In short. A telecom site is already a small hybrid microgrid: the rectifier feeds a DC bus, the battery carries the load the instant supply fails, and the generator covers long outages and recharges the battery. Making it work well means sizing the generator for load plus battery recharge plus shelter cooling, planning fuel and access for unmanned sites, and using solar to cut generator hours where the site and battery allow it.
Telecom power works on three timescales
Network equipment at a tower or exchange typically runs from a nominal 48 V DC bus fed by rectifiers, with a valve-regulated lead-acid or lithium battery floating on that bus. When AC supply is lost, there is no transfer at all: the battery simply continues supplying the DC load. That gives telecom a natural layered structure. In the first seconds and minutes the battery carries everything. Within minutes the generator starts, either on a timer or when battery voltage falls to a threshold. Over hours and days, fuel in the tank and the ability of a technician to reach the site decide how long service survives. Each timescale fails in a different way, and a microgrid design must cover all three.
| Timescale | Source | What limits it | Typical failure |
|---|---|---|---|
| Seconds to hours | DC battery | Usable capacity, age, temperature | Aged battery collapses well before its rated autonomy |
| Hours | Diesel generator | Start reliability, rating, recharge load | Fails to start on a flat starting battery |
| Days | Fuel and access | Tank size, theft, road access | Tank empty because refuelling was missed or fuel stolen |
| Daylight hours | Solar | Panel area, irradiance, shading | Underperforms in the monsoon, battery cycles deep |
Sizing the generator for recharge, not just load
The commonest telecom generator problem is not an undersized machine for the radio load; it is a machine that cannot carry the radio load, battery recharge and shelter air conditioning together after a long outage. When the generator comes on, the rectifiers begin recharging a discharged battery at their current limit, which can equal or exceed the equipment load itself. If the shelter has been without cooling, the air conditioner starts at the same moment.
P_gen ≥ (P_DC + V_bus × I_charge) / η_rect + P_cooling + P_aux
P_gen is the generator kW required, P_DC the DC equipment load, V_bus the float voltage, I_charge the battery charge current limit, η_rect the rectifier efficiency, P_cooling the running load of the shelter cooling and P_aux lighting and auxiliaries. Worked example (illustrative): a site with a 3 kW DC load, a 54 V bus, a 60 A charge limit, 92 percent rectifier efficiency and a 2.5 kW air conditioner needs about (3,000 + 3,240) / 0.92 + 2,500 ≈ 9.3 kW before auxiliaries and the compressor’s starting step. A set chosen for the 3 kW radio load alone would be overloaded, and the step for the compressor start must still be checked. Rectifier input is also non-linear, so the alternator should be selected with harmonic heating in mind.
Where solar and lithium batteries change the economics
At off-grid and bad-grid sites the generator may run many hours a day, and every hour costs fuel, a share of the service interval and wear. Adding solar charge controllers to the DC bus lets daylight energy supply the load and recharge the battery directly, so the generator runs only when the battery reaches a lower threshold, then charges it hard and stops. That pattern, sometimes called cyclic charge-discharge operation, keeps the generator well loaded when it does run. It works best with a battery chemistry that tolerates deep daily cycling; lithium iron phosphate is common for this reason, while lead-acid banks cycled daily age quickly in hot shelters. The lifecycle case must include battery replacement, charge controller and rectifier maintenance, not only the fuel saved. Solar and diesel hybrid systems and battery energy storage discuss the trade-offs.
Unmanned sites: monitoring, security and access
Most towers are unattended, so remote monitoring turns site condition into service action. At minimum the controller should report mains availability, generator run status and hours, fuel level, DC bus voltage, battery temperature, rectifier alarms and door access. Fuel theft and battery theft are real problems at rural sites in Telangana and Andhra Pradesh, so sudden fuel level drops when the set is not running, and battery string disconnection, should raise alarms in their own right. Access in the monsoon also matters: a site on a hill or across a flooded track may not be reachable for a day or two, which argues for larger tanks and longer battery autonomy than at a roadside site. Before deploying any emergency set, the service team needs the location, access route, load, fuel status, battery condition and alarm history. See telecom power.
Earthing, lightning and placement
Telecom sites combine tall metal towers, long cable runs and sensitive electronics, so the generator earth must be bonded into the site earthing and lightning protection system rather than driven as an isolated electrode. Rooftop installations need structural review before any generator is placed, along with fuel containment and exhaust routing away from air intakes. No single earth resistance value or generic diagram fits every site; soil resistivity and the operator’s specification govern.
Common mistakes
- Sizing the generator for the radio equipment load only. The set overloads after every long outage when battery recharge and cooling start together.
- Ignoring battery age when estimating autonomy. A five-year-old bank delivers a fraction of its rated hours and the site drops before the generator starts.
- Cycling lead-acid batteries daily in an uncooled shelter. The bank fails within a year or two and the hybrid fuel saving is spent on replacements.
- Monitoring generator status but not fuel level trends. Theft or a stuck float goes unnoticed until the site goes dark.
- Assuming a technician can reach every site within the battery autonomy. In the monsoon some sites are cut off for longer than the battery lasts.
What to send us
Send the DC load in amps at bus voltage, the rectifier rating and charge current limit, battery type, capacity and age, the shelter cooling load, current generator rating and controller, monthly run hours and fuel use, and site access notes. For several sites, a spreadsheet with one row per site works best. Send your application details. For larger installations, compare industrial microgrids.
Questions engineers ask
What size generator does a typical telecom tower need?
There is no single size; it follows from the DC load, the battery recharge current and the shelter cooling. Many tower sites fall in the small single-digit to low double-digit kVA range, but the recharge and cooling allowance often doubles what the radio load alone suggests.
How much can solar reduce generator running hours at a tower?
At an off-grid site with good irradiance and adequate panel area, solar can remove most daytime running and part of the night, but the result depends on the load, panel area and battery capacity. Bad-grid sites see smaller gains because the grid already supplies part of the energy.
Is lithium better than lead-acid for hybrid telecom sites?
For daily cycling at high shelter temperatures, lithium iron phosphate usually lasts considerably longer and allows deeper discharge. Lead-acid remains acceptable for float-service sites where outages are infrequent. Compare total cost over the site’s life, not the purchase price.
Should the generator start on a timer or on battery voltage?
On battery voltage or state of charge, with a timer as backup. Voltage-based start avoids running the set while the battery can still carry the load, and the backup timer protects against a failed sensor.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.