The days can be unbearably hot and if you have to stay inside then you could save on electricity that could be used to cool the room by blocking the sun. How? Easy. Use light curtains that let in the light but block out some of the heat. If you live in the country then planting a few trees around your house would provide you with some good shade [and coolness if The House is entirely surrounded] eventually.
We keep our blinds closed during the summer or it gets to hot. Same with the doors. But you're correct, curtains can make a huge difference! Also, turn off lights when you're not using them. Unplug things you are not using. Try not blast the air. I keep mine on 77 during the day. It is comfortable enough where I'm not sweating. I put it on 75 at night because I need it cool to sleep. Also clean your air filter! It will make a huge difference in cooling. I recently cleaned mine and it is cold in my house at 77. Makes a huge difference!
Funny, the first answer that entered my head when reading your question was: "Eat less ice cream". But joke aside, doing practical things such as keeping your blinds down during the day will help to save money spend on fans or air-conditioners. Having cold showers on hot days will make you feel invigorated and you will save on electricity. The same goes for eating more salads and fresh fruit instead of cooking three meals a day.
I open my windows in the morning and let the cool air inside. Then, between 10:30 a.m. and 11:00 a.m., I close them. This allows me to both cool down my place, but also get rid of some of the heat. Another money saver is a rotating, tower fan. They actually work well - better than the traditional square fans.
I keep the blinds down to keep the sun out, in the mornings if it is cool outside I will open the windows to let the heat out of the house and some fresh air in, as it gets hotter outside I will close the windows, we do not turn the air on until it gets up to 80 degrees in the house.
One thing I found works well is hanging the thermal emergency blankets in the window. It lets light in and keeps heat out. The lighting in the room will be as if you tinted the windows. I use hair clips to hold it on a tension rod so I can easily remove them when I want the windows open.
Go outside, this way you won't need to turn on your fan, but you will ultimately end up paying for the sunny beach.
Sometimes I bring my desk work to the library and work on it there. They have air conditioning, lights, internet, work tables, couches to sit on, a water cooler, bathrooms, and a place for people to charge their laptops and devices. What more do you need? The library is a couple of blocks from my apartment, so on really hot days, I shut down everything at home and take my desk work over there.
I also keep my blinds closed and the lights off during the day to help keep the house cool. We also have several trees that surround the house. They also help keep the house cool. I never thought about purchasing light curtains. That is a good idea. I may decide to purchase light curtains for next summer.
I run my ceiling fans all day long. They keep the cool air circulating. They provide air movement and that makes me feel cooler. I use sunblocking curtains as well. Also, I keep my house at a constant temperature by using a programmable thermostat. This helps the air conditioner not to be continually running or trying to catch up.
I would have to add that you can also just lie in your bathtub if you're feeling hot and sweaty and linger there, as compared to just sitting in a room in front of the electric fan or having your aircon turned on full blast in your room. Just soaking yourself in water can instantly cool your body, without the added expense.
The only part about sitting in a tub all day that would bother me, is that you can't multitask or make any money while you're sitting in a tub. At least while I'm sitting in front of the fan, I can list items on eBay without being electrocuted.
I would say that the biggest energy and cost saver this summer would be to leave your air-condition unit alone. People don't realize how much energy there are using and how high their electric bill will be once the get it in the mail? The solution? Tough it out and use the fan. If you don't have a ceiling fan get a cheap fan at Walmart. Drink cold water and endure the heat that way. This whole summer I've use the AC only for one night, and I live in the South, so it is doable.
For years I used curtains to block out the sun to make the house cooler. But I noticed that when i touch the glass window, it's still hot. Heat is still radiating off of the heated glass. So then I started blocking out the sun from outside of the house. This brought down the heat in the house by a few degrees, but it was noticeable. The glass was not getting as hot because of the lack of direct sunlight.
My 'roommate' (or is it 'housemate' if you're NOT in an apartment?) reminds me that the power costs more from 2 p.m. to 7 p.m. Staying home all day, I have to keep the house cool by not running any big heat-producers (the stove, oven, washing-machine, dryer, dishwasher) during that time. It's also good to remember to keep both doors on any double-door entryways completely closed. The area between the inner-door and the outer-door is part of 'the whole outside you don't want to air-condition'
It's either you choose a well-ventilated house or add more windows to your existing home for proper air circulation. Well indeed you can grow plants (not necessarily trees if you have limited space) around your house so that it will still feel cool even during summer. A properly ventilated house also prevents additional expenses. You don't need to turn on the AC. A single electric fan may suffice.
I still turn on the air conditioning and I will do it all day if I feel I have to. If I'm feeling a bit guilty about spending so much on electricity I just remind myself not to skimp too much at the price of my own comfort and instead I just try and get savings out of all the other things in my life such as food or entertainment. I also try to prepare my finances beforehand so I would have enough extra money for extra expenses during the summer since after years of going through extreme heat I've learned to prepare.
Maybe your area is 'properly fumigated' (i.e. zero-tolerance for creatures that--while they might serve purposes like 'pollen-distribution' outdoors--are deemed 'pests' indoors), but the first thing I think when I read your "properly ventilated" is 'you're letting all the bugs in!' ... Maybe it's just that I want to spread some viral form of entomophobia, which may be a result of a past bedbug-infestation ...
Summer is a huge money saver for us. Days are brighter longer, so lights are hardly used at all. No more paying for heat, which we do most of the year. We don't eat as heavily in the summer either, so that helps too. I also feel light headed when we use air conditioning, so we never use it.. plus I feel wasteful using it. As others have mentioned, keeping the curtains closed is a good idea.
The main thing I notice about the summer months is the amount of gas I save. That's the type of gas we use for cooking and heating here in the UK, not the sort that goes in the car. I'll typically use around £40 worth of gas per month during winter, this has currently dropped to around £18.