About Grid Tie Systems
Looking for an easy, Do-It-Yourself, solar panel kit? Check out our Grid Tie kits
If you are looking for a system that will save you money in energy costs and quickly pay for itself, then a grid tie system is what you want. Grid tie solar is the most cost effective way to add solar power to your house, and if done right, pay for itself in 5 years or less. However, many people end up paying more than they need to for a grid tie system. I will show you how you can get an entire system up for for less than you might think, and it doesn’t take any special knowledge or tools. So lets go over what is involved. Keep in mind that if you get a kit from us, you won’t need to do any of the calculations other than determining the size of your sytem, however it is still good to read through just so you know the details.
1- Determine the size of your system
You can really start with a system as small as you would like, but it is most cost effective to start with as large of a system as you can afford, but that is not larger than what you will use. The reason why you don’t want to get a system that is over-sized is due to the fact that most electrical companies will give you a credit for the power you generate. Meaning you may get free power, but they will never pay you money for what you generate. The best way to determine the power you use it to take the average daily usage for the last year (this will be in kwh). This information should be on your invoice from your power company, or on-line. You don’t need a full year, but the longer the better. Once you have the average daily usage you use, you will want to divide that number by 5 (this is due to the fact that you will average 5 hours of sun per day). So for example, if I found I used an average of 20 kwh per day, I would need a 4 kw system (I would say anywhere between 4-5kw would be perfect).
2- Find your power company requirements
You will want to contact your power company to find out any special requirements they may have before you start your grid tie system. Usually they will need to switch your meter over to a net meter to work with your system, and they won’t do that if you don’t meet their requirements. For me this was not much, they just needed me to put a disconnect within 5 feet of the meter (it also had to be labeled), and turn in a simple one line diagram of my system. Here is a sample of a one line diagram:
3- Solar panels
Solar panels are the main part of your grid tie system. They are also the most expensive part.
There are many different types of solar panels you can choose from, but I am only going to talk about the two most common, monocrystalline and polycrystalline. Monocrystalline solar panels are the most efficient (15-20% for monocrystalline and 13-16% for as polycrystalline), but are a little more expensive per watt than polycrystaline solar panels. Both have the same durability, and usually come with a 25 or 30 year warranty. So the only reason why you would opt for the more expensive monocrystalline solar panel would be if you simply don’t have room on your roof to fit the watts you want out of Polycrystalline solar panels.
As an example, the solar panels I use are polycrystalline solar panels that are 16.29% efficient and have a 30 year warranty. I also did a search for monocrystaline solar panels, and the cheapest I found 1.44 X more expensive, was 16.6% efficient and had a 25 year warranty. For me, I would choose the less expensive polycrystalline solar panel.
The inverter takes the DC power that is produced by your solar panels, and converts it to AC power that matches the frequency of the grid. It also raises the voltage slightly above the grid voltage in order to push power out to the grid (when you are using less power than the panels are producing, otherwise you will just use less power from the grid than you would without the grid tie system).
There are currently two types of inverters that are common. The most common is to have one large inverter that you connect all your solar panels to. This type of inverter is also the least expensive, and in most cases more efficient. However, it can be slightly more dangerous to install due to higher voltage. Micro inverters are starting to gain popularity, but currently cost about twice as much per watt. The appeal for this is that you put a small inverter on the back of each solar panel, which makes it very easy to increase the size of your system when you want to. For me it is worth the cost saving to simply save up and do the system I need right from the start rather than add one panel at a time. Especially when you consider you need to have an inspector inspect any size increases to your system, and report it to the power company (at least it is required in my area).
Matching up the solar panels and inverter
It is important that you match up the inverter and solar panels. For the micro inverter, it is simple, but you have to use panels that they suggest. For example, the Enphase inverter says: “Enphase M215 microinverters are ideally paired with solar panels 240 Watts or higher. Enphase microinverters only work with 60-cell modules.” Because of the popularity of micro inverters, This type of solar panel is very common (they can also be used for standard inverters).
For the standard inverter, the main thing you want to look at is your voltage. looking at the specs for a common inverter, it says the minimum start up voltage is 215, and the operating range is 200-450, and looking at the solar panels, we see the maximum voltage is 38.0V, and the voltage at power is 30.3V.
So we need to find a number of solar panels that will give us a voltage of at least 200V operating power, and no more than 450 maximum power. So the most panels we can run in a series is the maximum voltage the inverter can take divided by the maximum power the panels will put out .. 450/38 = 11.8 or 11 panels. The minimum panels we can run is the minimum voltage of the inverter divided by the operating voltage of the panel … 200/30 = 6.6 or 7 panels.
Now we know we can run a string of our solar panels with our inverter anywhere between 7 and 11 panels long. However I would suggest you don’t run it too close to the bottom level, because when your panels get hot, the voltage will drop a little, so I would say you should stick with 8 to 11 panels. in each series (I will explain more on how to actually do this in the wire section below). So looking at our example, the panels we were looking at came in a lot of 20 panels, so we would just wire them up in two strings of 10, and it would work perfect.
