The Optare Solo is a low-floor midibus manufactured by Optare in Leeds, UK since 1997. The name "Solo" is a play on the low-floor status of the bus, the manufacturer believing its vehicle having an entrance that is "so low" from the floor, namely 200 mm with kneeling suspension. The innovative design, featuring a front axle ahead of the entrance, gained the bus a "Millennium Product" award, along with "The Queen's Award for Enterprise 2000".
It is an integral bus (as opposed to a separate chassis and body) built in a modular design, with steel frame and GRP panels. The Solo is powered by a Mercedes-Benz OM904LA engine, which produces Template:Convert/bhp or 147 bhp (110 kW) according to specification, and it is typically mated to an Allison 2000 fully-automatic gearbox. Later, options of Cummins ISBe 6-cylinder 185 bhp (138 kW) and MAN engine became available. There is also the option of a 4-speed Allison AT545 gearbox, but this is not so common. In 2005 a hybrid Solo was constructed, using a small diesel unit and an Eneco (now known as Traction Technology) battery propulsion unit.
The Optare Solo is available in various lengths, 7.8 m, 8.5 m, 9.2 m, and 9.9 m, all at 2.5 m width. The chassis type code of the Solo carried the length - M780 corresponds to 7.8 m, M850 to 8.5 m, and so forth. Cummins-powered Solos required extra rear bodywork to accommodate the larger engine, which increased the length of the bus by 0.3 m. However, this is not reflected in the chassis code, so a Cummins-powered M990 Solo is in fact 10.2 m in length.
Along with the launch of the 9.9 m model, the Solo was also first offered with LED-type rear lights, as opposed to the standard rectangular clusters.
Seating capacities ranged from 25 for an M780, 29 for an M850, 33 for M920 and 37 for an M990.
A narrow-bodied version named the "Slimline" was launched in 2004 with the first examples entering service in August. It is 2.33 m wide, and identifiable by small wheelarch extensions mounted to the rear. Available across all lengths except the M990, the Slimline is identified by having an SL-suffix in the chassis code, e.g. M780SL for a 7.8 m long version. The compact size of an M780SL, with its 25 seating capacity, has seen it being a popular choice for replacing ageing vehicles from the minibus era, such as MCW Metrorider/Optare MetroRider, and other van-based buses.
In June 2006, Optare announced the arrival of another Solo model - the Solo SE. At just 7.1 m in length, it is the shortest Solo offered, and is capable of seating 23. It also utilises a single-piece entrance door. This is a variant of the Slimline - hence it is 2.33m in width, but noticeably the rear track has been reduced compared to previous Slimline models, eliminating the need for wheelarch extensions on the rear of the bus. Optare also plan to produce the SE in the 7.8 m length.
The first SE built, the former Optare demonstrator, entered service with Regal Busways, of Essex, in September 2006. The company has since acquired a further four examples.
In October 2007 Optare unveiled the Solo SR at the Coach and Bus show. It is a completely restyled version of the Solo drawing styling features from the Versa, such as the curved side windows and sweeping roof. Some features of the Solo such as the curved front windscreen and the unusual chassis layout, with the front wheels ahead of the doorway, were retained. Another new unusual feature to the Solo SR is the lack of a destination box on the standard model. However, Optare do offer this as an option to individual customer specification. It was predicted that the Solo SR would replace the standard Solo in the near future but this seems less likely when demand for the original Solo remains high.
In November 2008 the 'new' Optare unveiled the Solo+ - a completely restyled variant to celebrate ten years of the Solo and was launched at the Euro Bus Expo 2008. It shared the same styling with the Rapta, which was launched at the same show. It sees the return of the flat side windows and roof as well as a steeper front end with an integral destination box. Proposed options include a full electric drive.
However, the plan of producing the Solo+ was dropped afterwards. The new product met with a poor market response and has never made it beyond the prototype stage. The further development required to make the product an improvement on previous models was possibly deemed to be too great (and costly), the plans being shelved.
In March 2009, Optare launched the all electric version of the Solo, the Solo EV.  Vehicle top speed is limited to 90 km/h (56 mph), uses Enova Systems P120 AC induction motor rated at 120 kW and powered by two banks of Valence Lithium-ion phosphate batteries. The two packs work in parallel and provide 307V with a total capacity of 80 kWh.
The diesel-electric hybrid single-decker bus with room for 53 passengers; its configuration can be changed to provide seating for up to 34 passengers plus one wheelchair with additional standing room. Its peak power demands are met by batteries that are recharged on-board by the diesel generator. This was made possible by ENECOTemplate:Clarification needed and other companies with different models.
The Optare Solo is sold mostly in the United Kingdom, but the EuroSolo has been exported to countries in Europe, such as Denmark and most recently, the Netherlands, where the buses are fitted with dual entrance/exit doors. Exported models are typically M920 variants.
In the United States, a left hand drive version of the Solo was sold from 2003 to 2005 by North American Bus Industries (which at time owned Optare) as the 30-LFN. A major purchaser of the NABI 30-LFN was Miami-Dade Transit. NABI's sale of Optare coupled with poor sales led to its demise in the U.S. market.