Solar pv-everyday use

At BEC, we are committed to helping our customers gain control of their energy supply.

That means that for people who we meet with solar pv, the advise we give has developed over the years. When we first started out, the advise for effective solar pv management was pretty similar to the advise your mum might give you for hanging your washing out: when the sun is shining, use it!

We would encourage people to time their washing machine, dishwashers and other high load items to run during the day when the sun is likely to be shining and therefore solar pv system generating. Now there is nothing wrong with that advise. If you want to manage your solar pv system but don’t want to spend a further penny then this is still the advise I would give.

It has two big problems with it though. Firstly, it requires quite a lot of ongoing thought and juggling of all your other responsibilities with what the weather might be doing. Frankly, if the sun is shining I want to be in the garden in my underpants drinking a beer (to be honest I never actually do that-I burn at the thought of a 240W light bulb) but you get my point. Who wants to spend their time switching gadgets on and off as the sun comes in and out? If you’re in Scotland, on “sunny” days, this happens about once every 8 minutes.

Secondly, most people are out during the day. Sure, there are some things you can set a timer for. But there are plenty that you can’t. And even when you set your timer, there is no guarantee that this will coincide with periods of high irradiation.

Managing your solar pv yourself is ok but you will have to accept that unless you are REALLY on the ball with it, you will end up exporting most of the electricity that you generate. This is a big shame. It means that you aren’t as independent from the grid as you easily could be and more importantly, the electricity that you have generated by renewable means is effectively wasted and instead you end up using electricity generated by power stations.

For most people, this isn’t the reason you got into renewable energy. It wasn’t as an income stream but as a lifestyle choice: you want to help the planet go renewable. My exhortation to you is this-don’t stop at 90% of the way. Put the extra bit of effort in to live as sustainably as you can.

I’ll be writing a few blogs with tips to make the most of your solar pv. They’ll all cost in time, effort and money and some will just be ideas for the future, but consider, take note and look ahead.

Connecting solar to your hot water tank

If you want to make the most of your solar pv panels, the next step up from running around turning things on and off is a solar hot water diverter.

You can only have one of these if you have a hot water cylinder. If you have a combi boiler then this will work for you.

The way these gadgets work is by a little sensor clamp over your electrical incoming supply cable. This clamp constantly measures whether you are importing or exporting electricity. As soon as you start exporting electricity this clamp sends a signal to the immersion element in your hot water tank to turn on. But here’s the clever bit: only to the amount of electricity that you are exporting.

So say you are generating 2.5kW on your solar pv. You have the oven on and this is using most of it at 2.2kW. You are exporting 300W. Your immersion will automatically turn on and deliver 300W worth of heat into your hot water tank. You decide that your chips are taking a bit long so ramp up the oven a few degrees and the load shoots up to 4kW. As your solar generation has not changed the immersion automatically turns off until such time as your chips are done, you turn the oven off and you are exporting electricity again.

This will go on until you have a nice full tank of hot water. When no more heat is required, the built in thermostat within the immersion element will tell it not to turn on anymore. Of course, if you run off hot water (and cool your hot water tank down) before the sun goes down (and you stop generating electricity) then the process starts all over again.

These units are brilliant and frankly a total no-brainer if you have solar pv and a hot water tank. It will take a big bite out of your solar electricity export and at the same time save you a pile of cash on your gas bill (or whatever your current fuel supply is). In fact, I have even been advising people that if you have a solar pv system installed then you can do without solar thermal (and this is from a solar pv AND solar thermal installation company-what am I thinking??!). This will do nearly as good a job for a fraction of the cost.

So which one? There are a few on the market and the basic job that most of them do is the same. The industry standard is probably the Immersun. What is great about this is that it has a nice display which gives you real time data about whether you are importing or exporting.

It’s major drawback is that it does not come with wireless signal as standard to tell the immersion unit to turn on and off. This means that you have to either a) put the immersion unit in the fuse board cupboard-not ideal as they can often get pretty crowded; b) run a cable from the incoming meter to the cylinder cupboard or c) buy their wireless signal enabler for an extra £80. If the cylinder is in the same place as the fuse board though which it sometimes is then this won’t be an issue.

