I know many of you have been wanting this post for a while, but it’s finally here: my solar panel system for my tiny house. I wanted to get the feel for what it is like to live off the grid so I could share more details with you all about what it’s really like.
So first, the high level details of my system:
- 2.25 Kw panels – Nine, 250 watt panels
- Batteries 740 amp/hr total – Eight, 370 amp/hr 6 volt Trojan L16 flooded lead acid
- Cost for parts about $10,000 (excluding tax and shipping)
- Off grid, battery bank, plus 5,550 watt backup generator
- 24 volt system
- (9) Canadian Solar CS-6p 250 Watt Poly Black Frame (Spec Sheet)
- (1) Schneider SW 4024 (Spec Sheet)
- (1) Schneider MPPT 60 Charge Controller (Spec Sheet)
- (8) Trojan L-16 6v 370 AH Flooded Lead Acid Batteries (Spec Sheet)
- (1) Schneider System Control Panel (Spec Sheet)
- (1) Schneider Interconnect Panel (no spec sheet)
- (1) Midnight Solar MNPV 80AMP Dinrail Breaker (Spec Sheet)
- (2) Midnight Solar Surge Protection Device AC/DC (no spec sheet)
- 50 Amp RV power Inlet (Spec Sheet)
Before anything I needed to determine the best placement for the solar panels to make sure it had good solar exposure and didn’t fall into shadows too much. To do this I used a tool called a “solar path finder” which is a semi reflective dome that you position at the location, then snap a photo. The photo is then loaded into a program and spits out a whole bunch of calculations.
So once you upload the image into the software and then trace the treeline outline, you enter in your location, date and time. It then can calculate how much power you’ll produce based on 30 years of weather patterns for your exact location and tree coverage.
Then it spit out all the calculations:
With that in mind I knew what I could expect out of the system I had designed. It also was a way to verify my assumptions.
Once I verified that the system was going to be well suited to my needs I had to build my panel support racking. I did this out of pressure treated 4×4’s that were each 10′ long. These things about about 300 lbs each so I don’t have to worry about wind picking up the panels. I opted to build them because it was cheaper than some of the turn-key option out there and most of the for purchase ones required me to cement in the ground; I rent my land, so I wanted a mobile solution. The racking is technically mobile, but not easily so. If I remember correctly it was about $500 in materials to build this part.
Next we installed the panels. This part was pretty quick and the stands worked out perfectly. The panels are 250 watt Canadian solar panels. They are wired in groups of three, then paralleled into the system. To give you a sense of scale, these panels are 3.3 wide and about 4 feet tall.
Now I know many people want to know why I didn’t mount these on my roof or could they mount them. You technically can mount on your roof, but honestly the number of panels that you need to practically power your house is too many for the roof.
There is some other major bonuses of being on the ground:
- Much cooler, roofs are very hot places in the summer and solar panels drop in efficiency when hot
- I can put my house under deciduous trees, this means in summer I’m in the shade, in winter I get the solar gain
- Way easier to clean and monitor
Cleaning your panels is pretty important because you loose efficiency as residue (bird poop) builds up. Also as I learned just a few days ago, when it snows, you need to clear your panels. Cleaning becomes super simple and a lot safer when you don’t have to climb onto a roof via a ladder.
Just this week we got a decent snow, 3 inches, which is quite a lot for Charlotte. The first thing I had to do when I woke up was clear off the panels because with the snow, they made no power. This was compounded because since it was cold, I needed more heat. I can’t imagine having to drag the ladder out and try climbing on a icy roof… No Thanks.
Next I built a cabinet to house all the gear. I wanted a stand alone space because the batteries are so heavy. At 118 pound each, plus cabling and other equipment the whole unit is over 1,100 lbs. The top and bottom sections are divided so that the gasses from the batteries don’t go up into the electrical section and explode. More on that later.
