Major towns have electricity and the voltage available is 220-volts and 50 cycles. Power outage is sometimes experienced in Nepal. However, most major hotels have installed their own generators to avoid the inconvenience for its guests. Electricity is also available in main trekking routes from late evening and then again for parts of the morning. Some lodges charge a fee for recharging your laptop, camera and phone batteries. Bring electrical adapters and spare batteries for your laptop, camera and phone, as these are often not available except maybe in Durbar Marg (Kingsway) high end shopping district of Kathmandu.
Electricity used for light is available in some remote villages. The micro-hydro turbine generated electricity comes around 5/6 in the evening and goes out around 6/7 in the morning. During our travel through remote part of the country, we will arrange to recharge our camera and phone batteries wherever we have access for electricity. We have not yet found a way to solar charge these electric appliances, and if you have a lightweight, portable one that works for your needs, feel welcome to bring.