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    Questions and Answers on Solar Street lighting for cities

    Hello Indranil, If you have multiple sunny days in a row, is there an option to put energy back in to the grid?
    Currently the option of feeding back energy into grid is not available, but this is definitely something which we want to explore going forward.
    Hello, Indranil do you have the cost from a the solar streetlamp and the current on the grid LED street lamp.
    The all in one solar luminaire which has inbuilt battery and panel is around 3x than a standard grid connected luminaire of similar lumen output. 
    What are the lifetime of the charge controller? and batteries?
    Life of LiFePO4 batteries are 2000 cycles at 90% depth of discharge which is close to 5 years if every night the battery is fully discharge – it may be higher also if the battery is not completely discharged everyday. Life of a charge controllers is matching with battery life but may vary provided the quality of electronics used in it. 
    And what about the solar panels in term of maintenance (lifecycle, cleaning?)
    Solar panels are generally maintenance free devices which have long technical life of >20 years. To clean the panels, water with high mineral content should NOT be used. Water must be free from grit and physical contaminants that could damage the panel surface. Use of cleaning agent: A mild, non-abrasive, non-caustic detergent with deionized water may be used. Abrasive cleaners or de-greasers should not be used.
    In hybrid system the capital cost dorsnoy seem to be less because of rhe requirement of latency. The only economy will be on energy and nit on capital cost. even then it is a good concept
    The viability gap for hybrid system is reducing faster due to reduction in battery and panel prices year on year. However, from sustainability point of view, hybrid is an ideal solution as this  gives required lumen output (currently upto 24000 lumen) without chances of blackout, runs primarily from green energy and saves grid power to a large extent.
    Solar panel IK rating?
    The impact resistance of solar panel is defined in terms of hail impact it can withstand as in IEC61215 which is close to IK05.
    Where can I find more information on how to calculate the battery necessary for certain amount of Watts in the solar panel and the certain LED intensity, for example a 50W panel and a 150 lumen/watt LED. Thank you!

    Generally battery and panel sizes are calculated when the lighting load is known for a particular project. Solar sizing softwares are used by technical team for this purpose.

     

    Below mathematical formulae may be used to calculate battery and panel sizing-

     

    Battery size (Watt hour) = (Wattage of luminaire x number of back-up hours) / (Battery depth of discharge x charging efficiency of the controller x driver efficiency x cable efficiency)

     

    Panel size (Wp) = (Wattage of luminaire x number of burning hours) / (charge efficiency x cable efficiency x battery degradation factor x dust factor x peak sun hours)

