Will installing a solar hot water system increase the value of my house?

Residential Solar Power Question

I have been looking into whether it is practical to install a solar hot water system in my house.  Many of the solar hot water system companies claim that installing one will increase the value of my house as well as giving me free hot water.

None of the solar companies seem to be able to provide any real proof that the actual price I will get for my house will increase but I keep seeing it mentioned so I am wondering if it is true or just something else to try and make us buy their solar heating system.

Is it worth me asking a Realtor or someone who specializes in home valuations rather than trusting the word of the companies trying to sell me something.