January 29, 2020

Solar Power Day

Back porch: freezer, inverter, solar panels in background.

After all the excitement, anticipation, and build-up, solar power day was exceedingly uneventful. Switching our deep freezer from the grid to our solar electric system was just a matter of closing a circuit breaker, moving the plug from one socket to another, and turning on the inverter.

The back of the inverter with freezer plugged in.

We checked the freezer light—all systems go. Now we monitor.

Charge controller read-out screen.

There are two things we're keeping an eye on. One is how many amp-hours our freezer will use during a 24-hour cycle. We have 705 amp-hours stored in our battery bank, so we need to know how long the bank alone can keep the freezer running during a string of sunless days. The charge controller keeps track of this, so I must become familiar with the 100-page section in the manual dealing with reading the summary screens.

Charge controller manual

The other thing to monitor is the battery State of Charge (SoC). This is the percentage of energy still available in the battery bank. SOC varies by battery, so the exact numbers must be obtained from the manufacturer. Obviously, the goal is to not drain the batteries too low. This is of the utmost importance, because it relates directly to the life and longevity of the batteries.

My very first deep cycle battery was sealed, so I learned to check SoC by monitoring battery voltage. Turns out, it's more complex than that! To be accurate, the specific gravity of the batteries needs monitoring. This should be checked with regular maintenance anyway, but the voltage is an indicator, so we'll keep an eye on that. Most folks seem to use 50% as their bottom line, but others don't let their batteries drain that low to increase battery longevity.

What's surprising is that the 50% doesn't refer to voltage; it refers to battery chemistry. So for a 12-volt battery, 50% SoC isn't 6 volts, it's 12.10. That's why measuring the specific gravity is more accurate. But voltage is an indicator, so it's a quick and helpful way to keep an eye on things. Readings are always taken when the batteries are at rest, i.e. neither charging nor discharging.

Everyone who has gone to solar says the learning curve is such that everybody kills their first battery bank. We've done our best due diligence, so I sincerely hope that's not the case for us. But I know better than to assume anything!

I'm monitoring a few other things too. One is back porch room temp. For that I have a fridge and freezer thermometer that records highs and lows.

I like that these can be switched from °F to °C.

It came in a two-pack, so I have one on the porch and one in the pantry. I can monitor these rooms to get an idea of the temperature range during a particular season. They'll help us evaluate experiments to keep the rooms cooler.

I also bought two probe thermometers for monitoring the internal temps of freezer and upcoming chest fridge.

These come in Fahrenheit or Celsius only.

With a probe, I don't have to open the freezer or fridge door to check its temp. I've learned that my freezer turns on when the internal temp gets above 4.5°F (-15.3°C). It turns off when it reaches -11°F (-23.9°C). I'm sure that's fascinating information! LOL

Of course, we're curious how much we'll save on our electric bill. We still have a few more days left in the January billing cycle, so we really won't know the answer to the question until early March, when we get February's full bill. I'm expecting it will drop somewhat with the freezer now on solar, and even more once we get rid of my pantry fridge, an old energy guzzler. We plan to replace it with a chest fridge soon (watch this blog for more on that!)

When we started homesteading ten years ago, we wanted alternative energy, but for many years that seemed impossible. Step-by-step here we are. It's not what we originally envisioned, but it's good. Like all technology it isn't perfect, but it meets a true need, and that's what's important.

The next step is the chest refrigerator, and then we'll turn to phase 2 of our three-part plan to increase food storage efficiency: improving the pantry.

See also "Chest Freezer to Fridge Conversion."

Solar Power Day © January 2020


Sam I Am...... said...

You 2 are awesome! I used to do specific gravity tests on urine when I worked in the medical lab. Not sure how you would do it for a battery! LOL!
This is truly fascinating and glad that solar is finally becoming less expensive to install. I should get some roof panels here as we have so many sunny days here and my house faces south. I should look into it if I stay. Congratulations!!!

Boud said...

Congratulations! No ribbon cutting? I really didn't know how complex it is to install solar. What a great job you did.

Woolly Bits said...

great! I am sure you'll see the difference, never mind if it's not huge. one step more to be independent! and having electricity via the mains isn't perfect either - we have quite a few power cuts, where we have to worry about temperature feelers in the ovens, fridges, freezers etc.! I don't think there is a perfect solution, we just have to work around what we have...

Leigh said...

Sam, thanks! For battery specific gravity there are hydrometers that can be purchased in any automotive store or department. Inexpensive and easy to use.

Boud, almost a let-down when it got down to it, lol. It was more complex than I first thought, although I knew there would be a lot to learn. So there is a sense of accomplishment for making it all happen. I'm not going to congratulation myself too loudly, however, because we still have to learn how to keep it going in tip-top shape. :)

Bettina, I agree, there is no perfect solution. The most basic low-tech approach is to learn to live without being dependent on electricity of any sort. From what I read, our power grid isn't in the best of shape, yet technology wants to push onward which requires more and more energy. Sometimes I wonder how it's all going to work out down the road.

wyomingheart said...

