PV and Storage Heaters

rhiwfield

(You'll be pleased to know that the grid itself faces a similar problem, in that it has to match total generation to total demand in real time - and it costs megabucks to do that).

Since my arrays were installed I've wrestled with the same issue of how to concentrate consumption during pv generation. By deliberate design the 2 arrays are at an angle of 90 degrees to each other and this flattens out the production bell curve somewhat giving more usable hours.

Then installed monitors so that I can tell from house what production is at any one time.

Where possible adjusted auto timed use e.g towel rail to coincide with production.

Then switch on, one after the other key variable use items, to manually match pv production with consumption:

• washing machine
• tumble dryer if not line drying
• cooker/hobs (will often pre cook evening meal)
• breadmaker
• dishwasher
• and as a further use in fine but cold winter weather, an oil filled radiator on during the day

For really poor weather (heavily overcast) defer washdays!

Now those, together with base load, will take care of most of my winter pv production, and as I am at home its a feasible approach

In other seasons it will be harder, though a switch to an electric car should make for cheap summer motoring!

grahamc2003

rhiwfield wrote: »

(You'll be pleased to know that the grid itself faces a similar problem, in that it has to match total generation to total demand in real time - and it costs megabucks to do that).

Since my arrays were installed I've wrestled with the same issue of how to concentrate consumption during pv generation. By deliberate design the 2 arrays are at an angle of 90 degrees to each other and this flattens out the production bell curve somewhat giving more usable hours.

Then installed monitors so that I can tell from house what production is at any one time.

Where possible adjusted auto timed use e.g towel rail to coincide with production.

Then switch on, one after the other key variable use items, to manually match pv production with consumption:

• washing machine
• tumble dryer if not line drying
• cooker/hobs (will often pre cook evening meal)
• breadmaker
• dishwasher
• and as a further use in fine but cold winter weather, an oil filled radiator on during the day

For really poor weather (heavily overcast) defer washdays!

Now those, together with base load, will take care of most of my winter pv production, and as I am at home its a feasible approach

In other seasons it will be harder, though a switch to an electric car should make for cheap summer motoring!

Unless you have something like a 50kw capacity pv system, I think your maths are a little out! The above load looks to me like around 15kw!

But even if your maths were correct, you still wouldn't be able to match your pv generation with items such as washing machines, since the load from a washing machine varies a lot during the cycle - say from 0w to 4kw depend what it's doing at the paricular point in the washi8ng cycle.

Jon_Tiffany

grahamc2003 wrote: »

Unless you have something like a 50kw capacity pv system, I think your maths are a little out! The above load looks to me like around 15kw!

None of those items he listed will draw anyhere near 15kW. Washing machine and cooker will be the highest at around 3-4kW.

Maybe you could explain how you arrived at the 15kW figure?

The process he is using is exactly the same as what I and many others do to maximise our use of the generated leccy.

rhiwfield

grahamc2003 wrote: »

Unless you have something like a 50kw capacity pv system, I think your maths are a little out! The above load looks to me like around 15kw!

But even if your maths were correct, you still wouldn't be able to match your pv generation with items such as washing machines, since the load from a washing machine varies a lot during the cycle - say from 0w to 4kw depend what it's doing at the paricular point in the washi8ng cycle.

No, my maths are fine, note that not all variable units need to be on daily, also a washing cycle at 30C does not consume vast amounts of power. Yes, the power consumption varies during the cycle. The point was, how do I efficiently use the pv I'm generating, almost inevitably there is some additional but intermittent grid drawdown. Do you seriously want me to precisely match seven minutes at 2.5kwp + 200W baseload with like generation? Likewise, there will be times when I'm exporting during the cycle. FWIW my actual grid consumption is down 70% on 4 years back and I'm still a net grid user, but not by much.

Washing machine max consumption during cycle is 2.5kw, total consumption 0.5kwh.

Cooking during day is better controlled via hot plates rather than oven, but if oven is used everything goes in it.

Dishwasher is 1kwh for cycle, max consumption also 2.5kwh.

I suspect anyone who has invested in solar pv has an interest in energy efficiency as well as economic return. The fact that efficiency brings an economic reward is a bonus.

