The solar industry is booming in the United States right now. With a steady flow of solar energy entering the grid, the export value of solar has slowly declined. What’s more, many utilities have shifted on-peak hours that no longer coincide with solar generation. For many solar developers, the goal now is to keep solar a cost-saving endeavor for the end user. Read on to learn exactly just how to achieve that goal by building larger photovoltaic (PV) installations equipped with storage capabilities run by AI-driven software that controls when energy is generated, when it is stored, and when it is consumed.
The most frequently asked questions about Solar-self Consumption and the value of an energy storage solution are answered below.
What is Solar Self-consumption?
Let’s examine two key ways that an energy storage system (ESS) can benefit solar projects. Using an ESS to store excess solar production for later use is one key benefit. Another benefit, often overlooked, is that an ESS enables solar developers to size larger PV systems, which allows for greater renewable energy production that can be stored. In turn, the larger system leads to increased customer savings by consuming stored energy during peak periods instead of drawing from the grid. This is known as Solar Self-consumption (SSC).
To demonstrate how SSC can benefit a solar installation, let’s consider three scenarios: a small PV system without storage; a large PV system without storage; and a large PV system with storage. The data from the first scenario shows how solar energy generated at a small PV site can offset a customer’s load for an initial amount of savings. However, by increasing the size of the PV site and adding storage for energy to be consumed later, a solar developer can achieve maximum savings for the end user.
How does a small PV system without storage still save?
In the first scenario, a ‘small PV’ system can generate, for example, $100 in savings by consuming solar energy as it is generated. This is shown in Figure 1, where the gray line represents the customer’s load profile and the green area represents savings earned by generating and consuming solar energy instead of drawing from the grid. This represents a basic installation that does not benefit from the advantages of SSC.
Figure 1: Small PV system without storage
Why doesn’t a large PV system without storage achieve full benefits?
The second scenario is a ‘large PV’ system that generates more energy than the smaller PV system. This large PV system generates more solar energy than the customer can consume in real-time (represented by the ‘post-load’ curve that falls below 0 kW). Unfortunately, the utility does not compensate the customer for this exported energy. As a result, the additional energy goes to waste without a means to store it for future use.
Figure 2: Large PV system without storage
How does a large PV system benefit with storage?
The final scenario represents the ideal solar plus storage system in which a large PV system has installed batteries with enough capacity to store all excess PV-generated energy to be used later. The excess energy, represented by the green area below 0 kW in Figure 3, is now stored energy and becomes a valuable resource that was previously unattainable without an ESS.
Figure 3: Large PV system with storage
How does Solar Self-consumption enable the full potential of energy storage solutions?
Adding an ESS with Solar Self-consumption (SSC) to a large PV system achieves maximum savings. In Figure 4, the darker green shade represents the increased savings a large PV system with storage can obtain as compared to a small PV system without storage. SSC not only allows for increased customer savings by storing and then later consuming excess energy, but also allows for a larger PV system. This enables greater solar energy production, which in turn leads to even greater customer savings by offsetting grid-purchased energy.
Figure 4: Solar Self-consumption enables full potential of energy storage solutions
The full value of SSC is shown in Table 1 where storage increases savings by enabling the consumption of excess PV production instead of exporting.
Table 1: Total savings comparisons
How to determine optimal PV and ESS sizes
Determining the optimal size for a PV system and an ESS requires an iterative process and is subject to a few constraints, including space limitations for both the PV system and the ESS.
Stem has created a proprietary simulation tool, Athena Analyzer, to help developers compare the financial outcome of several different system sizes. Stem recommends that users of Athena Analyzer begin by sizing the PV system as large as possible given customer energy use and space limitations. Then, multiple ESS scenarios can be analyzed to determine the optimal size of the site.
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