The other good one is Power Diverter. This is a good bit cheaper, comes with wireless communication as standard but doesn’t give you the data you might like. It will simply flash green if the immersion is being switched on by the solar or red if it isn’t. There are others on the market which are perfectly good so if your installer suggests one and is confident with it then I would just go with that.

Installed cost for one of these babies by the way is somewhere between £350-£500.

How can I get good data on my electricity usage?

Optimising your electricity usage is the key to making the most of your solar pv system. The only way to do this is to have high quality data which tells you how much electricity you are generating, how much importing and how much exporting. High quality data will break this info down into real time (i.e. what’s happening now) and give you hourly, daily, weekly etc. info as well so you can work out when your peak loads are.

However, nobody (not even an enthusiast like me) whats to go to the trouble of doing this manually-you need a gizmo! So what is this gizmo? Its basically a smart meter. Now you may have heard that there is a government sponsored rollout of smart meters aiming to have one installed in every home in England, Wales and Scotland by 2020. When I hear this, the only thing that rolls out is my eyes. While this is government policy, it is hopelessly unrealistic and WILL NOT HAPPEN! Don’t wait for the your energy supply company to give you a freebie-they are as slow as a week in the jail-get on with it yourself now!

Strictly speaking, what I am describing is an energy monitor rather than a smart meter because a smart meter always reports to your supplier rather than you but they pretty much work the same.

A great and affordable option is the smappee energy monitor. There are a few options available-gas and water, energy and solar. These devises are great, cheap and very easy to install and use. Basically, the installation involves putting a little clamp over your electrical supply, and then linking it up to an app which you download to your smartphone (why does everything claim to be smart these days?) and then watching all the lovely graphs and charts to your hearts content.

What is great about the smappee is that it is recording data several times a second so is extremely accurate, unlike some of its rivals. You can have great fun phone in hand running around turning electrical items on and off and watching the power usage ramp up and down. The novelty of this does wear off however! What is truly amazing about smappee though is that it can accurately tell you which appliance is using electricity and give you the profile of each appliance over 30W. According to their website it does this by ‘listening’ to the background noise and identifying the appliance in a similar way to which Shazam identifies a song. Impressive.

Smappee energy monitor is prices at £169. If you have solar pv, definitely go for the solar energy monitor. This does all of the energy monitor stuff but also measures your generation and export to the same standard. This will enable you to understand when you are generating and get things turned on and off to suit.


Is battery storage all its cracked up to be?

Battery storage is the big thing in the solar pv world at the moment and like when any new big thing comes on the market there are a number of issues to be sorted through.

The first question people have is can it be retro-fitted? The answer to this is yes. If you have a solar pv system in your property, a battery storage system can be retro-fitted.

Do I need battery storage? This is a really important question and should be considered carefully. If you are exporting more than 40% of your solar pv generation then a battery will be worth it for you. If not, then you’re probably better sticking with it as it is. Just so you know, the average export for a UK household with a 4kW pv system is 75%. So the chances are that unless you have a really good grasp on what you’re generating at any one time and turning things on and off to suit then you are probably exporting above 40%. I would recommend installing a smart meter which will tell you: 1. how much solar pv electricity you are generating. 2. how much you are exporting and 3. how much you are importing. With this information you will have a great idea as to whether you need battery storage.

How big a battery do I need? This is a big question and there a lot of things that need to be considered. Battery storage is measured in kWhours. e.g. a storage capacity of 4kWh. Please note though that this is not the same as a 4kW solar pv system. a 4kW pv system working at full capacity will produce 4kWh of electricity in one hour or 8kWh in 2 hours etc. The 4kWhour battery is capable of storing 4kWh of electricity. So in this example, after the battery is full after one hour, it will stop storing electricity and the electricity will revert to being exported onto the grid. The ideal battery size then is one which will be small enough to be fully loaded by the end of most days and will also be big enough to supply most if not all of the electricity that you need when the solar pv is not generating i.e. in the evening and night time.