And my system is 3.8kwp.

grahamc2003

Jon_Tiffany wrote: »

None of those items he listed will draw anyhere near 15kW. Washing machine and cooker will be the highest at around 3-4kW.

Maybe you could explain how you arrived at the 15kW figure?

The process he is using is exactly the same as what I and many others do to maximise our use of the generated leccy.

I thought it was pretty obvious how I arrived at around 15kw. Simply add them up, just as he implied he did, turning appliances on, one after the other, until the output from the panels matches the demand. The maths is obviously wrong because the output - even on the sunniest midsummers day at midday - would be matched during part of the cycle by the washing machine only, and even then it would pull power from the grid during part of the cycle.

The idea that you have to have several high/reasobaly high powered appliances turned on to match the pv output is simply wrong, even with the panels generating their peak power.

So it's interesting Jon that you too turn on your wasing machine, then your tumble drier, then your cooker, then your breadmaker, then your dishwasher, and then, even on winter days, turn on an oil filled radiator - all just in order to supposedly match the panel output. That's totally absurd I'm afraid.

rhiwfield

grahamc2003 wrote: »

I thought it was pretty obvious how I arrived at around 15kw. Simply add them up, just as he implied he did, turning appliances on, one after the other, until the output from the panels matches the demand. The maths is obviously wrong because the output - even on the sunniest midsummers day at midday - would be matched during part of the cycle by the washing machine only, and even then it would pull power from the grid during part of the cycle.

The idea that you have to have several high/reasobaly high powered appliances turned on to match the pv output is simply wrong, even with the panels generating their peak power.

So it's interesting Jon that you too turn on your wasing machine, then your tumble drier, then your cooker, then your breadmaker, then your dishwasher, and then, even on winter days, turn on an oil filled radiator - all just in order to supposedly match the panel output. That's totally absurd I'm afraid.

Must you totally misunderstand what I've written?

The pv output is a bell curve over time.

Depending on time of the year and weather conditions the peak may be small, say 100-200W, or high, say 3.5kw. Currently my arrays are peaking at over 2kw in fine weather.

Power will be generated over several hours giving time to run several appliances, one after the other, not all at the same time as you incorrectly assumed. Baseload items will use that power generated up to say 200W. At the very peak, you may run 2 appliances at once, but with cycles offset so that heating elements dont come on simultaneously

On a fine day in winter, usually cold if high pressure, I will be line drying clothes and I have the option of using an electric radiator at 750W or 2kw settings for a while to soak up any low cost (3p) leccy.

Jon_Tiffany

grahamc2003 wrote: »

I thought it was pretty obvious how I arrived at around 15kw. Simply add them up, just as he implied he did, turning appliances on, one after the other, until the output from the panels matches the demand. The maths is obviously wrong because the output - even on the sunniest midsummers day at midday - would be matched during part of the cycle by the washing machine only, and even then it would pull power from the grid during part of the cycle.

The idea that you have to have several high/reasobaly high powered appliances turned on to match the pv output is simply wrong, even with the panels generating their peak power.

So it's interesting Jon that you too turn on your wasing machine, then your tumble drier, then your cooker, then your breadmaker, then your dishwasher, and then, even on winter days, turn on an oil filled radiator - all just in order to supposedly match the panel output. That's totally absurd I'm afraid.

You need to read rhiwfield's post again. You have mis-understood. None of those appliances will draw 15kW. Why are you adding them all together? They are run one after the other.

Those of us with solar panels try to make to most of the generated leccy, this is after all part of the idea of local generation, that the leccy is generated locally and used locally, thus saving on transmission losess.

So if you have solar panels doesn't it make sense that you would put your washing machine on during the day rather than at night?

Yesterday my panels started to produce around 800w by 10am (not bad for a small system on a November day) so the washing machine went on. By around mid day the washing machine had finished so the dishwasher went on. Maybe later in the day a bit of ironing before the output drops off too much.

Of course your consumption will never match the output, that is never the intention because it is almost impossible to do.

But surely you agree that it makes sense to run appliances at the time when the panels are producing electricity, even if they are only providing a portion of the leccy.

