Storage Heaters - Would charging them from a Solar System make sense?

blankscreen

Hi Guys, I'll likely go for solar installation next year, those who already have one say to use on your washing maching, dishwasher while you have daylight.

It occurs, our washing machine takes about an hour but is only on about every 3 days, dishwasher 30 minutes, so to use that excess available energy would fitting storage heaters to be recharged during daylight make sense?

never had them so no idea how long they would need to charge for, or consumption.

Alan

neilball

How would you control the power drawn by the heater to make sure it only used the excess generated power? I've had an online monitor reading my PV power generated and power consumed since July, and it is apparent that the generation is nowhere near constant, and at this time of year the generation levels drop dramatically meaning you would need several stages of heating in small amounts to be matched to your excess generation power to stand any chance of using it efficiently. For example, today my 4kW array only managed a peak maximum output of 300 watts, and generated less than 1kWh for the day. Therefore it would not be at all suited for heating as you could not heat your home with such a low power level.

Out of the 3100 kWH generated by our array to date this calendar year we have used about 2500 units, so only exported around 600 units, most of which was during our fortnight holiday in the summer when we had several days of continuous high PV output when the house as unoccupied.

At my location in the Scottish Borders it seems like the sun switches off in November and comes back on in February. For three months the PV output drops right off, meaning for this three month period we only generate what we normally otherwise generate in a single month, and this is at a time when you would most need heating. So using PV for heating is simply not going to work, you'd be far better liking to see if you could use the excess for hot water or some other electrical load that will be present year round as your greatest export periods will be spring through to autumn.

blankscreen

Thanks Niel,
I am a the typical mad scientist typ .

We are in Essex (Area 12) clear of any obstructions, the idea was effectively the substitution of white meter control to feed Solar power into one or two 1kwt heaters on their own circuit. I needed some informed comment (acheiving control aside) to see if it was viable.

As i understand it in good daylight times i'd get near 4kw for between 4 - 6 hours, a washing machine when heating up draws aroud a 2Kw for 15 minutes. So it seemed an obviousplan when no heavy duty units were being used to charge uo storage heaters from the unused solar power.

The ida is in i infancy, bu to sense when the Solar Panels are more than likely active, there is no hard output or indication from the kit, i buy a small stand alone solar panel normally used to trickle charge a car or boat battery, this is used to roughly confirm enough solar energy is available. a timer is used to limit the storage charging period as example 10am to 2pm, running washing machines etc restricted to between 2 - 4 pm, it would need some fettling and refining but thats the broad principal.

Given we don't use the washing machine or dishwasher every day, it seem prudent to use that spare caoacity for heating, and so reducing the gas bill. and we would only use the storage heaters to take the chill off at night in the dinning room and conservatory.

I was assured using Goverment charts a 4k system in my area would produce an average of around 2.5 Kw to per hour in winter as it works on converting daylight not sunlight into energy, but your figures do not seem to support anywhere near these claims.

what do you think?

Alan

neilball

My annual forecast for PV output based on my location/orientation was 3000-3500 kWh per year, and I'm right in the middle of these two figures this year. The sun is just up here and is struggling through some cloud low to the horizon, and the panels are not yet above 100w output. Within the hour there should be direct sun on the panels as the sun rises higher and clears the cloud so I'll see what happens.  During sunny days at this time last year I managed around 7.5kWh on the best days, but these were few and far between!

So you may get some useful heat on some days, but the amount of useful heating you achieve is never going to be great, and you still have the issue of what to do in the many months when you don't want/need the extra heat. Using appliances during this period is one way, but as you say it only uses a fraction of the available energy if you don't have a daily need to use them. I've got two boys who both play outdoor sports, so the washing machine is going at least twice a day, plus the dishwasher too. We also are an all-electric home with ground-source heat pump supplying our heating and hot water, so making use of the available power is never a problem, we simply have to manage when to use appliances through the day to stagger the load to utilise the available PV power.

Regarding storage heaters, I've only had experience of the standard Creda units from my first house nearly 20 years ago, and they did not make a great job of storing heat - the rooms they fed were always way too hot in the morning just after they finished charging, and by early evening they had little output left (just as you wanted the heat in returning from work). So in this case where your charging period would be much closer to when you wanted the heat it might work providing you can get enough energy to keep the heater operating for more than an hour or two each day. Otherwise you might be better to simply use a panel heater for direct heating to warm up the house directly when the PV energy is available, even if this is not quite at the time you would normally need the heat.

neilball

Just to add, now that the sun has cleared the cloud my output has risen to just over 2kW with the panels in full sun. I'll post again later when the sun has reached it's peak to see how much further this increases.

blankscreen

Many Thanks,
tbh i have a built in resstance to any early experience of storage heaters because they needed accurate weathercasts or they pump out during a heat wave lol! But i was also out of date about my views on Solar Panels.

I think later storage heaters have better heat retention as well as regulation design, a bit like recent hot water storage tank insulation that keeps heat for what i think are astonishing legnths of times - just as the home owners switch to combi boilers - timing is everything i guess .

Alan
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blankscreen

It would be good of any who knows to post how long a storage heater needs to reach a useful or full charge.

Alan

neilball

After a sunny day my PV generation has now dropped right down as the sun is almost perpendicular to my roof and starting to dip down low towards the horizon. With my orientation I've had 3.5 hours of useful PV generation above 2kW, right now the array is outputting less than 100w. So my total OV generation today will finish at around 7.5 kWh, in line with what I achieved last December on sunny days.

Hopefully that helps identify what you might expect from your own installation if you choose to go ahead. There is a massive difference between sunny days in Winter compared  to heavily overcast days, where my maximum instantaneous output can sometimes be as low as 150w leading to a total generation for the day as little as 0.2kWh! Being Scotland we certainly get more grey days than sunny at this time of year!!

blankscreen

Thanks Neil for all your time, really appreciated .

In our case, above 2 Kw for 3.5 hours - if we dedicated it as i think we could do for 3 or 4 out of 7 days would go a fair way to recharge 2 x 1 Kw heaters.

Not saying earth shattering but over the Autum to Spring period i doubt we would loose out.

Alan

neilball

Just one other thing to add, in the whole of November there were only three days where my output gave more than 5kWh for the day, and 10 days of output under 1kWh. Today will be another decent day once the frost has burnt off the panels, but this will be the first day in over a month where there have been two consecutive days of good clear weather up here in the Scottish Borders.

Don't let my figures put you off, but I am trying to give some real world feedback on the variability of PV output which only becomes really visible once you have real-time monitoring in place to record this information for later analysis.