I thought maybe I could make a dent in my home electricity usage by buying a couple of solar panels and a solar generator. A solar generator is a battery that can be charged up and has USB, AC electrical, and DC ports that you can use like a gas-powered generator. My electrical usage isn’t that high, maybe 300 kilowatt-hours per month on average, including the intensive summer months when usage goes to twice that for the central air system. So that only comes out to 10 kwh per day. There are a number of solar generator out there that can store 2 kwh, so if I could fill one of those every day and use that power, I could save 20% of my electricity, however, that only comes out to about 34 cents per day. Still, that’s $10 a month or $120 a year, so eventually a system could pay for itself.
I bought an Aferiy P210 generator at Amazon with 2 kwh of storage. It can power up to 2400 watts from six AC plugs. It is about $600 (links to Amazon are affiliate links, but I’m clearly not trying to sell anything). Although you can charge it up quickly with AC power at up to 1100 watts, it can only take 500 watts of DC input from solar panels, so it would need 4 peak hours of sunlight, which I figured I could get either on my roof or in my driveway. I got two 300 watt panels from a Walmart seller for about $300 and had to buy some cable to connect everything up for another $30. 3 months just to pay off the cables! If I ended up being able to collect more energy than I could store, I could just run stuff from the generator during the day to use the extra power. That would be a nice problem to have. It was key to match up the solar panel output with what the generator could handle. The generator is limited to 11.5 to 50 volts, up to 20 amps, and a maximum charge rate of 500 watts. I got two panels with maximum voltage of 20.5 volts and 15 amps. With two panels, if I put them in parallel, I keep the voltage at 20.5 and the current would go to 30, so that is no good. Instead I could wire them in series and the voltage would combine to 41 volts and the current would stay at 15 amps. If you multiply current and voltage, you get 615 watts. While you don’t ever want to exceed the maximum voltage, if you supply extra current, the generator just won’t draw it and it would be wasted.
The generator weighs about 40 pounds mainly due to the weight of the LiFePO4 batteries (lithium iron phosphate), a safer lithium-ion chemistry that Aferiy says should last 10 years or 3500 charge cycles. It even comes with a 7 year warranty, which is great because it will take 7.5 years to pay for itself. By the time I got the generator, the solar panels and cable had already arrived so I was able to put my panels in my sunny driveway and start charging right away. It came with a 24% charge out of the box. I wanted to test each panel, so I just hooked up one panel at a time and only got 150 watts from each, about half of what I was expecting, though it was already 3 PM and maybe I didn’t have the perfect angle. By 5 PM, the panels were in the shade and power had dropped off to about 10 watts so I unplugged the solar cable. I used the USB ports to charge my phone, iPad, and a portable power bank. Then I used the AC plugs to charge my laptop and run one of my backlit poster frames and a lamp, drawing about 40-80 watts, no sweat since it can do 2400 watts, but it was down to 12% by the time I went to bed. At 1 AM I have smart plugs that turn off the frame and lamp automatically and I hoped the battery would last until 9 AM when the poster is supposed to come on. I set the battery to shut down when it got down to 5% to avoid a really deep discharge and it turned itself off around 3 AM with some beeps that I heard. The next day I was wondering what time I would be able to start generating power. Sunrise is about 6:30 right now and I did have to get up early, but the panels were pretty shaded most of the morning. I thought maybe ambient light would work, but when I plugged the solar cable into the generator, it would just repeatedly click and nothing would happen. The manual says don’t leave it plugged in all the time because if light is sporadic it will keep turning itself on and off. That’s not great if I have to remember to plug it in every day and unplug it at the end of the day. Around 10 AM I was able to plug it in and it started up, telling me it was getting 10-20 watts. I moved the panels a little to be in complete sun a few minutes earlier and by 11 AM it was getting 200 watts and eventually about 300 watts. Nothing higher than that though.
