Battery backup that puts you in control of your own power
Store your own solar power, or cheap grid power, and use it exactly when you want. A battery sized to your real load, not a guess.
Start an assessmentBuying a battery without knowing your real numbers
Does this sound familiar?
The right battery size comes from your real load, worked out properly, not a number picked off a shelf.
We help South African homes and businesses size a battery from their real numbers
A battery stores power you already paid less for, either your own solar or grid power bought at its cheapest hours, and gives it back to you when you choose. That means using your own stored power at the priciest time of day, cutting demand charges for a business, and keeping the circuits you choose running on your own terms. This is control over your own supply, every day, not a plan for a crisis.
You can add battery storage two ways. A Backup Kit is an inverter and battery only, with no panels: it stores power bought from the grid and gives it back when you want it, and panels can be added later. A full system adds panels too, so the battery is charged for free by the sun during the day as well.
EFJS Printing runs a 30 kW FoxESS three-phase hybrid inverter, a 12 kWh battery and 27 x 550 W panels, and it paid back its investment in 2.5 years. Every FoxESS and Sigenergy battery and inverter we install carries our 10-year swap-out warranty.
And we can do the same for you.
The inverter, panels and the DC to AC conversion that makes a battery useful are covered fully on Solar Power Inverters and Solar PV Panels. This page covers what is specific to sizing and running a battery.
What a battery does on a normal weekday: a home
Early morning, while grid power is cheapest, the battery can top up from the grid, or from panels once the sun is up.
Mid morning into the afternoon, panels are at their highest output. Any solar power the home is not using right now charges the battery. A battery earns its keep every ordinary sunny day.
Late afternoon into the evening, household load rises: cooking, lights, and a geyser cycling on. This is also Eskom's evening peak window, the priciest time of day. The inverter switches to the battery automatically, using stored power instead of expensive grid power.
Once the evening peak passes, the home can draw from the grid again at cheaper rates, saving what is left of the battery for tomorrow, or for the circuits you have chosen to keep running on your own terms.
What a battery does on a normal weekday: a business
Morning, as production starts up, a battery can smooth the first big jump in power draw as machines switch on, the exact moment that can set a business's demand charge for the whole month.
Midday, solar output is at its highest. The battery is charged with any surplus once the site's own load is covered.
Afternoon into the evening peak, as the grid gets pricier, the inverter leans on the battery instead of the grid. This is called peak shaving: it lowers both the energy cost at the priciest hour and the demand charge that hour sets.
After hours, security lighting, servers and any equipment left running draw down what remains, or top up again from cheap off-peak grid power ready for the next working day.
Sizing a battery: kW vs kWh, and depth of discharge
kW measures power: how fast something uses electricity right now, like a car's speed. kWh measures energy: how much is used over time, like the distance travelled. A battery's size is given in kWh, its total stored energy. How fast it can push that energy out is its kW rating.
Depth of discharge (DoD) is how much of a battery's total capacity you can actually use. The maker sets this figure. FoxESS batteries run to 90 percent depth of discharge, so a 10.36 kWh FoxESS battery gives about 9.32 usable kWh, not the full 10.36. Sigenergy lists each module's total size, and the usable figure is a little lower. Always size on the usable figure.
Usable kWh is what matters for sizing: nominal kWh multiplied by the depth of discharge. Run time is then simple division: usable kWh divided by the kW your chosen circuits draw gives the hours they can run. An inverter never converts power at 100 percent efficiency, so real run time is always a little less than this arithmetic suggests.
A worked example: sizing a battery for a home
Example only, your numbers will differ. This shows the method. The free energy assessment measures your real load and confirms the size.
| Circuit | Running load | Hours you want covered | Energy needed |
|---|---|---|---|
| Lights and plugs | 400W | 5 hours | 2.0 kWh |
| Fridge, running | 150W | 5 hours | 0.75 kWh |
| TV, router and electronics | 200W | 5 hours | 1.0 kWh |
| Wifi and security | 50W | 5 hours | 0.25 kWh |
| Total | 800W | 4.0 kWh |
Add a 20 percent margin so the battery is never run right down to empty: 4.0 kWh x 1.2 = 4.8 kWh usable.
