Dear Jim: I am going to do some landscaping around my house, so I will need some garden tools. Is it more cost-effective, efficient and better for the environment to use gasoline-powered, electric or cordless tools? – Carol D.

Dear Carol: You left out the most efficient and Earth-friendly of all: hand tools. For most yards, much of the simple trimming and cleanup can easily be done with hand tools instead of using any powered ones. Also, hand tools are lightweight, use little material and contain less overall embodied energy. Also, using them is good exercise.

Power tools do come in handy for some typical yardwork. The largest and most energy intensive tool is the lawn mower. From an overall operating cost and environmental standpoint, a plug-in electric lawn mower is best. If you have a large yard with trees, handling the cord can be cumbersome.

The next best is a cordless lawn mower. I have used the same 24-volt cordless mulching lawn mower on my 1/3-acre backyard for six years, and I have spent nothing on maintenance. The electric cost to recharge it (takes about nine hours) after cutting the yard is only about 3 cents. The only drawback is it is somewhat heavier to push than a gasoline mower.

The newest, most efficient cordless mowers are robotic models that cut the grass automatically. When the battery starts to run down, it automatically finds its docking station and recharges itself. These use less than $10 worth of electricity for an entire year. The cutting schedule can be set, often at night, and more frequent cuttings of grass make it grow stronger.

The new cordless garden tools, such as string trimmers, pole pruners, blowers, hedge trimmers and cultivators, are lightweight and well-balanced. Both Black & Decker and Ryobi have new lines of 18-volt models that have adequate power to do most typical landscaping tasks. The batteries are interchangeable among the 18-volt tools in each product group.

The electric cost to recharge one after trimming a hedge, for example, is less than 1 cent. I have tested both companies’ models and they operate equally well. Ryobi’s 18-volt battery can be recharged in only one hour. Black & Decker’s charger requires three hours for a full charge, but it has the largest selection of compatible tools.

Although the life of the 18-volt rechargeable batteries is many years, they do eventually need to be replaced. The cost is reasonable. Be sure to recycle any rechargeable batteries. If you do not know where to drop them off, call 800-8-BATTERY. Input your ZIP code on the phone keypad and listen for locations of recycling centers in your area.

These companies offer cordless garden tools: Black & Decker, 800-544-6986, www.blackanddecker.com; and Ryobi, 800-525-2579, www.ryobitools.com. These companies offer cordless lawn mowers: Black & Decker; Husqvarna, 800-438-7297, www.usa.husqvarna.com; Kyodo America, 770-237-0364, www.lawnbott.com; and System Trading Corp., 212-239-8230, www.friendlyrobotics.com.

Dear Jim: Our house is in a sunny location with very little shade. I was thinking of installing either a solar water-heating system or solar cell panels to operate a tankless water heater. Which would be best? – Craig S.

Dear Craig: If your primary interest is just heating water, the solar water-heating system is best. You would need a huge amount of solar cell panels to provide enough electricity for a tankless water heater. The solar water-heating system will include a small electric pump. Installing a small solar cell panel can provide enough electricity to operate the pump when the sun is bright enough to heat the water.

Send inquiries to James Dulley, Bangor Daily News, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com.