Article #4 – Energy storage: a perfect partner for solar PV

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“Solar and storage are key to reducing geopolitical risk [1]"

Sérgio Granato de Araújo*

Solar PV stands out with unlimited energy supply, but variability in solar radiation challenges its integration into the grid. Storage mitigates this problem, increasing the value of the renewable energy as a whole. With great potential for generating energy from renewable sources, Brazil still has barriers to the use of storage for renewables integration. However, the future outlook is encouraging

THE VAST MAJOTIRY OF prospective economic analysis are converging on the idea that the energy transition should be seen as a consolidated trend [2]. Electrification, the #1 vector to bring about this transformation, continues to follow an increasing trend to reach nearly 50% of total final energy consumption by 2050, from about 20% in 2018, a 150% growth in a 32-year span [3].

There is a huge potential in electricity production from variable renewable energy (VRE) sources, in particular solar PV and wind, which are now more competitive than gas-fired gen [4] [5]. With no moving parts and low maintenance, solar PV systems stand out as the main VRE source to displace fossil-fired electricity.

Renewable capacity is expected to grow over 8% in 2022 compared with last year, reaching 300 GW. Solar PV is projected to account for 60% of the increase in global renewable capacity in 2022 with the commissioning of 190 GW, up 25% from last year [6].

But VRE sources have some features such as geographical and temporal variability that challenges their integration into the grid [7].

Storage need

Solar PV has an obvious major drawback as a primary energy source, only providing power when sunlight is available. Also, it generates the most power when the sun is shining its brightest, which may not be consistent with when energy is most valuable [8].

Battery energy storage system (BESS) is the ideal partner for VRE sources. Its ability to store energy for future use and rapidly respond (in fractions of a second) to power fluctuations eases the integration of intermittent sources, while maintaining system stability and reliability.

Solar PV plus BESS (S+B) make solar strongly competitive with thermal, nuclear, and hydropower plants. Taking advantage of the lowest LCOE, solar PV’s share in 2050 power supply will top 36%. One third of all solar production will be built with direct storage, and by 2050 S+B is expected to produce 12% of all grid-connected electricity [9].

S+B functions

The ability to deliver firm energy commitments during hours of the day is what most people think about S+B [10].

BESS comes in as an important accessory to add value to solar panels, mainly in situations where the tariff is not appropriate at the time of generation, which tends to increase with higher penetration level of distributed energy resources [11].

The addition of BESS to utility-scale solar PV installation allows system operators the opportunity to capture additional revenues thru functions as i) capacity firming, ii) energy time shifting (arbitrage), iii) clipping recapture, iv) curtailment and outage recapture, v) low voltage harvesting, and vi) ramp rate control [12].

Residential and commercial and industrial (C&I) customers are installing storage (typically 5-13.5 kWh and up to 5-10 MWh, respectively [13]) to add resiliency and ensure power quality. Behind-the-meter (BTM) S+B applications are also deployed to further reduce reliance on grid power and to protect against future electricity price rises [14].

S+B design basics (largely based on Fluence white paper)

In the design of S+B systems one has to determine i) whether DC (co-located) or AC (co-located or standalone) coupling is the best fit for the project, ii) the storage size, i.e., the storage-to-solar ratio, and iii) the inverter loading ratio (ILR), i.e., the DC-to-AC ratio for DC-coupled S+B [10].

Reduced equipment cost, higher round trip efficiency, and the capture of solar energy that is clipped are the main benefits of DC coupling, while less operational flexibility is its main drawback. Also, by co-locating BESS and solar panels, the project can share the balance of plant costs including the cost of land, labor, project management, permitting, interconnection, operations, and maintenance [10].

BESS are sized based on i) how fast the battery can deliver power (kW) and ii) how much energy in total (kWh) the system can deliver. So, given i) the hours of dispatchable power the grid needs and ii) the hourly solar generation profile, the power (kW) and energy (kWh) requirements of the system must be defined [15].

Determining the value of additional firm solar energy will likely be based on the avoided cost of existing generators or the cost of new capacity additions modeling, which requires a granular analysis at the hourly level to determine how much firm energy can be delivered for different time durations [10].

In most regions, solar developers overbuild their systems with extra PV panels to increase the energy output in months with reduced sunlight, maximizing the overall performance thru the year. Generally, the maximum ILR for S+B will be limited by i) land, to install solar panels, ii) interconnection, which limits the amount of power they can inject into the grid, and iii) economics, analyzing if revenues cover extra costs [10] [16].

Brazil: qualifications & regulatory issues for S+B (see bottom of this page)

14, October, 2022

* Professor at School of Electrical, Mechanical and Computer Engineering (EMC) of Federal University of Goiás (UFG)


















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