Electricity types

Electron flow in a cross-section of wire: Top- In a direct current circuit, the electrons only flow in one direction from positive to negative. Bottom- In an alternating current circuit the electrons flow in both directions as positive and negative alternate.

Voltage over time: Direct current maintains a steady voltage (red). Alternating current switches back and forth (blue).

There are two types of electricity – Alternating Current (AC) and Direct Current (DC). These two terms describe the way in which the current flows in a circuit. In a DC circuit, the current only flows in one direction, meaning that they have a constant positive (+) and negative (-). This relationship of positive to negative charge is referred to as polarity. In an alternating current circuit, current flow changes direction regularly, switching the polarity (positive (+) and negative (-)) each time. This back and forth switching of polarity in an alternating current circuit is reffered to as frequency and is measured in Hertz (Hz). Polarity in a typical AC circuit switches between 50-60 times per second meaning that the circuit has a frequency of 50-60Hz.

In any electrical system, whether AC or DC, all components or appliances must be rated to function with the characteristics of the electrical system - voltage, current, and frequency if AC. If they are used improperly it can lead to a failure that results in fire or injury.

Direct current

PV modules can only produce DC, thus all PV systems have at least one DC circuit. Anything that uses a battery, including PV systems, will be based on DC as batteries can only store energy in DC form. Powering a load directly from DC saves the step of having to use an inverter to convert from DC to AC, which can create losses of more than 10% in the process. Many small scall systems are DC only and work well for lightning and the charging of small electronic devices like cell phones.

Alternating current

World map depicting common frequencies for each country.

The grid is almost entirely built to function with alternating current, although the voltage, frequency and number of wires varies around the world. Nearly all electronic devices - cell phones, radios, computers and televisions - run on DC internally, but because they are typically designed to function with the grid they incorporate electronics to convert from AC to DC. Appliances with motors or compressors - refrigerators, fans and tools - have motors that can run directly on alternating current.

