Designing the Zero Emission Jobsite: A Guide to Utilizing Solar with Battery Energy Storage Systems

Introduction:

In recent years Battery Energy Storage Systems (BESS) have become increasingly popular on the jobsite. When used in tandem with a diesel generator in a hybrid set up these systems can save a substantial amount of fuel. By running the generator at full load, only when the BESS needs to charge, the generator avoids running inefficiently at low loads all day. This leads to reduced runtime, maintenance, and carbon into the atmosphere. However, if the jobsite utilizes solar to charge the BESS, diesel fuel costs, generator maintenance, fuel drop costs and carbon released reduce to zero.

 

In the past solar has been ignored as it can be difficult to set up, and the power to size ratio makes temporary systems cumbersome to ship. This is no longer the case with Full Charge Solar’s new OG914 Collapsible Array. These arrays use simple folding technology to pack the most panels possible into a 3.7kW array that can be set up within 5 minutes. Furthermore, they can be infinitely expanded in a modular system to charge any size BESS on the market.  This article will teach you how to size a system, as well as outline the potential cost and carbon savings of utilizing the OG914 Solar Array

Sizing A System Example: Powering a Mobile office

Step 1: Daily Power Needs

The first thing to consider is your daily power needs. If you have a diesel generator or a BESS already, this data should be easy to gather. If you are starting from scratch, this can be done by making a list of all planned electrical items (HVAC, computers, appliances etc), multiplying them by the amount of time used per day and then getting their sum. Using an appliance energy chart is a good place to start. Be sure to note the peak power needed (ie for starting an air conditioner). For the purposes of this example, we will assume a mobile office trailer is using 30kW a day, running 10 hours per day, six days per week (180kW per week).

Step 2: Power Redundancy

This is highly dependent on location, time of year and length of work week, but we will assume in this scenario the jobsite requires three days of backup power. If they are using 30kW a day, it would be best to go with a 100kWh BESS as they are not recommended to drop below a stage of charge (SoC) of 10%. Powr2’s PRO 60.100/480​ would be an ideal candidate. (The 60 kVa in this system could easily handle the start-up of a 5 ton AC.

Step 3: Determining Location and Time of Year

With our BESS size determined, it’s time to size our solar. To continue with our example we will assume this particular office trailer is in Los Angeles, CA. Our first step is to get an estimate of how much energy we can expect one OG914 solar array to produce throughout the year. To accomplish this, you can either use the chart with common cities provided below or go directly to the PV Watts calculator. OG914 inputs for the PV Watts calculator are at the end of the article.

Average Weekly Energy Harvest of OG914 Solar Array by Season (kWh)

Graph above shows average energy harvested in one week, per season by a 3.7kW OG914 Solar Array.

Step 4: Consider Project Length

With the data now available it’s time to consider how long this project will last, and what time of year it will take place in. For the purposes of this example, we will assume the project will last one year, which means we will design the system based off its lowest seasonal weekly average. From the chart we can gather this figure is 109 kWh per month. If another project were only for three months in the summer, or three weeks in the fall, we could simply use those numbers.

 

Therefore, if we need 180kWh per week all year, and each OG914 array produces 109 kWh per week in the winter, two (218 kWh per week), will be sufficient to get us through the winter with a 20% margin of error. Adjusting the angle of the panels seasonally can increase the energy output between 10-15 percent. To accomplish this, use the year-round angle tilt (the latitude of the location) for fall and spring, add 15 degrees for winter and subtract 15 degrees for summer

Cost Savings:

To illustrate the cost savings, we can use the example above of two OG914 Solar Arrays with a BESS and compare it to a 40kW diesel generator with a BESS.

 

If we include the initial cost of the diesel generator with the costs of fuel and maintenance and compare it to two OG914, it takes approximately eight months in the above example for the price of the two solar arrays to equal the price spent on diesel power generation. Solar arrays do not require maintenance, filter/oil changes, fuel or fuel delivery fees. Thus, the effective running costs per year for a solar array is zero, compared to an estimated $9,132* per year for the diesel generator. If we consider the lifetime of a diesel generator to be 20 years (compared to 25 years for a solar array) the running costs of diesel are no longer economical

Yearly Combined Running Costs of 40kW Diesel Generator vs Two OG914 Solar Arrays

Does not factor in inflation

Carbon Savings:

To calculate carbon savings, start with how much diesel fuel you have avoided. If you are moving from an entirely diesel, or a diesel/BESS hybrid system that information is likely available to you. The EPA’s carbon dioxide emission coefficient for diesel is 22.45. Meaning that for every gallon of diesel fuel burned, 22.45 pounds of CO2 is released into the atmosphere. Simply multiply the gallons of diesel you’ve avoided by 22.45 and you will have the amount of CO2 avoided.

 

If you are starting from scratch, you will need to use a diesel fuel consumption chart like this. In the example presented in this paper we used a 40kW generator. For the 180kWh of energy needed per week our generator ran at 75% load for 7 hours. Using the fuel consumption chart, we can ascertain we used 23 gallons per week, or 1,196 per year. Therefore, by using a Solar/BESS system (over a Diesel/BESS) we avoided an additional 26,850 pounds of CO2 in this example. If you are counting Scope 3 emissions you’ll likely be able to save more CO2 by avoiding fuel deliveries.

 

Solar works everywhere!

It’s a common misconception that solar is ineffective in the northern states. However, per year the area with the lowest solar radiation in the continental United States (Seattle) produces 58% of the solar energy of the highest solar radiation area (El Paso); in the summer months that number rises to 87%. With proper planning the Solar/BESS system is a viable replacement for diesel power generation throughout the continental US. See below for average yearly energy harvested by an OG914 solar array in an area near you. For any questions please contact us!

The inputs for an OG914 on the PV Watts calculator are as follows:

 

DC System Size (kW): 3.7

Module Type: Premium

Array Type: Fixed (open rack)

System Losses (%): 11

Tilt (deg): Latitude of Jobsite Location

Azimuth (deg): 180

*Running calculations include running time necessary to produce 180kWh per week at 75% load. Fuel costs associated with running time, oil changes, filter replacements, and fuel drop fees.