Solar PV + BESS plants are an economically more competitive solution to providing power for customers that do not have access to the electricity grid or for those who have unreliable grid connections.
Diesel generators are deployed extensively in East Africa to compensate for no grid to frequent outage scenarios:
Diesel generator power in East African countries
| COUNTRY | DIESEL PRICE /L(USD) | USD /kWh: Fuel Cost | Diesel LCOE: USD/kWh Adjusted for non Fuel Costs |
| Kenya | 0.99 | 0.3 | 0.36 |
| Uganda | 0.97 | 0.29 | 0.35 |
| Tanzania | 0.91 | 0.28 | 0.34 |
| Rwanda | 1.12 | 0.34 | 0.41 |
| Burundi | 1.27 | 0.38 | 0.46 |
(source: Energy Regulators websites, Authors models)
Levelized cost (LCOE) of diesel
The total costs of energy from a diesel generator can be broadly summarized as:
- Capital cost of acquisition
- Generator maintenance costs
- Diesel costs: purchase price, transportation & storage costs, working capital costs, pilferage & fuel shrinkage
To simplify the analysis, several technical and economic assumptions are made in this LCOE calculation including optimal generator efficiency, maximum lifetime run hours and generator usage.
Solar + BESS power (LCOE)
The illustration below demonstrates observed costs from a 650kVA / 2320kWh BESS plant coupled to a 900KWp Solar PV plant, which was able to achieve a LCOE of US$ 0.14.
Assumptions
| INPUT | ASSUMPTION | COMMENT |
| SOLAR PV PLANT | Installed Cost USD 1,200/KWp | 25yr Lifetime |
| SOLAR PV Plant Maintenance | USD 20/KWp per annum | |
| PV Plant Replacements / Upgrades | 15% of plant cost in YR 11 | PV Inverter Replacement |
| Solar PV Annual Yield | 1450KWH/KWp | 2% Degradation |
| BESS | Installed cost: USD 415/KWh | |
| BESS Warranted Lifetime | 15Yrs | |
| BESS Round Trip Efficiency | 90% | |
| BESS Depth of Discharge | 100% | |
| Discount Rate | 8% | |
| 10.BESS Replacement | YEAR 16 | 40% of today’s BESS Costs |
| 11. Curtailment | 10% of Solar PV Yield | |
| 12. Level of Diesel Replacement | 100% |
Solar PV energy prices have declined sharply over the last few years and the LCOE is now between USD 0.05/kWh and USD 0.08 /kWh for commercial scale systems in East Africa, making it competitive with several conventional sources.
However, mass adoption of Solar PV has been hindered due to its intermittent downfalls – both from a real time perspective (sudden cloud cover) and a long-term perspective (available only during the day).
The addition of energy storage solves this problem, but increases the overall cost of the solution. Therefore, optimal sizing of the energy storage system is a crucial step in increasing solar PV capacity to effectively and reliably meet electrical loads while delivering an economically competitive LCOE.
An Energy Storage Consultant will help determine the optimal solar PV and battery energy storage sizes required to yield a lower blended LCOE to the customer while also providing reliable power.
Examples of common sizing strategies include:
- No energy storage: In an off-grid microgrid with only diesel generators and solar PV. Real-time PV is intermittently mitigated by using generators as spinning reserves. Nevertheless, due to minimum loading requirements of the gensets, PV capacity is typically limited to 60% of day-time load.
- PV + storage sized for day-time load: With this strategy, battery energy storage provides real time firming of PV power and creates a base-load generator, thereby enabling the turning-off of gensets from a few hours a day.
- PV+ storage sized for 24 hr energy: To power the load entirely with renewables, Solar PV is sized to provide the load’s energy needs and the round trip efficiency of Battery Energy Storage System (BESS). The site controller intelligently charges/ discharges during the day (mitigating real time intermittency) and discharges when the sun goes down (mitigating long-term intermittency).
In summary, several selling points make solar PV with BESS an attractive alternative to using diesel generators to produce power:
- Falling solar prices,
- Falling storage prices,
- Expectations that diesel prices will increase,
- Reduction of greenhouse gas emissions, and
- Reduction in noise during operation.
Current prices of solar and storage make it feasible to turn off diesel gensets and provide firm power for several hours. Falling prices will expand the window of hours that diesel generators can be turned off completely.