Country or territory	Residential voltage	Three-Phase Voltage (L-L)	Frequency
Afghanistan	220 V	380 V	50Hz
Albania	230 V	400 V	50Hz
Algeria	230 V	400 V	50Hz
American Samoa	120 V	208 V	60Hz
Andorra	230 V	400 V	50Hz
Angola	220 V	380 V	50Hz
Anguilla	110 V	120/208 V 127/220 V 240/415 V	60Hz
Antigua and Barbuda	230 V	380 V	60Hz
Argentina	230 V	380 V	50Hz
Armenia	230 V	400 V	50Hz
Aruba	127 V	220 V	60Hz
Australia	230 V	400 V	50Hz
Austria	230 V	400 V	50Hz
Azerbaijan	230 V	380 V	50Hz
Bahamas	120 V	208 V	60Hz
Bahrain	230 V	400 V	50Hz
Bangladesh	220 V	380 V	50Hz
Barbados	115 V	200 V	50Hz
Belarus	220 V	380 V	50Hz
Belgium	230 V	400 V	50Hz
Belize	110 V 220 V	190 V 380 V	60Hz
Benin	220 V	380 V	50Hz
Bermuda	120 V	208 V	60Hz
Bhutan	230 V	400 V	50Hz
Bolivia	115 V 230 V	400 V	50Hz
Bonaire	127 V	220 V	50Hz
Bosnia and Herzegovina	230 V	400 V	50Hz
Botswana	230 V	400 V	50Hz
Brazil	127 V 220 V	220 V 380 V	60Hz
British Virgin Islands	110 V	190 V	60Hz
Brunei	240 V	415 V	50Hz
Bulgaria	230 V	400 V	50Hz
Burkina Faso	220 V	380 V	50Hz
Burundi	220 V	380 V	50Hz
Cambodia	230 V	400 V	50Hz
Cameroon	220 V	380 V	50Hz
Canada	240 V	120/208 V 240 V 277/480 V 347/600 V	60Hz
Cape Verde	220 V	400 V	50Hz
Cayman Islands	120 V	240 V	60Hz
Central African Republic	220 V	380 V	50Hz
Chad	220 V	380 V	50Hz
Chile	220 V	380 V	50Hz
China, Mainland	220 V	380 V	50Hz
Colombia	120 V	208 V 220 V 260 V 440 V	60Hz
Comoros	220 V	380 V	50Hz
Congo, Republic of the	230 V	380 V	50Hz
Congo, Democratic Republic of the	220 V	400 V	50Hz
Cook Islands	240 V	415 V	50Hz
Costa Rica	120 V	208 V	60Hz
Côte d'Ivoire	230 V	380 V	50Hz
Croatia	230 V	400 V	50Hz
Cuba	110 V	190 V	60Hz
Curaçao	127 V	220 V 380 V	50Hz
Cyprus	240 V	400 V	50Hz
Czech Republic	230 V	400 V	50Hz
Denmark	230 V	400 V	50Hz
Djibouti	220 V	380 V	50Hz
Dominica	230 V	400 V	50Hz
Dominican Republic	110 V	120/208 V 277/480 V	60Hz
Ecuador	120 V	208 V 480 V	60Hz
Egypt	220 V	380 V	50Hz
El Salvador	115 V	208 V 220 V 440 V 480 V	60Hz
Equatorial Guinea	220 V	[unavailable]	50Hz
Eritrea	230 V	400 V	50Hz
Estonia	230 V	400 V	50Hz
Eswatini	230 V		50Hz
Ethiopia	220 V	380 V	50Hz
Falkland Islands	240 V	415 V	50Hz
Faroe_Islands	230 V	400 V	50Hz
Fiji	240 V	415 V	50Hz
Finland	230 V	400 V	50Hz
France	230 V	400 V	50Hz
French Guiana	220 V	380 V	50Hz
French Polynesia	110 V 220 V		60 Hz
Gabon	220 V	380 V	50Hz
Gambia	230 V	400 V	50Hz
Georgia (country)	220 V	380 V	50Hz
Germany	230 V	400 V	50Hz
Ghana	230 V	400 V	50Hz
Gibraltar	240 V	400 V	50Hz
Greece	230 V	400 V	50Hz
Greenland	220 V	400 V	50Hz
Grenada	230 V	400 V	50Hz
Guadeloupe	230 V	400 V	50Hz
Guam	110 V	190 V	60Hz
Guatemala	120 V	208 V	60Hz
Guernsey	230 V	415 V	50Hz
Guinea	220 V	380 V	50Hz
Guinea-Bissau	220 V	380 V	50Hz
Guyana	110 V 220 V	190 V	60 Hz 50 Hz
		220/380 V	50 Hz
		230/460 V	60 Hz
Haiti	220 V	220/380 V	50Hz
	110 V	110/220 V	60 Hz
Honduras	110 V	208 V 230 V 240 V 460 V 480 V	60Hz
Hong Kong	220 V	380 V	50Hz
Hungary	230 V	400 V	50Hz
Iceland	230 V	400 V	50Hz
India	230 V	400 V	50Hz
Indonesia	220 V	380 V	50Hz
Iran	220 V	400 V	50Hz
Iraq	230 V	400 V	50Hz
Ireland	230 V	415 V	50Hz
Isle of Man	240 V	415 V	50Hz
Israel	230 V	400 V	50Hz
Italy	230 V	400 V	50Hz
Jamaica	110 V	190 V	50Hz
Japan	100 V 200 V	200 V 415 V	50 Hz 60 Hz
Jersey	230 V	415 V	50Hz
Jordan	230 V	400 V	50Hz
Kazakhstan	220 V	380 V	50Hz
Kenya	240 V	415 V	50Hz
Kiribati	240 V	[unavailable]	50Hz
Autonomous Province of Kosovo and Metohija	230 V	230 V 400 V	50Hz
Kuwait	240 V	415 V	50Hz
Kyrgyzstan	220 V	380 V	50Hz
Laos	230 V	400 V	50Hz
Latvia	230 V	400 V	50Hz
Lebanon	220 V	400 V	50Hz
Lesotho	220 V	380 V	50Hz
Liberia	120 V 240 V	208 V -	60 Hz 50 Hz
Libya	127 V	400 V	50Hz
Lithuania	230 V	400 V	50Hz
Liechtenstein	230 V	400 V	50Hz
Luxembourg	230 V	400 V	50Hz
Macau	230 V	380 V	50Hz
Madagascar	127 V 220 V	380 V	50Hz
