Photovoltaic solar for heating a room?

[gotwind2]

Hello all.

I must admit, a few times I have been asked, 'what do you use your renewably generated power for?'

I sometimes have trouble answering the question, as the mains is still so cheap per Kw/h compared to renewably generated energy, I tend to use mains power :-/

The Kw/h unit cost has risen considerably as we all know.

With autumn here in the U.K, I have a real need for free, heating in my office at home (and I also have 440w of solar panels doing nothing in a box, from the REcharge pod project)

Come October, mornings can be very chilly, I am looking at using a few of my eight 55W solar panels to charge a bank of batteries - maybe four 110A/h.

And then using a 1000w inverter to power a mains electric heater, probably an on-demand oscillating heater with a switchable 400, 800 watt settings for maybe a few 20 minute sessions a day..

I have read that all electric heaters have a very high efficiency, up to 100%, which makes sense, or maybe I might be better with a 12v Ceramic type  heater?

Any advice appreciated.

Ben.

[DamonHD]

A heat-pump of some flavour driven by electricity will typically yield between 2 and 4 times as much heat as plain (wasteful) resistance heating, ie efficiencies of 200% to 400% compared to resistance-heating's 100%.

Electricity is a very high-grade energy source, and wasting it as heat with resistance heating is a shame.

Rgds

Damon

[electronbaby]

Yes, many people often ask me this: "can I use my PV system to offset my electric heating costs?"

Usually the answer is sure, BUT because PV is so expensive, what you are now accomplishing is taking all the electricity that you just paid a premium for, and using it to waste in an electric heating element, when it could be used for running appliances. My detailed answer to them is there are much more cost efficient and cost effective ways to get heat energy. But IF you didnt pay anything for your PV modules or maybe paid very little, OR you have the PV modules sitting around doing nothing, it might be to your advantage to use it for heat.

Get those things in the sun where they belong!  :-)

[electrondady1]

well, until you get a heat pump it should  wood work ok.

kinda neat.

[windstuffnow]

I've actually been thinking on the same lines.  I plan to run a 1500 watt unit for 10 minutes on the hour.   I burn wood in the winter to heat the house and if I start it to soon I'll end up with all the windows open.  This transition period from fall to winter and winter to spring is always a pain ( of course so is winter ).

My batteries are usually charged by noon everyday so the rest of the day can heat the house or at least add to it.   No sense wasting the possible extra energy from the afternoon sun and wind...

.

[Chagrin]

How is an electric heater ever not 100% efficient?

[DamonHD]

By accidentally generating light?

There's some electric heaters that waste as much as ~10% of their energy as light, but luckily houses are full of sockets near the ceiling to put them in so you can make some use of that wasted light to read by, etc.  B^>

Rgds

Damon

[Airstream]

In order of efficiency: solar domestic hot water, solar to water space heat, solar to air space heat then PV electric to resistance heat.

As long as you are aware you are getting ~10% conversion efficiency instead of ~70% have at it...  : )

[Capt Slog]

As much as 10% ?  I think the figure on an incadescent bulb is nearer 3%, I don't know about CFLs.

Good point though  ;-)

.

[richhagen]

My dump load for my solar panels on my 48V system is resistance heating via old toaster elements.  About 500 Watts or so.  It is probably not optimal, but as a dump load for energy I cannot currently store and am not currently using, it works for now.  In the dead of winter, 500W contributes relatively little to the 5000+ watts of gas heating in use, but at least it does something and probably reduces my consumption by a couple percent.  Not as effective as adding additional insulation or weather stripping, or as Damon points out, powering a heat pump, but it beats open circuiting the panels. Rich

[Chagrin]

So if I built two insulated boxes and put a 100W ceramic heater in one box and a 100W light bulb in the other box, are you saying that the box with the heater in it would get hotter?

[DamonHD]

Hi,

No, all other things (eg box dimensions and construction) being equal.

But heat is a VERY low grade form of energy, eg 1kWh of heat can typically only make maybe a third of 1kWh of electricity or light and conversely 1kWh of electricity can make and pump considerably more than 1kWh of heat.

So the '100%' efficiency is a bit misleading.

Like I could burn books for heat fairly efficiency for example, maybe 100% in one of those boxes of yours, but that's missing most of their value.

Rgds

Damon

[tmcmurran]

Would not heating a water source for some type of radiant heating be more productive?  I only ask because I would like to be able to do something along the same lines and am a little unsure of what direction to take.  At least you would be able to retain some of the heat energy a little longer if it was contained and slowly released over time.  Also if produced with a diversion load once the system was charged you would be gaining a extra source of energy that would otherwise be wasted on a dump load that does very little.

Just a thought........

[Jon Miller]

Ok how about.

Knock a hole in your roof, fill hole with said PV Panels.

Seeing as PV's are at best 20% efficient, the left over energy from the solar radiation could radiate into the house.

This would give you the heat you are after Ben, as well as a bit of electricity on the side.