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.
SolarCity offers a 9-year Powerwall lease for $5,000 when part of a rooftop solar panel installation and financing contract. To buy and install the battery outside of financing a solar deal, the price is $7,140. Thatâs some pricey power, given how infrequently the lights go out.