Prepping for your DIY Solar Install

2. Determine your electrical needs.

By determining your electrical usage you will be able to figure out how many panels will meet your electrical needs. Look at your electrical bills to determine your energy consumption for at least one full year. Two or three years is best because weather differences between the years can fluctuate energy usage due to big energy consumers like central air conditioning and electric heating. Simply add up the monthly kilowatt-hours (kWh) to determine your annual kWh usage. If you use more than one year divide the total kWh usage for the multiple years by how many years you used.

*For reference, the average United States monthly energy consumption is 909 kWh/month.

3. Evaluate the installation area and get installation measurements.

Evaluate the space where you plan to install the solar panels. If you live in the northern hemisphere it is most efficient to have them facing south. If a south face isn’t possible, west and east facing will work as well but not as efficient. A spot that doesn’t get shaded from trees and such throughout the year is optimal.

As a general reference, 1 sq ft of solar panel  will produce 10 – 15 watts. If you require a 6,000 watt or 6 kW system, you will need approximately 600 sq. ft. of surface area for your array. 

If you plan to do a roof mounted system, it would be a good idea at this point to check your building checklist that you obtained from your local building division for setbacks to see how close you can mount your solar panels to the edge and peak of the roof, (5 – 10 inches is typical but you will want to verify) and if they require a firefighter traffic path. 

Area: Now you can measure the block(s) of area(s) where your solar panels will be placed. Keep in mind that you’ll want to measure around the area where vents and other obstructions are coming out of the roof. If the obstructions are tall you will also need to take into account the shadow that will be cast on your solar panels. You can draw an area measurement map on paper to make this process easier. 

The website PVWatts.nrel.gov will give you an estimated energy output of your system depending upon your location and the slope, azimuth and direction your roof or ground mount array will face, and the area of available space for your array. You will need to gather the area measurements, the slope and azimuth. Note: with a ground mount you will be able to choose the best slope of the array and azimuth. 

Slope: a quick way to measure the slope of your roof is to download a level app on your phone. Once downloaded, place your phone on edge on your roof and read the degree angle. If you don’t have a smartphone you can use the rise over run method. Do a Google search on rise over run to find slope if that is the way needed. 

Azimuth: is the compass direction the solar array will face. The easiest method to get the azimuth is to download a compass app as it will give you true north and you won’t need to worry about adjusting for magnetic north. If you don’t have a smartphone then a regular compass works just fine but keep in mind the adjustments needed for true north. 

In PVWatts you will be able to determine your annual output. You can play around with the input numbers to achieve your optimal setup. Keep in mind that your actual panel and setup will play into the number a bit depending on their efficiencies. 

4. Learning about Solar Hardware:

When buying solar products you are looking for manufacture quality, reliability, suitability, performance and value. 

The three main components of a solar panel system:

1. Photovoltaic Modules – Industry standard term for “Solar Panels”
2. Module Mounting Structure – Solar panel mounting system know as racking
3. DC / AC Inverters

The rest of the parts are generic and can be bought locally.

This is the time to get an idea of the components you think would work well, not the time to buy. You need to first complete the system design and get approval from the building department. 

Photovoltaic Modules: (Solar Panels)

When looking at the different solar panels on the market you'll want to keep the following in mind:

Performance – the performance of a module is it’s electrical output in watts. A module rated for 300 watts is capable of producing 300 watts of DC output. 

Power Tolerance – is how closely the PV module will perform to it’s rated output and is known as its STC rating. If a PV module has a power tolerance of +/- 4.5%, then a 300 watt module could potentially produce 286.5 to 313.5 watts. If a module has a power tolerance of positive only then the module is rated to perform at or above the STC rating. 

The STC is rated for best case output which is required for sizing the inverter, wires and other components. 

PTC Ratings – is similar to the STC rating but done under higher temperatures which may be more realistic because solar panels are less productive under higher temperatures. PTC ratings are typically 8% – 10% lower than STC ratings. Some modules may be rated PTC/STC. In PTC/STC the higher the number the better. A PTC/STC rating of 0.92 on a 300 watt panel is 0.92 x 300 = 276 as opposed to A PTC/STC rating of 0.85 on a 300 watt panel is 0.85 x 300 = 255. 

