The Deep winter greenhouse will heat a 5 feet deep bed of gravel throughout the day and is supposed to keep the temp above freezing for at least 3 days if it stays cloudy but we can have weeks of barely any sun so the solar heating will have to be supplemented with an electric space heater. Fortunately I will never pay that bill nor any of the other bills. I have grants that come in from government programs and independent foundations that literally throw us money here. There is so much money I have to spend it on needless things usually by the end of the year. Indian reservation.