Solar Power Systems Demystified

Solar Power is one of the unique systems of our times - since its pretty much feasible in most areas of the world - and can be set up from a micro scale solar light to large scale solar power plant to power cities ! 

Everyone I talk to, gets excited about Solar power and its potential to re-shape the power scenario in the next few years. While some of the users have had some bad experiences with early solar generation lights being very dull and unreliable, and are very skeptical about solar as a main line source of power - there are quite a few others who think that solar power can provide cheap power to run anything in their daily life. So lets take a quick look at what our current generation Solar power systems can power and what they may not be very well suited for. 

Basics about Solar power generation

First some basics  - Solar power most commonly is generated by PV panels- which are powered by Solar radiation - and produce a form of current called Direct Current (DC) - which can either be used  directly for some DC lights and DC appliances ( which are not that commonly available) or this Diect Current is usually converted to Alternating Current (AC) by Inverter/ PCU/IPS - which is the form of current that powers most of our homes from the Grid or Escoms. Once we get AC - this can generally power our normal household AC lights and appliances.  ( Note : Solar PV panel is quite different from your roof top Solar Water heater which use tubes/ fins to heat water !!) 

Solar off grid systems - are systems which can be standalone systems that can produce DC or AC power by themselves and power lights and appliances.  These systems can only power loads based on their capacity and type of loads  ( see typical loads that can run on solar given below) Solar On Grid systems - are systems which produce AC and are synchronized with  Grid power - to work in parallel with Grid power. These on grid systems can run any loads - as they are supported by Grid power for spikes and surge handling. The Solar on grid systems - can export excess power to the grid or draw a portion of the input power from the grid as needed to support their loads. 

Since Solar Energy is available only for about 8-12 hours a day, Solar off grid system invariably use batteries as a storage device to store excess energy and provide battery power during non sunshine hours , cloudy conditions and to cater to instantaneous high power if solar panel itself cannot meet the need.  Solar on grid systems - may or may not be connected to battery banks and may not run when Grid power is not provided, depending on the configuration. 

What can Solar power systems run ? 

Solar power systems - from user perspectives can be broadly in three types : 

  • Solar powered off grid DC system  - that can run DC lights, DC fans, DC pumps and DC motor based machines, DC coolers and freezers  ( depending on the size of PV panels & batteries)
  • Solar powered off grid or Hybrid AC System - smaller systems of 0.75 kVA to 2 kVA can power regular household lights, fans and computers, small fridge, kitchen appliances while medium systems from 3 kVA to 5 kVA can power all single phase household loads like fridge, washing machine, Air Conditioners, water heaters - as well as water pumps , motors and machines up to 2.5 hp. Larger off grid systems 10 kVA and above can power three phase AC loads like motors, heaters and machines. When it comes to ease of running on Solar off grid systems - lights, fans, computers and small printers can run on even small inverters. Next comes fridge , washing machine, kitchen appliances, small pumps - which may need medium systems ( 1.5 - 2.5 kva ) to run - while  AC, Water heaters, induction stoves, large pumps , laser printers , ,microwave ovens - may need larger systems ( 3kVA + ) to run. Solar inverters struggle to handle high motor starting loads and heating loads, so when such loads are to be powered - solar inverter and rest of the system may need to be oversized , which may inflate the system cost to unattractive levels. Some of the Solar off grid or Hybrid systems - can use Grid power as an additional backup , when solar power is exhausted - but switch over to Solar power when it again becomes available - such systems offer flexibility for cost saving and intermittent power situations.
  • Solar powered On Grid AC system - Solar on grid systems can range from 1kw to 1000kw or higher for roof top solar power applications and are installed with existing Grid connections - and these systems can run any load that would be supported by the capacity of user's Grid connection.

Sizing of Solar off grid power systems 

Off grid Solar power systems  have three components that affect their size or ability to cater to loads - Solar Inverter / PCU capacity, Solar Battery capacity and Solar PV panel capacity

  •  Solar Inverter/ PCU/ UPS capacity is decided based on which loads need to run at the same time - i.e. how many lights, fans , computer, fridge, pumps , etc  need to run  - so the kVA or KW capacity of  Inverter is arrived based on the total load to run ( Not all loads may need to run at the same time , this can help to optimize the inverter size )
  • Solar Battery capacity - the amount of electrical units consumed in a day , that has to be supported by the Solar off grid systems - determines the Ampere-Hour (Ah) of the battery ( if the system can be powered by Grid power for some time of the day, this can help to optimize the battery size, while if more than 24 hrs of storage is needed for cloudy days , higher battery capacity may be needed.
  • Solar Panel capacity - The Solar panel capacity is also decided by the electrical units consumed per day as well as the current charging capacity of the Solar battery. Lesser panel capacity may lead to lesser solar power than full day requirement, while too much higher panel capacity will result in un used panel capacity - unless there is any feature to export excess power to grid or other consumers.

Some rule of thumb for the sizing Solar power systems 

  • Every 1kwp solar panel can produce about an average of 3 kwhr ( 3 units) of electricity per day in off grid systems  ( 4kwhr per day for ongrid systems ) . 
  • So if your  loads consume 5-6 units a day - you may need  2 kwp Solar panels and an inverter that can take the 2kwp panel input  ( maybe 2.5kw to 3.5 kw inverter) .
  • To store 6 kwhr ( units ) of electricity per day - you may need battery capacity of about 7.25 to 8kwhr (at about 80% depth of discharge) , which would be approx 600 Ah to 650 ah of 12V batteries ( note 12V batteries come in various Ah capacities with the highest ones about 200 Ah each , and a 200 Ah battery can store a maximum of  200 Ah x 12V = 2400 kwhr of energy). 

Types of Solar system components 

There are different types of Solar Inverters - PWM, MPPT, others  and different types of batteries - Lead Acid, Lithium Ion, others and different type of Solar Panels - polycrystalline , monocrystalline. These come with different price points for some performance and durability premiums - which may be a factor for some applications , but for generic house hold applications - proven technology and value for money may be prime factors to go with.

The World of Solar opportunities ! 

Apart from the above applications - there are  exciting opportunities for Solar in powering stand alone EV charging stations,  Telecom towers, Advertisement hoardings, Remote island installations like hotels, unmanned small machineries and instrument systems.  In quite a few applications - Solar off grid systems with suitable energy storage can be a logical cost effective alternative to running Diesel Gensets, especially in remote locations where diesel has to be shipped from long distances. Solar power systems can be our true decentralized and portable power source - as long we understand what it can do and what it cannot !!

Questions or comments on the above , or more info needed for your specific applications - please drop a comment and we can try to provide a response. 


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