IKEA will invest in Swedish and European cleantech companies, through it's subsidiary IKEA Greentech AB. IKEA prospers from the interesting combination of a excellent distribution network and customer base and a very solid financial position.
In particular, IKEA will invest in cleantech companies with products that benefit it's clients (they amount to 500 000 000), warehouses (270) or suppliers (1500), from the alternative energy and energy efficiency areas.
So what should they focus on? Do the maths, 500 000 000 clients is a very interesting customer base. Hence, finding high-quality products relevant for IKEA's customer should be a top priorirt. Further on, they should be cost-efficient in small scale. An area that satisfies both of these conditions is energy efficiency (including water and material efficency). I would say that where the largest potential is to be found.
Small-scale energy generation using energy from the sun (solar power, solar heating and wind power) does fit with the first description. Small-scale energy generation is getting increasingly popular whit high petroleum prices, and solar insolation is favourable in many of the countries where IKEA is present. However, as discussed earlier, the efficiency of these installations is often far lower than medium- to large scale plants.
Considering what may be useful for their suppliers and warehouses, other areas may be interesting as well.