Calculators — AbsoEnergy

Solar power system

How many kW of panels your consumption needs in your city, and what they give month by month and hour by hour.

Calculate your system

Backup for outages

Which battery and inverter keep the boiler, fridge, pump and internet going for as many hours as you need.

Calculate your backup

Heat pump

The size for your floor area and insulation, heat over a year and a comparison with gas and an electric boiler.

Calculate your heat pump

Payback

How much a system saves on Russian and Vietnamese tariffs and when it earns its money back.

Calculate your payback

How we calculate

One model for every calculation on the site: in the calculators, in the typical solutions and in the live diagram on the home page.

Sun

PVGIS 5.3: how many kWh a month 1 kW of panels gives with 14% system losses — for five roof options — and how the energy spreads over the hours of the average day of each month. For Moscow, Saint Petersburg and southern Russia — the SARAH-3 satellite database; for the other cities and Vietnam — the ERA5 reanalysis; years 2005–2023.

Consumption

Monthly use is spread over the seasons (in Russia more in winter, in Vietnam in the hot season) and over the hours of a typical profile: a home, a home with air conditioning, a café or a round-the-clock load. The profiles are our assumptions, not measurements.

Battery

Each month is an average day, hour by hour: the sun goes to the house first, the surplus to the battery, and the rest to the grid or it is lost. Round-trip efficiency is 90%, and 10% of the capacity is kept in reserve.

Money

The bill before and after — by tariff: in Russia, the region’s price per kWh; in Vietnam, EVN’s five tiers or peak hours for businesses, plus VAT. Payback includes tariff growth, panels ageing by 0.5% a year and an inverter replacement in year 13.

Heat

The design temperature of the coldest five-day period and the length and average temperature of the heating season are our calculation from hourly ERA5 data for 2005–2023, following the method of the Russian code SP 131.13330.2020. Heat losses follow the insulation class; the heat pump’s seasonal factor is 45% (air) and 50% (ground) of the Carnot limit.

Range

Output and savings are ±7% for the satellite database and ±10% for ERA5; prices run from the lowest to the highest across the sources. Payback goes from the best combination to the worst.

Sources (12)

Sun by city

How many kWh a year 1 kW of panels gives at the best tilt and on a flat roof, and how many a day in the worst and the best month.

Russia

City	Best tilt, kWh a year	Flat, 10°	Per day, kWh	Database, tilt
Moscow	968	864	0.6–4.3	PVGIS-SARAH3, 41°
Saint Petersburg	907	802	0.2–4.6	PVGIS-SARAH3, 43°
Nizhny Novgorod	1,036	915	0.5–4.7	PVGIS-ERA5, 42°
Kazan	1,109	976	0.6–5	PVGIS-ERA5, 42°
Samara	1,196	1,054	0.9–4.9	PVGIS-ERA5, 42°
Rostov-on-Don	1,211	1,117	1.1–5.1	PVGIS-SARAH3, 36°
Krasnodar	1,240	1,145	1.6–5	PVGIS-SARAH3, 36°
Sochi	1,244	1,147	1.8–4.9	PVGIS-SARAH3, 35°
Volgograd	1,209	1,103	1.1–4.9	PVGIS-SARAH3, 37°
Astrakhan	1,291	1,183	1.4–5	PVGIS-SARAH3, 38°
Makhachkala	1,190	1,114	1.6–4.7	PVGIS-SARAH3, 34°
Yekaterinburg	1,101	940	0.9–4.7	PVGIS-ERA5, 45°
Novosibirsk	1,203	1,039	1.1–5	PVGIS-ERA5, 44°
Irkutsk	1,426	1,176	2.1–5.3	PVGIS-ERA5, 48°
Ulan-Ude	1,504	1,233	2.5–5.5	PVGIS-ERA5, 48°
Vladivostok	1,521	1,288	3.2–5.4	PVGIS-ERA5, 45°

PVGIS 5.3, 14% system losses. For Da Lat the PVGIS optimiser gives an odd tilt, so the best option there is a flat roof at 10°.

Vietnam

City	Best tilt, kWh a year	Flat, 10°	Per day, kWh	Database, tilt
Hanoi	1,064	1,058	1.9–3.6	PVGIS-ERA5, 17°
Hai Phong	1,178	1,170	2.3–4	PVGIS-ERA5, 17°
Hue	1,242	1,242	1.9–4.4	PVGIS-ERA5, 11°
Da Nang	1,308	1,308	2.1–4.6	PVGIS-ERA5, 10°
Quy Nhon	1,371	1,371	2.6–4.5	PVGIS-ERA5, 10°
Nha Trang	1,443	1,443	3.2–4.7	PVGIS-ERA5, 11°
Phan Rang	1,536	1,534	3.6–5.1	PVGIS-ERA5, 12°
Da Lat	1,478	1,478	3.5–5	PVGIS-ERA5, 10°
Buon Ma Thuot	1,372	1,363	3.2–4.8	PVGIS-ERA5, 16°
Phan Thiet	1,597	1,596	3.8–5.3	PVGIS-ERA5, 12°
Ho Chi Minh City	1,412	1,408	3.4–4.8	PVGIS-ERA5, 9°
Vung Tau	1,576	1,576	3.7–5.4	PVGIS-ERA5, 12°
Can Tho	1,350	1,350	3.1–4.7	PVGIS-ERA5, 10°
Phu Quoc	1,528	1,526	3.4–5.2	PVGIS-ERA5, 13°

PVGIS 5.3, 14% system losses. For Da Lat the PVGIS optimiser gives an odd tilt, so the best option there is a flat roof at 10°.

Why your numbers will differ

The sun varies from year to year by about ±5%, and databases differ by a few more per cent. For cities east of 65° E and for Vietnam, PVGIS uses the ERA5 reanalysis — it is coarser than satellite data.
The model does not see shade from trees, neighbouring houses and chimneys — only a site visit shows it.
The average day of the month smooths out cloudy and sunny days: in real life a little less of your own sun gets used.
The load profile is a typical one. If nobody is home during the day, less of your own sun gets used; if air conditioners and a kitchen run during the day, more.
Prices are installers’ benchmarks on the date checked; your estimate depends on the roof, cables, switchboard and delivery.
Tariffs change: in Russia they are indexed once a year; in Vietnam EVN revises the price by decision of the Ministry of Industry and Trade.

The basics

kW and kWh: kW is power, the rate at which energy flows; kWh is an amount of energy. A 2 kW kettle uses 1 kWh in half an hour.
Peak kW: The power of panels under standard test conditions: 1,000 W/m² of light and 25 °C at the cell. In real life a system almost always gives less.
Yield of 1 kW a year: How many kWh a year 1 kW of panels gives in a particular place with a particular installation — the key figure for sizing a system.
Self-consumption: The share of output the home uses itself — straight away or through the battery. The higher it is, the faster the payback.
Self-sufficiency: The share of consumption covered by the sun. 100% is a home off the grid.
Depth of discharge: How much of a battery’s capacity can be used without harm. For LFP — 90–95%.
COP and SCOP: How many kWh of heat a heat pump gives per 1 kWh of electricity — right now (COP) and on average over the season (SCOP).
Design temperature: The average temperature of the coldest five-day period that happens almost every winter — heating is sized for it.
Hybrid inverter: An inverter for both panels and a battery; together with a grid-disconnect switch it keeps the house running during an outage.
Microgeneration: In Russia — a system for your own needs on a grid of up to 1 kV, with the right to sell the surplus to the guaranteeing supplier (the regional retail supplier): since 26.09.2026, up to 50 kW of export for individuals and up to 150 kW for businesses and apartment buildings.