Hi.
I'm Amy Beaudet from the altE Store.
Thank you for watching our video series, this video is called "Designing a grid tied solar
electric system".
If you missed our previous videos, I recommend you go back and watch the earlier ones in
the series to get a good foundation, as they discuss the individual components.
In this video, we're going to walk through how to select the equipment for your grid
tied system, including the solar panels, racking, overcurrent protection, and inverter.
But first, here's a quick overview of a grid tied system.
It is the most common solar systems installed in locations that have electricity available
from the utility company.
A grid tied system simply takes the power generated from the solar panels during the
day, and uses it real time in your house.
If you have any extra power available, it sells that power back to the grid for a credit,
and at night or on days when you don't generate enough power, you use that credit to buy power
back from the grid.
Any more power needed is just bought as usual.
Let's go over how to size the different components.
And don't worry, you don't have to do this alone, a professional installer can figure
this out for you, or you can call us at the altE Store to do the system design for you.
But for those of you interested in how to design a system yourself, let's go through
the main steps, a peek behind the curtain, if you will.
First you need to determine how much power you currently use, if this is for an existing
house.
From your current monthly bill, you can figure out how much power you use a day.
Based on your location, and the amount of sun you get, you can determine the size of
the solar array needed.
From there you figure out what racking, inverter, and breakers you need.
Let's go through each of these steps.
First, how much power do you use?
Take a look at your electric bill.
It is generally billed by the month.
You can see here on this bill, it is higher in the summer due to using the air conditioner.
If we had electric heat, you might have seen higher bills in the winter instead.
The nice thing about higher usage in the summer, is that that is when there is the most solar
energy available as well.
From this bill, add up all of the monthly kwh, and divide it by 365 to get a daily kwh
average.
In my case, that's 50.6kwh a day.
We'll use that daily kwh number to size the solar array.
But first we need to figure out how much sun you get on average.
Insolation maps show the available sun hours for your area.
This map of he United States gives you a good idea of the solar potential.
The darker the color, the better the sunshine.
Obviously the southwest and Hawaii are the best for solar, but even locations not known
for their sunshine, like New England and the Pacific northwest still have enough sunshine
on average to make solar a very good solution.
Here's a quick peak to see how different regions of the world compare.
For our calculations, we need a more accurate number than what I can see on the map.
There are several online sources available to find more specifics for your area.
This chart shows for my area near Worcester Massachusetts.
You can see the monthly versus annual average numbers.
For a grid tied system, since I'm just supplementing the electricity I buy, so I can buy less,
I'm just going to use the average number.
The ideal angle for installing solar is at latitude, but my roof isn't that steep, and
I'm just going to mount them flush without tilting them up, so I'm going to use the Latitude
minus 15 degrees row.
The good news is, for my location, I'll get the same amount of power as if I was at the
"ideal" angle.
Because we don't live in an ideal world, I also need to take into consideration less
than ideal conditions.
Generally, for a grid tied system, we calculate that we will lose about 23% due to losses
in the system, from voltage drop in the wires to bird poo on the panels.
Now let's do some math!
We take that daily average kwh from earlier, multiply it by 1000 to get watt hours, divide
it by your annual average sun hours, to get 11,254W.
We divide it by 77% to take into account the system losses, which gives us 14,615 W of
solar to provide 100% of our electricity needs.
As we said earlier, most grid tied systems don't try to make all of their power, just
cut their existing bill.
So for this example, I'm going to cut that in half to provide half of my electricity
with solar.
So I need a solar array of about 7300 watts.
Now let's use this information to pick out the rest of the system.
Grid tied inverters are sized based on the size of the solar array they are connected
to.
There is a certain window of number of panels in series and in parallel that will work with
the inverter.
When selecting the inverter, you'll find that most inverter manufacturers these days have
an online calculator called a "String Sizer" to help select the right inverter for your
panels.
We'll walk through ABB's string sizer to find the right inverter and panel configuration.
I enter the temperatures that the panels will be seeing during daylight hours, and if I'm
mounting them on a roof or on the ground.
This matters because the solar panels' voltage changes pretty dramatically based on temperature,
so the string sizer needs to be able to calculate the highest and lowest voltages it will see.
I'm also selecting the solar panels I'm going to use.
I picked Kyocera's 250W panels, they are a terrific panel at a very good price.
Since I'm looking at around 7300 watts of solar, I picked the ABB Uno 7.6kW inverter.
I can see that depending on how many parallel strings I do, I can use series strings of
anywhere from 4 to 14 long in series.
