I dont think that govenment has any grant for this purpose. I am too looking for such thing but unable to find one UNITED US GOVERNMENT

Sorry - there are no grant programs that fit your needs. As stated, your customers might be able to receive a tax credit on this years taxes - but, they would have to wait until they file next year. Have you thought about partnering with solar manufactures? These organizations or even their trade groups and associations may offer either financial help or information on where to get financial help for companies like yours who are trying to get started in this growing green market. Also, depending on how much you are seeking, you might be able to leverage the income from the HVAC side of the business to secure some capital to get start on the solar side.

Actually, the current federal energy tax credit gives a 30% rebate on all solar power installations and setups; with not upper cap limit! This means your customers would recieve 30% of the money they spent back from the federal goverment; not including what rebates they could recieve from the state and local city level. They would also be able to save money through utlitiy companies as well since they as well offer rebates most of the time. Sadly, you won't be able to get a 'grant', you could get a loan from SBA.gov or private investors looking to get on the front line of solar power as it becomes a more viable solution. As what I've stated above you need to work this into your sales pitch to your local city, make it known the the total cost is reduced by X percent and will actually cost this.

Solar energy has a huge, huge future I believe. It's just a matter of making it affordable to produce the necessary equipment to harness it. Have you looked into SBA loans? there seems to be some money around for 'Green' businesses.