When grid power is cheaper than solar

Break-even math for small loads. When a $200/year electricity bill is cheaper than a $1000 solar system, and when backup, not off-grid, makes more sense.

Not every application needs to be solar-powered. For some loads, especially small ones with cheap grid electricity nearby, the honest answer is that plugging into the wall costs less than building a solar system, and the environmental benefit of a tiny off-grid system is negligible compared to grid power that's increasingly generated by renewables anyway.

Knowing when solar makes sense and when it doesn't prevents you from spending $1000 to avoid $30/year of grid electricity.

The basic comparison

Grid electricity has a simple cost: your utility rate ($/kWh) multiplied by consumption (kWh). There's no upfront investment, no battery replacement, and no maintenance.

Small off-grid solar has a complex cost: upfront equipment, pack replacement every 5-15 years, occasional component failure, and the time you spend on installation and maintenance. The "free" energy from the sun is only free after you've paid for and maintained the equipment that captures it.

Example 1: A small aquarium air pump (5W, 24/7)

Annual grid cost: 5W x 24h x 365 days = 43.8 kWh. At $0.16/kWh: $7.01/year.

Solar system cost to power this load: a 50W panel ($40), PWM controller ($25), 20Ah LiFePO4 pack ($80), cabling and connectors ($30). Total: $175. Pack replacement in year 10: $80. Twenty-year total cost: $255.

Payback period: $175 / $7.01/year = 25 years. The system barely pays for itself over its entire lifespan, and that's before counting the battery replacement.

For this load, grid power is cheaper unless the grid connection itself is the problem (no outlet nearby, frequent outages, or the system is in a location where running grid wiring is expensive).

Example 2: A greenhouse pump, fan, and lights (200W average, 14h/day)

Annual grid cost: 200W x 14h x 365 = 1022 kWh. At $0.16/kWh: $163/year.

Solar system cost: 600W of panels ($300), MPPT controller ($120), 200Ah LiFePO4 pack ($400), a DC-AC converter ($80), cabling and connectors ($100). Total: $1000. Pack replacement in year 10: $400. Twenty-year total cost: $1400.

Twenty-year grid cost: $163 x 20 = $3260 (assuming no rate increases).

Payback period: $1000 / $163/year = 6.1 years. Solar is significantly cheaper over 20 years, even with a pack replacement.

When grid wins

Tiny loads (under 50W average). The fixed cost of a solar system ($150-300 minimum for even the simplest setup) divided by the tiny annual savings makes the payback period absurdly long.

Grid already available at the location. If there's a weatherproof outlet on the shed wall and you just need to plug in a pump, the marginal cost of grid power is literally cents per day. No solar system can compete with the zero upfront cost of using existing infrastructure.

Short-term use. If you're renting the property, setting up a temporary system, or experimenting with a new hobby, the upfront solar investment may never be recovered. Use grid power while you learn, then evaluate solar once you've committed to the activity long-term.

Cheap electricity markets. At $0.08-0.10/kWh (parts of the Midwest, Southeast US, and some regulated markets), the annual savings from solar are so small that payback periods exceed 15-20 years for most small loads.

When solar wins

No existing grid connection. If the load location is 20+ meters from the nearest outlet and running cable requires trenching, conduit, and possibly a sub-panel, the cost of the grid connection itself ($500-5000 depending on distance and local codes) makes solar cheaper from day one.

Unreliable grid. If your area experiences frequent outages and the load is critical (fish tank aeration, greenhouse ventilation), solar with battery backup provides energy security that the grid doesn't. The value here isn't cost savings but avoiding losses: dead fish or a crashed greenhouse crop can cost far more than the solar system.

High electricity rates. Above $0.20/kWh (common in California, Hawaii, much of Europe, Australia), small off-grid solar becomes cost-effective within 5-10 years for moderate loads.

Replacing a generator. If you're currently running a gasoline generator, solar replaces ongoing fuel and maintenance costs. Even a small 2-hour daily generator run at $2-3/hour in fuel costs $1400-2000/year. A $1000 solar system pays back in months.

The hybrid approach

For many situations, the best answer isn't purely solar or purely grid. It's a grid-connected system with battery backup for outages. You use cheap grid power normally and switch to battery during outages. This avoids the cost of sizing a solar system for 100% off-grid autonomy while providing the critical backup functionality.

A simple version: a battery charger connected to grid power keeps a battery topped up. When the grid goes out, a transfer switch (manual or automatic) connects the battery to critical loads. The solar panel charges the battery during the outage and keeps it maintained during normal operation.

This approach costs less than a full off-grid system because the battery can be smaller (it only needs to last through outages, not provide daily energy). It provides the reliability benefit of solar backup at a fraction of the cost.

The solar cost calculator helps you compare the long-term costs of solar vs grid for your specific load and electricity rate.

Electricity rate trends

One factor often overlooked in the grid-vs-solar comparison is the direction of electricity prices. US residential electricity rates have roughly doubled over the past 20 years, from about $0.085/kWh in 2001 to over $0.16/kWh in 2025. Some states have seen steeper increases.

Solar system costs, by contrast, are fixed at the time of purchase. The panels, pack, and controller cost what they cost in year one, and produce energy for free (minus maintenance) for 15-25 years. If grid rates continue rising at 2-4% per year (the historical average), the payback period for solar shortens year by year as the avoided cost per kWh increases.

A system that takes 10 years to pay back at today's rates might pay back in 7-8 years if electricity rates rise 3% annually over that period. This doesn't change the analysis for very small loads (the savings are too small for rate increases to matter), but for moderate loads (200W+ average), rising grid costs tilt the economics toward solar over time.

Making the decision

Start by answering two questions: How much does the grid power I'd replace actually cost per year? And what would the solar alternative cost, including battery replacement over the system's life?

If the annual grid cost is under $50 and you have grid access at the location, solar is probably not the financial choice. If the annual grid cost exceeds $150 or there's no existing grid connection, solar is likely the better investment. Between those numbers, the decision depends on how you value the non-financial benefits (reliability, independence, environmental considerations).

The solar cost calculator models both scenarios and shows the crossover point for your specific situation.