About SolarResilient™

<p>Disasters such as floods, wildfires, tornados, earthquakes, storms, and hurricanes can cause severe damage to the electric power grid. To keep a building running to serve as a shelter or evacuation facility during a power outage, resilience planning is essential. Typically diesel generators are installed to provide back-up power, but such systems have some major drawbacks. For example, they do not provide any benefits during normal operation, they utilize fossil fuel and thereby emit carbon, and most importantly &ndash; they can only operate until the diesel tank is empty. Using a system of photovoltaic (PV) arrays combined with battery storage, can be a more sustainable solution.&nbsp;</p> <p>The intent of the SolarResilient tool is to provide building owners and managers with an estimation of what PV and battery capacities are needed to provide desired resilience. The recommended capacities are translated into required roof top and parking lot area for the PV array, and basement or garage space for the battery system. This gives the user an idea of what system sizes are feasible for their building.&nbsp;</p> <p>Please note that this tool should only be used for high-level estimation of required system sizes, and is not suitable to use as basis for any system design. The tool does not provide an economic analysis. We recommend that should you be interested in taking the design further, you undertake a detailed feasibility study for your building and work with vendors to determine costing and economic analysis.</p>

<p><strong>Photovoltaic (PV) array</strong></p> <p>PV output per kW (DC) of installed capacity is provided through NREL&rsquo;s tool PVWatts Calculator, which uses the following default assumptions:</p> <p>&bull; Module type: Standard</p> <p>&bull; Array type: Fixed (open rack)</p> <p>&bull; System losses: 14%</p> <p>&bull; Tilt: 20 degrees</p> <p>&bull; Azimuth: 180 degrees</p> <p>&bull; Inverter efficiency (nominal rated DC-to-AC conversion efficiency): 96%</p> <p>These parameters can be adjusted by the user in the Advanced Inputs section of the SolarResilient tool.</p> <p>The SolarResilient tool only includes one year of data in the calculation, and degradation over time is therefore not accounted for. However, the advanced section gives the user the option to include a degradation caused by environmental factors, such as ashes and dust (default is set to 0%). This degradation should to be used if smoke from large fires etc. is to be considered in the calculation.</p> <p>To calculate the roof/parking lot/other area needed for the recommended PV array, the tool uses following assumptions:</p> <p>&bull; Rooftop area: 15 W per installed rooftop PV per sq.ft. of unshaded roof. The user shall enter only the available roof space for PV, not the total roof area. As a rough guide, being able to use 40-60% of the total roof space would be typical and allow for panel spacing without shading, fire department access and miscellaneous items on the roof.</p> <p>&bull; Parking lot or other area: 9 W per installed PV canopy per sq.ft. of unshaded parking lot or other area. For parking lots this area should include both parking spots and driveways.</p> <p><br /><strong>Battery system</strong></p> <p>The SolarResilient tool allows the user to chose between 4 different battery technology options, available in the Advanced Inputs section:</p> <p>&bull; Lithium ion (Li-ion): Default option. Commonly used in electric vehicles and in the stationary storage market. Li-ion batteries are light-weight with a high energy density and can withstand deep discharges.</p> <p>&bull; Advanced lead-acid: This technology is a combination of the high-performance carbon ultracapacitor with the lead-negative electrode, and performs better than traditional lead acid batteries.</p> <p>&bull; Flow batteries: Work like rechargable fuel cells. Since the electrolyte is stored separately from the power generation unit, it is easy to scale up the capacity by making the tanks larger and is considered safer than traditional battery technologies.