Are solar panels the answer to our power needs? (well, most of the time)
If you are planning an off-grid solar system, what can you expect from your solar panels? How many panels do you need? Maybe I can answer these two questions.
On our house we have three 250 watt solar panels with four 12 volt AGM batteries wired in series, so we can operate a 24 volt battery bank. It is more efficient than a 12 volt system.
Although solar panels are rated by watts, watts don’t matter. Only amperes and volts matter. Volts matter for the batteries and amps are what charge the batteries. The amps coming into the system determine if you have enough power for your appliance. First step is to add up the amps needed for each appliance.
In my case we have:
Small freezer – needing 1.4 amps
Lap Top – needing 1.3 amps
Sewing machine – needing .7 amps
Electric mixer – needing 1.8 amps
That is all we have (no lights, no fans), so if everything is running at the same time, we need to generate 5.2 amps from the solar panels just to maintain the battery voltage at about 24 volts. It is obvious that we need to plan our power consumption at night and on cloudy days. At night I only operate the lap top off the internal battery and charge it when the sun comes up. The Mixer and sewing machine are used sporadically so they do not make much difference, but we usually wait for a sunny day and never use them at night. The freezer is the big power drain because it will cycle on and off 24 hours a day. However, at sundown we need at least 25.2 volts on the battery to run the freezer overnight. During the winter, it is not uncommon that we need to turn off the freezer until sunrise.
Power from a solar panel can vary greatly depending on the time of year: temperature, angle of the panel, dirt, ice, snow on the panel, clouds, shadow, and even chem trails affect their performance.
Following is what we experience for our 750 watt array.
At night 0 amps are generated
When there are dark thunder clouds, you will have 0 amps
On a normal mostly cloudy day, it may generate 0-6 amps
On an over cast day when you can almost see the sun, it will usually provide 5-8 amps.
Partial cloudy days are of course better than a cloudy day, but it will average around 8+ amps
On a bright sunny day with ideal conditions it can generate 18+ amps of power.
We have a 1000 watt charge controller from Midnight Solar, but it is like most controllers. It will charge our batteries to a maximum of 29 volts, then go into a float mode, and will not charge the batteries until they drop below 27 volts. A 12 volt system would charge to 14.5 volts and then float down to 13.5 volts.
If you are not getting enough amps from your system to operate your appliances, you might as well turn your inverter off until your batteries are charged. If your batteries go below 12 volts (in our case 24 volts) they will eventually die. Batteries don’t die, people kill them so they need protecting. On those dark winter days when there is limited sun for weeks at a time, we need to use a generator and battery charger to maintain voltage on the batteries. I hate using it, but the fact is a solar array will not work year round, so we keep our battery charger hooked up to our battery bank all the time.
I hope this helps for when you plan your solar system to determine how many solar panels you need. Bigger is better if you can afford it. In a following post I will address our wind turbine and how well it works to charge our batteries.
Have a great day and thanks for your up-vote, Tim and Joann
The answers to these questions are shocking.
Solar panels, and electricity, in general feels so complicated to me. But this is puts some of the things I haven't really understood in terms I can understand. Thanks!
Awesome to see a plan in action! Thanks for the post. I always wondered how much electricity I could produce from a solar system at the house.
Cool! This is some good information! Ill have to share this with my husband. Solar is an idea we have played around with for a while now. His main issue with it is that the batteries are expensive, and will need replaced periodically...
The batteries we have were about $250 each. You are correct, a solar system can be expensive. For us it was our only option. Maybe I will do a post on that.
That would be great! More info is definitely better!
Yes, we have priced setting up different sized solar systems here, and it is expensive no matter what we do. The problem is it will take years and years before it has paid for itself, and those batteries don't last forever.
One of the reasons we wanted to try solar is to be prepared for a grid-goes-down situation, but you would only be set as long as your batteries lasted, and then you would be out of power. Which is better than no power from the get-go, but I just wish there were a better solution.
As time goes by though, the solar equipment does get better made, and cheaper to obtain, so maybe it will become something more people can do in the near future.
Hopefully so!
it is great post, thanks for this great information and it is very good plan,
thumb up dear