Manufacturer Warranties – You will want to get a module with at least a 10 year warranty on manufacturing and a 25 year on power loss, anything less is not worth looking at. You'll also want to make sure the manufacturer is likely to be in business for the years to come or their modules are backed by an insurance policy.  

The good news is that quality crystalline-silicon modules only lose about 0.1% efficiency per year. 

Local building departments will most likely require the module carry the UL 1703 certification and they may also require additional certifications as well. 

Monocrystalline or Polycrystalline Modules – In recent years the two have become very comparable. Monocrystalline is a tiny bit more efficient and typically has angled corners. Monocrystalline also has a more consistent dark tint whereas Polycrystalline has a mottled blue tint.  

Module Mounting Structures and Grounding

The mounting system will be based upon your application, sloped roof, flat roof or ground array. The sloped roof system will be dependent up the slope and roofing material. 

Your building department will most likely require the mounting specs to make sure it will hold up adequately for the different weather conditions in your area. You'll also want to make sure your roof is structurally sound enough to hold the extra 3-5 lbs per sq ft. This may be done through some of the questions on the building permit or may require a structural engineer. 

You’ll need to ground your structure to modules with WEEBs. WEEBs stands for “washer electrical equipment bond”. They are a special washer with sharp “teeth” on them that will pierce through the protective coating on the rails and modules to electrically bond them together. Each pair of modules needs two WEEBs. If you have 8 modules you will need 8 WEEBs. But if you have an odd number of modules you will need one extra WEEB for the end row. For example, if you have nine modules you will need ten WEEBs. The extra WEEB will go into the end row. With all the modules bonded to the rails using the WEEBs all you will need to do is bond the rails with a bare copper ground wire. The ground wire will either go to the ground on your electrical service panel or to a rod buried into the ground, this is determined by your local building code requirements. 

DC / AC INVERTERS

Inverters convert the DC power generated from the solar panels to AC power which our household electrical appliances are set up to use. There are two types of inverters used in solar panel systems, String Inverters and Microinverters. 

String inverters are typically mounted on the ground floor or the basement, most often close by the hookup components. Most units have outdoor rated encasing and can be mounted on the exterior of the house. 

Microinverters are attached to the back side of each solar module or sometimes to the racking system. There is typically one microinverter for one or two modules. The great thing about microinverters is that if one solar module is getting shaded; it only affects that module and not the whole system. For example, if you had a 20 module string system and one of the modules was getting shaded by 30% the rest of the modules outputs would be reduced to match the one module that was getting shaded and you would have 70% output for your entire system. With microinverters only that one module would run at 70% and the rest would run at normal operations. 

Microinverters convert the DC output right at the module so the wiring running to the ground is AC.

In order to reduce system losses on string inverters due to shade or multiple module strings on different orientations/tilts you can use multiple inputs or DC optimizers. If you go with the multiple inputs option each string with a different orientation or tilt would have its own input to reduce the impact of a lower performing string on the entire system. On the other hand a DC optimizer is much like a microinverter in that each module has its own DC optimizer and makes adjustments on an individual level which then consequently won’t affect the entire system if one module is receiving less sunlight than another. 

Rapid Shutdown Protection

Rapid shutdown protection equipment allows your PV system to be disconnected automatically from the grid if the grid power goes down. This is required so that the utility company can safely work on the grid without being shocked by your PV system backfeeding the grid. It also allows you to shut off the grid from your system so that you can safely do work on your system if the case arises. 

To accomplish this you need to place two disconnects. One disconnect needs to be placed in between the PV array and the inverter to stop the DC current going into the inverter. The other needs to be placed between the inverter and the utility box to stop the AC power going out of your inverter.  You can buy inverters that have built in power disconnects for both the DC and AC power which makes the system simpler. But some utilities require a visible lockable disconnect on either side of the inverter, so double check to see which type you should go with.