However, these may not be the ideal string lengths, if there are any warnings, the string
sizer will alert you in a note.
I picked 2 sets of 2 strings of 8, for a total of 8000W, the inverter is very happy with
that size.
It's a little bigger than my 7300W that I calculated that I needed, so it will actually
generate more than half my power.
So now I've got 32 Kyocera 250W panels, and an ABB Uno 7.6k Transformerless inverter.
So how will I mount them?
Luckily for those of us doing a lot of designs, IronRidge also has a time saving Design Assistant
to help speed up the design work.
They've got one for roof mounts, and one for ground mounts.
We'll walk through the roof mount one.
You enter what solar panels you are using, how many, and how they are laid out.
I'm doing 2 rows of 16, flush against the roof.
For my area, the building code requires the system be designed to withstand 100mph winds
and a snow load of 40psi.
For 4' spacing between mounting feet, which lines up with every other rafter, it tells
me I can use the IronRidge XR100 rails.
Just a few more inputted details, like what color clamps to match the panels, And it outputs
a bill of material, and the manufacturer's suggested retail price.
They do suggest a flashing for an asphalt shingled roof, so if you have a different
type of shingle, you may need a different flashing to prevent leaks.
The last piece is over current protection, protecting your system in the event something
goes wrong.
In a grid tied system, there are 2 locations we need to put in over current protection,
on the DC side by the solar panels, and on the AC side in the Main breaker box.
The combiner box I chose for this system is a disconnecting combiner box.
It allows you to turn off the power coming out of the panels right by the panels, in
compliance with NEC 2014 Rapid Shutdown requirement.
Each string of panels gets its own fuse.
The datasheet of the panel usually tells you what size fuses to use, for grid tied panels
under 300 watts, it's usually 15A.
To calculate it, you take the solar panel's Short Circuit Current, and multiply it by
1.56.
The combiner box wires the strings into parallel, and gives you a place to transition the wire
into conduit.
It's also a good place to put a lightning arrestor.
The AC output of the inverter goes into a dual pole breaker in your home's Main breaker
box.
To calculate the size breaker to get, you take the watts of the inverter, in this case
7600 watts, divided by the AC voltage output, 240V, and multiply it by 1.25 to oversize
for NEC's requirement for devices being used for more than 3 hours continuous.
This gives you a 40 amp dual pole AC breaker.
So, what have we got?
We have a combiner box with 15A fuses, 32 of the Kyocera 250W panels, wired in 4 strings
of 8, an ABB 7.6k Transformerless inverter, and just over 200' of IronRidge XR100 rail,
with the and clamps, and mounting feet.
You would enter the details for whatever physical layout works for your roof.
Then you would get a 40A AC breaker that fits in your Mains breaker box.
Now let's look at a schematic to see how this all schematic that shows how this all fits
together.
We have 4 parallel strings of 8 panels in series, going to a combiner box with a 15A
fuse for each string.
The combined strings are sent in conduit to the string inverter.
The AC output of the inverter may be required by your electric company to go to a lockable
AC disconnect by your meter, so that the linemen can turn off your system if needed.
it then goes into a 40A breaker in your main breaker box, to your house.Then any excess
power goes out to your bidirectional meter, which will be spinning backwards or forwards,
depending on if you are selling or buying power.
From there, it goes out to the grid.
As a nice starting point, altE Store has put together packaged deals that include most
of the equipment needed for a solar install.
We have grid tied, off grid, and grid tied battery backup systems predesigned.
We are able to customize them to fit your specific needs.
For example, if you want to change the layout of the panels, switch to a different brand
panel or inverter, and select the correct flashing for your roof, that's very simple
to do.
This package here lines up nicely with the example we just walked through.
This has the pricing as of November 2014, pricing and availability is of course subject
to change.
Here's a list of what is included in the package.
We don't include the conduit and wire from the roof to inside, or the wiring and breaker
on the AC output of the inverter, as that is common electrical equipment that you would
buy locally based on your requirements.
The package doesn't include the flashing for the roof, as we need to know what kind of
roof you have, then the appropriate flashing can be added as we work out the details with
you.
So, that should give you a good feel for what's involved with designing a residential grid
tied solar system.
To get you started for your house, altE Store has got a bunch of calculators available,
including the Grid tied Calculator.
We also have many other Packaged Systems that we've already designed as a starting point,
allowing you to customize them for your particular needs.
Check out more of our video Series on our web site.
We've got a team of highly trained Technical Sales Reps available to help you plan your
system, give us a call.