Heat sources and Solar

[kcjeeves]

I'm new to the solar game, read a lot but never owned a system. We just purchased an offgrid home with an 800w panel, I think, 2k inverter, and a bank of batteries. The previous owner said to never run heat sources off the batteries, it's hard on them. I understand not running electric heat, dryers, etc..but don't the batteries just see the watts that the device pulls? Like a 450w rice cooker, wouldn't the batteries see that as just a 450w load like any combination of other smaller loads? I mean the batteries don't see it as a heating source do they?

Tks,
KC

[inetdog]

I'm new to the solar game, read a lot but never owned a system. We just purchased an offgrid home with an 800w panel, I think, 2k inverter, and a bank of batteries. The previous owner said to never run heat sources off the batteries, it's hard on them. I understand not running electric heat, dryers, etc..but don't the batteries just see the watts that the device pulls? Like a 450w rice cooker, wouldn't the batteries see that as just a 450w load like any combination of other smaller loads? I mean the batteries don't see it as a heating source do they?

Tks,
KC

Hi KC,

You are absolutely right that the batteries (and the inverter) cannot tell one 450 watt load from another 450 watt load.
What the previous owner was probably referring to is the fact that using propane or some other fuel will be far cheaper than taking the necessary energy from the batteries. (Even if you have to invest in a propane (or wood) stove on which to cook your rice, or run a generator when you are cooking rice.)

It is not that you cannot do it, it is that it is an inefficient use of battery power if there is any other way of doing the same job.
You are not paying directly for the power you draw from the batteries, and you will not affect the life of the solar panels or charger, but the more you draw from them, the smaller number of charge/discharge cycles will be left in the batteries and the sooner you will have to pay to replace them.

[russ]

Heat loads are maximum loads - usually over time. Heating is a poor usage of PV power.

[Sunking]

Well you got things half right but do not understand the scale and time element relationship.

Sure a rice cooker may use just 450 watts and will cook a pot of rice in 30 minutes so it uses 450 watt x .5 hours = 225 watt hours. That requires a 60 pound battery.

But let's say a 1200 watt toe warmer you buy at Wally World. About enough to heat a small closet running 10 hours per day. It will use 1200 watts x 10 hours = 12,000 watt hours and takes a 3600 pound battery.

Depending on where you live to generate 12 Kwh per day would cost you as little as $20,000 and up to $40,000 in equipment and batteries. $10,000 of that is in batteries and they need replaced about every 5 years. Not a very good deal to generate $1.20 worth of electricity every day.

[MikeSolar]

Well you got things half right but do not understand the scale and time element relationship.

Sure a rice cooker may use just 450 watts and will cook a pot of rice in 30 minutes so it uses 450 watt x .5 hours = 225 watt hours. That requires a 60 pound battery.

But let's say a 1200 watt toe warmer you buy at Wally World. About enough to heat a small closet running 10 hours per day. It will use 1200 watts x 10 hours = 12,000 watt hours and takes a 3600 pound battery.

Depending on where you live to generate 12 Kwh per day would cost you as little as $20,000 and up to $40,000 in equipment and batteries. $10,000 of that is in batteries and they need replaced about every 5 years. Not a very good deal to generate $1.20 worth of electricity every day.

excellent explanation...they are not often so well put