I am also really interested in sizing my batteries much smaller than a conventional solar system, since I am on a tight budget. One avenue I am exploring is lining the fridge with 2L pop bottles filled with water, then setting the thermostat to ~ 0 C, so that when there is plenty of sun, the bottles will freeze, and act as a thermal storage. Then if there is no sun, the bottles will melt, and keep the fridge nice and cool for hopefully a few cloudy days. One challenge with this is how to keep my food from freezing, while allowing the pop bottles to freeze. I'm hoping that placing the thermostat near the bottles, and insulating the gap between the food and the bottles, will solve this issue. We will have to see.
Anywho, my real question is how prevent the fridge from clicking on if there is a few cloudy days, while still allowing things like my water pump and lights to function normally. Ideally I would somehow like to have two inverters (or DC power lines), one that is live if there is any usable charge at all in the batteries, and the other that only works if the batteries have lots of charge in them. The fridge could then be wired to the latter, so that in the case of a few cloudy days, it would not come on, instead relying on the ice to keep itself cool, and allowing the other loads to use the battery. Then once the sun comes back out again, the battery first recharges itself, then the fridge would click on, refreezing the ice and 'charging' it's thermal storage once more.
Anyone had experience with something like this before? I would like as much as possible to keep costs down, as the whole point of this system is to save me $$$ on batteries. What would be really cool is to be able to schedule different appliances in terms of their importance. Communications could be used all the time, even if it means damaging the batteries, water pumps and lights would be next, fridge next, then wall outlets for laptops and washing machine.
Joseph Lofthouse wrote:
You could Install voltage controlled relays between the inverter and the various loads.
Joseph, are you saying that there are relays that will shut off various loads when they sense below-defined-threshold current coming in from the sources (PV array, wind, etc)? That would be huge for certain appliances!
“The most important decision we make is whether we believe we live in a friendly or hostile universe.”― Albert Einstein
Location: Cache Valley, zone 4b, Irrigated, 9" rain in badlands.
posted 2 years ago
John: I suppose that they are designed to be connected to a battery, and not directly to a stand-alone source but yes, the devices are readily available. A search for "Voltage Controlled Relay" returned more results than I wanted to sort through. Some in the under $20 price range control AC/DC loads up to 10 Amps and 600 Volts, and had variable set points on the DC sensing circuit.
Inverters are not 100% efficient. They get more efficient as they reach their max output so you should size your inverters with care if pinching every last watt is important to you (as it is for me). More electronic cut outs and sensors and whatnot are just going to be more electrical draws.
Solar living has three main components:
1. lower your power consumption
2. increase your power production
3. increase your power storage.
for your fridge, I wouldn't complicate things with relays and voltage sensors and automatic cut outs. Increase the efficiency of the fridge with better and more insulation while making sure that the fridge can dump out the heat it makes through the coils on the back. Put your fridge on a timer so it only comes on during daylight (charging) hours and don't open the door outside of those times.
If batteries are unaffordable, lower your standards and run the batteries that someone else thought no good anymore and test them frequently. Keep the ones that work well, recycle the others. 'They' say that batteries are only good for a short number of years but this is not really true. With care a good battery can last as long as twenty years without too much loss of overall capacity. More importantly, a battery that is only holding 3/4 of it's original capacity is still a viable battery and rich folks will throw them away as soon as they are no longer 'perfect'. You will still get some valuable use out of them.