EcoRenovator - View Single Post - Chinese 300w MPPT Grid-Tie inverter

SolarFix · 01-29-11, 11:22 AM

XRINGER: Thanks for the post on the Chinese MPPT inverter!

There is, at least to me, a very good reason for being able to deliberately ISLAND a grid-tie solar array. That reason is disaster preparedness. Tornadoes, Hurricanes, Fires, Earthquakes, Accidents, and Civil Unrest happen. Our power grid is pretty reliable... but it wouldn't take much for areas to have very prolonged outages. A disaster interrupting basic services (water, sewer, electric) of a couple weeks or more would drive most people out of their homes. I'm fortunate enough to have a well, a septic system, and a wood stove - BUT, the well pump requires electricity.

If, by replacing one grid-tie MPPT inverter on my solar array with a true-sine wave off-grid micro-inverter, I can have daytime power, then I have water and can stay in my home through tough times. -- Of course, taking such an action INCLUDES opening the main circuit breaker at the power meter so linemen are protected.

Being able to go "off grid" in this manner has a few challenges because grid sensors look for both frequency and voltage. If the grid goes down, a solar array won't be able to drive all the neighbors' loads, so the voltage will fall below specifications and trigger a shutdown. Furthermore, the array might not be able to drive all the loads in the house - particularly if there's not a lot of sunshine. So... you would have to disconnect the grid AND shutdown all unnecessary loads in the house. UPS systems for critical items like the fridge, freezer, and well pump may be required to provide surge current for start-ups. If you're going to try and trick grid sensors with a tiny 200W inverter... all loads in the house will have to be shutdown until the array is back online. Then...when a couple clouds come by and available power is less than the demand, voltage will fall below spec and the array will shut down again.

Tricking the GTI is only one part of the problem. Dynamic loading is another critical feature. Using something like the Enphase Envoy - or better yet, direct communications with the inverter modules, smart-loads could be implemented that could negotiate for "online" time with other loads based on available power and thus improve emergency system reliability.

Think it through, be prepared, and in doing so, be part of the solution in hard times.

01-29-11, 11:22 AM	#12
SolarFix Be Prepared Join Date: Jan 2011 Location: Idaho Posts: 5 Thanks: 0 Thanked 0 Times in 0 Posts	Deliberate Islanding XRINGER: Thanks for the post on the Chinese MPPT inverter! There is, at least to me, a very good reason for being able to deliberately ISLAND a grid-tie solar array. That reason is disaster preparedness. Tornadoes, Hurricanes, Fires, Earthquakes, Accidents, and Civil Unrest happen. Our power grid is pretty reliable... but it wouldn't take much for areas to have very prolonged outages. A disaster interrupting basic services (water, sewer, electric) of a couple weeks or more would drive most people out of their homes. I'm fortunate enough to have a well, a septic system, and a wood stove - BUT, the well pump requires electricity. If, by replacing one grid-tie MPPT inverter on my solar array with a true-sine wave off-grid micro-inverter, I can have daytime power, then I have water and can stay in my home through tough times. -- Of course, taking such an action INCLUDES opening the main circuit breaker at the power meter so linemen are protected. Being able to go "off grid" in this manner has a few challenges because grid sensors look for both frequency and voltage. If the grid goes down, a solar array won't be able to drive all the neighbors' loads, so the voltage will fall below specifications and trigger a shutdown. Furthermore, the array might not be able to drive all the loads in the house - particularly if there's not a lot of sunshine. So... you would have to disconnect the grid AND shutdown all unnecessary loads in the house. UPS systems for critical items like the fridge, freezer, and well pump may be required to provide surge current for start-ups. If you're going to try and trick grid sensors with a tiny 200W inverter... all loads in the house will have to be shutdown until the array is back online. Then...when a couple clouds come by and available power is less than the demand, voltage will fall below spec and the array will shut down again. Tricking the GTI is only one part of the problem. Dynamic loading is another critical feature. Using something like the Enphase Envoy - or better yet, direct communications with the inverter modules, smart-loads could be implemented that could negotiate for "online" time with other loads based on available power and thus improve emergency system reliability. Think it through, be prepared, and in doing so, be part of the solution in hard times.