Solar Energy

Hawai'i is the Saudi Arabia of sun. Everyone is going solar these days, and you can too. But the first thing to get clear is the difference between the two main residential solar technologies.

Solar hot water heating is the basic, most cost effective means of tapping into the sun. It simply takes advantage of the sun’s energy to heat water—typically through copper pipes encased in an aluminum box. You see solar water heaters on rooftops statewide. In fact, Hawai‘i leads the nation in solar water heaters per capita. This is the first solar technology that homeowners should employ—it can cut your electricity bill by up to 40%! Solar water heater systems cost around $2000 after credits and rebates, with a payback period of 2 – 4 years, depending on the water usage or family size.

The more advanced form of solar energy is solar photovoltaic, or PV. PV converts the sun’s energy into useable electricity through the photoelectric effect. Most PV panels use silicon wafers as the semiconducting material, which produce direct current that is fed into an inverter that converts the energy into household AC electricity. Depending on the system size, PV systems can cost between $5000 and $40,000 after tax credits and rebates. They have a payback period between 5 and 15 years, again, depending on size and usage (and the future cost of electricity).

Solar Water Heating

A solar water system is the most basic renewable energy device to harness the clean energy from the sun. The technology is mature, tested, and works. In fact, the Romans used solar energy to heat the water flowing to baths in aquaducts.

Solar water heating is an excellent clean energy resource for another reason: you can essentially store sunshine. The water heated by the sun during the day is stored in your insulated hot water tank, providing built-in storage that enables you to “use” the sun’s energy long after the sun has set.

Solar water heating systems are fairly simple. They consist of a solar collector (see photo), a circulation system (pump) and an insulated water tank. The water is simply circulated through the collector where it is heated up by the sun, then stored for use.

Economics
The cost of an average system is around $6500. With the Hawai‘i Energy rebate, your upfront cost at the point of installation becomes $5500. The system gets even cheaper when tax season rolls around and you claim up to 60% of the cost through state and federal tax credits—meaning you are only paying just over $2000 for the brand new solar water system.

There are three sources of incentives for the solar water heater:

• Hawai‘i Energy rebate: $1000
• State Tax Credit (35%) $1925
• Federal Tax Credit (25%) $1650

The solar water heater system uses 90% less electricity than a conventional electrical water heater. On average, an electrical water heaters uses 240 kWh per month while the solar water heater uses only 24 kWh.

Photovoltaic 

Although less than 1% of Hawai‘i residents have photovoltaic on their rooftops, the number of installations are growing rapidly. Most systems in Hawai‘i are grid-tied PV systems—the system does not have any storage capacity, instead using the electricity grid as “storage” through net energy metering. Some systems do have backup or storage capacity—usually a battery bank—that provide a few days of juice if there is a blackout or the sun isn’t shining.

Typical systems consist of silicon solar cells wired together within modules, an inverter to convert the direct current from the modules to alternating current, a device to quickly cut-off outgoing current should the power grid fail, and associated wiring and racks. Systems range from smaller, 1 kW systems to large 6 to 7 kW systems—enough to cover an entire home’s energy needs. The most expensive single component is the cell modules, comprising approximately 55% of the installed cost.

For more information on net energy metering, see Hawaiian Electric's site. For more information on applicable tax credits, see the State of Hawai'i solar site.

          

Senator Mike Gabbard's statement regarding Hawaiian Electric's solar moratorium, Feb 24, 2010.