Solar Plus Battery Economic Case (Sezibwa)

[!info] Conservative, bank-facing basis (revised after two independent review) All figures usereviews) Tariff: UEDCL Code 10.2 Q3 2026 (Peak 666.5 / Shoulder 562.1 / Off-Peak 429.7 UGX/kWh), taken as a configurable input, not hard-coded. Capex: turnkey installed capexprice (the pricewhat a lender finances, not the at-cost floor) andfinances). Generation: real day-to-day weather (a seeded variable-irradiancevariable year, not a clear sky every day)year). BothAll three pull the numbers down from an earlier optimisticdraft; draft. Theythese are the numbers to take to a lender. Reproducible from nfe_solar_model.py.

Headline

Adding 4 kWp of solar (7 x 600 Wp) to the existing SRNE inverter and 8.9 kWh battery offsets about 5655 percent of the site's electricity bill on the real loadload, current tariff and real weather. The inverter and battery are already bought (9.4M UGX sunk), so thisthe decision is only the marginal cost of the panels.

• Year-1 saving about 217,205,000 UGX per month (about 5655 percent of a ~390,374,000 UGX/month bill).
• Turnkey installed cost about 5.0M UGX.
• PaybackIRR about 48 percent; simple payback about 1.92.1 years;, IRRdiscounted payback about 512.7 percentyears; 20-year NPV about 10.4M9.6M UGX at 15 percent.percent.

Load basis

The analysis rides on the site load, so it is worth stating the evidence. The aggregate meter (meter_100) has now recorded five consecutive months (March to August 2026), and every month sits between 21 and 25 kWh per day:

Month	kWh/day
April 2026	22.5
May 2026	22.2
June 2026	21.3
July 2026	25.0
August 2026 (to date)	25.4

Full-month average about 22 kWh/day (~660 kWh/month), trending up as more customers connect.connect, The meter isand cross-validated against the independent sum of the 10 customer submeters to within 4 percent (ratio 1.04). The model uses a deliberately conservative 21.3 kWh/day, below the full-month average and well below the recent months, so the savings below are if anything understated. An older utility bill showedshowing about ~14 kWh/day,day but it wasis a September 2025 period, roughly six months before the meter began logging, during earlier commissioning with fewer customers; itand is not representative of the current site. A current UEDCL bill for meter U214624 would be a paper formality; the load itself is settled empirically.

Why solarsolar, and nothow just the batterymuch

The load trough is overnight (cheap off-peak) and the load peak is the evening, inside the expensive peak tariff window (18:00 to 24:00 at 753666.5 UGX/kWh). Solar generates midday, so the two miss by about six hours. The battery bridges the gap, but only the evening slice; the bigger win is solar serving the daytime load directly. That is why solar, not arbitrage, carries the case.

How the spill happens (why 4 kWp, not more)

Midday surplus solarpast has three possible homes: serve the small daytime load, charge the battery until it isa full at 8.9 kWh, or export to the grid, which is not possible because Uganda has no net metering today (a policy is anticipated but not yet enacted). Once the load is served and thekWh battery is full, extra solar is curtailed (spilled), because there is no economically usable export for Sezibwa today (see the spill)net-metering note below). A bigger array fills the fixed battery faster and spills more,more.

so

[!note] 4 kWp versus 5 kWp — two different questions, not a contradiction 4 kWp is near the pointefficiency wheresweet almostspot: nothingit isoffsets wasted.

~55

(The spill diagram is a clear-day illustrationpercent of the mechanism;bill while curtailing almost nothing. 5 kWp is the headlinefinancial savingsNPV aboveoptimum already apply(see the real-weatheroptimal-allocation haircut acrosscase): the year.)fifth kWp still spills a little, but its useful generation is worth slightly more than its marginal cost, so total NPV is marginally higher. Minimising curtailment and maximising NPV are different objectives; both conclusions are correct.

[!note] Net metering ERA has published the Electricity (Net Metering) Regulations, 2024, so an export framework exists in principle. But eligibility for this site, the interconnection process, and the credit value are unresolved, and net-metering credits typically pay well below retail. The base case therefore assumes no economically usable export for Sezibwa, which is why surplus is curtailed rather than sold.

Capex (from the Rincol catalog)

Basis	4 kWp installed cost
Turnkey (bank-financed, incl. DC PV surge arrester and MC4)	about 5.0M UGX
At-cost floor (if NFE self-builds via Rincol)	about 4.0M UGX

The headline uses the turnkey number. Two BOM items the catalog was missing (a DC-rated PV surge arrester and MC4 connectors) are now included.

Investment metrics

Ranked as an investor reads them (15NPV percentand costIRR offirst; capital)cumulative ROI last because it is undiscounted):

Metric	Value
IRR	about 48 percent
NPV at 10 / 15 / 20 / 25 percent	14.7 / 9.6 / 6.5 / 4.4M UGX
Simple payback	about 2.1 years
Discounted payback (at 15%)	about 2.7 years
20-year cumulative ROI (undiscounted)	~790 percent
Upfront cost (turnkey)	about 5.0M UGX
Payback	about 1.9 years
IRR	about 51 percent
ROI (20-year, undiscounted cumulative)	about 836 percent
NPV at 15 percent	about 10.4M UGX
NPV at 22 percent (commercial loan)	about 6.1M UGX

Year-1 saving about 217,000 UGX/month; 20-year total saved about 47.2M UGX. Payback is time to recover the upfront cost; IRR is the effective annual return, andreturn; a lender funds a project when its IRR comfortably exceeds the loan rate (here 5148 percent versus an 18 to 26 percent loan,loan). a clear yes);The NPV is the wealth created in today's money. The project stays stronglyclearly positive even at a 22punishing 25 percent discountcost rate.of capital, so the case does not depend on cheap money.

Battery aging over 20 years

With the battery's usable capacity fading to 50 percent by year 20 (a conservative assumption)conservative), the saving declines only gently, far less than a battery-only system which halves, because daytime solar self-consumption does not depend on the battery. Solar makes the income resilient to aging. (A battery replacement strategy is discussed in the optimal-allocation case; the existing battery here is sunk, so its fade is a maintenance question, not part of this investment.)

Related

Companion cases:cases (same basis): Battery Arbitrage (alone), Optimal Solar and Battery Allocation, and Battery Price Break-Even. All four share the same conservative basis (turnkey capex, real weather, battery aging).