Getting Your Off-Grid Power Systems Ready for Winter
Written by Alan Smith
The winter season has arrived on schedule. For those of you in cold and snowy climates, now is a good time to review the maintenance and condition of your off grid power system. For those of you in warm and dry climates, now is a good time to review the maintenance and condition of your power system. Better to check on your system at your convenience rather than when something goes wrong in the middle of the night in three feet of snow. Below is a checklist of considerations for your review.
Seasonal Angle for Solar Panels
If you have an adjustable rack mount for your solar panels, it is worth tilting them to the ideal angle to properly capture the winter sun. An appropriate angle can make a big difference in the amount of power collected, especially during the shorter, cloudier days of the winter when sunshine is at a premium.
The ideal angle for your panels is easily determined. Use the latitude of your location and add 15 degrees. The result is the angle of tilt of the panels, measured up from horizontal that will yield the best harvest during the winter months. Example: Sandpoint, Idaho is at 48 degrees north. Ideal winter angle is 48 + 15 = 63 degrees.
For the folks that have vacation cabins that may only be visited once a month or so during the winter, consider a steeper angle to accommodate easier shedding of snow.
Clear the Snow Off
Seems obvious, right? Keep a broom or brush on a telescoping handle if needed, and clear any freshly fallen snow off the panels on a routine basis. By letting the snow sit and freeze on the panels, it will take that much longer until your panels are collecting again. It’s a horrible feeling to be sitting at work, when the grey skies open up to sunshine, and you know your array is sitting at home with six inches of snow on it.
Now is the time to do your annual maintenance. Besides the basics; oil, belts, coolant level, air filter, and spark plugs, be sure to check your owner's manual for items specific to your machine.
Check on the starter battery. If the generator has not been run since the previous winter it is very likely that the starter battery may be dead or heavily discharged. Replace or recharge it before you need it.
Batteries can be kept in a relatively cold area, with a couple of considerations. The energy storage capacity of batteries in a cold climate is temporarily reduced. Instrumentation such as battery monitors can be fine-tuned to reflect a more accurate state of charge. Temperature sensors for both your charge controller and inverter/charger should also be used for optimum charging points of your batteries.
Fully charged batteries, being used on a daily basis, will not freeze until the temperature drops to -70 degrees F. A battery at 50% state of charge, though, can freeze in temperatures as “warm” as -10 degrees F. Don't let the batteries get too low.
The sulfuric acid in batteries that are being stored or lightly used will tend to stratify. This means that the water begins to separate out from the solution, resulting in layers more like water near the top of the battery and denser layers of sulfuric acid towards the bottom. If this occurs, it is very possible for the water layer to freeze at temperatures near 32 degrees F and crack the battery casing.
Flooded lead acid batteries respond best to daily use, so we have to make the best of a non-ideal situation when the power system will be unattended for extended periods of time. Depending on your installation and equipment there are a couple of options available, and opinions on the best approach will vary. If you have an automatic generator start (AGS) function tied to your inverter/charger, and you consider your generator to be highly reliable, the inverter can be left on so that a charging source is available if the panels become covered in snow. If you do not have AGS, turn the inverter off. Turn all DC loads off. Leave the charge controller on, with the goal of supplying at least a bit of float charge to the batteries each week. If available, ask a neighbor to check your array after any major snow storm, to brush the snow off.
One school of thought suggests reducing voltage settings, to reduce water consumption, and setting the equalization to automatically occur once per month.
Tuning Gear, More Panels, Winter Behavior
The sun tends to be shy in the winter. Let’s take advantage of the days it does show up. An experienced system owner will know how their system responds to normal charging and equalizing. Consider increasing the absorb time and the equalize settings on your charge controller for the winter months. Keep a notebook handy in your power room, and write-down the summer and winter settings that you find work best, so you know what to change them back to when the seasons change.
Search mode on an inverter should be enabled year-round, but especially so during the winter. A couple hundred watt-hours per day can make a big difference.
Here's a controversial tip for your consideration. You honestly can never have too many solar panels, we can all agree on that. How much is too much though? Advocates of “winter” arrays will say “more, more, more!” The idea being that if you can manage to get one good sunny day a week during the winter, you'll really harvest some good power and minimize your generator run-time and fuel use. The flip side of the coin is why spend all that extra money, when it will just result in massive overkill on system design during the summer months. It's up to you. Keep in mind that pricing on solar panels is currently at an all-time low!
Long time off-gridders will tell you they simply change their behavior during the winter months. Leaving the coffee pot on for an hour is fine in the bountiful sunny days of summer, but the coffee maker gets turned off after 15 minutes in the winter, and the coffee goes into a thermos. Or better yet, wait until you get into work and make the coffee there! Less TV time, and more book reading cuts down on the power used. Simple conservation in several small steps can add up to a big difference in the amount of power needed during the winter.
In conclusion, it's better to take care of your system now, than to experience failures at the most miserable time imaginable. Routine maintenance and a thorough knowledge of how your system responds to your daily usage will serve you well, not only for the winter, but for the lifespan of your system as well. Stay warm and don't forget to keep your snow chains, a shovel, and a bag of sand in the trunk of your car!