Solar Photovoltaic Off Grid Weekend Power Costs

Photovoltaic (PV) electric power is available off grid wherever the sun shines. The amount of PV power that can be harvested depends on the amount of available sunshine which varies by latitude, cloud cover, season of the year, and of course the time of day.

An off grid PV system uses a battery to store electricity for use at night and on cloudy days. In practice, the off grid weekend battery should store two-days of electricity necessary to supply the electricity demand of the installation, and be recharged with four-days of PV charging power, leaving a one-day margin per week to assure full performance.

You will find that the cost of an average off grid weekend installation varies by available solar resource, electricity demand of the installation, type of PV technology and its power rating, power conversion efficiency ratings, special site conditions (shading and mounting technique), and the labor rate.

In the following table the Labor Cost figure is what the able DIY person should expect to save by performing the corresponding tasks.

Off grid weekend power: provide and install the complete system according to regional climate conditions to supply a minimum of 1,600 watt-hours per day of 120V AC power using roof-mounted fixed-tilt PV panels, battery charging and storage, AC power converter, mounting structure, protections, and cabling. Include electrical design drawing, battery life expectation, and all related materials, supplies, transport, equipment, finish-trim, final adjustments, and clean-up.

• Higher solar resource zones are like eastern Arizona.
• Moderate solar resource zones are like eastern Oklahoma.
• Lower solar resource zones are like New Jersey.

The off grid weekend installation counts on four-days of battery charging with little or no electricity demand. When you arrive on Friday afternoon the battery is fully charged and prepared to supply electricity demand for two-days and two-nights.

Latitude and cloudiness factors are quantified by the regional Minimum Daily Peak Sun Hours (PSH, kwh/m2/day) that in the United States ranges from 1.5 at cloudier northern latitudes to 7.0 at Death Valley, CA. Using this factor provides that electricity demand will be satisfied under winter conditions, and results in surplus power availability under summer conditions that can be used for seasonal tasks like fan ventilation or water pumping.

The AC power converter delivers electricity compatible with common appliances (up to 300 watts continuous duty). Electricity demand depends on both the power rating of appliances and their daily duty-cycle in hours. A 100 watt appliance running 1 hour per day is a 100 watt-hour daily demand.

Some examples of common appliances and their power ratings are:

• Lap top computer: 60 to 250 watts.
• Lighting: 20 to 100 watts per fixture (CFL to incandescent).
• Low-head water pump (for shower and kitchen): 100 watts.
• 25” color television: 150 watts.
• Satellite dish: 30 watts.
• Stereo: 10 to 60 watts.
• Cell phone recharge: 2 to 4 watts.

Other considerations and costs

• Taxes and permit fees are not included.
• The Labor Cost figure does not include displacements, overnight stays, or any special engineering intervention.
• Rebates and other incentives may be available locally or nationally.
• During the initial inspection the contractor should inform the homeowner of any and all necessary modification or upgrade on electrical circuits or building structure.
• Batteries have a definite cycle-life according to their technology, be sure to get a statement of expected battery life from the provider.
• An electrical design drawing should be provided and may be necessary if local inspection is required, or if incentives and rebates are applied for.
• The off grid installation is standalone and to some extent one must live within an energy budget in order to achieve expected performance.

Check out our guide if you need a loan for your home improvement project.

DIY considerations

• Packaged kits are available from distributors that are DIY friendly.
• Roof-top work is among the most dangerous of construction activities, and roof penetrations must be weather-tight.
• Electrical circuits require attention to ratings and the prevention of fire-risk.
• Batteries should be installed in well ventilated areas, and protected against extreme climate conditions.

References

• Wholesale Solar: http://www.wholesalesolar.com/ and http://www.wholesalesolar.com/solar-information/how-to-save-energy/power-table​