Array position: due south, titled at an angle equal to the latitude
Ulm is located at a latitude of 47° 25′ 43″ N
Winter orientation: latitude + 10-15° = 47 + 10-15 = 57-62°
Summer orientation: latitude – 10-15° = 47 – 10-15 = 37-32°Insolation (incident solar radiation):
Great Falls, Montana
kWh/day (sun hours/day)
High: 5.70    Low: 3.66    Average:  4.93
(source: kWhrs per day per square meter per month.
For Great Falls, Montana there are 4.8 average kilowatt-hrs per square meter per day (sun hours per day) with a high of 6.6 and low of 2.7.  With a fixed-tilt at latitude (47.48 degrees) the monthly averages of sun hours are:
Jan – 3.0
Feb – 4.0
Mar – 5.0
Apr – 5.4
May – 5.6
Jun -  6.0
Jul – 6.6
Aug – 6.3
Sep – 5.5
Oct – 4.6
Nov – 3.3
Dec – 2.7




Install a grid-tied PV system without battery backup.


Description: PV modules generate DC power which is converted to AC power by the inverter and delivered to the main circuit breaker panels where the power displaces an equal amount of utility-generated power.  If incoming PV power exceeds what the building needs at that moment, the excess power is fed into the utility, which the utility pays for.  If PV power is insufficient, the utility makes up the shortfall.  If utility power fails, the PV system stops generating electricity.


•    no need for battery storage
•    excess power can be sold to the utility
•    grid is the backup when PV system doesn’t satisfy load
•    number of modules in array can be increased without increasing storage capacity
•    PV system need to be sized to accommodate load’s peak and occasional high surge
•    system can be sized to handle any desired portion of total load requirements
•    system cannot operate when utility power is down
•    system requires electrical current variables such as frequency, power factor, harmonics and wave shape be much more carefully regulated in order to assure compatibility with utility-supplied line current which requires high-quality power-conditioning equipment = more expensive
•    to add a battery backup at a later time requires different equipment


Details: Components, Net metering, Tax incentives/loans


1. Components


Summary: PV panels, mount, inverter, circuit breaker, wiring


PV panels:


Mount: rack mount – modules mounted on support structure above flat roof of a building in a plane different than that of the roof
•    free-air ventilation – keeps modules cooler
•    exposed rear – ease of access to connections
•    ability to adjust array angle for seasonal differences


Seasonally adjustable fixed mount or fixed mount with winter orientation (57-62°) if the load remains constant throughout the year.





2. Net metering (buyback)


Summary: North Western Energy participates in net metering, where the customer will receive credit for surplus energy at retail rates on renewable energy systems of less than 50 Kw capacity.


1978 Federal Public Utilities Regulatory Policies Act (PURPA) – any private renewable energy producer in the U.S. has a right to sell power to their local utility company.  Utility usually will pay its “avoided cost,” otherwise known as wholesale rates.


“Net-metering is a special installation that allows any surplus energy generated by the customer’s system to go back on the utility electric system and allows the customer to receive “credit” for the electricity put back on the system at retail rates. The customer’s meter measures the electricity the customer uses from the utility system less the electricity the customer’s system puts back.


Net metering is available on the North Western Energy and the Montana-Dakota Utility systems. Renewable installations of less than 50 kW capacity are eligible for net metering on NWE’s system. You can get further information by contacting John Campbell, NorthWestern Energy (406-497-3364) or see NWE’s interconnection agreement at their website. For information on net metering on the MDU system, contact Gary L. Paulsen, Director of System Operation and Planning, Montana-Dakota Utilities Co. (701-222-7649).”



3. Tax incentives


15-6-201(4) Property tax exemption for buildings using renewable energy
15-24-1401 Property tax reduction for renewable generating facilities 1 MW or more
15-31-124 New or expanded industry tax credit
15-32-401 Alternative energy investment tax credit


17-6-401 Microbusiness loan program
75-25-101 Alternative energy revolving loan program




To do/need:
Research microclimates (early-morning fog, afternoon cloudiness, etc.) and regional climatic info.
Timeless’ power requirements – both amount and time when it is required.
Size array based on power info.
Make list of local solar businesses.
Take photos of building and site.
Calculate energy payback on investment.
Run performance calculator for grid-connected PV systems (



Notes: If Timeless wants to add battery backup in the future, this needs to be decided before installation since the equipment needed is different (and more expensive).