Like rhiwfield, I too have seen a large drop in my electricity use, due to a combination of energy efficiency and the solar panels.

albyota

I remember when working on a building site, we had to take it in turns to use the electrical power tools (before battery powered) because we only had the one 110 volt 2kvA transformer, if more than four (450 / 500 Watt) tools were used at the same time, it would throw the circuit breaker or trip the transformers thermal cut-out.

There were probably ten or eleven of us…. different trades, all needing to use drills, planers, table saws, sanders, skill saws, routers, lights etc intermittently…all ranging from 400 Watts to 1800 Watts or more, the transformer fed several splitter boxes plugged into other splitter boxes. When we added up all the tools loads it was around 9.3kW.

The key was to listen and wait till only two or three tools were in use before using yours; we always (most of the time) managed to stay under the 2kVA of the tranny.

Most domestic appliances are rated at their maximum power, i.e. a washing machine is rated at between 2 and 3kW (depending on size) with the heating element anywhere between 1,200 watts to 2,500 Watts, but will only use the majority of that full load when heating the water with the element and revolving the drum (wash cycle…. not spinning), for around 20 minutes, the rest of the time it will just be using the motor (c500W) to revolve the drum, final fast spin may use up to 700 Watts.

Trying to match the PV panels’ output and use it on site rather than export it can be done.

It is quite possible to switch on different appliances one after the other (either using time clocks or manually) as suggested above as long as the total load at any time does not exceed what the PV panels are outputting at that time or you will be drawing from the grid. (Easy on a clear bright cloudless day).

Although difficult to do in practice, (unless you have a lot of time on your hands) for example, you would need to know when the heating element is actually on during a wash cycle, then, when finished, switch on a 1.5kW cooker element for twenty minutes, when the spuds are done switch on the bread maker for three hours, etc… not sure about using a tumble dryer though, a dehumidifier is another way of drying clothes and at c300 Watts per hour (max 4 hours) a bit cheaper.

So well done Jon Tiffany and rhiwfield for proving this possible.

Kontiki

I think to some extent it is trying to maximize the use of the electricity you are generating. It isn't a case of just using the surplus for the sake of it, even if your panels are only giving you 500w & you run an appliance of 1kw you are saving not having to pay for 500w. It then makes sense to run one high power appliance at a time saving 500w on each rather than running 2,3 or more at the same time using 4kw but still only saving 500w.
I am due to have my panels fitted next week but I assume that anybody who already has them knows they won't produce all the power they need BUT with a bit of thought you can get the best out of them.

A thread on tips of ways to get the best out the panels along with figures showing what savings could be made would be useful.

We are probably at the low end of electricity users (when I have worked out our average use over the years it is 2200Kw) it will possibly be a bit more this year as we haven't been away as much. I will be happy if I can halve that amount. The figures I have been given for my system are that it should produce 2927kw per year, I should receive £1209 in FIT's & save £322 from my electricity usage (be interesting to seo see how they match up). Figures are calculated using Sunny Design software. All the other quotes gave similar sorts of figures. The guy who we are going with seemed very thorough, he was the only one to get a ladder out & took readings for direction & measurements from the bottom of the roof line.

grahamc2003

Kontiki wrote: »

I am due to have my panels fitted next week but I assume that anybody who already has them knows they won't produce all the power they need BUT with a bit of thought you can get the best out of them.

.

But you (not you personally) have to have some idea of the implications of turning on applicances, and some idea of how they work. It appears to me that the situation is more subtle than some imagine.

Simply turning on a washing machine will never match the output from the panels. It won't even use all the output the panels make during the wash cycle In isolation, doing that will alternate using zero of the panel output, using some of it and using all of it and, considering the load from the grid, none or some power will be taken. It's quite possible (and even frequently likely imv) that some users with cheap night rate electricity will actually pay more for their grid electricity if they switch running their machine from nightime to daytime to take advantage of PV output (as I have seen advised on these boards). (There are also potential detrimental environmental effects too, with the smaller amount of grid power taken during the day potentially producing more co2 than a higher amount taklen at night).

I expect there will also be a temptation for people to run a washer when it isn't full, just because of the perception that it is 'free' to do so at that time, which it rarely will be.

There's a poster called something like mf3dc who both has panels and is very informed of the various theories involved about getting the maximum use from them. I don't have links at the moment to his posts, but I'm certain they would be of interest to this discussion if you search for them (or if someone could post a link).