On this then there are a number of options available and most jump around the 2-6kWh of storage capacity and price and quality varies with manufacturer. The big thing to remember though is that the vast majority of these batteries cannot be fully drained down. If there is a storage capacity of 4kWh then the drain down limit might be only 3kWh or less. This is a serious limitation on the solar battery storage industry at the moment and serious attention to detail must be paid to this point when purchasing.

There is one big exception to this rule (that I know of!) and that is the Tesla battery. Tesla, as you may be aware, have led the way in the last few years in the electric car industry and they are now clearing the way on the solar battery storage front. Because I am not an employee of the BBC I have no problem saying that the Tesla battery is by far and away the best battery in the industry (other battery storage options are available…they are just not as good!).

The first thing about a Tesla battery is that its a beautiful piece of kit. Its the iphone of the battery world. I don’t know if that is a big deal for you but the battery will probably be stored on an outside wall (mainly for cooling purposes) so having a nice looking battery is quite important.

More important though is how it works. The Tesla battery is bigger than most and has a storage capacity of 6.8kWh. This is huge and will comfortably provide even a large household with all the electricity it needs in the evening. What’s more though, there is no limitation on storage use. So every last drop of your stored 6.8kWh of electricity can be used up. This is a fantastic selling point for the Tesla.

How big are they? The different batteries vary in size but generally they are a little bigger than the inverter that is probably installed in your loft.

Where do they go? Some batteries can be installed in the loft. However, this is not very wise as they will need to cool down and lofts can be very hot and stuffy. This then is also true of understair cupboards and airing cupboards as old coats, towels and old football kits are likely to get thrown on top of them. The best place is on an outside wall as this provides great cooling and you can also boast to your neighbours about it!

How much does it cost? Again, price varies dramatically but the Tesla installed is about £4500 plus VAT. Most other systems are likely to be cheaper but you get what you pay for. If you want the best, you have to pay more.

Battery storage

Battery storage is the new big thing in solar pv. What is great about it is that it is the perfect fit for the golden rule of great solar pv utilisation: make the load match the supply.

For most people, most of the time, matching the load with the supply is very difficult. Unless you are physically watching your solar generation and ready to jump up and turn things on and off to suit (and also have a pretty good idea what appliance uses how much electricity etc.) then you have a problem. Frankly, most of us have better things to do so what’s the answer?

You may have guessed: battery storage. Here’s the stats. Most people export around 75% of their solar generation. 75%!!! Say you produce 3000kWh of electricity over a year you are exporting 2250kWh which if you are on a very cheap electricity rate (12p/kWh…its probably costing you more than this) will cost you £270 to import from the grid. It seems crazy to be exporting this electricity when you could be using what you’re already generating onsite. Better for you and better for the environment as the further electricity has to go down the line the higher the losses and the less efficient.

Whenever you’re not using the electricity it is automatically stored in your battery for use later on in the evening or at another time. After having a battery installed with a solar pv installation onsite usage rockets up to an average of 95%! That is a lot of saved electricity.

Which is better a combi or system boiler?

One of the trends of the domestic heating industry in the last twenty or so years has been the switch from system boiler to combi boiler. A combi boiler provides hot water straight from the boiler so that there is no need for hot water storage. The main advantage of this is all the space it frees up in the airing cupboard so you’ve got lots of space to put all the rubbish you can’t agree with your spouse should be thrown out!

In addition to this, much emphasis was put on the energy efficiency of combi boilers, especially as when they first arrived on the scene, storage tanks were about as well insulated as a Geordie on a night out. Storing hot water was inefficient, took up lots of space and frankly with the scalding possibility from uninsulated copper heating-dangerous.

However, times have changed and I think its about time the balance was redressed. Hot water cylinders, whether vented or unvented are not the inflexible dinosaurs of old. If anything, they form a key part of a energy efficient building and careful thought should be given before discarding them.