At 90 percent depth of discharge, the nominal FoxESS battery needed is 4.8 divided by 0.9, about 5.3 kWh. A FoxESS EP5 battery (5.18 kWh nominal) gives about 4.66 usable kWh, just under this 4.8 kWh target. One FoxESS EP11 battery (about 9.3 usable kWh) covers it with room to add circuits later. A Sigenergy 6 kWh module (6.02 kWh total, a little less usable) also covers it.
A worked example: sizing a battery for a business
Example only, your numbers will differ. This shows the method, using typical figures, not a real client's numbers.
| Load shifted through the evening peak | Running load | Hours shifted | Energy needed |
|---|---|---|---|
| Critical production equipment | 3kW | 2 hours | 6 kWh |
| Office lighting and computers | 1.5kW | 2 hours | 3 kWh |
| Cold room or refrigeration | 2kW | 2 hours | 4 kWh |
| Total | 6.5kW | 13 kWh |
Add the same 20 percent margin: 13 kWh x 1.2 = 15.6 kWh usable.
At 90 percent depth of discharge, the nominal FoxESS capacity needed is 15.6 divided by 0.9, about 17.3 kWh. Two FoxESS EP11 batteries stacked (20.72 kWh nominal, about 18.6 usable kWh) cover it with room to spare. With Sigenergy, two 9 kWh modules (9.04 kWh total each, a little less usable) also cover it, well inside the six modules allowed on one controller.
A business's real number depends on which loads it chooses to shift and for how long, which is exactly what the free energy assessment works out from your own bill and demand charges.
FoxESS and Sigenergy battery sizes
| Brand | Battery | Size | Depth of discharge | Adding more | Chemistry | Weather rating |
|---|---|---|---|---|---|---|
| FoxESS | EP5 | 5.18 kWh | 90 percent | Up to 4 units on one system (20.8 kWh) | LiFePO4, high voltage | IP65 |
| FoxESS | EP11 | 10.36 kWh | 90 percent | Up to 4 units on one system (41.6 kWh) | LiFePO4, high voltage | IP65 |
| Sigenergy | Battery modules | 5, 6, 8 and 9 kWh modules | Usable figure a little under the total | Up to 6 modules on one controller | LiFePO4 | IP66 |
| Sigenergy | Larger batteries ZenSolar also fits | 12 and 16 kWh | Ask us | Ask us | LiFePO4 | Ask us |
Choosing and growing a battery
| Question | What it means for you |
|---|---|
| Separate boxes or one stack | FoxESS batteries are separate boxes, up to four units on one system. Sigenergy's SigenStor is one stack of controller and up to six battery modules. Choose by how you would rather grow. |
| Adding capacity later | With either brand you start with the capacity your budget allows now and add more later, without buying a new inverter. |
| High voltage batteries | FoxESS's high voltage batteries run at 192V (EP5) and 384V (EP11). A higher voltage draws less current, which means thinner cables and less power lost to heat. |
| Battery chemistry | Both brands use LiFePO4 (lithium iron phosphate) cells, chosen across the industry for their stability. |
Connecting to an existing diesel generator
ZenSolar connects battery systems to a site's existing diesel generator, so a generator already on site can work alongside your battery and solar.
Charging cheap, discharging at the priciest hours
Eskom runs time of use tariffs: Homeflex for homes, and Megaflex and Miniflex among others for businesses. On the shared time of use schedule, weekday peak hours in the high demand winter months (June, July, August) run from 06:00 to 08:00 and 17:00 to 20:00. For the rest of the year, weekday peak hours run from 07:00 to 09:00 and 18:00 to 21:00. Weekends carry no peak period at all.
A battery can be set to charge from solar or from the grid in the cheap off-peak hours, then discharge through those peak hours instead of drawing from the grid. For a business, this is peak shaving: using stored power at the moment that sets your demand charge, which lowers that charge as well as the energy cost at the priciest hours. See Solar Power Inverters for the fuller picture on demand charges and time of day.
Sigenergy's stack also has an optional DC EV charging module, 12.5kW as standard and upgradeable to 25kW. See EV energy for the full picture.
Not sure how much battery your property actually needs?
Get your load assessedA real job: EFJS Printing
"ZenSolar was excellent in all that they did. The installation at my Printing Shop and home was done to the highest standard."
Bernard Synman, Director, EFJS Printing.
Sizing is finalised in the free energy assessment
The method above shows how sizing works. Your actual battery size is finalised in the free energy assessment: a review of your bill and demand charges, with on-site logging for bigger sites, ending in a report with your recommended system size, equipment list and payback time. It takes about 1 to 2 weeks from booking to report. See Services and Energy assessment.
