DIY Grid-Tied Solar Project

A DIY Grid-Tied Solar Project - An Example From San Diego

This is a blog about how I installed Solar on my house in San Diego including getting it permitted and interconnected to the local power utility (SDG&E).  I'm an Engineer and a guy who likes to do thing himself.

This post is intended to help others like me that want to install solar but not sure if they could do it.  Here was my journey.

Key Points

Safety first
Know the building codes
Design it for the full warranty life (25 years)

Who Can Do This

You can do this if you are:
1. Comfortable with construction
2. Comfortable on a ladder and working on a roof
3. Familiar with building codes & electrical work
4. Can flash a roof
5. Someone who has a basic set of tools

You should not install your own solar system if:
1. Your idea of a set of tools is a universal screwdriver and a toy hammer for hanging pictures.
2. You plan to save money by using inferior parts.
3. You've never finished a project.

A comment about item 2.  If you size your system correctly and pick quality parts, you can expect to save money on the labor that professional installers would charge you.  However, I would not expect to save much more than that.  Why?  Because solar contractors are buying in bulk on parts.  You probably won't get the same discounts. 

Disclaimer

WARNING - Working on the roof and with high voltage electricity is dangerous.  You can be injured or killed.  Proceed at your own risk.

Preparation

Besides safety, this is the most important part of this project.

Sizing the system

The ideal system:
1. Unobstructed view (no shading) of the sun all year round
2. Exactly south facing exposure (azimuth equal to 180 degrees)
3. PV Module tilt (roof pitch) equal to the same angle as the latitude of your house
4. For a grid tied system, the energy generated should be equal to the energy demanded (on a yearly basis)

Sizing the solar system requires balancing a few things:
1. The electrical demand you plan to cover with your new system
2. The available south facing roof square footage
3. How much you're willing to spend

For my application, I choose to cover the full electrical demand including demand from an electric car plus some growth.  After talking to some who have PV systems they all agree, after you get your system installed you will get pretty liberal with using electricity.  Also, as we all know, we are using more electricity over time, so factor that in.  Adding an extra panel or two upfront is pretty cheap, more expensive later.

Doing the math

Energy demand
Collect your power bills for at least the last 12 months and sum up all the kilowatt-hours (kwh).  Adjust accordingly based on your forecast.  This is your yearly demand.  Divide by 365 to get the daily energy demand.

Production hours
Also, you'll need to get the solar irradiance for your location.  Specifically, you want to get the number of hours of sun per day for each month of the year.  Solar irradiance is in units of kwh/m2/day or for a standard amount of sun (1kw/m2) is the same as hours/day .  There are various sources online that can give this to you.  The average of these value for each of the months is the production hours per day.

System efficiency
Converting the sun to AC voltage will incur losses.  Look at the datasheets for inverter you would like to use.

System size (kw) = Energy Demand (kw-hrs/day) / ( Production Hours (hrs/day)  * System Efficiency )

Have a look at this spreadsheet that will help you calculate the system size, performance & cost.  It's in Google docs but you can download it as an Excel spreadsheet.

PV Estimator

Plans & Permit

In order to get interconnected to the grid your solar system will need to be inspected and therefore you need to submit plans for a permit.

I did find some examples of plans online, in fact the city of San Diego had a template you could follow.  However to avoid going back and forth to the building department making edits along the way I choose to go with a professional.  I used SanDiegoSolarPermits.com a full service outfit that prepared my plans for me.  You can see some examples of plans on that site.

System Configuration & Ordering Parts

Configuration types

Three common PV system configurations
1. PV modules > central inverter
2. PV modules > optimizers > central inverter
3. PV modules > microinverters

Optimizers are DC to DC devices that optimize the energy for each panel
Microinverters are similar to optimizers except they convert DC to AC

Rapid shutdown

One new capability that is called out in the code is a rapid shutdown capability.  This is intended to safe the system during access by emergency workers.  Configurations #2 and #3 are inherently safe because if the AC is disconnected there is no AC source to sync off of for either the microinverters or central inverter (which communicates with the optimizers).  Therefore wires leading away from the panels will not be energized.  However, config #1 could have a high voltage line coming off the roof.  A remote disconnect device is required to make config #1 safe.

