Expensive electricity, half-solutions
Water sources are among the largest electricity consumers in municipal systems. Three core problems with the status quo:
- Electricity bills keep rising — business electricity prices in Croatia have been climbing for years, and water supply has a high, constant load profile.
- Grid-tied solar is a half-solution — peak shaving lowers the bill, but the system still depends on the grid; grid outage = water-supply outage.
- Solar + batteries solves autonomy at a steep price — battery packs double the CAPEX, require chemistry replacement, and carry a non-trivial carbon footprint.
▼ Wider market context More details
- Croatian water-supply consumption statistics (TBD: concrete figures)
- Business electricity price trend, HEP 2020–2026
- Regulatory pressure: EU decarbonisation, Just Transition Fund, NRRP measures
The reservoir is already an energy store
All solar energy is fed straight into the pumps; water flows into the reservoir and is consumed gravitationally when needed. The water reservoir physically becomes the energy store.
Three direct consequences:
- No batteries — CAPEX 30–55 % lower, no chemistry replacement, 25+ years of life
- Offgrid — no grid-connection cost, grid-independent, resilient to outages
- Existing infrastructure — reservoirs typically already exist or are planned anyway
Operating principle
A typical day: morning solar ramp-up → pumps start → reservoir fills through the afternoon → at night, water flows gravitationally to consumers.
Seasonal variation: more energy in summer, but also more demand; the reservoir is sized for transition periods.
Cloudy days: the reservoir buffers 24 h to several days — a sizing parameter.
▼ Technical depth More details
- Sizing: PV ↔ pump ↔ reservoir balance. Typical ratio: 1 kWp PV per ~12 m³/day of water at 80 m head.
- Control logic: VSD pumps, MPPT for PV, soft-start to protect the network.
- Hydraulic losses: typical pumping efficiency 65–75 %; pipe losses an additional 5–10 %.
- Calculator caveats: does not account for PV degradation, local hydraulic variability, or seasonal demand patterns.
Comparison of 3+ approaches
Values are derived from the parameters you set in the calculator (Scenarios section below).
| Metric | Grid only | Solar + grid | Solar + battery | Our approach |
|---|---|---|---|---|
| CAPEX (€) | — | €38,727 | €318,727 | €78,727 |
| OPEX/year | €10,512 | €4,730 | €526 | €526 |
| Autonomy | 0 | 0 | 72 h | ≥ 72 h |
| Lifespan | n/a | 25 yrs | 10–15 yrs | 25+ yrs |
| Footprint | small | moderate | moderate | moderate |
| Maintenance | grid | annual | regular (chemistry) | mechanical |
| Grid-failure resilience | none | none | limited | full |
| Incremental retrofit cost (reservoir already exists). Figures from calculator · 72 h target autonomy. | ||||
Cumulative cost over 25 years
Three typical scenarios
50 m³/day
Rural water source, small water utility
- PV size
- 4.0 kWp
- CAPEX
- €20,508
- Savings/yr
- €788
- Payback
- 26.0 yrs
- Footprint
- 22 m²
- CO₂
- 0.9 t/yr
500 m³/day
Municipal water supply centre
- PV size
- 51.6 kWp
- CAPEX
- €303,727
- Savings/yr
- €10,512
- Payback
- 28.9 yrs
- Footprint
- 284 m²
- CO₂
- 11.7 t/yr
5,000 m³/day
Regional water-supply network
- PV size
- 550.5 kWp
- CAPEX
- €2,612,896
- Savings/yr
- €131,400
- Payback
- 19.9 yrs
- Footprint
- 3,028 m²
- CO₂
- 146.0 t/yr
▼Advanced settings (pricing and constants)More details
Benefits
- Financial — lower CAPEX, zero pumping electricity bill, fast payback
- Operational — fewer components, simpler maintenance, no battery chemistry
- Environmental — no battery waste, lower carbon footprint, local production
- Resilience — offgrid means grid independence and water-supply energy security
About IMGD
IMGD is an engineering firm specialising in water-supply and energy solutions. (TBD: short team description, projects, partners.)
Contact us
▼ Methodology More details
Calculator values are indicative and based on public sources:
- GHI: PVGIS v5.2, 2005–2020 average
- Hydraulics: EN 805 + standard handbooks; default 0.4 kWh/m³ per 100 m of head
- Pricing: HEP price list, HOPS balance, publicly available market references 2025–2026
- CO₂ factor: 0.20 kg CO₂/kWh (HR grid 2025)
The calculator does not account for: PV degradation, pump efficiency variability, local terrain conditions. For a real project, contact IMGD for a detailed analysis.