REP LLC Academy

Hello All,

To all the technical people out there who would like to join the solar force or who are struggling to learn the basics of designing a residential solar PV system, here is a quick description of how to design a system.

Please follow these steps:

1. Determine the annual kWh usage for your house.

2. Now lets assume that 1 kW of solar PV produces 110 kWh per month or 1320 kWh/Yr (applicable to the East coast)

3. Divide your annual kWh usage (step 1) by 1320 to figure out the kW system size you would need to produce the desired kWh in an year.

4. Measure your roof using google maps.

5. Layout of the panels would be in portrait mode. Lets assume we are using SolarWorld SW 280 Watt panels. Panel dimension: 39.41″ x 65.94″

6. Lets say your roof has a dimension A” x B”. “A” being the length and “B” being the depth

# Rows along the depth of the roof= B / 65.94

# Panels in a row- along the length of the roof= A / 39.41

7. Now from step 3 you know the #panels you needed to offset 100% of your usage and from step 6 you know the actual #panels you can fit on your roof. If #panels you can fit is more than the #panels you need to offset 100% usage then you would only install the number of panels you need to offset 100% usage.

8. At this point we have figured out the number of panels to be installed. Now we need to figure out the stringing in to the inverter.

The following link takes you to different sizes of residential string inverter, Fronius- http://www.fronius.com/cps/rde/xchg/SID-5ECEF354-FAFFD472/fronius_usa/hs.xsl/2714_11381.htm

To start with the stringing, we need to check the operating voltage range of the inverter which has the maximum and minimum DC input voltages that an inverter can handle.

Maximum # panels in a string = Max operating voltage of inverter / Open circuit voltage of solar panel (Voc)

Minimum # panels in a string = Min operating voltage of inverter / Voc

# Strings = Max DC input current / Solar Panel’s short circuit current (Isc)

Always check the maximum number of allowable string into an inverter. For example, Fronius Primo 5.0-1 208-240 has 4 DC connection terminals, which means we can input 4 strings into that inverter.

9. We need to now determine the rating of over current protection devices. We need an over current protection device between each DC input string and the inverter and then one over current protection between the inverter and the point of interconnection (which could be a breaker in the main electrical panel in case of load side connection and could be a supply side tap in case of supply side connection)

10. For overcurrent protection devices:
DC side (before inverter)- The current of one string in parallel = Short Circuit current of one panel (Isc) x 1.56.

AC Side- Maximum output current of the inverter x 1.25

11. Point of interconnection: According to the 120% rule, you cannot install a solar feedback breaker greater than 20% of the main electrical panel’s rating. So figure out the Amperes of the service coming to your house (Should be on the main electrical panel) and check if the inverter’s maximum output x 1.25 is greater than or lower than 20% of Main electrical panel Amperage.If it is less than we can install a breaker, if more then we need to do a supply side connection (Tapping into the utility wire between your meter and the main electrical panel).

Hope this helps. Comment on this blog with your questions.

FYI- every inverter manufacturer have their own string sizing tool where in if you plug in the # panels, and panel wattage, it would tell you how many strings and how many panels in a string you should design.

Lighting the way forward one solar lantern at a time

Since time immemorial, the sun has helped blossom life on this planet which we fondly call ‘Mother Earth”. The sun’s limitless and tremendous energy has created and nurtured life for such a long time making it an obvious choice when the question of sustainable life on earth is raised. 

The inception of Responsible Energy Partners was done based on a firm belief that Solar Energy in the 21^st Century is not an unreliable, non-conventional source of energy, but an economically viable alternative fuel to the likes of Diesel, Petrol, Coal and Natural Gas. Headquartered in Maryland, USA, REP has gone forward in realizing the true ‘Solar Powered Dream’ through affordable and easy to install Solar Panels having the capacity to run a typical American household. 

With the recent boom in the alternative energy market there are myriads of solar energy companies that all claim to provide safe and affordable solar energy for all. So what is it that makes sets Responsible Energy Partners apart? I would say it is our commitment to provide clean and accessible energy to the people living in the remotest corners of the world. Even to this date there are around 1.2 billion people in the world without access to electricity and around 2.6 billion people without access to clean cooking facilities and as a part of a promise the founders made to themselves at the inception of this company we hope to slowly but steady bring this number down to 0 by the end of 2030.

As part of a pilot, project Team REP is going to donate one solar lantern to a family without access to electricity in energy starved regions of the world. To kick it off, we have decided to work with a non profit organization called ‘Bihari More Education Project (BMEP)’, based out of Durgapur, town in the state of West Bengal in India. 

The Bihari More Education Project (BMEP) started as an independent initiative by students of a major engineering college in India to nurture and mentor the underprivileged kids in & around the campus. 
The BMEP team is doing a tremendous job of giving a future to the underprivileged kids of the area, kids who’s only hope of escaping poverty and destitution is education. I urge the readers to kindly check out their Facebook page and help them out in whatever manner you can. 

That being said, it is always a challenge There is hardly any electricity in the slums where they live, which means total darkness after nightfall. The harmful smoke from the feebly burning oil lanterns and oil lamps only add to their woes by causing many respiratory diseases in children and adults alike. Most fall prey to eye problems early in life due to poor lighting. The kids are forced to complete their school assignments before nightfall which also deprives them of quality play time.

REP with the help of our valuable customers have pledged to donate Solar Lanterns to these families in the hopes that  the children growing up in these areas become valuable participants in the development of mankind. And with more and more projects coming up, REP hopes to light the way forward, one solar lantern at a time.

Kids posing with the solar lanterns!

The REP interns Subhodeep and Atreya helping distribute the lanterns. The smallest effort counts and they are making it really count.

Shubhodeep explaining how to use the lanterns.

After studying under street lamps for years, these kids now have a hope to a brighter future and each one of them deserve every bit of it!