I have a 3kW on-grid solar system running on my roof top for almost a year now. I’ll share the things I learned, some technical details and my thought process while selecting the system. Hopefully this information helps if anyone is looking forward to setup their own.
Disclaimer, this might sound like an ad for Enphase energy. And that is because I’m genuinely impressed by their engineering. I will try my best to be as objective as possible.
3kW total capacity
At the moment in Kerala the rate of energy exported to grid is around ₹4 per kWh and ₹8.5 per kWh for import. Because of this I decided to match plant capacity with our consumption instead of getting a bigger one like 5kW.
Getting solar panels to make money by exporting to grid may not be a good reason to get it in my opinion. Get it if you can maximize the home utilization, aspire to be energy self sufficient, want to reduce emissions and promote renewables. Energy abundance you achieve from this will change a lot of decisions and trade offs you make for the good. I might even dare to say standard of living is directly proportional to the energy you consume and solar makes it cheap and guilt free.
The system produces 15 kWh on most days. More than 10 kWh is guaranteed if there are no power outages. Around 5-6 kWh if there are dense rain clouds. 15 kWh per day is more than enough for us. Rest is fed to grid and whenever we charge EV we will be consuming from grid and reach to a net zero export. And if there is rain our usage is anyway less because AC/fans wont be running, pumps wont be running because most of pump use is for watering plants.
Enphase IQ7A micro inverters
These are low power (< 400W) inverters that you can attach to each solar panel and they convert solar 24V DC power to normal household 230V AC then and there. They are all connected parallel to get the full 3kW power and are controlled by another module called Envoy.
Advantage of this configuration is that even if one inverter stops working rest of them will continue to produce energy. And if one solar panel degrades or doesn’t get enough light due to tree shades or has more dust on it etc. it won’t affect other panels’ production. This is how our public grid works, multiple power plants work together to match the demand. These micro inverters essentially create a micro grid.
In conventional systems if the main inverter fails then the whole system goes down. It is a single point of failure. And if one panel has lot of shade it will reduce the system efficiency as the panels are usually connected in series.
6 x 500W monocrystalline solar panels from Trina
Monocrystalline panels have higher efficiency and power output but at a higher cost. These also have very less annual degradation, ie. how much of the efficiency is lost per year. For these panels the specification says they will maintain at least 85% efficiency after 25 years. This was the most important aspect for us.
In conventional systems a large inverter will produce lot of heat and need fans to cool it down. It might require indoor installation to protect from weather. But since micro inverters deal with less power they produce less heat and has no moving parts. So they are completely weather sealed and water and dust proof. This increases their reliability and they are able to guarantee longer life. Enphase products also conforms to many safety standards (UL, IEEE).
So the installation is completely outdoors. This was important to me because I didn’t account for such space when I designed the house. And there is no complicated wiring required.
We spent a month related to regulatory things. Actual installation was done in a day.
There is an app to monitor the performance of panels if you connect Envoy module to internet via WiFi. This is optional. With an additional sensor (Current Transformer - CT) app can also monitor your home energy use. This is really useful to understand our energy consumption behaviors. There is also an API to get the data from Envoy if you want to use it for home automation purposes.
From our observation you don’t have to clean solar panels that often. There is no visible dip in the production when solar is covered in some dust. Especially if you get rains every now and then panels are automatically cleaned. But my dad loves to do it anyways.
Repairs should be easy in theory. The entire system runs on 230V AC unlike conventional systems which uses >300V DC lines. So no special tools/wires/learning are required for maintenance. Every component is pretty much plug and play. Your usual electrician can work on it. I do a little bit of electrical work in my house but I never got a chance to do anything on this system because it never had an issue so far. You can also buy replacement parts right from Enphase store.
Extending in the future
Families get bigger and so does the energy consumption. In this system I will be able to add more panels and micro inverters fairly easily. In conventional systems you might have to replace the inverter, the most expensive part, to match the capacity. And the installer told me you will have to get permission from energy distributor only if you are increasing the capacity by a lot like upgrading 3kW to 5kW. If you are adding only one more panel you don’t have to. Envoy is also designed to handle 3 phase, only wiring changes are required for the upgrade.
The most important thing I’m looking forward to is the battery pack. I was told that battery pack launch in India got delayed due to some government regulations. This seems to be the case with every portable battery pack products (Ecoflow, Jackery, Anker). Adding this to the system is also straightforward. They are simply the same micro inverters used with solar panels, but attached to Lithium ion Phosphate batteries (this is a safer, fire proof variant of Lithium ion). This essentially converts the system into a hybrid one, but without the catches.
Adding battery packs brings a lot more fun controls. If you are getting a small battery pack then you can run system in a normal “backup” mode where system will switch to batteries during power outages. If you can get larger or multiple battery packs then you can run your system in a “grid independent” mode. This maximizes the battery use and uses grid power as little as possible. This brings it in line with Tesla Powerwall in terms of functionality.
This is the only downside. It cost me ₹2.6L for a 3kW system. This is on the expensive end. I didn’t get any subsidy because that is applicable to only panels from select manufacturers. If your focus is economy then you will be able to setup a system with same capacity for 80K-1L less. But I find more value in the engineering intricacies, extensibility, self repairability and the peace of mind that comes with all of it.
Even though my system is rated 3kW, maximum power it will output is 2.2kW. This one is hard to swallow. There are many factors at play - solar panel efficiency, inverter efficiency, solar irradiation changes etc. But most important reason is using inverters rated for lower power than solar panels connected to it. It is called over sizing and there is a research paper on why this is efficient and economical long term.
My system was commissioned on end of May 2022. So far we have produced 3,730 kWh. For a year I expect it will be ~4400 kWh. At ₹8.5 per kWh that is ₹37,400. If we do the math this is ~14% return (did I beat the index? :P). If I consider ~₹25 per kWh, the standard rate at fast chargers, for charging car this will be higher. If I were to go by the economy route and bought a cheaper system for 1L less, this will be ~20% but without guarantee on the durability of the parts.
Enphase is a US company. But a significant chunk of inverters, including the one in my system, are manufactured in India and are exported to other countries. And co-founder Raghu Belur is a Bangalorean.