The batteries are wired in series parallel. The batteries are 6 volt each, in series of 4 the create a 24 volt unit, then I have two of these 24 volt units in parallel. The reason I choose to go 24 volt over a 48 volt (which is more efficient) was because the equipment was a little cheaper, but also it allowed me to select components that I could add more panels and batteries very easily without doing equipment upgrades (just a factor of the abilities of the units I choose). This way I can add up to 15 panels and a lot more batteries without upgrading the electronics; I can also stack these inverters so if I ever go to a normal sized house, I just add another unit and it just plugs into my current one.
In this photo going left to right: Din Breaker Panel, Charge Controller, Interconnect w/ control panel, inverter. In general the power flows in the same manner (but not exactly).
- Breaker Panel: manages power from solar panels
- Charge Controller: manages power to batteries etc.
- Interconnect: a main junction box and breaker, holds control panel interface
- Inverter: takes power in many forms then outputs to they type of power you need
Once the power goes through the system it outputs to a huge cable that you can see sticking out of the bottom of inverter then goes right. From there it runs to this:
This is a 50 amp RV style plug. The reason I did this was two fold. City inspectors are less picky when it comes to non-hard wired things. This setup also lets me roll into any RV campground and hook up seamlessly.
The plug goes into a 50 amp RV female receptacle. This is important that you don’t have two male ends to your cord. This is dubbed by electricians as a “suicide cord” because if you plug in to a power source, you have exposed conductors that are live; accidentally touch them, you complete the circuit and zap!
You want a female end to your cord so that you reduce the chance of being shocked. I also turn off my main breaker at the power source when I make this connection, then turn it back on.
If all these mentions of watts, volts, amps, amp hours etc are making your head spin a little, you may need to go back to the basics. I have an ebook called Shockingly Simple Electrical For Tiny Houses which guide your through all the basics. As of now, it doesn’t go too deep into the solar aspects, but the basics of electrical, wiring, power systems and determining your power needs are covered in depth and designed for those who are totally new to the topic.
So once the power passes through the power inlet it goes to the panel. Near the bottom you can see the backside of the power inlet, it has a large black cord coming out of it, into the box and ties to the lugs. From there it goes out to the house.
Back outside now, looking at the cabinet, on the sides of it, you can see the vents. When you use lead acid (LA) batteries you have some off gassing as the batteries discharge and recharge. These gasses are volatile and can ignite, possible leading to an explosion. So to take care of this I installed two vents like this which provide adequate venting. As mentioned before my battery section is isolated from the electronics section where a spark could occur.
This off gassing is a concern with Lead Acid Batteries, but other battery technologies don’t have this issue. I choose LA batteries over AGM (absorbent glass mat) because LA’s have more cycles and cost a bit less. Lithium Ion at this point is cost prohibitive. My batteries should get about 4000-5000 cycles (11-14 years) before I need to replace them. I figure in about 5 years battery technology will have progressed so much I’ll change early. New batteries will cost me about $4,000 of the LA variety.
Here is my grounding wire for my system. This is actually one of two, another is located at the panels them selves. My house is also grounded to this through the cable hook up and to the trailer itself. A really important note: ground depends on a lot of things, one of which is if you house electrical panels is bonded or not, if you don’t know what that means, read up on it, its very important.
The other component of this system is the generators. In the winter months I may need to top off my batteries every now and then, basically when its been really cold and very cloudy for a week or more. I had a Honda EB2000i already which I really like. It’s very quite and small. The one downside to the Honda is that it only does 1600 watts and only 120V and I needed more power and 240V. So I picked up another generator, a 5500 watt 240 volt Generac for $650.
Here is a video that compares the two generators in terms of size, noise, output and price.
So that’s the surface level details of the system, I’m going to be doing something in the future which will be a how to size, choose parts, hook up and all the other details of doing solar for your tiny house, but that is a longer term project, most likely will take about 6 months to pull together in the way I’d like to do it.