Time for use? How to prepare PV systems today for storage tomorrow

solar storage inverters buying advice

This is an excerpt from the 2018 Inverter Buyer’s Guide. Be sure to download the full free report, complete with specs on 136 inverters at the bottom of this page.

We know that a PV system is a 25-year asset, but we maybe don’t think enough about what that means outside the viability of the initial system components. Consider what life was like 25 years ago, 1993, for example. VCRs. Zach Morris phones. Would a PV system installed on a home or business in 1993 meet the demand and performance expectations we have today?

Obviously we can’t predict what life will be like 25 years from now, but one pretty safe assumption is the rise of energy storage. Twenty-five years from now — hell, five years from now — adding storage to a solar project will be an assumption, not a novelty, so the PV systems you design today should factor this in.

Designing for storage starts with:

• A deep understanding of the load profile
• The impact of the PV system generation
• A plan for how the storage will be used

“The designer must conduct a thorough study on load behaviors and based on those results simulate cycle times and discharge levels in order to determine the lifetime of the energy storage and days of autonomy,” says Jani Kangas, VP of product lines and technical sales for ABB. “If the storage design is used for peaks management, then special calculations are to be done based on market value of peak-time shifts . The system should be designed based on ROI models and higher compensation during off-peak times.”

“Start with the basics, by asking your customers if they ever lose utility power. If so, what is the average duration?” says Alan Santos-Buch with Magnum Energy. “Battery backup is not for everyone and should address the needs of the customer, including the approximate length of time they will need battery backup. What are their critical loads? What do they need to keep running in the event of a power failure? Once those loads are determined, plan for a sub-panel to house those essential load breakers.”

If the storage design is used for peak management then special calculations are to be done based on market value of peak-time shifts. The system should be designed based on ROI models and higher compensation during off-peak times.

Component selection

Key to a design is deciding on a battery charge controller. This is the brain that’s running your energy storage system. Regardless of your generated energy input and batteries you choose, designers need to find the right controller to manage storage, loads and battery charge levels. Some examples:

  • As part of its Magnum Energy product line, Sensata has an integrated solution that complements a variety of system designs, including microinverters.
  • The Ideal Power Stabiliti is a multiport inverter that accommodates PV and batteries at different input voltages, without the need for external optimizers or charge controllers.
  • The Tabuchi EIBS is an all-in-one system that includes the inverter and storage battery.
  • The Pika Energy Island [pictured above] allows for a solar-only install today and then an easy plug-and-play storage option down the road.

“It’s crucial to consider future changes: If you want to avoid peak rates, or improve resilience (backup power), or simply net meter solar, it’s relatively easy to find a system that can cover one of those applications well. What has proved more difficult is finding a system that will fit the needs of today and the needs of tomorrow,” says Jeremy Niles, marketing manager for Pika Energy. “For many, it’s very difficult to break away from thinking in terms of AC coupling, 2V battery increments, bank design, hydrogen sensors and giant aluminum conductors. Grid-tied solar-plus-storage is now a plug-and-play proposition with the right system.”

For PV-plus-storage systems, one efficiency metric to consider is the number of AC-DC conversions. The fewer amount of conversions, the more efficient the system and thus the more energy available for system owners. A DC-coupled system is simpler in this way.

“The PV system should be large enough to meet both the requisite energy demands and also charge the battery,” says Lior Handelsman, SolarEdge’s VP marketing and product strategy and founder. “A DC-coupled solution will decrease energy loss from inefficient conversion and increase the amount of energy that can potentially be routed to the battery. This will potentially allow oversizing of the system so that the additional energy can flow directly to the battery.”

For more info on the newest inverters on the market download our free 2018 Inverter Buyer’s Guide

— Solar Builder magazine

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