Wow! You have to celebrate this milestone! You have energized me to get our solar panels up this summer. Do you think the freezer fridge will impact your battery discharge during cloudy days? We are very happy that you are sharing your knowledge and experience with us. I know outcomes will vary, according to use and setups, but we are excited that you are giving hands on experience. Great post!

Leigh said...

Wyomingheart, thank you! I'm always delighted to encourage others on their own journey toward self-reliance! I should have mentioned that it isn't just the freezer and chest fridge that will draw from the batteries. System components like the charge controller, inverter, and vent fan all use some of it as well. So my total amp-hours and kilowatt-hours will include those in the read-out totals. But we need them, so it's all good to know.

Ed said...

I remember the days of checking battery fluids at every oil change with a hydrometer. Can't say I've even seen one in over a decade though as you mentioned, they are probably around at any automotive place. Seems like if one was smart enough, this would be a good programming exercise to have a computer check all the data and make changes on the fly but I'm not the one who would be able to do the programming. Those days have passed me by.

Nancy In Boise said...

Wow quite a project!

Leigh said...

Ed, I was thinking the same thing about the hydrometer. I hunted for digital models, but nothing for checking car batteries. It would be great to stick in a probe and get an accurate digital readout.

Nancy, and a very welcome one!

Unknown said...

That's exciting - congratulations!!

I just paid my first electric bill in ages - obviously my panels weren't able to keep up in Jan/Feb with my electric needs, sad. Hopefully that's the only bill I'll have to pay each year, other than the $20/month to stay on the grid!

Hill Top Post said...

Yay for Solar Power Day! I am sure you have done your homework well so that the battery will have a long productive life. Happy sunny days to all of you who have worked so hard!

J.L. Murphey said...

Woohoo!WTG! Congrats!Expertly described along the journey too!

Leigh said...

Debbie, oh my. I'm sure it was a "well darn" moment. But you have backup, and I know that's a relief. The grid is still my backup too, except that I must manually move the freezer plug from the inverter to the house.

Mary, I hope we've done our homework! So much of mastering a skill comes with experience, however. Here's hoping for smooth sailing!

Jo, thanks! I like having notes to refer to in case we tackle this project again. We have two more solar panels, and have thought about using them for the workshop for barn lights and Dan's power tools. We'll see!

Retired Knitter said...

Congrats on what you have accomplished. Looks too complicated for me. haha!

Behind on all my reading but will catch up soon.

Leigh said...

RT, the charger manual looks incredibly complicated! As long as I can figure out how to keep track of the batteries and usage, I hope it's enough!

Quinn said...

"Uneventful?" "Just moving a plug"? After all the planning and researching and pondering and considering and decision-making and equipment-gathering and...
I mean, didn't you and Dan hold hands and sing a song of celebration or something?
I would have! I may do it now, on your behalf!

Leigh said...

Quinn, we got barbecue for dinner! :)

Cathy Kennedy said...


This sounds like a lot of interesting info should I ever want to learn more about solar energy. There's sure a lot of things to consider. Best of luck as y'all navigate your way through the process of learning as you go in what works best. Thank you for visiting me on Thursday taking a peak at my latest artwork. Have a good weekend!

CityCreekCountryRoad said...


Congratulations! There's been so much to learn and Dan and you keep plugging away.
I love reading the technical descriptions even though 95% goes over my head.

In last month's Popular Mechanics, I read about a truck in Switzerland running on kinetic energy stored in a battery. It goes up and down mountains from the gravel mine to a cement factory. What will people think of next?

City Creek Country Road

Leigh said...

Cathy, I appreciate that. There's a lot of good starter information out there, but the particulars were pretty much learn-as-we-go.

City Creek Country Road, thanks! Yes! They are coming up with so many interesting alternatives. It's fun to be part of it.

Chris said...

Wow, there really is a lot to it! Every time I hear a conversation about the specifics, I always learn something new. The rule of thumb I heard relating to how low you can go, with battery storage, is not to dip below 70% charge. Of course, I have no real life experience with it, but thought I'd share in case it might be useful to you. :)

Anyway, well done! I'm looking forward to seeing that March bill, along with both of you.

Leigh said...

Chris, there's more to it than we first imagined! On the other hand, basic information at first at least gives a grasp of the concepts. Too many details would have been confusing at first, but the questions logically presented themselves and we built the system.

70% charge seems to be a highly recommended number, so that's likely what we'll aim for too. So far so good. Even on overcast days we generate a little, and the freezer doesn't take much. But we still keep a close eye on things!