Off-grid microgrids provide power for remote mining areas. They combine PV systems, energy storage cabinets, and diesel generators. It cut reliance on costly grid extensions. Provide low-impact, reliable, cheap power. Key solutions are to optimize PV and ESS capacities. This will boost self-sufficiency and cut costs.
Table of Contents
Off-grid Microgrid Projects
An off-grid microgrid is not connected to the main power grid. It consists mainly of PV systems, Energy Storage Cabinets, and diesel generators. The diagram below shows the structure and components:
Key:
- PCS: Power Conditioning System (ESS inverter)
- BMS: Battery Management System
- MG: Microgrid
- EMS: Energy Management System
The main components include:
- PV arrays and PV inverters
- Energy storage system with PCS and BMS
- Diesel generators
- Microgrid bus (0.4kV low voltage bus)
- Microgrid switch
- Microgrid load
- Power transformer (to public grid if required)
Project Characteristics
- Located in an overseas mining area, covering 25 km2, about 60 km straight-line distance from the nearest town
- Building new transmission lines would require 90 km of 33kV overhead lines
- Typical of remote mining areas:
- Far from city centers
- No nearby villages, often in uninhabited areas
- Inconvenient transportation
- Tens of kilometers often separate these areas from the nearest power grid and transmission lines.
Power Supply Characteristics
- Long transmission distances, high line construction costs, large line losses
- To save on initial investment, mining areas often use heavy oil or diesel generators, which have high operating costs and noise
- Power supply usually includes 24-hour work power, living area power, and production power
- Requires reliable power supply, higher load levels, and larger load fluctuations
Load Conditions
Given the mining area’s power needs, the owner is considering a mix of PV, Energy Storage Cabinets, and optional diesel generators. For a gem mining area, the main power equipment includes excavators and ore dressing equipment. The load is 250kW for mining equipment (160kW for the motor) and 50kW for the living area. Considering future load growth, experts estimate the total load at 300kW. We consider the load to be 24 hours uninterrupted, with the main load during 8:00-16:00 daytime and a night load of about 100kW. You can calculate the power consumption as 300×8+100×16=4000kWh. The local industrial average electricity price is 12 to 13 US cents/kWh.
The next sections will analyze the power balance. They will find the best PV-storage ratios. Then, they will conduct an economic analysis. It will determine the initial investment and cost per kWh under different ratios. The goal is to select the best solution, calculated over 10 years.
Solution 1: Grid Power Supply (New Overhead Lines + Substation)
- Build 90km 33kV overhead lines and 33kV/0.4kV substation
- Based on average grid electricity price of 0.13 USD/kWh
- Initial investment + grid electricity price, the converted cost per kWh is about 0.45 USD
Solution 2: Independent Diesel Generator Power Supply
- Diesel generator set procurement cost is generally 75 USD/kW
- Diesel generator fuel consumption (L/h) = generator capacity (kW) * 0.25 (L/kWh), i.e. 0.25L diesel consumed per kWh generated
- Diesel generator set operation and maintenance costs include:
- Generator overhaul: Needs one overhaul every 25,000 operating hours (3 years). After three overhauls over 10 years, the maintenance team scrapped the unit due to high costs after three times. Maintenance cost: 1st time: 30% unit procurement cost; 2nd time: 40% unit procurement cost; 3rd time: 50% * unit procurement cost
- Unit maintenance cost: Every 500 hours, engine oil and filter need to be replaced.
- Overall analysis shows the cost per kWh is about 0.29 USD
Solution 3: PV + Energy Storage Cabinets + Diesel Generator (Backup Emergency Power)
- Requires 1MW PV + 1.6MWh ESS + 200kW*2 diesel generators
- During the day, 1MW PV power directly supplies the load, excess power enters the ESS
- At night, the ESS discharges to supply the load
- Diesel generators are only used as backup power and only started during continuous rainy days (estimated 50 rainy days per year)
- The overall cost per kWh is about 0.1 USD
Solution 4: PV + Energy Storage Cabinets + Diesel Generator (Night Power)
- Requires 600kW PV + 0.5MWh Energy Storage Cabinets + 200kW*2 diesel generators
- During the day, 600kW PV power directly supplies the load, PV system generates 2400 kWh per day
- ESS is only used for power smoothing control, and does not store power for nighttime
- Night load supplied by diesel generators, generating about 1600 kWh per day
- The overall cost per kWh is about 0.13 USD
Summary
- To reduce initial investment, PV+Energy Storage Cabinets+Diesel (diesel for night power) can be selected
- For the lowest cost per kWh, PV+Energy Storage Cabinets+Diesel (emergency backup) can be selected
- In the above analysis, equipment costs mostly use analogous data. For some projects, detailed inquiries and research should find the exact investment costs.