I did get it to 60% charged by time I unplugged it at 6 PM. I plugged in the lamp and poster again and did some charging and the charge was dropping fairly fast. I hoped it would last the night, but it finally shut itself down sometime before I got up. I think a big part of the problem is that when the generator is on, it is drawing maybe 30 watts just to run its screen and whatever electronics it has. So if you are running it for a long time, you are going to lose a lot due to that overhead. From 5 PM to 10 AM when it starts collecting solar power the next day, at 30 watts, that’s 500 watt-hours, 25% of the total charge (30 watts is just a guess, it might be more or less). It has wifi, so you can control it from your phone, but only if you are on the same wifi network. That makes some of the settings easier to get to, but it is pretty slow, taking ten seconds or so to register a setting change from the phone. So I don’t think leaving it powered on to keep the smart plugs running is a very good use of its power. It seems more geared towards just using it for a shorter period of time.
The next day I decided to try using it to keep the refrigerator running, so at 5:00 I carried it into the kitchen and then plugged it in to the generator. The fridge is one of my biggest consumers of electricty, but is still only 1300 watt-hours per day. It takes 140 watts when the compressor is running, but the compressor doesn’t run most of the time. It uses 40 watts when you open the door and the light comes on, then drops back down when you close the door, so I feel like the light really does go off when you close the door. Another possibility would be to put my window air conditioning unit (750 watts) in and power that for a while to help cool the house and maybe take some load off of the central AC, but that is more of an indirect savings than with the refrigerator where every watt-hour used while on the generator is a watt saved on my power bill (except the 30 watts of overhead). It might allow me to raise the thermostat and just cool off the living room with the window unit during the afternoon.
I am not sure why I am not getting more than 300 watts from my 600 watts of panels. Atlanta is kind of hazy and it was also partly cloudy, so the voltage would drop down periodically, maybe to 20 watts when a cloud would go by. The 300 watts was when there wasn’t a cloud. It could be some of the light is being filtered by the haze. The bad thing is we are close to the longest day of the year, so in terms of total solar power I can collect this is about as good as it gets. If I installed the panels on the roof, they would get as much as an hour more sunlight than in the driveway, but would still be affected by trees starting around 4:00.
The Werchtay 250605001 panels sold by Rayscape on Walmart’s website were pretty cheap with very few reviews, but they are real panels, with aluminum frames, not the fold up portable kind. They are advertised as N type panels, which are supposed to be a little better and have 18 bus bars, if that helps. Reading some reviews of panels on Amazon, it is not uncommon for off brand panels to produce less power than they say, whereas Amazon reviews state a more reputable brand like the Callsun 200 watt panels actually produce 200 watts, but would also cost more. Still buy two 300 watt panels that only produce 300 watts for $260 isn’t as good a deal as buying two 200 watt panels that produce 400 watts for $330. I did look at the Callsun panels, but they produce 27 volts I don’t have much of a way of testing if the panels are really 300 watts each, but I could try measuring the amps and voltage while everything is working to see what current is actually going into the generator, since maybe more is going to the generator than it is reading out. My understanding is that if they aren’t getting full sun, they will still provide close to full voltage, but the current will be lower than the max.
There could also be resistance in the cables. There shouldn’t be, I bought heavy duty #10 AWG wire and they are only 30 feet long. I even took the generator outside and hooked it up directly to the panels, but got about the same charge rate bypassing my cables. Looking at the cable that connects the solar cables to the XT90 port on the generator, those wires don’t look like #10 AWG wires. That adapter cable is what came with the generator, so I ordered a heavier duty version for $20 from Amazon and should get it next week. That isn’t going to double the wattage, but maybe I will see some increase. The cables on the panels also aren’t #10, but again, they are pretty short, so losses shouldn’t be much. I don’t think they can be replaced.
Another possibility is the generator isn’t very efficient in converting the incoming voltage to something that it uses to charge its batteries. 50% would be pretty terrible since MPPT DC to DC voltage converters are supposed to be around 90% efficient. Could also be a combination of all of the above. Even though I am only getting 300 watts instead of 600, really the generator maxes out at 500, so I am at 60% of what I expected. I am also taking a hit by charging it down to 5% instead of 0, plus the overhead losses of the generator itself which add up the longer it is in use. So it doesn’t look like there is any way I can hope to save 2 kwh per day.
One advantage to not being able to fill up the generator every day is that it takes away the pressure to use up all of its power every day since it is going to fill up.