Malawi	230 V	400 V	50Hz
Malaysia	230 V	400 V	50Hz
Maldives	230 V	400 V	50Hz
Mali	220 V	380 V	50Hz
Malta	230 V	400 V	50Hz
Martinique	220 V	380 V	50Hz
Mauritania	220 V	220 V	50Hz
Mauritius	230 V	400 V	50Hz
Mexico	127 V	220 V 480 V	60Hz
Federated States of Micronesia	120 V	[unavailable]	60Hz
Moldova	220 V	400 V	50Hz
Monaco	230 V	400 V	50Hz
Mongolia	220 V	400 V	50Hz
Montenegro	230 V	400 V	50Hz
Montserrat	120 V 230 V	400 V	60Hz
Morocco	127 V 220 V	380 V	50Hz
Mozambique	220 V	380 V	50Hz
Myanmar	230 V	400 V	50Hz
Namibia	220 V	380 V	50Hz
Nauru	240 V	415 V	50Hz
Nepal	230 V	400 V	50Hz
Netherlands	230 V	400 V	50Hz
New Caledonia	220 V	380 V	50Hz
New Zealand	230 V	400 V	50Hz
Nicaragua	120 V	208 V	60Hz
Niger	220 V	380 V	50Hz
Nigeria	240 V	415 V	50Hz
North Korea	110 V 220 V	380 V -	60 Hz 50 Hz
North Macedonia	230 V	400 V	50Hz
Norway	230 V	230 V 400 V	50Hz
Oman	240 V	415 V	50Hz
Pakistan	230 V	400 V	50Hz
Palau	120 V	208 V	60Hz
Panama	110 V 120 V	240 V	60Hz
Papua New Guinea	240 V	415 V	50Hz
Paraguay	220 V	380 V	50Hz
Peru	220 V	380 V 440 V	60Hz
Philippines	230 V	220 V 440 V	60Hz
Poland	230 V	400 V	50Hz
Portugal	230 V	400 V	50Hz
Puerto Rico	120 V	480 V	60Hz
Qatar	240 V	415 V	50Hz
Réunion	220 V	400 V	50Hz
Romania	230 V	400 V	50Hz
Russia	230 V	380 V	50Hz
Rwanda	230 V	400 V	50Hz
Saint Helena, Ascension and Tristan da Cunha	220-240 V	[unavailable]	50Hz
Collectivity of Saint Martin	220 V	[unavailable]	60Hz
Sint Maarten (Dutch)	120 V	220 V	60Hz
St. Kitts and Nevis	110 V 230 V	400 V	60Hz
St. Lucia	240 V	400 V	50Hz
Saint Pierre and Miquelon	230 V		50Hz
St. Vincent and the Grenadines	230 V	400 V	50Hz
Samoa	230 V	400 V	50Hz
San Marino	230 V	400 V	50Hz
São Tomé and Príncipe	220 V	400 V	50Hz
Saudi Arabia	220 V	400 V	60Hz
Senegal	230 V	400 V	50Hz
Serbia	230 V	400 V	50Hz
Seychelles	240 V	240 V	50Hz
Sierra Leone	230 V	400 V	50Hz
Singapore	230 V	400 V	50Hz
Slovakia	230 V	400 V	50Hz
Slovenia	230 V	400 V	50Hz
Solomon Islands	220 V	[unavailable]	50Hz
Somalia	220 V	380 V	50Hz
South Africa	230 V	400 V	50Hz
South Korea	220 V	380 V	60Hz
Spain	230 V	400 V	50Hz
Sri Lanka	230 V	400 V	50Hz
Sudan	230 V	400 V	50Hz
Suriname	127 V	220 V 400 V	60Hz
Sweden	230 V	400 V	50Hz
Switzerland	230 V	400 V	50Hz
Syria	220 V	380 V	50Hz
Taiwan	110 V 220 V	110 V 380 V	60Hz
Tajikistan	220 V	380 V	50Hz
Tanzania	230 V	415 V	50Hz
Thailand	220 V	400 V	50Hz
Timor-Leste (East Timor)	220 V	380 V	50Hz
Togo	220 V	380 V	50Hz
Tonga	240 V	415 V	50Hz
Trinidad & Tobago	115 V	115/230 V 230/400 V	60Hz
Tunisia	230 V	400 V	50Hz
Turkey	230 V	400 V	50Hz
Turkmenistan	220 V	380 V	50Hz
Tuvalu	220 V	50Hz
Uganda	240 V	415 V	50Hz
Ukraine	220 V	380 V	50Hz
United Arab Emirates	220 V	400 V	50Hz
United Kingdom	230 V	415 V	50Hz
United States	120 V 120 V 240 V 240 V	120/208 V 277/480 V 120/240 V 240 V 480 V	60Hz
U.S. Virgin Islands	110 V	190 V	60Hz
Uruguay	230 V	380 V	50Hz
Uzbekistan	220 V	380 V	50Hz
Vanuatu	220 V	400 V	50Hz
Venezuela	120 V	115/220 V 220/440 V 230/460 V	60Hz
Vietnam	220 V	380 V	50Hz
Yemen	230 V	400 V	50Hz
Zambia	230 V	400 V	50Hz
Zimbabwe	220 V	415 V	50Hz

AC or DC?

If so many appliances internally function on DC, why not just use direct current for every circuit then? Each one has different characterstics that make it useful for certain applications. AC has important properties that make it useful in the electrical grid. It is cheaper to transmit AC over long distances as it is easier to change between high and low voltages. High voltages are ideal for long distance transmission as they require less current, which means you can use smaller wires. DC works well in off-grid applications as PV modules produce DC and batteries store energy in DC, meaning that using AC appliances requires the added expense and loss of efficiency that come with an inverter.