First thing that needs to be said is that a combi provides reliable hot water only on small properties. There may be some exception to this but its generally true. A decent combi can probably provide ok hot water pressure to two showers at a push but beyond that, forget it! A hot water tank on the other hand, provided that the incoming pressure is good and distribution pipes have been sized accurately etc. can give hot water to pretty much as many outlets as you like. This is potentially an issue on fairly large houses and any kind of commercial premises where multiple outlets are required simultaneously.

Secondly, hot water tanks are not the uninsulated monstrosities that they used to be. In old airing cupboards you will see hot water tanks with loads of bare copper showing and a thin old jacket sellotaped on (on occasion I have seen actual coats…for humans!!!) and its like a sauna in there. A modern hot water thank though is so much better. Its foam insulation integral to the tank (ie it can’t just fall off). You could literally cuddle one of these things and have no idea if there is hot or cold water in it.

Where a hot water tank really comes into play though is its potential for optimising renewable energy sources, particularly solar thermal and solar pv. Solar thermal works by thermally absorbing heat from the sun onto rooftop collectors and passing that heat into stored water. It is possible to use the heat for space heating but this is generally quite a complicated process and not really suitable for domestic. There are a couple of combi boilers on the market that will take pre-heated water but generally the best way to use this heat is through a storage tank.

A hot water tank is also one of the best ways to make full use of solar pv. The nature of solar pv is that generation goes up and down with the solar irradiation. It is often the case that when you are generating lots of solar electricity you don’t actually have a use for it at that moment in time. In can be exported to the grid but it is much better to use it if you can.

A product known as a solar hot water optimiser can come to the rescue. These work by constantly registering the solar pv generation and how much of this electricity is being utilised. Should an excess be detected then the immersion heater in the hot water cylinder is switched on to the relevant power. Apart from during the depths of winter, this will comfortably give a full tank of hot water daily. Obviously, this amounts to a serious saving in gas or oil over the course of a year. Its a no-brainer if you have both solar pv and a hot water tank.

One final word on the space issue. Obviously a tank does take up space, no two ways about it. However, there are options. There are slim line versions, there are even horizontal versions. They don’t have to go in the cupboard, they can go in the loft. If you’re getting a new one, have a good chat with your heating engineer and see what can be done.


Electric cars

Although electric cars are really a separate thing to renewables I think it is important to say something about them.

First of all, your domestic solar pv will never be sufficient to provide enough electricity to power up your car. You will have up to a 4kW pv installation. Most car powerpoints are around 6kW. That means that even if your solar pv is blasting out at 100% capacity that it still won’t be enough to not bring in anything from the grid. I’m not saying this to put you off-I think electric cars are amazing-I just don’t want you to go in with false expectations.

That’s not to say that solar and electric cars do not work together. An electric car is a great way to make sure a large proportion of your generated electricity is effectively used. A friend with solar pv installed at her house owns two electric cars and she has been measuring her exported pv generation. It is down to 7%. This is amazingly efficient.

So, electric cars: which one? There are basically two types. All electric and hybrid (i.e. with a petrol reserve for when you run out). Some examples of electric are the Nissan Leaf, Tesla and BMW i3. These all come in at around £30,000 new. A good review of the cars can be found here:

As for hybrids you’ve got Mitsubishi Outlander, BMW i3 Range Extender amongst others. Check out for a run down on the different models.

The first thing about electric cars which is absolutely amazing is that there is a pretty significant network now of car chargers around the UK which are absolutely free to use. Yes, you read right they are free to use. When you think for a moment about how much you spend on petrol and diesel this is a potentially phenomenal saving.

Hold on though. It’s not all good news. Getting an electric car means a shift in thinking. The current petrol/diesel mindset is fill your car up, drive until you notice its getting a bit low, fill it up again. If you have an electric, you need to think about charging. There are several different types of chargers and they all work slightly differently.

A slow charger is just a 3-pin 13A plug which can be fitted to your house and taken off your main board. This is the one in which solar comes in. Obviously, if you want to make the most of your solar on this you must charge during the day when the sun is shining. This will take 6-8 hours to fully charge your car. For most people then overnight or at the workplace is the best option. This means that solar and electric vehicles aren’t necessarily a great fit.

