Solar heating - EV vs Heatpump

[Heinds]

Hi Guys

In the final stages of completing a newly built home. Planning on installing the following:

18 x 350W canadian Solar Panels

8MW Solarsync hybrid inverter

9.6kWh Dyness power box L-Ion Battery

 

Here is the roof:

House has 4 bedrooms with bathrooms (3 upstairs and one guest below)

Only 2 people staying in the house for the greater part of the year (Guests will use room below and maybe upstairs but no longer term stays until children arrive in few years)

Shower in evenings and mornings

My idea was to install 2 x 150L kwikots and use the 1 for main bed and kitchen downstairs and only turn on/use the other one when guests arrive

So my question is:

What would be the best here when it comes to saving water and electricity and available roof space? (Note North and also note that i have no problem moving panels.)

EV Solar, PV Solar or Heatpump?

The inverter also has the function/ability to feed excess power to the geysers.

This is in Cape Town.

 

Any advice/opinions would be appreciated.

[PeterP]

As with most of these questions - it depends. If you have enough excess PV power during the day to run 2x 1.5-2kW element for 2hours then thats your solution. If your load-profile won't allow the geyser load without having to add panels then it will be slightly cheaper to much of a muchness to add EV-tubes as opposed to adding extra PV panels. Heat pumps are typically only viable on bigger systems for water heating + they require maintenance and have shorter lifespans.

[Heinds]

6 hours ago, PeterP said:

As with most of these questions - it depends. If you have enough excess PV power during the day to run 2x 1.5-2kW element for 2hours then thats your solution. If your load-profile won't allow the geyser load without having to add panels then it will be slightly cheaper to much of a muchness to add EV-tubes as opposed to adding extra PV panels. Heat pumps are typically only viable on bigger systems for water heating + they require maintenance and have shorter lifespans.

Thanks for your reply Peter

[Jaco De Jongh]

On 2019/10/13 at 9:08 AM, Heinds said:

EV Solar, PV Solar or Heat-pump?

Solar PV is the least efficient way of heating water, Ev tubes much more efficient and Heat-pumps by far the most efficient way of heating water. 

21 hours ago, PeterP said:

Heat pumps are typically only viable on bigger systems for water heating + they require maintenance and have shorter lifespans.

This statement I can not agree with. Heat pumps works brilliantly combined with a normal residential geyser. Yearly maintenance are recommended and its the same as maintaining an aircon. Cleaning and blowing out the unit and checking the strainer from time to time. (EV tubes also has a recommended yearly maintenance interval), And I know of some heat-pumps thats been running for 10 years without any issues. (10 years are normally where EV tubes start acting up)

15 hours ago, Heinds said:

1.5-2kW element for 2 hours then thats your solution.

I have done this for years and a 1kw element will only add 1kwh heating energy to the water, with a heat-pump, you will need 1.25kwh to add 3kwh heating energy to the water. So if you have 1.2kwh Spare in your system, I will rather use that to run a heat-pump with a COP of 3 - 3.5 than an element with a "COP" of 1 

In Short, you will need to run your 1 kw element for 3-3.5 hours to get the same increase in temperature as what you will get from running the 1.25kw heat-pump for an Hour. 

[PeterP]

32 minutes ago, Jaco de Jongh said:

 

In Short, you will need to run your 1 kw element for 3-3.5 hours to get the same increase in temperature as what you will get from running the 1.25kw heat-pump for an Hour. 

Yes but at what cost? For the amount of money you spend installing the heat pump you can have the PV power (at zero marginal cost and 25 year life) to run the normal geyser element plus plenty excess power for other loads when water is up to temp. Heat pumps are more energy efficient for sure by the factor of 3.5 but I'm assuming he is looking at best option financially and if you factor in extra upfront cost, 10 year life and maintenance then the heat pump for such a small system may lose out. But as I said, it depends - if he doesn't have other loads or battery to push the excess PV power into then it might not work. If he was only heating water then heat pumps might work.

[DeepBass9]

Is this a grid tie system? Then EV tubes, and throw Eskom a bone in cloudy weather will be most cost effective.

[Jaco De Jongh]

14 minutes ago, PeterP said:

But as I said, it depends - if he doesn't have other loads or battery to push the excess PV power into then it might not work. If he was only heating water then heat pumps might work.

