Off-grid solar: how many panels and what battery without grid
With no grid there is no deposit and no buying power in winter. The weakest month sets the size, the number of sunless days sets the battery.
Yearly output
6,300 kWh
1,050 kWh per kWp · saves PLN 3,425 a year
| Used directly and from the battery | 1,698 kWh |
| Exported to the grid | 4,603 kWh |
| Deposit (×1.23) | PLN 1,569 |
| Deposit spent on energy | PLN 1,408 |
| Overpayment refunded | PLN 162 |
| Bill before / after | PLN 4,373 / PLN 1,110 |
| Pays back in 10 years up to | PLN 34,253 |
Hourly model of an average day in each month; surplus priced at the last 12 months of RCEm (PSE) plus the gain from negative RCE counted as zero. An estimate, not an offer; fixed charges excluded.
| Month | Output | Used on site | To grid | From grid |
|---|---|---|---|---|
| Jan | 187 | 99 | 88 | 240 |
| Feb | 294 | 109 | 185 | 201 |
| Mar | 538 | 148 | 391 | 192 |
| Apr | 717 | 160 | 557 | 168 |
| May | 796 | 178 | 618 | 161 |
| Jun | 817 | 179 | 638 | 150 |
| Jul | 797 | 181 | 616 | 158 |
| Aug | 756 | 173 | 583 | 167 |
| Sep | 623 | 148 | 475 | 181 |
| Oct | 431 | 133 | 297 | 206 |
| Nov | 196 | 100 | 96 | 229 |
| Dec | 147 | 89 | 59 | 251 |
Off-grid solar is a system with a battery and no grid connection: all the power you need has to come from the panels and the battery. It is sized differently from a net-billing system, where the yearly balance counts. Here the weakest month decides. According to PVGIS, one kilowatt of panels tilted at 45° facing south gives on average 0.88 kWh per day in December across Poland and 4.4 kWh in the best month. A summer cabin using 3 kWh a day therefore needs about 0.8 kWp if you use it from April to September, but as much as 3.4 kWp if it must also work in December. The battery follows from the number of sunless days: two days at 3 kWh a day need 6 kWh of usable capacity. A system not connected to the grid needs no notification to the operator, but it also earns no deposit or refund for its surplus.
Checked by Radif Partners · Editorial policy · Method
Sizing panels and battery to your use
The table shows the size of panels tilted at 45° facing south and the usable battery capacity for four levels of daily use. The seasonal version covers the weakest month from April to September, the year-round version December.
| Use per day | Size: April–September | Size: all year | Battery for 2 days | Battery for 4 days |
|---|---|---|---|---|
| 1 kWh | 0.3 kWp | 1.1 kWp | 2 kWh | 4 kWh |
| 3 kWh | 0.8 kWp | 3.4 kWp | 6 kWh | 12 kWh |
| 5 kWh | 1.4 kWp | 5.7 kWp | 10 kWh | 20 kWh |
| 8 kWh | 2.3 kWp | 9.1 kWp | 16 kWh | 32 kWh |
Usable capacity is the energy the battery can deliver, not the nominal capacity on its label. The maker gives it on the product sheet. Inverter and charging losses come on top, so it is worth adding a margin.
What off-grid system for your use?
Size for the whole year, December included
3.4 kWp
| Size for the April–September season | 0.8 kWp |
| Usable battery capacity | 6.0 kWh |
| 1 kWp per day: weakest / best month | 0.88 / 4.4 kWh |
Average municipal yield from PVGIS 5.3, an average day of the month: cloudy weeks need the battery or a generator.
Output of 1 kWp month by month
| Month | 1 kWp per day (45°) |
|---|---|
| Jan | 1.11 kWh |
| Feb | 1.85 kWh |
| Mar | 2.99 kWh |
| Apr | 3.98 kWh |
| May | 4.17 kWh |
| Jun | 4.37 kWh |
| Jul | 4.15 kWh |
| Aug | 4.02 kWh |
| Sep | 3.54 kWh |
| Oct | 2.45 kWh |
| Nov | 1.18 kWh |
| Dec | 0.88 kWh |
For your exact location check the output in the calculator at the top of the page: pick the municipality and you will see the yield in each month. If the plot has a grid connection, or one can be made, compare this result with solar with a home battery settled under net-billing, where in winter you buy the missing energy from the grid.