Like this. Make sure you drop the temp table (at the end of the code block, after you're done with it) or it will error on subsequent runs.
SELECT
tblMEP_Sites.Name AS SiteName,
convert(varchar(10),BillingMonth ,101) AS BillingMonth,
SUM(Consumption) AS Consumption
INTO
#MyTempTable
FROM
tblMEP_Projects
JOIN tblMEP_Sites
ON tblMEP_Projects.ID = tblMEP_Sites.ProjectID
JOIN tblMEP_Meters
ON tblMEP_Meters.SiteID = tblMEP_Sites.ID
JOIN tblMEP_MonthlyData
ON tblMEP_MonthlyData.MeterID = tblMEP_Meters.ID
JOIN tblMEP_CustomerAccounts
ON tblMEP_CustomerAccounts.ID = tblMEP_Meters.CustomerAccountID
JOIN tblMEP_UtilityCompanies
ON tblMEP_UtilityCompanies.ID = tblMEP_CustomerAccounts.UtilityCompanyID
JOIN tblMEP_MeterTypes
ON tblMEP_UtilityCompanies.UtilityTypeID = tblMEP_MeterTypes.ID
WHERE
tblMEP_Projects.ID = @ProjectID
AND tblMEP_MonthlyData.BillingMonth Between @StartDate AND @EndDate
AND tbLMEP_MeterTypes.ID = @MeterTypeID
GROUP BY
BillingMonth, tblMEP_Sites.Name
DROP TABLE #MyTempTable