What is solar?

The amount of sunlight that strikes the earth's surface in an hour and a half is enough to handle the entire world's energy consumption for a full year. Solar technologies convert sunlight into electrical energy either through photovoltaic (PV) panels or through mirrors that concentrate solar radiation. This energy can be used to generate electricity or be stored in batteries or thermal storage.

Solar radiation is light – also known as electromagnetic radiation – that is emitted by the sun. While every location on Earth receives some sunlight over a year, the amount of solar radiation that reaches any one spot on the Earth’s surface varies. Solar technologies capture this radiation and turn it into useful forms of energy.

Learn the basics of solar, how it works on the United States Department of Efficiency and Renewable Energy website.

How the City of Madison uses solar

The City uses solar technologies to offset gas and electric use in our facilities in several different ways including:

To heat air used by the building’s ventilation system

This technology (also called Solarwall or Transpired Solar Collector) reduces natural gas use and is being used the Larry D. Nelson Engineering Operations Building, 1600 Emil Street, Madison, WI, and the City of Madison Fleet Service and Radio Shop Facility, 4141 Nakoosa Trail, Madison, WI

We estimate that these two systems save approximately 6,000 to 7,000 therms of gas consumption per year which equates to ~$3,000 to $3,500 per year in reduced operating costs.

To preheat water for a variety of building uses

This technology reduces the use of natural gas and is being used at a number of City buildings for different reasons.

To preheat domestic hot water:

  • All Fire Stations (1-14)
  • Badger Road Streets Facility
  • Sycamore Ave Streets Facility
  • Engineering Operations Building (1600 Emil St)
  • Olbrich Botanical Gardens


To preheat process water for vehicle washing:

  • Sycamore Ave Streets Facility
  • Fleet Service and Radio Shop Facility


To preheat process water for plant irrigation:

  • Olbrich Botanical Gardens


To reduce space heating as part of radiant floor heat system:

  • Fleet Service and Radio Shop Facility, 4141 Nakoosa Trail

The City has 23 of these systems ranging in size from 3 to 24 panels. In total, the systems 101 panels have a total collector area of ~4,000 square feet and offset up to 6,000 therms of natural gas per year or $3,000/yr in operating costs.

Using solar energy collected in panels to offset building electric use.

This technology reduces the need for electric power provided by Madison Gas & Electric and Alliant Energy. The solar panels (also called solar electric or photovoltaic PV panels) are being used at over 20 city facilities. Additional details can be found in the map below.  

City of Madison 1 MegaWatt Goal

At the end of 2020, the City has over 1 Megawatt of installed solar electric capacity distributed across many building sites and generate over 1,000,000 kilowatt-hours (kWh) of electricity per year. This is about 1-2% of the City owned facilities annual electricity consumption.  

The City purchases approximately 20 million kilowatt-hours of Renewable Energy Credits (RECs) from five western Wisconsin utility scale solar arrays, constructed by OneEnergy Renewables’ as the Butter Solar portfolio. These arrays are owned by municipal utility co-ops (Upper Midwest Municipal Energy Group), consist of a public/private partnership and total 14 MW of generation capacity. Info at this link.

The City is in the process of purchasing electricity from a new seven Megawatt Madison Gas & Electric solar array. The City will purchase 5 Megawatts and the Madison Metropolitan School District will purchase two Megawatts.