Make sure that the solar lights you are going to buy are effective, and use them wisely. To be effective, the solar lights should provide uniform coverage of the area you want to light.
New outdoor solar products
Solar lighting technology has come a long way in the last years. Cheap solar lights are polluting in their manufacturing process and do not last significantly, besides being little more than useless. Avoid them.
The best solar outdoor lighting products combine micro LED bulbs with a small solar panel and a rechargeable battery (Ni-Cd). The panel can be incorporated in the light fixture or come as a separate unit.
These solar outdoor units are a lot more expensive than discount products, but they worth their price. Inexpensive products may cost you a couple of dollars per unit, but they are very fragile and short-life; and they have a poor and unreliable output.
The prices of quality outdoor solar products may range from $30 to $50, or more, per unit. Groups of fixtures powered by a single panel, for common yard applications, will cost you $200 or more… Also expect high prices for flood solar lights with a large light output: $200 and $800.
Unfortunately, there is not yet an Energy Star or similar certification, and that makes the choice more difficult.
Solar-powered lights vs. low-voltage outdoor lighting systems?
Low-voltage outdoor lighting can provide a more constant and reliable source of lighting than solar outdoor lights, except in sunny climates; low-voltage kits also offer more control over the placement of the lights and the amount of light. Do not over-light your yard... Take into account your safety, but also your neighbors’ rights and the impact of over-lighting on nocturnal life (see: IDA pdf).
But solar yard lights have also significant advantages. Installation is very simple: common solar lights are designed to be pushed into the ground or to be fastened to a fence or other convenient location; they do not require access to outlets, or transformers, and can be easily installed in many places without electrical wiring and all that without ... running costs…
Just do not forget that you should not over-light your property and that solar lighting - like other outdoor lighting systems - may have an adverse impact on the night environment.