For my installation I choose configuration #2.  I liked the idea of module by module optimization & status.  I detailed all the parts I needed in a spreadsheet and then went about trying to find them online.

There are numerous solar supply houses online to source your pv modules, racking, inverter, etc.  Use them to find the best deals.  I ended up buying my parts from multiple sites for the best prices.  Of course you'll need to factor in shipping which usually involves a truck shipment for panels and long rack rails.

I ordered the labels/plaques I needed from pvlabels.com

Wire sizing can be calculated using this template.

Before Construction - Safety First

Besides a good ladder, you'll need a basic set of work gloves.  If you're going into an attic a mask is a must.  

The roof will turn into a trip hazard.  When you start installing rails & wiring every foot step needs to be considered carefully or there's a chance you could fall off your roof.  A harness is a good idea.

Construction

1. Prepare the roof

Before adding anything to your roof you first need to ensure the roof is in good condition.  Since PV systems last 25 years, it's a good idea to consider replacing a worn out roof.  In my case my roof condition was ok, but there were a few plumbing vents that were in the way.  I decided to redirect them in the attic and patch the roof in those locations.

Code note: You can combine plumbing vents.  They cannot just be capped off. They cannot be covered by PV modules.  Methane from these vents and electricity do not mix.

2. Install the rack mounts

Roof rafters are typically spaced every 24 inches on center.  Rack manufacturers have specifications about how far apart mounts can be installed.  For my installation the max was 6 feet.  However to add extra wind resistance I reduced that to every 4 feet along the ends.  I followed the directions from the racking manufacturer regarding the correct hole to drill before lagging each mount down.  Have a tube of roofing cement on hand to make a wet seal and to fix any holes that missed the roof rafter.  Following the roof shingle courses, chalk lines and the 3-4-5 triangle are useful to get things laid out.

3. Run the conduit

DC wiring in your home is required to be in conduit.  for my system I ended up with two PV strings and the lookup tables (to show the current carrying size) showed I needed 4 x #10 thhn wires plus a ground #8 thhn.  I elected to use 3/4" EMT conduit for these 5 wires. There are charts that can tell you how many wires can fit within a size of conduit.

Code note: A label (sticker) was applied every 10 feet that said "CAUTION SOLAR CIRCUIT".

The roof penetration took a while to figure out.  I ended up with a 2 gang outdoor box supported from rigid conduit that was anchored to a roof rafter below the roof (see next few graphics).  I saw some other flimsy alternatives online that were more expensive. I felt they would not hold up to the weather.  Avoid plastic boxes & conduit too as they will break down over time.

4. Install the central inverter

Review your inverter datasheet to ensure it will work in your designated location.  A cool dry place, out of the sun is typically recommended.  I choose an indoor installation in my garage next to my circuit breaker panel.

5. Pull wire

Pulling wire through conduit is basic work, but be sure to mark each wire.  Colored tape is useful here.  Be sure to turn off the power to the breaker box before pulling wires into it.

6. Assemble the racks

Cut the rails to length and bolt them to the roof mounts.  For long runs you may need more than one rail.  In that case, be sure to bond them together with the appropriate hardware (grounding straps).  For PV module rows that are next to each other be sure to adjust the height of the rails so they are in alignment.  I used a long board as a straight edge.  This way all the panels were at the right height.

7. Add the grounding

Each row of modules need to be grounded.  Per my plans I used a #6 solid copper wire to connect each rail using grounding lugs.

8. Add the optimizers

Using stainless hardware with the appropriate washers (for grounding purposes) attach the optimizers for each panel.  Be sure to install them with the wiring down, so water will not ingress the devices.  I cut a board the width of my panels to make spacing the optmizers easy.