5- Mounting the panels
There are a lot of ways to mount solar panels. The way I have been mounting the panels is very easy, and works very well, it involves Electrical struts. Also the advantage of using this system is that you can adjust the angle of the panels during the winter to optimize power produced, and help the snow to slide off.
I am able to mount three panels on two 10′ struts. However first you will want to mount the struts to the roof, because once the panels are mounted, it is very heavy. You will simply need to mount four L shaped brackets to the roof. I used lag bolts, and put tar or silicone under it before I tightened it down to prevent any leaking.
You will also want to mount one of these on each end of the strut with a spring nut and bolt. For the lower mounts, you will just bolt them together, but make sure not to tighten the bolt (it needs to turn in order for the panels to rotate up). Even if you don’t plan on rotating your panels up and down, you will need them up to mount the panels, and tie up all the wire. So we will start with the mounting stood up. I used the same struts to hold the panels up at an angle, but I used the thinner 14-gauge instead of the larger 12-gauge I used for the frame. I also cut them in half so they are only 5′ long instead of 10′ (depending on how steep your roof is, you may need this to be longer or shorter). Then just lift the top end of the larger (frame strut) up, and bolt the smaller strut to both ends.
Now to mount your panels on, you will probably need to drill some small holes in the solar panel frame so you can bolt it to the new frame you have built. As a note, be careful not to drill through the frame and into the solar panel behind it. I used a small 1×2 and held it inside the frame so that the drill bit would hit it and stop before it hit the panel.
Start with the lowest solar panel (it will be the hardest, and it would be best to have someone to help you hold it). You will need to hold it in place on the raised frame, and put in 4 bolts, but don’t fully tighten them (you will also want to use some large washers to make sure the don’t slip through the large slits on the strut). Do the same for the two more panels (these will be easier because you can sit them on the frame, and let them slide down and rest on the one you have bolted on). Once you have all the panels in place, make sure the frame is square (they don’t have to be perfect, I just eyed them up, but you can use a square or measure the diagonal to make sure they are square) and then tighten up all the bolts holding the solar panels in place.
Before we get into the wiring, I need to make sure you understand the dangers. You cannot shut off solar panels, so you have to always be careful. If you are not familiar with electricity or don’t feel comfortable working with high voltage (grid tie systems usually run about 300-600V where a house is 110v or 220v) you may want to hire an electrician to wire up your panels and inverter. If you mount your solar panels and inverter, you should be able to get an electrician to wire it all up for not more than a few hundred dollars (depending on your house and what they have to do) since our grid tie system is so simple.
For solar panels, you want to use wire specifically designed to withstand the weather they will be exposed to, and the high voltage you will be running through them. Your solar panels also will come with a few feed of wire with MC4 connectors on the wires. These are very nice and make a good water tight connection, and you will be able to just plug the negative of one panel into the positive of the next to make a series connection. The only extra wire you will need is what will be needed to run from your panels to your inverter (usually located near a breaker panel). However if your power company requires you to have a disconnect close to your power meter, you will need to run your wire to the disconnect first, then to your inverter.
So lets look at our example, since we needed to have two strings of 10, we would need to wire up our solar panels like this (except you would put 10 panels in each series instead of only 7 as shown):
To make the connection from the two positives to one positive, and the two negatives to the one negative, you can do several things. One you can just run two positive and two negative wires to your inverter (or disconnect) and combing them there, or you can use Y connectors, to make it look just like the picture.
Along with wiring, you will need to tie up your wire under the solar panels so they don’t rub on the roof. I found stainless steel clips to be very good, and hold the wires up nicely. You will need about 3-4 per panel to hold the wire up good.
I have not wired a micro inverter myself, since they are more expensive, I have always just used the standard inverter. However to wire up the micro inverters, you will need special wire made for the inverter that contains the special plug to plug into the inverter and run the wire. Each brand does it a little differently, so I am not going to go over each one.
7- Mount and wire up inverter
Follow the instructions that came with your inverter to install it and wire it up. If you are not comfortable with wiring, this is a place where you may want to hire an electrician. Although it is not hard, it is important it is done safely (the solar panels will be putting out between 200 and 600 Volts, and you can’t just shut them off while you wire them up ) and the it meets local wiring codes.
8- Have it inspected
Most likely before your power company with switch out your meter, they will require you to have your installation inspected by a building inspector. Once it has passed the inspection, contact your power company, and have them get you a new meter installed.
9- Turn on the inverter
Now you are ready to turn on your inverter and start saving power and money! Enjoy!
I know this can all be a little confusing, especially if you are just learning about solar panels, inverters, etc. Even though it may sound a little confusing, it really is not difficult, it just takes a little time to get used to what everything does. To make it a little easier I have put together some off grid kits that include everything you will need, and they are all configured and planned so that everything works together correctly.