Small solar heating system for shed?

[SamuelCB]

Hi everybody,

OK so I am completely new here and almost a complete noob with solar panels but was hoping for a little help. OK so I often like to work in my shed for my hobbies etc but it gets very cold and I cannot afford to keep a heater running in there at all times. Now recently my dad returned home with 4-5 various sized working solar panels which would fit nicely onto my shed roof.

I want to do something as simple as power a 12v/24v heater from these solar panels but wanted to know how basic I could keep the system as I am low on money. Now I know the solar panels output DC current and therefor could not power a AC heater without an inverter but if I was to have a 12v DC heater could I simply attach the solar panel to it causing it to output heat? Would this direct method with no inverters or voltage regulators damage the heater or just simply power the heater when the sun was strong enough to cause the panels to output the correct voltage and amps?

I apologies if this is a stupid or simple question but do not want to cause damage to the panels or the heater due to lack of care.

Thanks in advance!

[Sunking]

I want to do something as simple as power a 12v/24v heater from these solar panels but wanted to know how basic I could keep the system as I am low on money.

Very simple it is not going to happen. If you cannot afford a few dimes for fuel, you certainly cannot afford a $100,000 worth of panels and batteries to keep your feet warm.

[russ]

Solar thermal - either water or air - would be a better choice.

[inetdog]

Solar thermal - either water or air - would be a better choice.

Even given that you have an assortment of solar PV panels already, it will still cost more to get any use out of them for heating than to go completely DIY with a solar thermal heat system. There are some very interesting and low cost ideas and complete systems for small buildings described in other threads on this forum.

[SamuelCB]

OK firstly thanks everybody for your replies, secondly I already have the panels so don't need $100,000 worth of stuff.

Whilst bored today I decided to hook all four of my panels up in serial and they outputed a fairly constant 90v which isn't to bad. However the panels are completely unmarked so I do not know their wattage or amp output. Is there anyway to measure one or the other so that I can do the calculations to find out the other outputs?

Secondly, if I had a 12v DC to 240v AC converter like used in cars, can I not power that off a standalone 12v car battery and then charge the battery with the panels fairly cheaply, either with my own home made charge controller or a shop bought one?

Thanks again!

[inetdog]

However the panels are completely unmarked so I do not know their wattage or amp output. Is there anyway to measure one or the other so that I can do the calculations to find out the other outputs?

Simple thing. What you want most is the easiest to get, the short-circuit output current, Isc. With that and the open circuit voltage, Voc, you can do a decent enough job at estimating the rest. Note that the output power will NOT be all the way up at (Isc x Voc). You can figure that Imp will be about 90% of Isc and Vmp will be about 80% of Voc. Maximum panel power under normal conditions will be (Imp x Vmp).

1. Cover the panel.
2. Connect a DC ammeter capable of handling at least 10 amps, preferably 15, just in case to the plus and minus terminals of a single panel.
3. Uncover the panel and read the meter. (Make sure it is near solar noon on a clear day and the panel is pointed within 20 degrees of straight at the sun. You can set this up easily by temporarily putting a short stick at right angle to the panel and making its shadow go away. Then take it off before measuring. Panel output can be reduced by even the smallest amount of shade on one cell.
4. Cover the panel, and disconnect the meter.

It is not really necessary to cover and uncover the panel for just one small panel, but it will be a good habit to get into and will keep you from being startled by sparks as you connect and disconnect the meter.

[SamuelCB]

Fantastic, thanks for the quick reply. I thought I had tried this today and got not reading at all but I think I must have had my multimeter on the wrong setting and so will try again when I have a spare sunny day!

[inetdog]

Fantastic, thanks for the quick reply. I thought I had tried this today and got not reading at all but I think I must have had my multimeter on the wrong setting and so will try again when I have a spare sunny day!

If you have the meter on the right setting, have the meter leads plugged in in the right place, and have not blown a fuse, you should be able to see some current even on a cloudy day. It will be 1/10 or less of that for a sunny day, but it should be readable.
If not, there may be a problem within the panel. A very high resistance almost open circuit, or a broken cell, can let you read a voltage but the panel will not deliver a noticeable amount of current.

[SamuelCB]

Ah it might have been a case of not having the cable connected to the correct part of the multimeter then as I did not think about this at the time. I am at university at the moment but will definitely try that when home or tomorrow!

Thanks again!

[Sunking]

OK firstly thanks everybody for your replies, secondly I already have the panels so don't need $100,000 worth of stuff.

You are going to need several dozen more panels.

Let's play the numbers game of simple high school physics. You want to run a simple electric heater right? Say one of the small floor models from Wally World that use 1500 watts, and you want to run it 6 hours per day on a Off-Grid Battery system and you live in say Kansas City where you get a decent 3 Sun Hour day in winter.

1500 watts x 6 hours = 9000 watt hours or 9.0 Kwh. To generate 9 Kwh hours will require the panels to generate 13.5 Kwh
Solar Panel Wattage required = 13,500 watt hours / 3 Sun Hours = 4500 watts.

As for the battery is going to require a 48 volt battery and the battery capacity needed is 45 Kwh.
48 Volt Battery Capacity = 45,000 watt hours / 48 volts = 937 Amp Hours @ 48 volts. That battery will weigh in around 2300 pounds and cost around $10,000.

What you have to work with is not going to run a 1500 watt heater for more than a couple of minutes before you destroy the batteries and left with nothing but heartache and questions. Basically what you are trying to do is pull a 18-wheel tractor trailer with a bicycle. It is not going to work no matter what you try.

[inetdog]

What you have to work with is not going to run a 1500 watt heater for more than a couple of minutes before you destroy the batteries and left with nothing but heartache and questions. Basically what you are trying to do is pull a 18-wheel tractor trailer with a bicycle. It is not going to work no matter what you try.

How about recharging the batteries for electric socks, mittens and vest? That seems more in line with reality.

More seriously, a 150 watt infrared heat lamp is also within possibility for 30 minutes at a time.

[hubster5]

How about recharging the batteries for electric socks, mittens and vest? That seems more in line with reality.

More seriously, a 150 watt infrared heat lamp is also within possibility for 30 minutes at a time.

This reminds me of my current home electrical (grid). Turn on the toaster, crock pot, and hair dryer at the same time - count to 5 - room goes dark...

Resistive heat is the great white shark of electrical consumption... If using solar cells were viable in creating it, there would be entire section here dedicated to it...

Your solar cells would be much better used in powering the fan for your solar heater, that converts the radiant heat from the sun directly into the foot warming pleasure you so desire! I am in the panning stages of doing that just now...