Efficiency of plant operation was very low during this period of time
and in 1926, it was decided to convert the plant to diesel operation.
In 1927, the first of two McIntosh & Seymour 4-cycle air injection
engines, 17X25, 600 HP, 200 RPM engine, driving a 410 kW, 2300 volt, 60 cycle
AC generator, was installed. The second unit was started up in July of 1928.
Beloit's power plant was now converted to all diesel. Old audit reports had
shown that for the period, Sept. 1926 to Aug. 1927, the cost of fuel was $29,850.00,
and the same period, 1928-29 was $5,043.00 on full diesel. This represented
a great saving to the citizens of the community.

In 1930, a third McIntosh-Seymour (4-cycle, air injected, 17X25, 675
HP, 225 RPM) engine, driving a 460 kW, 2300 volt, 60 cycle AC generator, was
installed. Total cost of the first three diesel units was $94,000.00 plus
$8,924.00 for switchgear and improvements to the distribution system. The
cost of these improvements was paid off in 1932 from electric revenues, due
to the increased efficiency of diesel over steam. At the same time the customers
were given a reduction in rates of 13% on the first 300 kWh, and 12% for all
kWh's over 300. For a period in the 1930's, Beloit had no city tax levy, with
revenue from the power plant paying for all services.
A forth diesel engine was added to the plant in 1941. It was an American
Locomotive (4-cycle, 720 HP, 600 RPM, solid injection) engine, which was later
turbo charged to produce 1050 HP, driving a 700 kW, 2400 volt, 60 cycle AC
generator, at a total cost of $49,750.00.
In 1942, the City of Beloit contracted to furnish energy for the Jewell-Mitchell
R.E.A., resulting in a new peak demand of 1040 kW. This was greater than the
peak demand of 860 kW in 1941. A fifth unit was added to the plant capacity
in 1946. It was like unit #4, with a slightly higher rating of 1080 HP, driving
a 750 kW generator.
The citizens of Beloit, in 1946, voted in a $400,000.00 bond issue to build
a new light and water plant away from the threat of the Solomon River flooding.
Unit #5 was installed at the location of the new plant and was operated in
conjunction with the old plant for a time. The total cost of unit #5 was $50,725.00.
With the building of the new plant, two Fairbanks-Morse 31AD18, dual fuel,
2-cycle (18X27, 2100 HP, 277 RPM) engines were purchased and installed in
1950. They each drove a 1500 kW, 2400-volt generator. The #5 unit was converted
to dual fuel at the same time for a cost of $15,000.00. The plant now had
a new nameplate rating of 3750 kW. The cost of the Fairbanks-Morse engines
and related equipment was $196,000.00.
The new water plant was put on line in 1950, and on July 12, 1951 the new
electric generation plant was put into service as flood waters from the Solomon
River were four feet deep on the operations floor of the old plant. Units
#1 through #4 at the old plant were removed and disposed of after the floodwater
had subsided.
R.E.A. terminated their contract with the city in 1952, with a drop in peak
demand of 150 kW. By 1959 the peak demand had risen to 3050 kW, and a forth
unit was purchased and installed at the new plant. Unit #3 was a Cooper-Bessemer
4-cycle, turbo charged, tri-fuel, LSV-12 (3200 HP, 327 RPM) engine. It drove
a 2000 kW, 2400-volt AC generator. The cost of this unit was $245,000.00.
At the same time of the installation of unit #3, the jacket water cooling
system was converted from a spray tower, to a closed system, using four radiator
units at a capacity of 15,400,000 Btu/hr., at a cost to the city of $32,000.00.
By 1964, peak demand had raised to 4950 kW, and another unit was purchased
and installed at a cost of $468,126.00. The new unit #4 was a Cooper-Bessemer
4-cycle, turbo charged, tri-fuel, LSV-16 engine rated at 4910 HP, 360 RPM,
driving a 3500 kW, 2400-volt generator. In 1967 the jacket water system was
enlarged to 30,800,000 Btu/hr, at a cost of $40,000.00, to accommodate better
and more efficient cooling.
The 6450 kW peak demand of 1969 showed the need to purchase unit #6. It is
a Cooper-Bessemer 4-cycle, turbo charged, dual fuel, LSV-16 engine, rated
at 5744 HP, 400 RPM, driving a 4100 kW, 12,470 volt AC generator. The cost
of this project was $588,000.00. At this same time, low voltage in outlying
parts of the city, during heavy load periods, required the building of five
miles of 12,470 volt distribution lines around the perimeter of the city to
better service those customers. Two 2400 kW substations were constructed,
one at the plant and one in the north part of town, just south of the large
water tower. The substations were set up with remote switching at the power
plant. The cost of the substations and structures was $80,885.00.
As of 1971, Beloit had 1980 metered customers, 23 miles of three phase, 2400
volt lines, two miles of single phase, 2400 volt lines, five miles of 12,470
volt, three phase lines (with 1.5 miles to build). The city had $1,360,000.00
in electric revenue bonds outstanding and a property and equipment, after
depreciation, valuation of $2,148,594.13, for plant and distribution systems.
All of Beloit's generating and electric distribution systems equipment has
been paid out of the plant revenue since 1926.