The best-known of these tools is probably the hand-held window squeegee, used to remove the cleaning fluid or water from a glass surface. A soapy solution acts as a lubricant and breaks up the dirt, then the squeegee is used to draw the now water-borne dirt off the glass leaving a perfectly clean surface.
Another way of estimating the cost of electricity would be the cost of an ordinary solar system, or $21,000 as shown in the example above. So the cost of a Tesla retrofit system would be in the range of $33,000 to $37,500.
Tesla said the cost of its new system amounts to the cost of an ordinary roof plus the cost of electricity. If one were to re-roof a typical 2,000-square-foot roof, the cost would be about $12,000 to $15,000 (including quality shingles, underlayment, other materials, removal and sheathing repair).