BTM Solar/BESS Case Study - Finding the right size
Published:
By Jeff MacKinnon, P.Eng.
In the previous post I introduced the example case study and ran through the initial calculations with a 8000kWdc PV system.
At the end of those calculations we recognized 2 things:
- BESS is expensive and driving the cost of the system
- The load profile is very summer heavy.
In this run through the calculations we will see if a smaller PV system will have a similar cost savings with a lower capital cost.
The main role of this system is to power the critical systems, that have an average load of 500kW, and to have a minimum storage of 24h for the cases when there isn't enough PV to fully charge the BESS during extended outages.
Smaller PV Solar System
For this pass through the calculations I'm using 4200kWdc/3300kWac of solar with a 15deg tilt.
The previous 30deg tilt is great if we are looking of the most MWh over an entire year, but since the load is such summer heavy, a 15deg tilt makes more sense. It will not have as much production during the winter months, and will have slightly more for the summer months.
This generation profile looks like:
Expected PV Solar Generation
This has a similar profile/look to the generation profile last time, but much lower peak and slightly more drop off in the winter months.
During the winter months the peak solar matches closely to the peak load from the plant, be it a bit early.
4200kWdc generation vs plant demand - January
In the summer the peak plant demand is much higher than the solar generation.
4200kWdc generation vs plant demand - July
Since there is much less solar, there the instances where the net demand is negative are much fewer, and smaller than in the previous example.
The maximum potential export is approximately 2MW vs the 5MW in the previous example.
In fact, based on our calculations there shouldn't be any scenario where the net generation will result in energy being shifted over days. All generation will be able to be absorbed on within a 24h period.
Daily net demand - energy
Sizing the BESS
In this scenario the driving factor for the PCS is the maximum net-demand, however in this case it is much load, including a safety factor the PCS should be specified as around 2.6MW.
The BESS storage size is going to be the same as the critical power specification, or 24h* 500kW = 12MWh. This is a 2MWh reduction from the previous example, and the minimum based on the Basis-of-Design (BOD) specifications.
Configuration Cost Savings
This configuration has the potential to produce 8,090 MWh of generation and save a total of 16MW of total excess demand charges. This results in a total annual cost savings of $684,997/yr.
Configuration Capital Cost and Conclusion
The expected capital cost for this system is approximately $12,960,000, with the BESS accounting for $7,500,000 of this. With some tweaking of the design, including lowering the time period needed for the critical power storage from 24h to 12h the payback for a project like this could be improved.
The placement of these projects make a lot of sense in areas that have:
- high utility costs, both energy and demand
- low power reliability
- long lead times for utility connection
I want to elaborate on that last point. If a facility is interested in expanding faster than the utility can accept that load, whether they are transmission, generation or simply personnel constrained, a PV Solar/BESS system may be the best way to get that new portion of the plant online without increasing your demand and energy requirements for the facility.
If you have any questions, or would like for me to do some of the front end work for your project, contact me below.
What's next
I want to continue developing this project with the assumption that the project will operate with this configuration. How will integrating into the existing power system look? What areas of the plant will need to be modified? How will the scop of work (SOW) be laid out to ensure that the project can be a success?