    What means Northern Europe - what countries?
    Northern Europe typically means Scandinavian countries, norther part of Eastern Europe and UK. 
    Francis from Ghana, please i want to know when the battery is over charged is not going to affect the lifespan of the battery? or is that there are systems put in place to cut off power when the battery is fullly charged?
    Overcharging of batteries are prevented by battery management system and charge controllers. When battery is fully charged the charge controllers goes into float charge mode for sometime and then gets disconnected.
    Can you please give a quantitative example to show how much savings can be gained by increasing the efficiency of the light. What is a typical cost breakdown between the light, the panels and the batteries?
    Typically cost breakdown of a solar system may be 15% luminaire, 20% panel and 40% battery (25% for charge controllers and accessories such as cables). If we increase the luminaire efficacy by 25%, battery and panel size may be reduced by 20% where other conditions remain same. Thus overall system cost may be reduced by 12%.
    Hi Indranil, for solar streetlights, you spoke about LED and batteries. Does it require a driver?
    Solar system requires a charge controller which manages power flow between panel, battery and luminaire. To drive the LEDs, a driver is required which may be integrated into the charge controller.
    In terms of lighting control for dimming, are these solar lamps only be controlled wirelessly? meaning through WIFI?
    There may be multiple system architecture used to dim a solar system. E.g. zigbee / cellular network. It is also possible to have 1-to-1 controller through low energy Bluetooth communication or Infra-red remote. Suitable user interfaces are available to execute the control function.
    I believe normally we will design 20% extra for our solar. How about in future we have add additional or change the high watts lighting, would the solar panel easy to upgrade?
    It depends on the rating of charge controller. To upgrade to a higher load or higher panel size, the charge controller must have capacity to accommodate this.
    How many years return of investment using solar street lighting 40 watt compared to electricity 1000 Kwh per month? Let us say 1 Kwh = USD 1
    In this case monthly saving is 1000US$ as an off-grid solar light won’t consume any electricity. If we consider avg price of solar system around 500 US$, in this case there would be return in no time. But 1000Kwh / month would be consumed by a much higher load and we need to see whether a 40W solar street light can replace it or not.
    For product solar all in one lithium battery can be replaced if broken?
    Yes, Lithium batteries are typically replaceable. 
    What will be the maximum wattage of luminaire could be considered for solar lighting?
    Currently we can run up to 150W which is equivalent to 24000 lumens as a standalone light point.
    Solar or conventional street lighting, which will be the cost-effective solution for long run-in consideration with battery life?
    Solar systems are cost-effective in long run as in case of off-grid solar, there is no cost related to electrical infrastructure such as cabling, trenching, switchgears etc.  – therefore the additional cost of battery/panel is compensated.
    Is it possible to create a solar kit that may be universal to mount on other fixtures?
    Size of battery depends on load/back-up hours needed and size of panel depends on battery size/solar energy available at the location of project à therefore a universal solar kit may not be possible as those factors vary from one project to another.
    What is the end-of-life process to dispose batteries? Is it possible to create a solar kit that may be universal to mount on other fixtures?
    Battery disposal process depends on local regulations as applicable to the country. Batteries like Lithium Ferro phosphate are RoHS compliant and often recycled.
    What is the cost to recycle batteries and disposal fees, in proportion?
    Disposal fees may vary from one country to another depending on local regulations.
    You still use Lead acid batteries?
    Lead acid Gel batteries are still being asked by our customers we have a range of Gel batteries.
    I don’t see a street luminaire with integrated PV panels, battery & controller is efficient.
    SunStay All-in-One luminaire is having efficacy > 180 lm/W
    How do solar panels works as per my knowledge solar panels need south facing irradiation?
    In northern hemisphere solar panels can generate maximum power when facing equator i.e. south. In southern hemisphere they become north facing. The angle of tilt may be decided by looking at solar irradiance data from any reliable database.
    How to manage the solar streetlight where I need to install it in north/east/west direction?
    No matter what is the direction of the luminaires, the pv panel must face the equator. If panel is integrated then generally luminaire is kept horizontal.
    Batteries are stored in the luminary, in pole or other location?
    There are many architectures possible, in-fact batteries may be integrated into luminaire, can be placed inside pole, can be underground or mounted on pole with help of a suitable mounting box. The IP rating of batteries should be seen before placing into these locations, e.g. underground should be IP68.
    Are there plans to launch all in one solar fixture with higher outputs than 4500 lm?
    There is already luminaries upto 12000 lumen in all-in-one architecture (SmartBright All-in-one solar streetlight)
    Are the optics offered in solar street lights suitable to replace the existing LED street light installation on roads? (7mtr, pole with 35wattled street light, 9mtr pole with 70watt Led Street Light , 12mtr pole with 160watt Led Street Light)
    Yes, solar streetlights come with optics suitable to road lighting such as DM, DW1, DW2 DWV/DWP etc. depending on what luminaire is being used.
    For what type of Roads Solar streetlights are recommended?
    Solar luminaire can go upto 24000 lumen, therefore it can be applied to main roads as well.
    Wonderful Presentation Mr. Indranil! The performance of Solar Streetlighting in India is a big question mark! What should be the way forward?
    There are good solar systems and bad solar systems. The performance of solar system depends on quality of the subsystems such as luminaire, battery, panel and most importantly how they work together with a charge controller at the center. The charge controller needs to ensure all the subsystems perform optimally when connected with each other and necessary protections are built into it.  In a good solar system above are taken care of and performance can also be promised. 
    Taking maintenance of solar panels into consideration, would you say solar lights might end up costing more especially in cities that are particularly dusty environments?
    Dust / mud deposition can temporarily reduce generated power from solar panels, however they may be cleaned easily. Solar panels are environmentally protected, therefore such temporary depositions don’t damage internal silicon cells, bus bars etc.
    What is the average efficiency of the solar panel used? What type of cells do you use silicon based or thin films?
    Efficiency of solar panel could be 16-17% depending on cells used. Mono or polycrystalline cells are used.
    Is Signify developing its own battery and solar technology?
    In Signify we have exclusive range of panel and batteries from our approved partners which are validated to work with our luminaires and charge controllers.
    Thank you for the presentation. If we are using a presence sensor, will it use more energy? or it won't cost too much but make it more effective?
    Generally presence sensors optimize energy performance of luminaires and common in all-in-one products where the panel and battery sizes are limited due to compactness of the product.
    Will the cold weather reduce battery life in winter
    Battery chemistry defines the higher and lower temperature limits and if the ambient temperature is lesser than the lower limit then performance and life is adversely affected.
    What is the maintenance requirements for the solar panels?
    Solar panels are generally maintenance free devices which have long technical life of >20 years. To clean the panels, water with high mineral content should NOT be used. Water must be free from grit and physical contaminants that could damage the panel surface. Use of cleaning agent: A mild, non-abrasive, non-caustic detergent with deionized water may be used. Abrasive cleaners or de-greasers should not be used.
    Exterior Lighting- What are the lumen packages and color temp. packages being offered in the USA market?
    In all-in-one category currently up-to 4500 lumen is available in USA with 4000K CCT and options of 5700K/3000K is also available. For non-integral please connect with local team, our global solution can go up-to 24000 lumen.
    How do we keep the batteries healthy? especially in hot areas?
    For any battery chemistry, higher and lower limit of temperature is defined for charging, discharging and storage conditions which must be adhered to keep them healthy. Please refer to battery specification sheet.
    And how does charging current and charging cycles factor into that?
    For any battery chemistry, higher and lower limit of temperature is defined for charging, discharging and the cycle life at any particular depth of discharge is also defined accordingly. The limits must be adhered. Please refer to battery specification sheet.
    Does the efficacy will differ when dealing with AC Source rather than DC in case of solar lighting?
    Generally the efficacy is higher in DC-DC system and compared to AC-DC system as during the conversion at driver level leads to some efficiency loss.