Definition of Terms
- Photovoltaic
- Solar electric
- Cell
- This is the smallest unit of a solar electric system
- Module
- Cells wired together in series form a module
- Array
- Modules wired together in series or parallel form an array
- kW
- Kilowatts. The size of array is measured in kW.
- kWh
- Kilowatt hours. The output of an array is measured in kWh.
- BOS
- Balance of System, which can include charge controller, combiner, box, inverter, batteries and the wiring to complete the system.
 What kind of solar system do I need?
 There are five different types of solar electric installations.
- For a small cabin without grid connection and low demand for electricity, a low voltage direct current (DC) system makes the most sense. This system includes a solar array under 1 kW, charge controller and a small battery pack.
- For a home without grid connection, an independent alternating current (AC) system requires a larger array, over 1 kW, a charge controller, a large expensive battery pack and inverter, which changes the low voltage DC generated by the photovoltaics to 110 or 220 AC house current to run standard household appliances.
- The most inexpensive grid connected system is a net-metered system without batteries. This system includes an array large enough to satisfy most of the electric needs of the house and an inverter that synchronizes with the utility and can run the utility meter backwards.
- If there is concern about rolling blackouts, a small inexpensive battery pack may be added to a grid connected system and only used in the case of a utility outage.
- If there is concern for long utility outages on a grid-connected system, then you may want to use the utility as a backup battery charger and put in a system similar to #2 with a large expensive battery pack.
What components make up a complete system?
Combiner boxes to combine the wires coming from different modules. Inverters to change direct current to alternating house current. If storage is desire, charge controllers and batteries will be necessary.
How many kW of solar electric roofing will I need?
An ideal system provides exactly the amount of energy needed. As a general rule, an average building needs about 1 Watt of solar roofing per sqft. or 1 kW per person.
How much energy do I need?
If you are connected to a utility you will be able to look at your bill and find out how many kWh you use per day, per month and per year. If you are constructing a new building you will have to estimate your demand based on the size of the home and the efficiency of the appliances you purchase.
How can I estimate the size of the solar roof I need?
It takes about 200 sqft. of roof area with solar access per kW of electricity generated.
Can any roof accommodate solar panels?
Solar access is the primary requirement. The orientation, slope, size and shape are also determining factors. Southern orientation and slopes from flat to 45 degrees can accommodate PV roofing. Presently there are 9'6" 12 Volt 64 Watt and 18' 24 Volt 128 Watt laminates available from UNI-SOLAR. Wiring for these laminates is either in the ridge cap or the eave soffit. If the length between the ridge and eave is 9.5' to 18', then 64-Watt laminates can be used. If that length is over 18' then 128-Watt modules can be used. Vents, chimneys, skylights and other roof penetrations, as well as shaded areas from adjoining buildings or trees must be avoided.
Does the output of my array depend on my location?
If you live on the North Coast or in areas with over 50 inches of rainfall, you can expect about 1.5 kWh per year per installed Watt. If you live in an area with few days of fog and between 10 and 50 inches of rain, you can expect about 2 kWh per year per installed Watt. If you live in a desert area with less than 10 inches of rain, you can expect about 2.5 kWh per year per installed Watt.
Example 1 - You live on the North Coast in a home that uses 6,000 kWh per year. To calculate solar electric panels needed, divide 6,000 by 1.5 = 4,000 Watts, or 4 kW of solar electric roofing panels.
Example 2 - To calculate the roofing required to power an energy efficient home in Sacramento or Los Angeles that consumes 4,800 kWh a year, divide 4,800 by 2 = 2,400 W or 2.4 kW of solar electric roofing.
Example 3 - An energy-wasting home in the desert that burns 12,000 kWh a year will need 12,000 divided by 2.5 = 4,800 Watts, or 4.8 kW of solar electric roofing.
What will my solar electric system cost?
The installed cost for small systems (less than 10 kW) without batteries runs between $ 8 and $12 per Watt. For larger systems (over 10 kW) without batteries the installed cost can be as low as $6 per Watt. For a small battery pack $1.50 per Watt should be added. For a large battery pack $3 or more should be added.
Are there incentive programs available?
There is a $3 per Watt rebate available through the California Energy Commission (CEC) for systems that receive a bill from the three major investor owned utilities (PG&E, SCE, and SDG&E). This rebate will pay up to half the cost of a system and also includes other tax incentives. There is also a $750 rebate available from the CEC for batteries.
How can I save more money on my PV roof?
The first step in considering a PV roof is to do an energy audit that will suggest the least expensive conservation measures that will increase the efficiency of energy used in your building. Energy efficient lighting and appliances, insulation, weather stripping and insulating windows will quickly pay back the investment in energy savings and reduce the cost of the PV array necessary to serve your needs.
Approximately how large are the related items other than the actual panels, such as: batteries, switches, etc.? We need to design space for these items.
Batteries will take up about 1 cubic foot for every 2kWh of storage necessary. If flooded cells are used they will need to be in an airtight box that vents to an outside wall. Sealed batteries can be installed anywhere.
The inverter for a grid connected system requires about 4 sq ft of wall space at eye level. If batteries are included in the system, about 16 sq ft of wall space at eye level is needed and the batteries must be within 10 feet of the inverter. The inverter does make a humming noise and most also have a fan which comes on at high temperatures, so they should not be mounted adjacent to a bedroom or a room where quiet is needed. |
Standing Seam