</p> <p>&bull; Aqueous hybrid ion (AHI): Saltwater ion is a new battery technology which is safer and more sustainable than traditional batteries. It can withstand deep discharges and contains no heavy metals or toxic chemicals.</p> <p>To simplify the calculations the batteries are assumed to run at a charge-discharge cycling of 0.25C. This means that the batteries can discharge 25% of its maximum capacity each hour, e.g. a 200 kWh battery system can discharge up to 50 kW during 4 hours before it needs to be recharged. The charge rate is assumed to be the same as the discharge rate.</p> <p>The risk of the batteries being discharged at the beginning of the outage depends on how they are used during normal operation. The user can choose from 3 grid service alternatives (described below). Each option determines the state of charge at the first hour of the outage, which is used for sizing of the battery system. A lower minimum state of charge level will result in larger battery capacity to compensate for the risk of the batteries being discharged when the outage occurs. The minimum state of charge assumptions are based on feedback from industry.</p> <p>&bull; Demand charge mitigation: The batteries are used to shave the building loads during hours when the electricity rates and demand charges are high. The lowest state of charge is assumed to be 40%.</p> <p>&bull; Frequency regulation: ancillary service where you are paid by the independent system operator to help balance the grid. For this service the batteries are typically not discharged as deeply as for demand charge mitigation, but can have several discharge and charge cycles per hour. The lowest state of charge is assumed to be 50%.</p> <p>&bull; Resilience only: The batteries are only used to provide emergency power and are assumed to be fully charged at the beginning of an outage.</p> <p>The input assumptions for each battery type are summarized in the table below:</p> <div style="text-align: center; overflow-x: scroll;"> <table border="1px" width="1036" align="center"> <tbody> <tr style="background: #999; color: #fff;"> <td style="text-align: center;" width="399"> <p style="text-align: left;"><strong>&nbsp;Type</strong></p> </td> <td style="text-align: center;" width="120"> <p><strong>Lithium ion</strong></p> </td> <td style="text-align: center;" width="136"> <p><strong>Advanced lead acid</strong></p> </td> <td style="text-align: center;" width="120"> <p><strong>Flow</strong></p> <td style="text-align: center;" width="120"> <p style="text-align: center;"><strong>Aqueous hybrid ion</strong></p> </td> </tr> <tr> <td style="text-align: left;" width="399"> <p>&nbsp;Average capacity available (of rated capacity) for 0.25C cycling</p> </td> <td style="text-align: center;" width="120"> <p>100%</p> </td> <td style="text-align: center;" width="136"> <p>62%</p> </td> <td style="text-align: center;" width="120"> <p>100%</p> </td> <td style="text-align: center;" width="120"> <p>66%</p> </td> </tr> <tr> <td style="text-align: left;" width="399"> <p>&nbsp;Round trip efficiency for 0.25C cycling</p> </td> <td style="text-align: center;" width="120"> <p>90%</p> </td> <td style="text-align: center;" width="136"> <p>81%</p> </td> <td style="text-align: center;" width="120"> <p>65%</p> </td> <td style="text-align: center;" width="120"> <p>77%</p> </td> </tr> <tr> <td style="text-align: left;" width="399"> <p>&nbsp;Max charge normal operation</p> </td> <td style="text-align: center;" width="120"> <p>90%</p> </td> <td style="text-align: center;" width="136"> <p>90%</p> </td> <td style="text-align: center;" width="120"> <p>90%</p> </td> <td style="text-align: center;" width="120"> <p>90%</p> </td> </tr> <tr> <td style="text-align: left;" width="399"> <p>&nbsp;Space required cu.ft./kWh installed capacity</p> </td> <td style="text-align: center;" width="120"> <p>0.85</p> </td> <td style="text-align: center;" width="136"> <p>1.50</p> </td> <td style="text-align: center;" width="120"> <p>3.46</p> </td> <td style="text-align: center;" width="120"> <p>&nbsp;2.12</p> </td> </tr> </tr> </tbody> </table> <p>&nbsp;</p> </div> <p>The user can also choose to create a custom battery. This option gives the user the possibility to adjust each of the battery system properties used in the calculations.</p>

