You learned from the last blog post about how much electricity you are using. This post is about generating that electricity yourself rather than relying on the power system. There are two ways to go about doing this:
Grid-Tied System
In a grid tied system, you only need to buy solar panels and a grid tie inverter. The solar panels connect to the grid tie inverter, which then connects to your house. Any excess energy that you generate actually gets sent back into the electric system, and you can potentially be paid by the electric company instead of the other way around.
This is not as interesting to me though because you need a professional electrician to connect the grid tie inverter to your house. Also, if the electric company's power goes out, your house goes dark, even if your solar panels are generating electricity. You need to add batteries if you want to use it as a backup solution as well.
Off Grid System
In an off grid system, you are generating your own electricity and storing it in batteries. This is good for a cabin in the woods. It was also good for me in my case to just learn what solar stuff is all about.
Parts to the Off Grid System
Solar Panels: These will be rated by how many watts they'll generate with direct sunlight shining on them. There are 3 types of solar panels:
- Polycrystalline: Your basic panel
- Monocrystalline: Your basic panel, but more efficient (and more expensive). So a 100W monocrystalline panel will most likely be smaller than a 100W polycrystalline panel.
- Amorphous: Whereas the two types above are rigid, this is more pliable. I believe some companies pretty much just print this stuff out. It is less efficient (so a 100W amorphous panel is comparatively HUGE), but it also does better in indirect sunlight (like a cloudy day) than the other two do.
Most brick and mortar stores don't seem to have these in stock, but you can buy them online, particularly from Amazon and Home Depot. You can also simply buy some off some guy on Craigslist. The panels last ~20-25 years with 80% of their original power.
Charge controller: Depending on the amount of sun on your solar panels, they'll either generate a whole lot of electricity, just a trickle, or even none at all. In fact, when it is dark, the solar panels will actually try to take electricity rather than give it. A charge controller will regulate that electricity going to the battery, and also make sure the solar panels don't suck electricity away at night time. It will let the battery be charged at the right levels when it is empty, and stop the charging when it is full. There are 2 types of charge controllers:
- PWM (Pulse Width Modulation): Your basic charge controller. Any voltage over the limit is simply dropped. Unfortunately this can be inefficient (say 80% efficient).
- MPPT (Maximum Power Point Tracking): Newer, fancier charge controllers (also far more expensive). Instead of simply dropping any voltage, it'll convert the extra volts to amps instead (I'll talk about the math of this later), radically increasing the efficiency of your system (like 97%).
Batteries: You pretty much want to charge your basic 12V car battery. Except apparently 12V marine batteries (specifically deep cycle batteries) and 6V golf cart batteries are actually better suited for the task. Car batteries are meant to have a big pull right at the beginning (starting your car), and then not much else. Apparently boats and golf carts are more likely to drain a battery all the way down, and then charge it all the way up again, just like a solar panel system would.
How much the battery can store will be measured in amp hours. However, a battery should never go below 50% charge (or it'll damage the battery), so you'll really only get half that number.
Power Inverter: Solar panels and batteries give you DC (Direct Current) power, while your house electric plugs give AC (Alternate Current) power. So a power inverter connects to your battery, converting your 12V battery DC power to 120V house AC power. This is the same exact device that you'd use in your car to be able to plug your laptop or whatever in. There are also 2 types of power inverters:
- Modified Sine Wave Inverter: Your basic DC/AC inverter. It'll give a bit of a choppy AC signal, which will work fine for most of your appliances, but not all. For example, laser printers won't work, fans and fluorescent lights may buzz, and generators/motors may run hot.
- Pure Sine Wave Inverter: This gives you the same type of signal at your wall outlet. Much more expensive.
How to Hook it all Up
Connect the solar panels to your charge controller. Then connect your charge controller to your batteries. Connect the power inverter also to your batteries. Then plug whatever you want into the power inverter.
I recommend getting a Kill a Watt meter (from my last post) so you can see exactly how much power you're drawing from your batteries.