- The analysis method used above is for preliminary estimation (investment opportunity judgment). Due to a focus on simplicity and speed, we use only basic financial tests as a guide for judging investment opportunities.
- For real projects, calculate the cash flow statement for the entire life cycle. Use project fundraising, procurement, construction costs, and operations and maintenance. Use strict financial methods to calculate the project’s ROI, cost per kWh, and other metrics.
System Design
- Increasing PV installed capacity also increases the microgrid’s self-balancing rate. Adding energy storage can reduce renewable energy transmission to the grid. This can improve the microgrid’s self-balancing rate.
- As ESS capacity increases, the system’s annualized cost increases approximately linearly. Appropriately increasing PV capacity has a certain effect on improving microgrid economics.
- Given the microgrid’s cost and island area, it must power the island during its operation. Also, it must have a self-balancing rate of 28%. So, the final plan is to use a 300kWp PV and a 4MWh ESS.
System Structure
- The microgrid’s two segment buses connect to two 10kV lines of the Luxi substation. They do this through fast switch 1 (KS1) and fast switch 2 (KS2), with fast switch 3 as the segment switch.
- Sub-microgrid 1 will research wind-PV-storage microgrid energy management. It will also study multi-energy coordination control technologies.
- Sub-microgrid 2 studies hybrid energy storage to smooth wind power fluctuations.
- The BESS System: Construction, Commissioning, and O&M Guide
FAQ
What is a microgrid?
A microgrid is a localized group of electricity sources and loads. It usually runs in sync with the centralized grid (macrogrid). But, it can disconnect and operate autonomously as conditions dictate.
What are the main components of an off-grid microgrid?
The main components of an off-grid microgrid typically include:
Photovoltaic (PV) arrays and inverters for solar power generation
Energy storage system with power conditioning system (PCS) and battery management system (BMS)
Diesel generators for backup or supplementary power
Microgrid bus for power distribution
Microgrid switch for grid connection/disconnection
Loads (power consumers)
What are the characteristics of power supply in remote mining areas?
Power supply in remote mining areas often faces challenges such as:
Long transmission distances leading to high line construction costs and large line losses
Far from main power grid, often no nearby transmission lines
Use of heavy oil or diesel generators resulting in high operating costs and noise
Requirement for reliable power supply to support 24-hour operations
Higher load levels and larger load fluctuations compared to typical power consumers
What factors should be considered when selecting a microgrid solution?
When selecting a microgrid solution, key factors to consider include:
Initial investment costs
Operating costs (e.g. fuel costs for diesel generators)
Reliability and continuity of power supply
Environmental impact (e.g. carbon emissions)
Space constraints for equipment installation
Projected power consumption and load profiles
Potential for renewable energy integration
Maintenance requirements and equipment lifespan
How does increasing PV and Energy Storage Cabinets capacity affect microgrid performance?
Increasing PV capacity can improve a microgrid’s self-balancing rate. This is the percentage of power demand met by local generation. Adding Energy Storage Cabinets can cut excess renewable energy exports to the grid. This would help with self-balancing. However, increasing Energy Storage Cabinets capacity also leads to higher system costs. Properly sizing the PV and Energy Storage Cabinets components is key. It optimizes microgrid costs and ensures reliability.
What is the purpose of the microgrid switches?
Microgrid switches allow the microgrid to connect to or disconnect from the main grid. Fast switches 1 and 2 (KS1 and KS2) connect the microgrid to the external grid. Fast switch 3 connects the two internal microgrid segments. This setup lets the microgrid operate in two modes. It can work independently (islanded mode) or sync with the main grid as needed.
What are the research focuses of the sub-microgrids?
The two sub-microgrids in this project have different research focuses:
Sub-microgrid 1 focuses on energy management and control tech for microgrids that integrate wind, PV, and energy storage.
Sub-microgrid 2 focuses on using hybrid energy storage to smooth wind power fluctuations.
