How do you select Solar Off Grid Power System Components

 So you have decided to go for a Solar Off Grid Power system for your Home, Office, Shop or any location - and now its time to select the right critical equipment of your off grid power system.

If you have checked our previous blog on basics of Solar Power systems - we had listed the basics of sizing solar power systems and also reviewed what type of devices can run on solar power . Here we are going to talk about the types and uses of Solar Inverter, Solar Panels and Solar batteries for Solar Off Grid Power System.

Solar Inverter is the critical device of a Solar Off Grid power system that converts Direct Current (DC) to Alternating Current (AC)  and so we will start with selecting Inverter first. Solar Inverter or Solar UPS or Solar Power Conditioning Unit (PCU) for small Solar Off grid power systems are off broadly two types - Pulse Width Modulation (PWM) systems and Maximum Power Point Tracking (MPPT) systems. PWM systems provide basic functions of battery charge control and providing Solar power on priority - so that the inverter charges batteries with DC power from Solar panel and this battery power is provided on priority to the loads , instead of  providing Mains power or Grid power,  even if Mains power is available. The PWM inverter cannot directly provide power from Solar Panel to the loads, it powers up batteries with Solar power and then provides battery power to the loads. PWM inverters usually can be connected with solar panels capacity in kW only for a portion of their kW capacity, they may not be able to handle solar panels to their full rated capacity - for example a PWM PCU of 1 kw capacity may take a maximum of 600W to 700W of Solar panel kwp.

A MPPT solar Inverter has the ability to process the DC power from Solar Panels in different ways - it can either supply full power from Panels to load, it can use the full or partial power to charge batteries and it can  provide combined power from solar panel and power from batteries to meet the load. As a result MPPT inverters can maximize the usage of Solar power generated by the panels. MPPT inverters can usually be connected up to their full kw capacity with kwp of solar panels. MPPT inverters are about 60 % to 100% more expensive than PWM Inverters of the same capacity.

So if you are planning for light usage of Solar power for lighting, fans, computers, TVs-  primarily during non sunshine hours (for about 12 hours a day) and looking for a cost effective solution - PWM type solar inverter would be better choice for you. If you would like to maximize power from Solar panels - with your loads running during daytime as well as non sunshine hours, and with a consumption of power beyond 15 hours a day- then a MPPT inverter would serve you well. Solar inverters are offered with warranties of 2 years to 10 years by manufacturers - but are expected to work up to 25 years with any break down maintenance as required.

Once you have finalized on a Solar Inverter - then you can look at selecting Solar Panels. Before we go into types of Solar panels - One quick information for those not familiar with which Solar panels sizes are available in the market, For a small off grid solar power system- the solar panels would be in the range of say 50Wp at the low end to about 350Wp or 400wp at the high end - so when you decide on your Solar panel total capacity you need to use multiple panels of available sizes to  achieve say 1kwp or 2kwp solar panel capacity.  

While there are quite a few variety of Solar PV panels in the market currently - the most common type of solar panels used for small off grid solar power systems are either polycrystalline or mono crystalline. Polycrystalline PV panels have been market for a few years and provide DC power with efficiencies of  15% , to 18% which translates to an output of  3 kwhr to 4 kwhr  (electrical units) per day for every 1kwp Solar panel installed. Monocrystalline panels are more efficient in the range of 19-21% and provide more output for the same kWp capacity, and they are also more expensive by about 30% to 40%. 

If you are looking for basic solar power system with no space constraints for PV panel placements and a limited budget Polycrystalline PV panels would be the first choice , if you are looking for a high efficiency system to maximize power output from Solar panels then you can go for Monocrystalline PV panels. The last factor in Solar Panel selection is to ensure that your Solar panel DC output voltage matches the input DC voltage of your Inverter - it could be 12V, 24V or even higher. Some times you would have to connect your solar panels in series to achieve the input voltage for your inverter. Solar Panels are static components have a predicted life time of 25 years - with some companies even offering performance warranties up to 25 years. Based on these factors you can go for any of the solar PV panels in the market for your solar power system.

There are other types of panels such as Bi-facial, Building Integrated PV, Thin film PV which are not commonly used for small solar off grid applications - so we will not be talking about them in this blog.

Finally - the last major component of your Solar Off Grid power system are the batteries. In Solar off Grid System the batteries get used quite heavily and are subject to many cycles of operations during their lifetime-so its important to select the right type of battery for your system to get the right performance and life. The two broad categories of batteries for small power storage systems are Lead Acid and Lithium Ion . Common Lead Acid batteries with liquid electrolytes in them ( sealed or non sealed type) generally used for power back up are of C20 class - they need 20 hours to charge fully if drained, whereas Lead Acid batteries recommended for solar duty are C10 - which means they can charge fully in 10 hours and they also have ability to handle higher number of cycles of charge and discharge. Solar duty C10 lead acid batteries come with warranties 3years to 5 years and expected lifetime of about 7 years. 

Lithium Ion batteries are compact and have more power density , they can also charge faster and have higher life up to 10 years - however they are about 100 % 150% more expensive than Lead Acid batteries of same capacity, as the market for Lithium Ion batteries of such storage capacities is still developing. Its expected that the strong growth of Electrical Vehicles will also expedite the market growth of Lithium Ion batteries that can be utilized for such Energy storage systems. Since batteries come in different voltages 12V, 24V and higher - the voltage rating of the battery has to match with the rating of the selected Solar inverter. Batteries can also be connected in series or parallel to achieve the correct voltage  levels and  current flows. Battery capacity in given as Ampere-hour rating of the which can be  chosen based on the number of electrical units to be stored per day for your system , batteries for solar power systems are  usually available in the range of 60Ah to 200 Ah for 12V batteries or other voltage ratings.

So that's a summary of quick selection criteria for Solar of grid power system - which we hope will help you to select the key components of your Solar Off Grid Power System. If you have not checked our previous blog called Solar Power Demystified on tips for sizing the capacities of Solar inverter, Solar Panels and Solar batteries for your solar Off Grid power system - please check that out. We will be talking more about how to utilize solar off grid for different applications in our next blog.  Thank you!