
| On-Grid | Works only with Grid; Stops when grid fails because of its built-in anti-islanding feature; Good for Feed-In-Tariff; Net-metering; incentive schemes etc. |
| Grid / Hybrid | Off-peak harvesting, peak hours utilization and feeding to grid (Peak shaving); Good for FIT; Net-metering etc. |
| Grid-Tied | Utility scale PV power plants (unidirectional flow to grid only). |
| Grid-Tied / Hybrid | The best configuration in grid environment for rampant load shedding areas making full prioritized use of solar asset (unidirectional flow to system/load from Grid) |
Naturally, the classification of Solar Inverters is based on two of its main facets i.e., the input source(s) and how its output is connected, below table classifies the types of inverters for different input combinations and output schemes or operational modes:
| What are the DC Source(s) to Inverter: | Where the output of inverter is connected to (the possible scenarios): | ||
|---|---|---|---|
| Battery represents any DC source other than Solar (the possible scenarios of inputs to inverter) | No Grid (But to Load only) | Grid (Bidirectional Flow) | Grid (Unidirectional Flow) |
| Solar PV | Off-Grid / Solar | On-Grid | Grid-Tied |
| Battery | Off-Grid / General | N/A | N/A |
| Solar PV + Battery | Off-Grid / Hybrid | Grid / Hybrid | Grid-Tied / Hybrid |
Additional Notes:
- A hybrid type of inverter means when the load can be served by mixing at least two energy sources available.
- Some inverters just switch between available energy sources, that types of inverter is not a hybrid inverter by definition
- Hybrid inverters are expensive than simple one-source & switching type of Inverters
Inverters are designed for markets with varied grid/utility standards in terms of voltages and alternating frequencies. In Pakistan, we have 220V and 50 Hz standard for single phase AC power; 380/400/440 volts are standard in 3-phase AC.
For instance, a photovoltaic module (solar panel) is a DC source for Inverter; battery is another DC source etc.
Inverter is a device that inverts (or you can also say converts) the DC into AC – simply. It means, you can attach some specified “direct current (DC)” to its input and it will give you some particular type of “alternating current (AC)” output.