Solar Energy Solutions
Battery energy storage (BESS)
A battery energy storage system (BESS) keeps your operation running through grid interruptions and load-shedding, and lets you use your solar energy when it is most valuable rather than only when the sun is shining. We add storage where it earns its place, so the starting point is always your load profile and what you need the battery to do.
- Chemistry
- Lithium iron phosphate (LFP)
- Used for
- Backup, solar shifting, peak shaving and time-of-use savings
- Installed range
- 60 kWh to 3 000 kWh
- Equipment
- Sigenergy, Atess, Deye, Freedom Won and Highon
What a BESS is made of
A commercial battery system is more than batteries. Each part has a job, and the system is only as dependable as the way they work together.
Battery modules
Lithium cells assembled into modules and stacked in racks or cabinets. Together they set the system's energy capacity, measured in kWh.
Battery management system (BMS)
The electronics that monitor every cell's voltage, current and temperature, keep the cells balanced, and disconnect the battery if anything moves outside safe limits.
Inverter or PCS
A hybrid or battery inverter, called a power conversion system (PCS) on larger installations, converts between the battery's DC and the site's AC. It sets how much power, in kW, the battery can deliver or absorb.
Energy management system (EMS)
The controls that decide when to charge and when to discharge: from solar, from the grid in off-peak hours, or held in reserve for an outage.
Enclosure or container
Indoor cabinets for smaller systems, and outdoor-rated cabinets or containers for larger ones, with climate control to keep the cells in their preferred temperature range.
Fire safety
Detection on every system, and on larger systems suppression and venting, designed to the manufacturer's requirements and the conditions of the local fire authority.
Why lithium iron phosphate (LFP)
Almost all commercial and agricultural storage installed today uses lithium iron phosphate, written LFP or LiFePO4. It is a lithium-ion chemistry with a very stable cathode material, which makes it considerably more resistant to thermal runaway, the self-sustaining overheating that can lead to fire, than the nickel-based chemistries used in many vehicles and consumer electronics.
LFP also handles deep daily cycling well, contains no cobalt, and retains its capacity over thousands of cycles. It is heavier for the same stored energy, which matters in a vehicle but rarely on a farm or factory site. Lead-acid batteries are still found on older installations, but their shorter cycle life and smaller usable capacity mean they are seldom the right choice for a new commercial system.
Key terms, in plain language
Capacity (kWh) and power (kW)
Capacity in kWh is how much energy the battery stores, like the size of a fuel tank. Power in kW is how fast it can deliver that energy. A battery with 200 kWh usable and a 100 kW inverter can supply 100 kW for about two hours.
Depth of discharge (DoD)
How much of the stored energy is used in a cycle. LFP batteries are commonly operated to 80 to 90 percent depth of discharge, within the manufacturer's warranty conditions.
Usable capacity
The energy you can actually draw, after the reserve kept for battery health and outage backup. We size systems on usable capacity, never on the nameplate figure.
Cycle life
How many full charge and discharge cycles the battery is rated for before its capacity falls to a stated level, often 70 to 80 percent of the original. LFP is commonly rated for several thousand cycles.
Round-trip efficiency
The share of energy you get back after charging and discharging. LFP systems typically return around 90 percent; the rest is lost as heat in the battery and inverter.
C-rate
The rate of charge or discharge relative to capacity. At 0.5C a battery can be fully discharged in about two hours; at 1C in about one hour. It sets how much inverter power a given battery can support.
What storage is used for
Most systems do several of these at once. The EMS is programmed for the combination that suits your tariff and your operation.
Backup through outages
Keeps essential loads, or the whole site, running through grid interruptions and load-shedding, with an automatic changeover. On farms that protects milking, cold storage and packing; in a business, IT, tills, security and production.
Solar self-consumption shifting
Stores midday solar production that would otherwise be limited or exported, and releases it in the late afternoon and evening when the site still needs power.
Peak shaving
Many commercial tariffs include a demand charge based on the highest demand recorded in the month, in kVA or kW. The battery discharges during those peaks to lower the maximum demand that is billed.
Time-of-use savings
On time-of-use (TOU) tariffs, such as Eskom's Megaflex, Miniflex, Ruraflex and Homeflex and the TOU tariffs many municipalities offer, energy costs most in peak periods. The battery charges from solar or off-peak supply and discharges during the peak.
How we size a battery system
- 01Read the load profileWe start with interval data from your meter or a temporary logger, showing demand every 15 or 30 minutes across weeks and seasons, alongside your tariff and bills.