I am a bit confused, If you use less energy to heat the water, then you will have more available to power some additional loads, or am I missing something

[Heinds]

The upfront cost for me is not really the issue. I'm more interested to get the running costs down. With Eskom pushing for anther big increase i want to ensure that i have the most efficient system that will use the least amount of energy from the grid. Also need to consider water wastage. 

[Heinds]

2 minutes ago, DeepBass9 said:

Is this a grid tie system? Then EV tubes, and throw Eskom a bone in cloudy weather will be most cost effective.

Yes its grid tied

[Jaco De Jongh]

1 minute ago, Heinds said:

The upfront cost for me is not really the issue. I'm more interested to get the running costs down. With Eskom pushing for anther big increase i want to ensure that i have the most efficient system

In that case, i would definitely go for the Heat-Pump

[PeterP]

3 minutes ago, Jaco de Jongh said:

In that case, i would definitely go for the Heat-Pump

Heat-pump is more energy efficient but not necessarily more cost-effective. EV Tubes and PV have zero marginal cost, heat-pumps reduce the marginal cost. If the goal is minimizing running costs then zero marginal cost should win.

If ROI is not a concern then a heat-pump wins on it's efficiency

 

[DeepBass9]

BUT, when the sun is not shining, EV will do much better than PV and element or heat pump. EV still heats to an extent even when it is cloudy. 

[Jaco De Jongh]

54 minutes ago, DeepBass9 said:

and throw Eskom a bone in cloudy weather will be most cost effective.

 

6 minutes ago, DeepBass9 said:

BUT, when the sun is not shining

 

53 minutes ago, Heinds said:

use the least amount of energy from the grid.

If its cloudy, and you have to throw Eskom a bone, the most energy efficient way to do it, will be with a Heat-pump, that will ensure the least amount of energy drawn from the grid. 

[Bobster.]

22 hours ago, PeterP said:

As with most of these questions - it depends. If you have enough excess PV power during the day to run 2x 1.5-2kW element for 2hours then thats your solution

Say what? I have two geysers in my house. The main geyser (that we use) is on a heat pump so is not too big a problem. They guest geyser (on a timer and usually turned off) has an electric element and chews in excess of 3kw on startup. That is a problem. Is there something wrong there, or should I just go for a lower rated element and accept that it will run longer (I usually have spare power in the afternoon that could be used to warm that water). 

The 3kw load is not backed up, but it will usually be close to or even exceeding the PV output, so it's going to ultimately draw from the grid.

Edited October 14, 2019 by Bobster
clarify that geyser is on a timer

[Jaco De Jongh]

3 hours ago, calypso said:

but they are expensive and require maintenance

This is the second time in the thread alone that someone mentioned the maintenance. Can I please ask if you can tell me what maintenance is required on a heat pump?. Unless you are in a very dusty area, yearly cleaning of the evaporator fins is all you need to do. That will normally take 10-20 min. The Y-strainer might clog up, but the system should let you know when that is becoming an issue, and cleaning that takes 15 min max (Personally I never needed to do that.) .

3 hours ago, calypso said:

Has anyone done the maths to see if they take the cost of a heat pump and instead of buying it then add additional panels to that same value.

You can have a good heat-pump installed for roughly R16-R18k, then it will use 1.25kwh for every hour to add the same heat as a 3kw element will do over an hour. 

So theoretically (If you leave the 3kw element intact) and you chose to add panels, you should add at least kwp 3.7kwp (Losses included) to do the same. Now to add 3.75 kwp to your system will cost about R26k for 10 x 400 watt panels, plus the mounting structure plus the labor. 

Those panels can help to power other loads while the sun shines and heating up the geyser will be limited to sunlight hours, and lets not forget, your inverter should be able to handle this extra load as well. 

The heat pump on the other hand, uses almost 2/3 less energy to do the same work, whether the sun is shining or not, The COP is effected by very low ambient temperatures, but in most areas of South Africa, it remains the most energy efficient method of heating water. 

[Heinds]

2 hours ago, Jaco de Jongh said:

This is the second time in the thread alone that someone mentioned the maintenance. Can I please ask if you can tell me what maintenance is required on a heat pump?. Unless you are in a very dusty area, yearly cleaning of the evaporator fins is all you need to do. That will normally take 10-20 min. The Y-strainer might clog up, but the system should let you know when that is becoming an issue, and cleaning that takes 15 min max (Personally I never needed to do that.) .

