Hiding in plain sight: The case for rooftop batteries leading the next era of solar + storage

Hiding in plain sight: The case for rooftop batteries leading the next era of solar + storage
Yotta Solar

Yotta Solar has an intriguing rooftop battery system that can double as “ballast” to mount PV.

Although self-evident in retrospect, game-changing innovations are rarely immediately obvious. Velcro bindings, wheelie suitcases, and the now-ubiquitous InstaPot are all modest examples of refinements to products that existed for decades before anyone thought, “Couldn’t this be better?”

The drive for reliable renewably sourced energy is at a similar crossroad. Although a workable solution for some, today’s standard centralized energy storage systems are not always reliably safe or cost-effective. Moreover, safety concerns relating to lithium-ion batteries, the most commonly used cells in today’s battery systems, can put the brakes on the engine of the renewable energy train just as it is picking up speed. To enable everyone to get on board to a clean energy future, alternative approaches need to be considered.

Panel-level storage is one such potential alternative that makes storage both affordable and accessible. The idea is to mount a safe, thermally protected battery behind each solar panel. This modular storage system would be easier to design and install, avoid certain soft costs and prolong battery life with less risk. Let’s dig into it.

Better safety through design

The main concern with a standard centralized storage system is, of course, the risk of fire. Container/building storage solutions use lithium-ion batteries, which have been shown to catch fire through a state known as thermal runaway. While rare, thermal runaway is difficult if not impossible to predict and may cause collateral damage and fires. When it does occur, having batteries stacked together — a common configuration in a centralized storage system — simply compounds the issue and can make the fire even more dangerous.

A panel-level storage solution could address this risk in three different ways. It starts with using lithium iron phosphate (LFP) cells in the storage system. Unlike lithium-ion, LFP batteries are less prone to thermal runaway, so they have minimal-to-no fire risk while retaining the benefits of a lithium cell. Next, would be housing the battery in an IP67 fire-preventive enclosure (like Yotta Energy’s SolarLEAF). Lastly, by mounting each unit behind a solar panel, the batteries are evenly distributed 3 feet center to center throughout the array, eliminating the opportunity for cascading thermal effects.

Climate-agnostic tech

Temperature extremes are tough on batteries, which is why centralized storage systems need heating, ventilation, and air conditioning (HVAC) or liquid-cooling. To safeguard cell life, it is smart to contain a thermal protection system similar to the technologies that protect electronics and batteries in satellites. This type of energy storage system uses passive cooling, using no external power to cool the battery in summer and minimal power consumption in freezing temperatures, with no moving parts to maintain or replace.

Regulating temperatures within a prescribed operating range has many benefits: the battery operates with a 95% round-trip efficiency, the system is safer, and the battery’s operating life is maximized for up to 20 years—three times the life of a standard Li ion battery—allowing the batteries to live as long as the solar array itself.

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Smarter installation

By redesigning energy storage, panel-level storage systems address multiple installation issues. For example, each 1 kWh-capacity battery is designed to be plug-and-play, mounting easily between the PV modules and the inverter. The units are just as simple to retrofit or swap out should needs change, with no steep learning curve for installers.

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Keeping the batteries with the panels pulls double duty because the batteries also replace the usual concrete ballast — PanelClaw is specifically supporting one such mounting system design. With no dead weight to ship or install and no additional wiring, building solution or maintenance to deal with, a panel-level storage system comes together faster and can cost less than a centralized system.

Filling the gaps

The energy storage market is rife with products that are too big for the majority of market consumers. No one wants to buy XL or XXL when what they really need is a medium. By developing an energy storage solution that is small enough to handle the needs of a 5 kWh consumer yet scalable enough to handle 300 kWh or even 1 MW consumers, panel-level storage can bridge the void between no storage and too much storage and can be optimized down to the kWh to maximize payback for any given project.

Lower cost of power over time

By eliminating the necessity of battery specific inverters, environmental control and safety equipment, the balance of solar costs for panel-level storage would be much more manageable. In addition, panel-level storage has none of the land, building envelope, fencing, HVAC, fire suppression, trenching, or additional wiring costs of centralized systems, simplifying the total hardware system and minimizing or eliminating any lifetime maintenance cost.

Now let’s think about a project’s “soft costs,” which can be dramatic. Siting, in particular, can be tricky in C&I, especially for larger-scale installations, where engineering, financial, and legal experts are involved. Larger systems like the example above need a dedicated plot of valuable real estate with approximately the same footprint as a shipping container, if not bigger, with a cost to match. By making storage as easy to install as the PV panels themselves and leveraging the PV installation process, panel-level storage avoids these kinds of unpleasant, sometimes unforeseeable costs.

Other ways that panel-level storage reduces costs include the ability to design the system remotely, as well as the elimination of many standard storage O&M costs, such as facility, HVAC and fire suppression, and battery maintenance.

The next level of innovation

Energy storage has come a long way over the last twenty years, and we have further to go. Viable in any climate, and safe everywhere you put it, a panel-level system puts storage on wheels, freeing it to go wherever solar panels can. With a low risk of thermal runaway and no siting requirements, panel-level storage can be installed in locations where centralized, large-scale lithium-ion battery storage is not desirable, permittable, or economical.

To really grow in the storage market, our industry needs to have smart, elegant solutions that are also intuitive, safe, and cost-effective. Panel-level storage eliminates the expense and risks of centralized storage, creating an easy add-on for developers and installers and enabling them to expand their customer base with a solution that releases the throttle on energy storage for everyone.

Authored by the team at Yotta Energy.

— Solar Builder magazine