Battery maker Trojan claims its new proprietary ‘Smart Carbon’ technology can improve the cycle life of lead acid batteries by as much as 15%, through effective management of the cell in a partial state of charge.
The company, which has been in business since 1925, produces lead acid batteries for use at various scales. It claims that its new products are particularly suitable for use in partial state of charging (PSOC) applications, such as those involving PV and where grids are backed up by diesel generators.
PV Tech spoke to Trojan’s senior applications engineer for renewable energy, Kalyan Jana at the Intersolar Europe show in Munich last week. Trojan was exhibiting in the expanded electrical energy storage area at Intersolar.
“About five years ago, Trojan recognised that the problem of deep cycling batteries will not go away, especially where renewable energy applications are concerned. We came up with ‘Smart Carbon’. It’s a proprietary addition, of special carbon additive to the negative paste and what we’ve found is that in a PSOC cycling applications, the addition of Smart Carbon improves cycle life by as much as 15%.”
Jana explained that while lead acid batteries are still cheaper and more readily available than more modern technologies such as lithium-ion, the need to optimise battery performance is much more acute when you have a lead acid battery being only partially charged and then discharged.
“Carbon has been used in lead acid batteries since the very beginning but this [Smart Carbon] is something different. It has been designed to improve the performance of lead acid batteries in a partial state of charge cycling application. What happens is that you start with the charged battery. You then discharge it to maybe 50%, perhaps then charge it back up to 80% and then discharge it again, so the battery never quite gets fully charged and that is a bad scenario for a lead acid battery as it compromises the cycle life. Usually for the best battery performance, you need to fully charge it after each discharge, so in a partial state of charge cycling application that is not happening. In a renewable energy application that is a fact of life,” he said.
“You might not have full power from solar and even if you have a diesel gen-set on site, you might not want to run it because of fuel costs, noise pollution and every few thousand hours the diesel gen-set needs to be maintained so the lesser you run it, the longer the time it lasts.”
Jana said that for the last few months the company has already begun shipping systems to India, where the use of noisy, expensive and polluting diesel systems is still fairly common. He also pointed out one other, widespread opportunity for the PSOC system’s use.
“They have a lot of off-grid systems and a lot of diesel. Telecom back-up is another example because of the unreliability or lack of availability of grid power. Because of the long power outages, that is really a cycling application.”
At present the company produces batteries from 12V 33Ah up to 2V, ‘almost’ 1200Ah which Jana describes as a “considerable range” of capacity. PV Tech wondered whether lead acid can remain competitive in the way it adds value to renewable energy systems in these days where European renewable energy subsidies are being phased out or disappearing, for example. Jana highlighted the versatility of storage in performing tasks such as peak shaving or allowing generators to sell electricity back to the grid.
“For all of that you need storage. Lead acid, even today, probably offers the lowest storage cost per cycle,” Jana said.
Jana went on to give some rough figures on the performance of batteries made with Trojan’s ‘Smart Carbon’.
“[How long the batteries will last…] depends how deeply you discharge the cycle. Our industrial flooded line, at 50% depth of discharge can give you something like 2,700 cycles. If you assume that you’re cycling it once a day, it can give you about eight to nine year life. An AGM battery, at 50% you get 1,000 cycles, so that is about a three year life. It depends on which battery or family of products you’re looking at.”
Jana said that although Trojan is at present focused on lead acid systems, he said in terms of chemistries and technologies, the company is “always looking at other options”. He did however say that in the short term, the simplicity of lead acid is another advantage for Trojan.
“[You] don’t generally require a battery management system it’s not mandatory as it is with lithium-ion, so lead acid is a lot simpler, less expensive. That’s not to say you can’t connect a BMS. You can - you can track voltages, currents, what kind of temperature it’s exposed to, how many discharges. In some cases it might be useful for potential warranty claims or something like that but it’s not a ‘must-have’, unlike lithium-ion.”
“We do work with a lot of systems integrators and we are component agnostic, who’s charge controller, whose inverter as long as the battery is charged in line with our recommendations.”