You can have a good heat-pump installed for roughly R16-R18k, then it will use 1.25kwh for every hour to add the same heat as a 3kw element will do over an hour. 

So theoretically (If you leave the 3kw element intact) and you chose to add panels, you should add at least kwp 3.7kwp (Losses included) to do the same. Now to add 3.75 kwp to your system will cost about R26k for 10 x 400 watt panels, plus the mounting structure plus the labor. 

Those panels can help to power other loads while the sun shines and heating up the geyser will be limited to sunlight hours, and lets not forget, your inverter should be able to handle this extra load as well. 

The heat pump on the other hand, uses almost 2/3 less energy to do the same work, whether the sun is shining or not, The COP is effected by very low ambient temperatures, but in most areas of South Africa, it remains the most energy efficient method of heating water. 

Is the ITS a good option? My concern has always been the humming sound of the heatpump when you are trying to sleep. So for 2 x 150L i would need to look at 2 x 3.0kW?

[Jaco De Jongh]

13 minutes ago, Heinds said:

Is the ITS a good option?

I think they are on top of their game currently with serious thought and development that went into their products. I prefer using ITS... 

13 minutes ago, Heinds said:

So for 2 x 150L i would need to look at 2 x 3.0kW?

Its not that simple, normally we connect a recorder on the geyser for a few days to determine the best unit for the clients consumption habits. 

The 4.7KW  is most commonly used, the 5.0 kw Super is in a class of its own, but sadly over specked for most normal house holds. The 3kw however is for low demand. 

I recommend you prepare yourself for the 4.7kw unit, the additional 1.7kw comes at roughly R2k more depending on your supplier.  

 

[PJJ]

2 hours ago, Jaco de Jongh said:

The 3kw however is for low demand.

I think this could actually work for me, wouldn't it be possible to use this in  conjunction with my existing flat plate collector?

We are 4 people using a 150L geyser and 3 of the 4 shower in the evening, leaving the hot water pretty much exhausted at 22:00.

But then I have to start the element at 6AM for the last morning shower (which is horrible since I would rather have the sun do most of the heating) but I have no choice.

[phil.g00]

10 minutes ago, PJJ said:

We are 4 people using a 150L geyser and 3 of the 4 shower in the evening, leaving the hot water pretty much exhausted at 22:00

I'd be inclined to get a bigger geyser, or be 1 of the first 3 to shower at night.

[PJJ]

19 minutes ago, phil.g00 said:

I'd be inclined to get a bigger geyser, or be 1 of the first 3 to shower at night.

Well person nr 4 still has a piping hot shower in the morning courtesy of me wasting energy on heating the water to 55C

Thereby not leaving the flatplate collector with much to do the rest of the day.

[phil.g00]

I know I was being a bit flippant, but seriously though is your issue not making and storing enough hot water when you can.

Even heat pumps should really work during the day time, from the point of view that that's when you have solar electrical power and that's when the ambient air is warmest.

[Jaco De Jongh]

1 hour ago, PJJ said:

wouldn't it be possible to use this in  conjunction with my existing flat plate collector?

They do compliment each other, and work together pretty well. 

1 hour ago, phil.g00 said:

Even heat pumps should really work during the day time, from the point of view that that's when you have solar electrical power and that's when the ambient air is warmest.

This part is true, but we have experienced that it is not practical in all household, I must admit, even where we allow the heat-pumps to run from 4 in the morning, they still do a very good job of heating the water. 

[phil.g00]

4 minutes ago, Jaco de Jongh said:

This part is true, but we have experienced that it is not practical in all household, I must admit, even where we allow the heat-pumps to run from 4 in the morning, they still do a very good job of heating the water. 

I don't doubt, the point I am trying to make is, is this a storage volume issue?

If he had 200L of hot water stored by the evening, instead of 150L, would that resolve things in a more efficient manner?

He is using still using 200l of hot water a day, he is just using mains electricity to pre-heat 150L of it in the morning, so his solar flat-plate can idle all day.

Even the reduced heat pump power is mains electricity, (or worse, battery power) at night time.

It should be the flat plate that's doing the heavy lifting, with the mains for top-up, not the other way around.

[Jaco De Jongh]

3 minutes ago, phil.g00 said:

is this a storage volume issue?

I neglected to comment on that part,  but you are 100% correct, it will improve the situation, but only with 50 liters. If it will solve the issue, thats a different question.  

[phil.g00]

People in Cape Town would probably get by on a 50L shower.