The warranty
Every FoxESS and Sigenergy battery and inverter ZenSolar installs carries ZenSolar's own 10-year swap-out warranty.
Registering your system
A hybrid system with any point of connection to the grid must be registered, even if it never exports power. CoC and SSEG application handled for you, and SSEG fees and meter costs are included in your quote. See Solar Power Inverters for the full South African rules.
How we size your battery
1
Book the free energy assessment
We review your bill and demand charges, with on-site logging for bigger sites, so we know what your battery actually needs to cover.
2
Get your report and design
A report showing your recommended system size, equipment list and payback time, about 1 to 2 weeks from booking.
3
We install and maintain your system
Installed by our team and preferred, vetted installers approved by the brands, with CoC and SSEG application handled for you, and backed by a 10-year swap-out warranty. Then you use your own stored power when you choose, at the hours that cost you most.
Why have ZenSolar size and fit your battery?
With us
- Battery sized from a real energy assessment, not a guess
- FoxESS and Sigenergy only, backed by a 10-year swap-out warranty
- CoC and SSEG application handled for you
- Expand your battery later without starting over
- We install and maintain your battery system
With them
- A size picked off the shelf
- No clear warranty behind the battery
- Paperwork left to you
- Locked into today's size
- No one checking the install is compliant
Frequently asked questions
It depends on which circuits you want running on your own stored power, and for how long. Add up the running watts of those circuits, multiply by the hours you want covered, then divide by your battery's depth of discharge to get the size you need. The free energy assessment checks your real numbers and confirms the size.
A business usually sizes its battery around its demand charge and its priciest hours, not only its total daily use. So a business battery is sized differently from a home battery. The free energy assessment measures your actual load and demand pattern to size it properly.
Divide your battery's usable kWh by the kW your chosen circuits draw, and that gives you the hours. A FoxESS EP11 battery gives about 9.3 usable kWh at 90 percent depth of discharge, so running 1kW of chosen circuits gives about 9 hours. Your own run time depends on your battery size and your chosen loads.
kW measures power, how fast something uses electricity right now. kWh measures energy, how much is used over time. A battery's size is given in kWh, its total stored energy. How fast it can push that energy out is its kW rating.
Depth of discharge is how much of a battery's total capacity you can actually use. FoxESS batteries run to 90 percent depth of discharge. Sigenergy lists a usable figure a little under each module's total size. It matters because it is your real, usable kWh, not the number on the spec sheet, that decides what your battery can actually run.
LiFePO4 (lithium iron phosphate) is the chemistry used in both the FoxESS and Sigenergy batteries ZenSolar installs, chosen across the industry for its stability. Sigenergy also names its own "5-layer Battery Protection" as a feature of its battery.
For the same power, a higher voltage battery draws much less current than a standard 48V bank. Lower current means thinner cables and far less heat lost in the wiring, because heat loss rises with the square of the current. FoxESS's EP5 and EP11 batteries both run at high voltage, 192V and 384V.
Yes, with both brands. FoxESS batteries stack up to four units on one system. Sigenergy's battery modules connect with guided quick connectors that auto plug once stacked, up to six modules on one controller, and Sigenergy states its stack supports mixing old and new batteries together.
Yes. A hybrid inverter can charge your battery from the grid as well as from your panels, so you can top up during cheap off-peak hours, or during extended cloudy weather, not only from sunlight.
Yes. ZenSolar connects systems to existing diesel generators, so a generator already on site can work alongside your battery and solar.
Peak shaving means using your battery's stored power at the moment your business draws the most from the grid, instead of drawing more from the grid at that moment. Since a business's demand charge is often set by that single highest draw, peak shaving can lower that charge as well as your energy cost at the priciest hours. See Solar Power Inverters for the fuller picture.
Yes. A hybrid system with any point of connection to the grid must be registered, even if it never exports power. Whether you need to register depends on having a connection to the grid, not on whether you export. CoC and SSEG application handled for you.
FoxESS batteries are separate boxes you add to, up to four units. Sigenergy's SigenStor stacks the controller and battery modules together as one unit, up to six modules. Both use LiFePO4 chemistry and both are backed by ZenSolar's 10-year swap-out warranty. See Solar Power Inverters for the full comparison.
Not ready for a full assessment? Contact us and we will answer your questions first.