Grid Tie and Off Grid Solar Design Considerations for a Northern Climate

It’s January in Western Montana and it’s the time of year that the solar energy discussion tends to be about the lack of solar production.  We’ve had snow covered solar arrays for the past week or more so most arrays aren’t really producing any energy.  This situation is often challenging for a person who has recently bought a grid tie solar array; causing them to wonder if they should figure out a way to pull the snow off the array on their roof or ground mount.  Of course, that decision is up to whoever owns the system.  But if a solar array is sized properly based off the average amount of peak sun hours for the location as well as their kWh use then it’s really worth considering just leaving your array alone and let it do it’s job once there’s more peak sun hours available.  This is because if you’ve sized the system correctly then the array should be big enough to make up for the lack of power production during the winter months.

Now, does the situation change when applied to a stand alone solar system?  My answer is yes and no.  First, what stays the same is both systems start to rely on a different power source during this time of year and both systems can be designed to automatically switch back and forth between different power sources.  The grid tie array switches to use conventional power supplied by the grid and starts to use up the credit it has accumulated over the summer months. The stand alone system starts to use another source to recharge batteries such as a propane generator.

What is different is that the off grid system owner needs to input a lot more system programming in order to have an auto generator start turn on a generator to run loads and protect a battery bank.  There are many ways to monitor your stand alone system during the winter months and time of use is a really important factor.  By practicing good load management tactic’s such as running big loads while battery charging instead of running loads after charging you are really maximizing your system’s lifespan by reducing battery cycling and generator run time.  To achieve this, you need to have a generator that is big enough to put out the amps needed to recharge your batteries within a few hours and also run additional loads while charging.

That’s my argument for a properly sized solar design in a northern climate.  Regardless of whether a system is grid tie or off grid, the system owner needs to be comfortable with the fact that a secondary source of power should always be part of the system.  With grid tie this means using the utility grid provider as the main power source for the winter months and with off grid the additional source is generally a generator.  Along with having a secondary power source properly sizing a solar array and generator to overproduce at desired times of the year is essential for northern climates.


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