9. Make the connections

Connect each optimizer together (MC4 type connections) using additional solar wire to route them to the junction box.

For wire management I used 3 methods:
A. Clips designed to snap into the rail to route wires
B. Outdoor UV resistant wire ties
C. Heyco SunRunner clips to attach PV wires to the modules.

A&B were used to attach wires to the rails.  I found the rail clips did not support the wires enough so i added zip ties, item B.  Item C was used to support the wires from the modules to the optimizers.  You want to prevent future abrading of the wires so support is needed.  Do not over bend wires, no more than 5x the diameter of the wire.  Be sure to support wires from module junction boxes within 12 inches.

To make the connections to the junction (also called a transition box) I used some strain reliefs (also known as glands) to ensure a watertight connection.  Within the jbox I used wet location use wire nuts to transition from solar wire to THHN type wire.

10. Install the panels

I had the fortunate setup where the roof edge was a step stool away from a deck.  I was able to place each panel on the roof one at a time onto an old blanket.

Make the connections to the optimizers and attach the panels to the rails using the appropriate hardware (mid clamps & end clamps).  In my case I used IronRidge UFO clamps that can be used between panels (midclamps) and on the ends.

11. Install the grounding rod
Per code in my area, I needed to install a second 8 foot ground rod (there was one there already) for my PV system.  Unfortunately, my ground is heavy clay.  I read online of professionals using a jack hammer to make quick work of it.  My solution was to use a post hole digger to go down 3 feet, so I would only need to hammer it in 5 feet.  I filled it up with water to help loosen up things.  This turned out to be not too difficult.  I think it took 15 minutes using a sledge hammer.

12. Install the plaques

Your plans should call out the necessary plaques that indicate shutoffs and system layout.  They were simple peel and stick.

13. Connect the inverter to the network

SolarEdge inverters have different connection options.  I elected for the standard RJ-45 LAN connection.  So I ran a CAT-5/5e/6 type cable from my router inside my house to the inverter in the garage.

Unfortunately my network switch did not have enough power to support that length (about 70 feet).  So I replaced the switch with a modern one and the inverter was able to make connections.

14. Setup the monitoring software

Since I elected to use optimizers, it made sense to setup the online tool that's part of SolarEdge.  This is a nice way to verify that all the optimizers are working and detected by the inverter.

I ended up with an optimizer that did not work initially.  However, it was easy to track down as it was the only serial number that didn't report.  I removed the panel cycled the connections and the optimizer worked.  I'm still not sure what happened there.

15. Schedule an inspection

Contact your building department to schedule an inspection.

In San Diego, I elected to use an online system to schedule the appointment.  Unfortunately my inspector did not show up the first time, I needed to reschedule it.

http://sandiego.gov/development-services/opendsd

16. Request utility interconnection

In San Diego, the inspector will initiate a communication between the building department and the utility.

Unfortunately in my case my inspector failed to initiate this communication until I came calling a few days later.  For me the delays in items 15 & 16 caused a full week delay in getting my system approved to activate.

Here's a useful link from SDG&E that shows a flowchart of the process steps and how to start the registration:
https://www.sdge.com/clean-energy/apply-nem/apply-nem

It took 4 working days for SDG&E to authorize my system to operate once the building department notified them.

17. Activate system

For me, this part was anti-climatic.  Because of the delays from the city and utility it took too long before I got the go-ahead to turn on the system.

Applying for Rebates & Credits

As you probably know, there is a 30% federal tax credit for residential installations.  There could be other state and local rebates and credits.  Be sure to track receipts for your tax return.

For my installation in California, only the federal credit applied as the state rebates have long been exhausted.

Wrapping Up

I am really glad I did this project.  I learned a lot and saved some money.  I'm always happy to talk to people about my experience and help promote solar.

If you have any comments or corrections, please advise.