Solar Builder spent some time talking with Dean Middleton, director of renewable energy sales for Trojan Battery Co., about the basics of using batteries with solar installations and what’s in the future for energy storage. Here’s a crash course in batteries and energy storage in the solar industry.
What type of batteries does Trojan manufacture for the solar industry?
Trojan Battery Co. focuses exclusively on deep-cycle battery technology. It’s not a sideline for us; we’re not building automotive batteries and then having a minor focus on deep-cycle. The company was started in 1925, and we’re in the fourth generation of the original family.
There are two general classifications for deep-cycle batteries — flooded and VRLA (valve-regulated lead acid). A flooded battery is an open-cell battery that has removable vent caps and requires maintenance on a regular basis, consisting of topping off the electrolytes with distilled water. VRLA is often referred to as maintenance-free — you cannot remove the vent cap and refill the electrolytes. That means you essentially have a partially sealed battery, and it’s designed so that you don’t have to maintain it.
VRLA falls into subcategories: gel and AGM. Each one has plusses and minuses depending on the details of the application. We as a company are focusing on expanding our AGM line. We feel that AGM is the technology that has the broadest applications in the solar market in the future.
Why would people choose a flooded battery over a maintenance-free VRLA?
The benefit of a flooded battery is that you’re going to get longer-term performance, better cycle life and, more importantly, it’s going to be at a lower cost. You’re going to get more for your money with a flooded battery over any VRLA technology in any size.
With a VRLA, why would anyone pay more for less performance? You have to take into account the application. For example, if you have a lighting project that has 1,000 light poles along a highway that are solar powered, and you have one battery at each light pole in an enclosure, 30 ft off the ground, the last thing you want is to have a service truck go around to each battery on a monthly basis, climb the pole, open the battery and add distilled water. It doesn’t make economic sense. In an application like that where you have low power and multiple systems deployed in an isolated project, maintenance is a real issue. It makes sense to go with a maintenance-free battery even with the loss of cycle life. You really have to take into account the economic drivers of a project.
What is “cycle life”?
A deep-cycle battery is designed to be deeply discharged and then recharged over and over again, unlike a car battery. When you take a car battery down to zero, you kill it. The deeper you discharge a deep cycle battery, the less cycles you get out of it. If you take the battery down to 100 percent depth of discharge (DOD), meaning you’ve taken all the energy out of it, you’re going to get X amount of cycles. But if you take it down to 50 percent DOD, using half of it on a regular basis, you’re going to get more than X. Every deep-cycle battery is going to have that curve, showing you the relationship between the DOD and cycle life. The more conservative you are in your design, the longer your system will last. Most manufacturers, Trojan included, don’t recommend that you design your system for any more than 50 percent DOD, to get the most life out of a battery.
Are there any standards/testing for batteries?
In the battery industry, we don’t have an equivalent test (compared to module testing). If I show you a cycle life graph for my battery, it’s not necessarily based on the same conditions as my competitor. It’s a very unfortunate situation for the end-user. Customers are out there comparing cycle lives, assuming all things are equal, and nothing could be further from the truth.
One of the things that we spent a lot of time on in the last year is bringing to people’s attention that there are some internationally recognized standards available (IEC 61427, more specifically), and we test our products to those standards, and we feel that other manufacturers should do the same. We’re doing a lot of education in that regard. IEC 61427 is specific to deep-cycle batteries and it comes closest to representing a battery-based solar system. It’s a very challenging test that puts the battery through a workout that is closest to what it’s going to experience in the field. We also do third-party testing to prove that a battery rated to this standard with a healthy cycle life is better than one that doesn’t.
What do you expect in the near future for energy storage?
We’ll start to see more incentives for energy storage to be included as a part of grid tied solar systems which have historically not included on-site storage — that is the trend in Europe. There will be more incentives to add battery banks to both existing and new grid tied solar system installations. I think we’re going to see a lot of new products in the next few years in terms of better integrated packages, more consumer-oriented packages. I don’t see too many companies out there with well designed, consumer-friendly packages. That is a huge opportunity for U.S. distributors and integrators that are already working in that space.
There is a lot of excitement about energy storage, but I think there are a lot of people that aren’t sure which way to go. There are a lot of people out there looking for solutions. Who can provide me with the whole package? I see a window of opportunity to integrate the inverter component, the battery component, the disconnect component, the circuitry into a single system that can be sold on the residential scale. I think that’s where we’ll see quite a bit of change in the next year or two.
Dean Middleton has spent more than 18 years in global sales and export of PV and solar thermal systems and joined Trojan Battery in 2009. Visit trojanbattery.com for more info.
— Solar Builder magazine
[source: http://www.solarbuildermag.com/featured/trojan-battery-company-solar/]
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