Although we have titled this article the future for PV, the reality is that we have being implementing PV storage systems since the beginning of our industry. The systems were being deployed in what we call the 'off-grid' market, telecom, coast guard, cottages and RV. The big change that is coming will be the amount of PV storage connected to the grid. The grid connected PV storage will play a big role in our future grid with applications such as: back-up power, load shedding, time of use, frequency/voltage regulation and autonomy. Rocky Mountain Institute put together an excellent research paper on the economics associated with these functions. We know that if we can make money at selling storage related functions, the industry will grow.
Because there is a big potential for all these PV storage revenue streams, the race is on to pick the best technology to do it with. All the functions listed in the economic study rely on the quick reaction of electrochemical storage (Batteries). When these are coupled with an inverter, there are a wide variety of services that can be offered. Out of all the battery technologies we researched, those ones that seemed to be the most active in the market were Lead-acid, Lithium Ion and Salt Water.
The salt water batteries didn't make sense to us due to its limitations. When we look at storage, we don't just consider the storage capacity and costs. We look at cycle life, size, weight, instantaneous current, and operating temperatures. The salt water batteries seemed to be a backwards step, going to larger and heavier systems to store less energy. The big issue was the limited amount of instantaneous current (you can't power big loads) and the freezing temperature near zero (not great for Canada). It appears the rest of the industry agreed, as unfortunately, the salt water battery manufacturer Aquion announced bankruptcy this week.
Lithium Ion seems to be the technology that is making the most headway, due to the size and weight being low for the amount of energy stored. There are limitations on their instantaneous current and operating temperatures, but we are hoping that these will improve in the next few years. If you are planning to use one of these batteries, be aware of the current limits to be able to handle your loads. Also, ensure your manufacturer is reputable, as we have seen issues (especially thermal runaway) with low end manufactures, and make sure your inverter will interact properly with the batteries management system (BMS).
This brings us back to the beginning of PV storage with lead acid. We see this as the current leader in battery storage. The biggest asset to lead acid is that it has been around forever. We know everything there is to know about this technology. It’s tried, trusted and proven. We know how to connect it, charge it, maintain it and most importantly of all, we know how to recycle it (not the case for the other two types of batteries). This is only our opinion and we welcome your feedback on this topic.