The next is a rapid charger. This doubles the current to 32A and halves the charge time. You will find plenty of these at shopping centres and supermarkets around the country. Very handy for topping up the car whilst doing the shopping.

The best chargers are the rapid ac and rapid dc chargers. These have important technical differences but the headline figure is that they can get cars up to 80% capacity in 30-60 minutes (dc chargers are a bit quicker than ac). The important thing to remember is to check whether the car you are interested in is ac or dc and then make sure you have an access to the relevant kind.

So in conclusion, electric cars are great and surely the future is going that way but you need to think carefully about how you are going to use it and charge it. Answering these questions will help:

  1. Will I (or more importantly my car) be at home during the day to take advantage of my solar generation?
  2. Will I regularly need to travel further than the range of the car? If so, is there a convenient charging point on the way and am I willing to wait while it charges?
  3. Is there an ac/dc (whichever is relevant) charging point nearby for rapid charging?
  4. How much am I currently spending on fuel and is the high price of the car justified by the savings that I will make?

How to maximise solar if I am out all day

So to catch up from last blog, we have established that in order to maximise solar use, you need to match supply (from solar) with demand. To do this, you need a smart energy monitor which can constantly update the difference between the two. As a starter I recommend the Eco Eye. But what if you need remote control because you’re not around to turn things on and off during the day?

For this you need to go up a level and the people who are doing most to solve this problem are Elios4you. This system is constantly monitoring the solar generation but comes with an immersion switch and a maximum of four plugs or switches to turn on appliances.

First of all the immersion switch. This works by turning on the immersion element in your hot water tank whenever you have excess solar generation. On a half decent day this will give you a free tank of lovely hot water having used no gas. There are quite a few different manufacturers doing these systems though. I’ve done a review of different manufacturers here.

Where Elios4you really comes into its own though is the SmartPlug and SmartSwitch. These work in a similar way to the immersion switch except that they will turn on a plug in or switch devise such as a washing machine, dishwasher, tumble dryer or other high load items. Obviously, some of these work on a cycle so the smart plug would wait until you are producing sufficient energy for say the washing machine, turn it on and then if the solar generation drops the machine will continue running on grid energy.

With this installed you are getting into some pretty high level of control so it does come at a significant cost. Materials will be around £500 and you will need an electrician to install which will be about £200. So £700ish altogether. It’s pretty good value though for the control that you get and it will have paid for itself in savings in 3 years. That’s an excellent investment.

Making the most of solar panels

Many people in the UK have had solar panels installed in the last 8 years or so but very few know how to most use the electricity generated most effectively. This is understandable as most installations were presented to the customer as ‘fit and forget’. This isn’t total rubbish as solar will work ok when its just fitted and left to do its thing. However, even a bog standard domestic application can be used to cut energy bills dramatically.

The big concept you need to get your head around is getting solar export down to zero. That’s the goal…we probably won’t get there but we’ve got to aim high, right? Or low in this case. Anyway, we want to be exporting as little as possible because this means that we’ve used it onsite and therefore haven’t imported expensive electricity from the grid.

As solar electricity is very rarely stored (you will know if you have a battery-it will have been installed quite recently and will have been pretty expensive!), we need to match supply and demand. i.e. when you are generating lots of electricity get everything turned on, when its raining and you’re generating next to nothing, turn it all off. There’s obviously a problem here though-how do you know?

The answer is an easily read monitoring devise. There are a number out there and generally you get what you pay for. However, I believe that the best is the Eco-Eye SMART PV Energy monitor. Not too pricey at £79.95 but what it does which I really like is give you a traffic light system of:

red: you’re importing more than you’re generating. Turn off the tumble dryer!

amber: you’re pretty much at parity (give or take a watt or two). As you were.

green: you’re generating more than you’re importing. Turn something on quick!

Obviously this does require a bit of work initially but you’ll soon get into the pattern of peak times and you can know when things should be turned on or off.

I know what you’re thinking…what if I’m not in the house all day everyday poised to press buttons at a moment’s notice? More on that next time…