Also, you may want a 12V system, a 24V system, or a 48V system. I'll show you why in the next section, but you'll want to hook everything up a little differently depending on what kind of system you have. Say you have 4 12V batteries. If you just want a 12V system, then hook them all up in parallel (connect the positives parts all together and the negative parts all together). If you want a 24V system, then hook up two sets of two batteries each in series (connect the positive on one battery to the negative of another). Then hook up your two sets in parallel. Or for a 48V system, just connect all the batteries in series.
Remember to have the right equipment. For a 24V system, make sure you wire the batteries correctly, and purchase a 24V charge controller and 24V power inverter. Otherwise you may explode something :) One tip is many MPPT charge controllers can easily switch between a 12V or 24V battery bank. An MPPT charge controller also means you can have 24V panels, but a bank of 12V batteries without losses. A PWM charge controller would drop half your volts in the same system, effectively losing 50% of your power.
Also, one thing that's great about this is nearly everything is expandable. Want more solar panels? Just hook them up in parallel or in series as necessary. Too much power for your charge controller? Just add another and hook them up in parallel on the battery side (not verified, but I've read that a couple times). Need more battery storage? Just add more batteries in series or parallel as necessary. The only thing that isn't expandable is the power inverter. If you get a 200W power inverter, but you need 500W, then you'll need to buy a new one.
Important Math
Volts * Amps = Watts (Power)
So if you plug a 100W light bulb in the wall, you know you're getting 120V from the wall, and the total power draw is 100 watts. A little math (100 Watts / 120 V) means you're pulling 0.83 amps. This is important because the higher the amps are in your system, the thicker your copper cable runs will need to be.
Say you have 1000W of solar panels connected to 12V batteries. The same math tells me you'll have 83 amps running on the cable between your solar panels and your batteries. To keep the power loss to an acceptable level, you'll need a cable the size of your arm. However, the same 1000W on a 48V system is only 20.8 amps, which is a much better cable size.
This also comes in use for determining battery size. If your battery is a 12V battery, and it is rated at 100 amp hours, that means it can run (12 volts * 100 amp hours) 1200 watt hours before being completely drained. Remember you can only drain it 50% of the way though, so you really only get 600 watt hours from full to empty. The power inverter should automatically detect when the battery bank is too low and turn off.
Hybrid System
Eventually when you have your off-grid system working how you want it to, you may want to get a grid-tie inverter and have a professional electrician connect it to your house. That way you can get the benefit of powering your own house (perhaps sending extra back onto the grid for credit), and still staying on in the event of a city power outage because of your batteries.
Do remember that each component you introduce also makes the entire system slightly less efficient though, so a normal grid tied system will be slightly better. As mentioned before, however, a normal grid tied system does not give you any advantage during a power outage.
Is it Worth It?
The short answer is it will take 5-10 years to be worth it (but the panels last 20-25). You'll want to be your panels at around $1.50 or below per Watt. For example:
A 250W panel costing $350 is $1.40 per watt. Assuming a price of $0.12 per kWh from your utility company, that panel will take 11,666.67 hours (or about 1.33 years) to make up its value. However, there isn't direct sunlight for 24 hours/day, so assuming you get full power from the panel at an average of only 5 hours each day, it'll more realistically take 6.39 years to make up its value. Of course this does not take into account the cost of batteries, etc. (if that's the route you choose to go), but that gives you a good ballpark figure.
My Test System
- Solar panel: I bought a small 5W panel to test with for $25. I'm looking to get some cheaper, larger panels off craigslist now that I have a better idea of what I'm doing. I'd like to stick them on my shed in the backyard, and they'll provide power for parties out back.
- Charge controller: I got a small 3 amp / 12 V charge controller to test with for $11.
- Battery: I got a deep cycle marine battery from Walmart with 100 amp hours for $75.
- Power Inverter: I got a 200W Whistler power inverter years and years ago for Christmas that I just kept in my car.
- Misc
- $6 for some 14 gauge copper wire at home depot
- $10 for an add-on cable to connect my power inverter directly to the battery ($10 was a huge rip-off, like everything else at radio shack)
- A battery trickle charger, wire strippers, and a multimeter all came in handy at different points that I already owned as well.
Total: $127 for science
