They can go without UVB for several days no issues
If the house gets too cold and you need short term heat, put chameleon into a shoebox (he'll settle down after he's been in the dark for a while) with a towel wrapped:
hot water bottle (your hot water tank will stay warm quite a while, or boil water on a BBQ)
or one of those chemical heat pads such as are used for shipping or keeping hands warm in gloves
or the salt(i think?) based ones in which you snap a metal disk and the liquid gets hot as it hardens, then you can reuse it after boiling.
Some emergency animal hospitals have generators to keep their buildings warm, and may allow emergency day care, for a fee.
Consider a little UPS to run a small watt lightbulb - just enough to keep him warm in a smaller cage covered with a blanket.
You can buy small human-powered generators - you pedal a bike to create current to run his heat light bulb or an electric blanket (this isnt as far fetched as you might think:
http://www.los-gatos.ca.us/davidbu/pedgen/pppm_electric_blanket.html
or
http://www.windstreampower.com/Human_Power_Generator.php
or
http://www.econvergence.net/easy.htm
Consider a generator if storms arent rare where you live, if power outages are yearly or typically long lasting.
Consider living somewhere with an alternate source of heat, such as propane or a wood fireplace, or a gas oven/stove.
Solar panels / wind turbines that charge batteries, which can then be used to power a heat bulb or whatever is needed.