<p><strong>Create an emergency load profile</strong></p> <p>Depending on what data that is available to the user, the tool offers three different ways to estimate the hourly electricity profile during a disaster event.</p> <p>&bull; <strong>Quick</strong> The user inputs the annual electricity peak demand of the building (typically found on the electricity bills), the location of the building (by clicking on the map), and the desired outage duration and percentage of the total electrical load that the user wants to support during a disaster event. The tool creates an hourly emergency load profile based off an electrical load profile for a typical office building in the chosen climate zone, scaled to match the entered peak demand and desired load percentage. The default profiles are modeled load data representing DOE&rsquo;s large office reference building (see http://energy.gov/eere/buildings/commercial-reference-buildings) for more information. Other building types are not modeled, however this options is to allow a very quick sizing estimation only. </p> <p>&bull; <strong>Standard</strong> The user uploads the actual electricity profile for the building. This data must contain hourly or 15-minute data for a full year starting at 12 AM on January 1st, to match the hourly PV data used in the calculations. All of the data must be in column A and there must not be other data in there, such as dates and times. The user also enters the percentage of the total electrical load that the user wants to support during a disaster event. The tool creates an hourly emergency load profile by multiplying the uploaded electricity data with the emergency load percentage.</p> <p>&bull; <strong>Detailed</strong> This is the most accurate method. The user enters the following information about each load type that will be running during a disaster event:</p> <p>&bull; Wattage per fixture/appliance/device</p> <p>&bull; Quantity</p> <p>&bull; # run time (% of the time each fixture/appliance is used) </p> <p>&bull; Daily schedule (start and stop hours)</p> <p>&bull; Annual schedule (start and stop months)</p> <p>The tool uses this information to create an hourly emergency load profile for a full year.</p> <p><br /><strong>PV generation data</strong></p> <p>NRELs tool, PVWatts Calculator (http://pvwatts.nrel.gov/) provides estimated PV electricity generation for different locations throughout the USA. The user inputs information about the location of the building (address, city, state, zipcode), which is used in the PVWatts Calculator to get access to hourly output data for 1 kW DC of installed PV array for that specific location.<p/> <p>The output is based on the default settings for module type, array type, system losses, tilt, azimuth in the PVWatts Calculator, but the advanced section allows the user to adjust these settings.</p> <p><br /><strong>Design scenario selection</strong></p> <p>The sizing calculations are performed for every hour of the year and the design outage start hour and system capacities are determined based on the chosen design scenario (Typical or Worst):</p> <p>&bull; <strong>Typical</strong> (default setting) Represents the average outage hours of the year. The PV and battery systems are sized to provide desired resilience with a probability of at least 50%.</p> <p>&bull; <strong>Worst</strong> Represents the worst outage hours of the year in terms of largest PV and battery sizes. This scenario can result in unreasonably large system sizes, but gives the user an idea of the size required to guarantee desired resilience.<br /> <p><br /><strong>Existing on-site power generation</strong></p> <p>The Advanced Input section gives the user the option to include any existing PV arrays and back-up diesel generators.</p> <p><br /><strong>Existing PV array</strong></p> <p>An existing PV system will reduce the additional PV capacity required for desired resilience. The tool will assume the same power output for the existing PV array as for the new, and simply subtract the existing capacity from the total PV capacity to calculate the additional PV capacity needed.</p> <p>If no additional PV capacity is desired, the user can check the "Don't add additional PV?" box. The tool will then calculate the battery capacity required to meet desired resilience for the specified existing PV array.</p> <p><br /><strong>Existing diesel generator</strong></p> <p>Some buildings (for example police and fire stations) might have emergency diesel generators. If that is the case, it is possible for the user to include the generator output in the calculations and thereby reduce the PV capacity required for desired resilience. <br />The user enters the rated capacity and the available fuel storage, and the tool calculates the hourly output based on following assumptions:</p> <p>&bull; The generator runs every hour the PV output is less than 30% of its rated capacity (based on evaluation of different scenarios)</p> <p>&bull; The diesel tank is assumed to be empty by the end on the chosen target duration</p> <p>&bull; The generator output is constant over the hours it is operating and any excess generation will be used to charge the batteries</p> <p>&bull; The efficiency varies with load, according to Cummins Pacific - Diesel Fuel Consumption Rate Calculator</p> <p><br><strong>PV array sizing</strong></p> <p>The PV system is sized to generate enough electricity (in kWh) to cover the net energy demand (emergency load minus any diesel generator or existing PV array output) during the target outage duration and any conversion losses in the solar+storage system.</p> <p>The PV capacity (in kW) required is calculated using the PVWatts generation data for 1 kW of PV for the desired target outage duration during the design outage hours.</p> <p><br><strong>Battery system sizing</strong></p> <p>To make the most use of the battery system, it should also be used during non-emergency mode. The chosen grid service (see the Assumptions tab) affects the risk of the batteries being discharged when a power outage strikes. To account for the worst case scenario in the system sizing calculations, the tool assumes the batteries to be at their lowest level typical for each grid service, which means that extra capacity needs to be added to compensate for this risk.</p> <p>The battery system is sized based on 4 criteria:</p> <p>&bull; Discharge rate (in kW) required to meet the net load for every hour during the outage</p> <p>&bull; Charge rate (in kW) required to capture any excess PV output for every hour during the outage</p> <p>&bull; Discharge capacity (in kWh) required to provide enough energy during the hours with a positive net load each day during the outage. Extra capacity is added to compensate for the risk of the batteries being discharge at the start of the outage. </p> <p>&bull; Charge capacity (in kWh) required to capture all excess energy during the hours with an excess PV output each day during the outage.</p> <p><br /><strong>System duration probability</strong></p> <p>The probability that the calculated system will provide desired resilience (i.e. support the emergency load) varies depending on when the disaster strikes. The variations are due to seasonal and daily changes in load and PV output, as well as chosen grid service. To determine if the proposed system provides desired resilience, the system duration for an outage happening every hour of the year is calculated. The probability of providing resilience for a certain number of days is presented in the bar chart. </p>

<p><strong>Acknowledgment:</strong> This tool was developed with support of the U.S. Department of Energy under Award Number DE-EE0006906.</p> <p><br /><strong>Disclaimer:</strong> This tool was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.</p>

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Welcome to SolarResilient™, a solar PV system and battery storage system sizing tool

This tool estimates the rating and physical size of grid-connected photovoltaic (PV) and battery energy storage required to provide power for extended periods when there is a large scale grid power outage. SolarResilient is designed for buildings that form part of a cities resilience strategy - it allows building owners and city departments to develop equipment sizing before embarking on more detailed studies. When used on a portfolio of buildings, optimum performing scenarios can be selected to provide a holistic energy surety strategy for a city or county.