If you want to query the results from a temporary table inside the same query, you can use # temp tables, or @ table variables (I personally prefer @), for querying outside of the scope you would either want to use ## global temp tables or create a new table with the results.
DECLARE
@ProjectID int = 3,
@Year int = 2010,
@MeterTypeID int = 1,
@StartDate datetime,
@EndDate datetime
SET @StartDate = '07/01/' + CAST(@Year as VARCHAR)
SET @EndDate = '06/30/' + CAST(@Year+1 as VARCHAR)
DECLARE @MyTempTable TABLE (SiteName varchar(50), BillingMonth varchar(10), Consumption float)
INSERT INTO @MyTempTable (SiteName, BillingMonth, Consumption)
SELECT tblMEP_Sites.Name AS SiteName, convert(varchar(10),BillingMonth ,101) AS BillingMonth, SUM(Consumption) AS Consumption
FROM tblMEP_Projects