- 02Identify the critical loadsTogether we decide what must keep running during an outage and what can wait. Backing up essential loads only often allows a smaller, more cost-effective system.
- 03Set the backup durationHow long those loads must run without the grid sets the usable kWh. The largest combined load, including motor starting currents, sets the inverter kW.
- 04Model the daily cycleWe model solar production, charging and discharging against your load and tariff hour by hour, so the battery is put to work every day and not only during outages.
- 05Choose the architecture and equipmentAC-coupled or DC-coupled, the inverter platform and the battery product, chosen for the site, the warranty conditions and room to expand.
AC-coupled and DC-coupled storage
Both work well. The right one depends mainly on whether there is an existing solar system and how the site may grow.
| Aspect | AC-coupled | DC-coupled |
|---|---|---|
| How it connects | The battery has its own inverter and connects on the AC side, alongside the PV inverters | The battery shares a hybrid inverter with the PV array on the DC side |
| Best suited to | Adding storage to an existing grid-tied system, and larger sites with several inverters | New systems designed with storage from the start |
| Charging from solar | Slightly less efficient, as energy is converted from DC to AC and back | Slightly more efficient, with fewer conversions |
| Flexibility | Battery and PV can be sized and expanded independently | Battery and PV are tied to the hybrid inverter's ratings |
Installation, safety and monitoring
Location and environment
- A ventilated, shaded location away from escape routes, with the clearances the manufacturer specifies.
- Temperature held within the manufacturer's operating range. Heat shortens battery life, so larger systems use climate-controlled cabinets or containers.
- Protection from dust, vermin and vehicle impact on farm and industrial sites.
Electrical and fire safety
- DC protection, isolation and earthing designed and installed to SANS 10142-1, with a Certificate of Compliance on completion.
- Battery products certified to recognised safety standards, such as IEC 62619 for industrial lithium batteries.
- Smoke or gas detection, and suppression on larger systems where the design, the insurer or the fire authority requires it.
- Clear signage and emergency shutdown procedures for your staff and for emergency services.
Monitoring
- Remote monitoring of state of charge, cell temperatures, alarms and energy flows.
- Alerts when something needs attention, so faults are found before they become failures.
- Regular reporting, so you can see how the system performs against its design.
Lifespan, warranty and our installed range
LFP battery systems typically carry a manufacturer's warranty of around ten years, or a stated number of cycles or total energy throughput, whichever comes first. Terms vary by manufacturer and depend on correct installation, operating temperature and depth of discharge, which is why the design and installation matter as much as the product.
Batteries age gradually rather than failing suddenly: usable capacity reduces over the years. A battery operated at a sensible depth of discharge and kept cool lasts longer. Over the 25+ year life of a solar system, plan for the battery to be replaced or extended at some point.
We have deployed storage from compact systems of around 60 kWh at a business, through 324 kWh on farms and 1 024 kWh at a galvanizing plant, to 3 000 kWh at a 1.5 MWp commercial plant, using Sigenergy, Atess, Deye, Freedom Won and Highon equipment.
Questions about battery storage
How long will a battery keep my site running during an outage?
It depends on the usable capacity and what is connected to it. Divide the usable kWh by the average load in kW for an estimate: 100 kWh usable carrying a 25 kW essential load gives about four hours, before any recharging from solar. We size the system for the duration you need.
Can I add batteries to my existing solar system?
Usually, yes. An AC-coupled battery with its own inverter can be added to most grid-tied systems, or the existing inverters can be replaced with hybrid units. We assess the existing installation first.
Can a battery reduce my demand charges?
On tariffs that bill maximum demand, it can, if the battery and EMS are sized and programmed for it. The benefit depends on how sharp your peaks are, so we model it from your interval data rather than promise a figure.
Is a lithium battery a fire risk?
Any stored energy carries some risk, which is why chemistry and installation matter. LFP is the most thermally stable lithium-ion chemistry in common use, and our installations follow the manufacturer's requirements, SANS 10142-1, and the conditions of your insurer and fire authority.
Do I still need a generator?
Not always. Where outages can be long or the operation is critical, a generator integrated with the battery system provides extended backup, while the battery covers short interruptions and gives a seamless changeover.
Find out whether storage earns its place on your site
Send us your load-profile data or recent bills and tell us what must keep running. We will show you the backup, shifting and peak-shaving value storage could offer, and size it honestly.
Power On!